摘要:

~~~~~~~~~~~ ~ Contemporary Organic Synthesis Editorial Board Professor G. Pattenden, FRS (Chairman), University of Nottingham Professor P. D. Bailey, Heriot- Watt University Dr S. E. Gibson (nee Thomas), Imperial College of Science, Echnoloa, and Medicine Professor P. J. Kocienski, University of Southampton Professor C. J. Moody, Loughborough University of Technology Professor E. J. Thomas, University of Manchester International Advisory Board Professor E. J. Corey, Harvard University Professor S. Hanessian, Universitk de Montrkal Professor M. Julia, Universitk de Paris XI (Paris-Sud) Professor P. D. Magnus, University of Texas at Austin Professor G. Mehta, University of Hyderabad Professor K. C. Nicolaou, The Scripps Research Institute and University of Professor R. Noyori, Nagoya University Professor L.E. Overman, University of California, Irvine Professor L. F. Tietze, University of Gottingen California at San Diego, La Jolla Contemporary Organic Synthesis is a bimonthly journal which aims to review and provide perspective in all aspects of methodology, selectivity and efficiency in contemporary synthesis. As well as covering all the principles and methods in functional group chemistry and interconversions, organometallic chemistry and asymmetric synthesis will feature prominently; so too will modern aspects of strategy and computer aided design, biotransformations and protecting group protocols. Special methods and techniques, such as sonochemistry, FVP, electroorganic synthesis and supported catalysis will be included as occasional articles, and the manner in which synthesis addresses problems and provides solutions in biology, medicine, agriculture, the environment and new materials, will also be encompassed.Contemporary Organic Synthesis aims to be proactive, drawing attention to new opportunities and new directions, providing timely information to the synthetic chemist who needs to keep abreast of developments in the field. Although the majority of articles are intended to be specially commissioned, the Society is always prepared to consider offers of articles for publication. In such cases a short synopsis, rather than the completed article, should be submitted to Dr S. R. Buxton, Managing Editor, Organic Publications, The Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge CB4 4WF, UK.Members of The Royal Society of Chemistry may subscribe to Contemporary Organic Synthesis by placing their orders on the Annual Subscription renewal forms in the usual way. All other orders accompanied with payment should be sent directly to The Royal Society of Chemistry, The Distribution Centre, Blackhorse Road, Letchworth, Herts SG6 lHN, England. 1996 subscription rates: EEA 1185, USA $350, Canada 1190 (plus GST), Rest of the World E190. Contemporary Organic Synthesis is published 6 times a year in February, April, June, August, October and December. Airfreight and mailing in the USA by Mercury Airfreight International Ltd, 2323 Randolph Avenue, Avenel, New Jersey, NJ 07001, USA and at additional mailing offices.Second class postage is paid at Rahway, NJ. USA Postmaster: Send address changes to Contemporary Organic Synthesis, c/o Mercury Airfreight International Ltd, 2323 Randolph Avenue, Avenel, New Jersey 07001. All other dispatches outside the UK are by Bulk Airmail within Europe and Accelerated Surface Post outside Europe. 0 The Royal Society of Chemistry, 1996 All rights reserved No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form, or by any means, electronic, mechanical, photographic, recording or otherwise, without the prior permission of the publishers. Typeset in Great Britain by Unicus Graphics Ltd Printed in Great Britain by Whitstable Litho LtdContemporary Organic Synthesis Editorial Board Professor G.Pattenden, FRS (Chairman), University of Nottingham Professor P. D. Bailey, Heriot- Watt University Dr S. E. Gibson (nek Thomas), Imperial College of Science, Technology, and Medicine Professor P. J. Kocienski, University of Southampton Professor C. J. Moody, Loughborough University of Technology Professor E. J. Thomas, University of Manchester International Advisory Board Professor E. J. Corey, Harvard University Professor S. Hanessian, Universiti de Montrial Professor M. Julia, Universiti de Paris XI (Paris-Sud) Professor P. D. Magnus, University of Texas at Austin Professor G. Mehta, University of Hyderabad Professor K. C. Nicolaou, The Scripps Research Institute and University of Professor R. Noyori, Nagoya University Professor L. E. Overman, University of California, Irvine Professor L.F. Tietze, University of Gottingen California at San Diego, La Jolla Contemporary Organic Synthesis is a bimonthly journal which aims to review and provide perspective in all aspects of methodology, selectivity, and efficiency in contemporary synthesis. As well as covering all the principles and methods in functional group chemistry and interconversions, organometallic chemistry and asymmetric synthesis will feature prominently, so too will modern aspects of strategy and computer aided design, biotransformations, and protecting group protocols. Special methods and techniques, such as sonochemistry, FVP, electroorganic synthesis, and supported catalysis will be included as occasional articles, and the manner in which synthesis addresses problems and provides solutions in biology, medicine, agriculture, and environment, and new materials, will also be encompassed.Contemporary Organic Synthesis aims to be proactive, drawing attention to new opportunities and new directions, providing timely information to the synthetic chemist who needs to keep abreast of developments in the field. Although the majority of articles are intended to be specially commissioned, the Society is always prepared to consider offers of articles for publication. In such cases a short synopsis, rather than the completed article, should be submitted to the Senior Editor (Reviews), Books and Reviews Department, The Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge CB4 4WF. Members of the Royal Society of Chemistry may subscribe to Contemporary Organic Synthesis by placing their orders on the Annual Subscription renewal forms in the usual way.All other orders accompanied with payment should be sent directly to The Royal Society of Chemistry, The Distribution Centre, Blackhorse Road, Letchworth, Herts SG6 lHN, England. 1995 subscription rate: EEA 2165, USA $303, Canada 2173 (plus GST), Rest of the World 2173. Air freight and mailing in the USA by Publications Expediting Inc., 200 Meacham Avenue, Elmont 1103; USA Postmaster, send address changes to Contemporary Organic Synthesis, Publications Expediting Inc. Second class postage is paid at Jamaica, New York 11431. All other dispatches outside the UK are by Bulk Airmail within Europe and Accelerated Surface Post outside Europe. 0 The Royal Society of Chemistry, 1995 All rights reserved No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form, or by any means, electronic, mechanical, photographic, recording, or otherwise, without the prior permission of the publishers. Typeset by Unicus Graphics Ltd Printed in Great Britain by Whitstable Litho Ltd

ISSN:1350-4894    

DOI:10.1039/CO99502FX001

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

EUCHEM Conference on “Cycloadditions and Related Reactions: Theory and Practice” Alicudi 0 wo Ramcolmo wo Vaticmo Vulcano Island, Italy, 21=24 June, 1995 A d d m for Correspondence: Prof. Mario Gattuso - Universith di Messina Dpt. di Chimica Organica e Biologica - Salita Speriine 31, S. Agata 98166 MESSINA, Italy - FAX +39 90 392840EUCHEM Conference on “Cycloadditions and Related Reactions: Theory and Practice” Alicudi 0 wo Ramcolmo wo Vaticmo Vulcano Island, Italy, 21=24 June, 1995 A d d m for Correspondence: Prof. Mario Gattuso - Universith di Messina Dpt. di Chimica Organica e Biologica - Salita Speriine 31, S. Agata 98166 MESSINA, Italy - FAX +39 90 392840

ISSN:1350-4894    

DOI:10.1039/CO99502BX003

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

The hydrometallation, carbometallation, and metallometallation of heteroalkynes SHARON CASSON" and PHILIP KOCIENSKI Department of Chemistry, The University, Southampton, SO1 7 1 BJ, U. K . Reviewing the literature published up to the end of July 1994 1 2 2.1 2.2 3 3.1 3.2 3.3 3.4 3.4.1 3.4.2 3.4.3 4 4.1 4.2 4.3 4.4 5 6 Introduction Hydrometallation 1-Alkoxy- 1 -alkynes 1 -Phenylthio- 1-alkynes Carbometallation Organolithium reagents Organoborane reagents Organocopper reagents Metallacycles Zirconium-alkyne complexes Tantalum-alkyne complexes Titanium-alkyne complexes Metallometallation 1 -Trimethylsilyl- 1 -alkynes 1 -Alkoxy- 1 -alkynes 1-( Pheny1thio)- 1-alkynes 1 -Amino- 1-alkynes ( ynamines) Conclusion References 1 Introduction The hydrometallation and carbometallation of terminal and internal alkynes (Scheme 1 ) is a powerful method for generating alkenylmetals.The former proceeds well for Al, Zr, B, Sn, and Ge, while Cu and A1 have proved useful for the 1atter.l More recently, metallometallation has emerged as a means of simultaneously generating two adjacent regio- and stereo-defined alkenylmetal bonds of differential reactivity. To date metallometallation has been used mainly to introduce Si or Sn in conjunction with Li, Mg, Al, Cu, B, or Zn. Unfortunately, poor regiocontrol detracts from many hydrometallations and M'-M2 Metalkmetallation H-M 3; * Hydrometallatbn Carbometallatbn r: Scheme 1 metallometallations and in some cases stereocontrol is a problem too. Regio- and stereo-control in carbometallations exhibit a marked sensitivity to proximal heterofunctionalities.In this review we survey the valuable influence of heteroatoms (0, S, N) on the crucial issue of regio- and stereo-control in hydrometallations, carbometallations, and metallometallations of alkynes. 2 Hydrometallation The hydrometallation of alkynes offers the simplest and most direct route to alkenylmetals. There are over 50 potentially useful metals (including the lanthanides and actinides) which participate in the reaction, though in practice only a handful of metal hydrides have found general favour and these include B,2-10 Al,11-14 Zr,15-23 and Sn.24-30 In the case of Sn, Si,31-3x Ge,32,34330 and Mg,4Q-42 the reaction is best achieved under transition metal catalysis. The hydrometallation of unactivated terminal or internal alkynes generally proceeds with clean cis-stereoselectivity initially although isomerization can subsequently take place.On a simplistic level, the uncatalysed hydrometallation of an alkyne involves two principal steps (Scheme 2 ): (i) reversible coordination of the alkyne to a vacant orbital on the metal atom and (ii) insertion of the coordinated metal-hydride bond into the alkyne n-bond. The overall rate of formation of 2 will be related to the product of the equilibrium and rate constants K and k. The concentration of intermediate 1 should decrease as the size of substituents attached to the unsaturated bond increase but the effect can be comparatively small since coordination takes place at the centre of the alkyne bond where steric effects are minimized.On the other hand, the concentration of 1 should increase as the electron density in the n-system increases; hence the 1 2 3 4 X=O,N 5 X=S,P Scheme 2 Casson and Kocienski: The hydrometallation, carbometallation, and metallometallation of heteroalkynes 19presence of electron-donating substituents should favour formation of the intermediate 1 and promote reaction. However, if intermediate 1 is too stable, the In keeping with the vast store of precedent, hydrometallations of 1 -alkoxy- 1 -alkynes adhere to the preference for syn-addition. An apparent exception is second step (insertion) may be slow or precluded alt~gether.,~ regiochemistry of the hydrometallation by polarizing the alkyne bond. In the case of trialkylsilyl and other electron-releasing metal groups, polarization is governed by a-bond hyperc~njugation~~ resulting in stabilization of electron deficiency p to the M-C bond as in 3; hence the metal is attracted to the carbon bearing the silyl group.In the case of mesomeric donors such as N or 0, the metal is attracted to the electron-rich /3-carbon as in 4. Mesomeric donors with non-bonded electrons in the third shell show inverted regiochemistry relative to their second shell siblings. Thus, thio- and phospha-alkynes react as if they were polarized in the sense depicted in 5 . In the following sections we will consider in more detail the hydrometallation of 1 -heteroalkynes R'-C = C-X-R2 where X = 0 and S. The heteroatoms under consideration determine the 2.1 1-Alkoxy-1-alkynes The benefits of increased functional diversity and improved rate and regiocontrol offered by dialkylamino and alkoxy substituents has hardly impinged on hydrometallation chemistry.No doubt one reason for the paucity of data is the comparative instability of 1 -( dialky1amino)- 1 -alkynes and 1 -alkoxy- 1 -alkynes, making them awkward compounds to handle and prepare. Information has mostly been gleaned from reactions with the only alkoxyalkyne which is commercially available: ethoxyethyne. Hydroboration,2.3 hydrozirconation, ' 5.' 7.18 and uncatalysed hydr~stannylation~~ of ethoxyethyne have all been accomplished and in every case the metal became attached to the distal carbon in accord with the electronic effects discussed above. Hydroalumination of somewhat more interesting alkoxyalkynes was investigated by Eisch and co-workers with the same regiochemical consequence.13 An example which illustrates the improved opportunities for exploiting the heteroatom is shown in Scheme 3.Hydroboration of ethoxyethyne3 with diborane gave trialkenylborane 8 which underwent Pdo-catalysed coupling under basic conditions with iodobenzene. The significance of this transformation lies in the effective appendage of acetaldehyde to an sp2 centre-a reaction normally beyond the pale of traditional enolate chemistry. A similar transformation was accomplished using hydrozirconation followed by Nio-catalysed coupling. A synthesis of the aurantioclavine precursor 11 attests to the synthetic utility of the sequence.' The p-alkoxy-alkenylzirconium derivative 10 of ethoxyethyne has also been employed in the two and four carbon homologation of aldehydes;22 thus alkenylmetal 10 adds cleanly to an aldehyde in the presence of silver perchlorate and subsequent hydrolysis provides end 12 in high yield and excellent ( E)-selectivity.the uncatalysed hydrostannylation of ethoxyethyne (Scheme 3 )24 which gives the anti-adduct 9 in excellent yield contaminated with minor amounts of the syn-adduct 7. However, once again this was no exception: the syn-adduct forms as the kinetic product which then easily isomerizes by addition-elimination of stannane. In the case of transition metal catalysed hydrostannylation, only syn-adducts are observed though with diminished regioselectivity. For example, Guibe and co-workers found that the Pdo-catalysed hydrostannylation of ethoxyethyne produced regioisomers 6 and 7 in a 58:42 ratio.25 HIH + EtO SnBuB 6 5 8 : 42 7 Pd', M F Bu3SnH.r.t. I 10 min. PhL P d I 3fr!Y.!E' h I +s 11 Scheme 3 The electronic bias in favour of p-metallation in the hydrometallation of ethoxyethyne amply demonstrated in Scheme 3 is subverted in higher alkoxyalkynes: hydrostannylation of 1 -( benzy1oxymethoxy)- 1 -hexyne 13 (Scheme 4 ) occurs rapidly and efficiently on reaction with 1.1 eq. of Bu,SnH in benzene at ambient temperature in the presence of 1 mol% of Pd( PPh,), to give an inseparable mixture of the a-regioisomer 14 and /?-regioisomer 1 5 ( 14: 15 = 2 : 1 ). However, selective destruction of the p-regioisomer to the (Z)-enol ether 16 occurs on rapid passage of the mixture through a column of basic alumina allowing 20 Contemporary Organic Synthesisisolation of pure 14.Hydrostannylation of a further nine alkoxyalkynes revealed that the preference for the a-regioisomer is general but the regioselectivity is strongly dependent on the size of the alkyl substituents. Bu ‘OBn ca. 100% ‘OBn 13 ‘OBn 14 15 16 Scheme 4 2.2 1-Phenylthio- 1-alkynes Thioalkynes are more stable than their oxygen counterparts in accord with diminished communication between the non-bonded 3 p electron pairs on the sulfur atom and the n-system of the alkyne at level 2. Their improved stability and ease of preparation makes thioalkynes more practical substrates for hydrometallation studies. The phenylthio group is an electron sink and polarizes the alkyne in a sense opposite to that observed with alkoxyalkynes (see Scheme 2 ).The net reversal of polarization determines the regiochemistry of hydrometallation as shown in Scheme 5: there is a strong preference for attachment of the metal to the a-position. With a putative CuH reagent prepared by reaction of stiochiometric amounts of CuBr with LiAlH( OMe),, thioalkyne 19 undergoes syn-hydrocupration (path a) affording the diene 1 8.45946 Furthermore, the same combination of reagents-but with CuBr present in catalytic amounts-accomplished the hydroalumination of alkyne 19 (path b), giving the diene product 17. The regiochemistry of both reactions was determined by deuterolysis experiments. Complementary anti-stereochemistry can be obtained by hydroalumination of 19 with LAH (path c).Kim and Magriotis4’ have prepared the (2)-iodoalkene 2 1 in excellent yield by the hydroalumination of 1-phenylthio-1-propyn-3-0120. In the example shown in Scheme 6, anti-hydroalumination was predominant ( 10 : 1 ). The (Z)-iodoalkene 2 1 served as a precursor to a-phenylthioalkenyl silane 22 via 1,4 0 -+ C silyl migration of an alkenyl-lithium intermediate. 1 -phenylthio- 1 -alkynes undergo easy and efficient Pdo-catalysed hydro~tannylation.~~~~~ Scheme 7 illustrates the procedure and shows that the reaction is both regioselective and stereoselective. Stannane 23 Two groups have recently shown that I AH CUH.L~BPAI(OM~), MF-HMPA 18 Scheme 5 - I1 I (ii) 12, -78 -c I SPh 20 path c LiAIH, (1 eq.) M F , 50-60 OC 1 H r O H 21 (11 TBSCI. DMAP (ii) Bu’Li (2 eq.) Et3N / CH&l2 THF, -78 “c + r.t.I HroH PhS SiMe2But 22 Scheme 6 does not participate readily in Pdo-catalysed cross-coupling reactions but the corresponding a-( pheny1thio)alkenyl zinc reagent 24 reacts with a wide variety of substrates under mild conditions, thus providing a significant enhancement to the cross-coupling chemistry of a-heteroalkenyl metals. Since a-( pheny1thio)alkenes can be hydrolysed to ketones or cross-coupled with Grignard reagents in the presence of Ni’ catalysts, reagent 24 serves as an exceptionally mild substrate for the nucleophilic acylation and alkylation of arenes and hetarenes. The catalytic hydroboration of 24 with catecholborane provides the corresponding (E)-isomer with high regio- and stereo-selectivity Casson and Kocienski: The hydrometallation, carbometallation, and metallometallation of heteroalkynes 21Bu&H TBso PhH, r.t.95% 23 I -78-+0%, 1 h (I) Bu"Li I THF, (io ihBrz/THF. -78 "c. 15 min. SPh Pdo I M F 76% from 23 24 Scheme 7 (Scheme 8). The usual syn addition of the metal hydride occurs with the boron atom sited at the carbon /3 to the sulfur atom.x Cross-coupling reactions with aryl, alkynyl, and vinylic halides occurs with retention of configuration, thus providing a new method for the synthesis of stereodefined vinylic sulfides. 24 SMe Scheme 8 OTBS OTBS I BySnH, Pdo CH c SnBua CH20TBS ___) '11 PhH. r.t. p h - s ~ s n B u ~ Ph,SAH II 0 II 80% PhO'*O 0 2 : l Scheme 9 methodology. Such carbometallations are usually highly stereoselective and they are sufficiently mild in many cases to tolerate the presence of some functional groups.The resultant alkenylmetal can be further transformed in such a way that the overall result is the introduction of two new substituents in a cis manner. The kinetic and thermodynamic effects of proximate heteroatoms in directing carbometallation across C-C multiple bonds have been exploited in organic s y n t h e s i ~ ~ ~ , ~ ~ and their virtues extolled in some of the extensive reviews on carbometallation reactions which are e ~ t a n t . ~ ~ . ~ ~ - ~ ' However, in this review we restrict attention to the activation and regiochemical advantages of heteroalkynes as substrates in carbometallation reactions. 3.1. Organolithium reagents Organolithium compounds are generally too strongly basic to be of appreciable synthetic utility in addition reactions to terminal and unactivated internal alkynes.There are some exceptions however. Kooyman and co-workerss3 showed that prolonged heating of a solution of ethoxyhexyne and hexynyllithium in dioxane at 100°C followed by hydrolysis of the adduct 25 afforded diyne 27 in addition to a small amount of the ether 26 (Scheme 10). The latter compound became the main product when the reaction time was shortened to 12 hours. Rapid trans-elimination of LiOC,H, from the intermediates precluded the isolation of addition products of other alkynylation reactions. Bu dioxane- id Bu-OEt + 100 "C, 12 h - Bu-Li Bu OEt (1 -0 eq.) 25 11""" Alkynes with sulfur substituents in higher oxidation states are also known to undergo hydrometallation.12 h, HZO 70 % -LiiEt The enhanced polarization of the n-system should, if anything, reinforce the regiochemical preference for a-attachment of the metal. Hydroalumination of alkynyl sulfones behave as expected in a regiochemical sense but they give anti-add~cts.'~ However, Pdo-catalysed hydrostannylation of alkynyl sulfoxides Bu OEt exemplified in Scheme 9. - - - H JBU Bu 27:26=4: -:- 26 1 Bu has been reported28 to give mixtures of regioisomers as 26 Scheme 10 3 Carbometallation Perhaps the most cogent illustration of the powerful activating effect of heteroatoms on alkyne The addition of a C-M bond to an unactivated alkyne represents a significant advance in synthetic carbometallation was recently provided by Funk and c o - ~ o r k e r s ~ ~ who discovered that alkylthio- and 22 Contemporary Organic Synthesisalkoxy-alkynes participate in cyclization reactions with a variety of stabilized lithio-carbanions to provide functionalized exocyclic and endocyclic enol and thioenol ethers.Thus, treatment of sulfone 28 with BuLi at 0"C, followed by a methyl iodide quench provided cyclopentene 32 in 96% yield (Scheme 11). The proposed mechanism for the transformation involves trans-carbometallation of alkoxyalkyne 29 by the a-phenylsulfonyl anion to afford the alkenyl anion 30 whose equilibration to 3 1 and regiospecific methylation with methyl iodide furnished 32. The a-methylated sulfone 33 also cyclized smoothly to 32 suggesting that the cyclization reaction was not driven by the formation of stable anion 3 1.However, attempts to trap the vinyl anion intermediates were unsuccessful owing to deprotonation of the solvent (THF ) and ortho-metallation of the phenylsulfonyl moiety. OEt 'k (i) Bu"Li THF,O"C* (1 eq.) yL (ii) Me1 S02Ph 96% S02Ph 28 OEt 29 1 OEt 31 30 ?Et S02Ph (i) Bu"Li (1 .O eq.) THF,-78 -0 "c 88 % 32 33 Scheme 11 High (2)-stereoselectivity was observed in the formation of the exo-adducts, possibly due to an atypical trans-carbometallation reaction or, alternatively, to cis-carbometallation followed by equilibration of the intermediate allyl/a-phenylsulfonyl anion to the (Z)-stereoisomer as a result of stabilization by coordination of the lithium atom with the enol ether heteroatom. Preference for nucleophilic addition at the a-carbon of the alkoxyalkyne moiety was not sufficient to overcome a kinetically favoured attack at the P-carbon leading to a smaller ring system.However, the preferred site of intermolecular attack by nucleophiles on thioalkynes is at the @-carbon; consequently these cyclizations were completely regioselective (Scheme 12). Other carbanion stabilizing groups such as phosphorus ylides, ester and ketone enolates, and cyano-derivatives could be employed in the c yclization. Scheme 13 provides a typical example of carbocyclic annulations highlighting the potential of the carbolithiation reaction in natural product synthesis. YEt , XEt V x=o, 66 : 34 (54%) x=s, loo : 0 (57%) Scheme 12 LDA (2.1 eq.) OH HMPA(5q.) THF b EtO 0 Hp OEt 0 0 P H Scheme 13 3.2 Organoborane reagents In contrast to boron hydrides, triorganoboron compounds do not readily add to alkynes unless exceptionally reactive substrates are employed.For example, 1,2-bis( trimethylstanny1)ethyne reacts quantitatively with triorganoboranes (Scheme 14). Allylboranes, like other allylmetal reagents derived from zinc, boron, magnesium, and aluminium can add to alkynes via a six-centred transition state (metallo-ene reaction) leading to alkenylmetal adducts. However, with simple terminal alkynes allylmetallation is complicated by side-reactions such as hydrogen abstraction which accompanies the allylzincation of terminal alkynes;' 7 s and allylmetallation of internal alkynes fails altogether in the absence of electron-donating groups such as alkoxy substitutents. A case in point is the cis-addition of triallylborane 34 to 1-ethoxyethyne (Scheme 15)58 which proceeds at - 50 --+ 20°C to provide adducts 35,36, and 37 in 85, 80, and 65% yield respectively depending on the ratio of reagents.Cleavage of the B-C bond of compounds 35-37 with alcohols, water, and bases at 20-100°C gave 2-ethoxy- 1,4-pentadiene and thermally-induced cyclization of adduct 35 occurred at 120°C to provide the boracycle 38. Crotylboration of ethoxyethyne also occurs at room temperature to form stable a d d ~ c t s . ~ ~ A rnetallo-ene reaction of tribenzylborane 39 with ethoxyethyne occurs in ether, THF, isopentane, or neat to provide intermediate 40 which ethanolyses to 1-ethoxy-1-o-tolylethylene 4 1 in 79% yield (Scheme 16). Casson and Kocienski: The hydrometallation, carbometallation, and metallometallation of heteroalkynes 23Scheme 14 E'op d 38 l , , t E t O w 0 ri 34 f EtO 47 37 nonanol, r.t.87% 1 Eton Scheme 15 85% EtOCSH 65 % - r;' 35 I / EtO L -9 OEt 39 -p OEt 41 Scheme 16 24 Contemporary Organic Synthesis Wrackmeyer and co-workers60 observed easy cis-addition of triethylborane to alkynylstannane 42 to give adduct 44 via rearrangement of alkynyl borate intermediate 43 (Scheme 17). r 1 BEb hexane -78 "c-+ r.t. SnMe3 65% 42 44 43 Scheme 17 3.3 Organocopper reagents Carbocupration of alkynes by lithium-and magnesium-derived copper reagents can be an efficient means of preparing stereoisomerically pure di- and tri- or tetra-substituted double bonds but the method has some synthetic limitations: (i) internal alkynes are usually inert towards carbocupration; (ii) aryl-, alkenyl-, and alkynyl-copper derivatives do not add to alkynes; (iii) methylcupration of alkynes is sluggish; and (iv) carbocupration of alkynes with secondary alkylcopper compounds has, in some cases, been found to be less regio- and stereo-selective!1*62 Pioneering experiments on the carbocupration of various heteroalkynes carried out by the groups of Vermee~-~~ and N ~ r m a n t ~ ~ more than 20 years ago established that carbocupration of 1 -heteroalkynes is much easier than simple terminal alkynes and that regioselectivity depends on the nature of the heteroatom and its influence on the polarity of the n-system.For example, in 1 -alkylthioalkynes the complementary inductive effect of the P-alkyl substituent and electron-withdrawing effect of the S heteroatom causes location of the copper on the carbon atom adjacent to sulfur in adduct 45 (Scheme 1 8)!3 Improved yields and regioselectivity were achieved when THF was used instead of ether.In the absence of Cu' salts, reaction of Grignard reagents with 1-thioalkynes can lead either to substitution at the sulfur group with the formation of alkynylmagnesium derivatives or proton removal to form allenic sulfides. SMe I (i) PhMgBr (1.1 eq.) CuBr (55 d%) THF H+Me c 20 + 30 OC, 10 min. Ph '1' (b) NH&VNaCN 89% Et L. 45 Scheme 18 A major limitation to the traditional methods for accomplishing carbocupration has been the incompatibility of most functional groups with the highly nucleophilic and basic organomagnesium and lithium reagents used to prepare the requisite cuprates.A significant extension of the synthetic utility of carbocupration with the stereoselective construction of tri- and tetra-substituted alkenes was recentlyachieved by the use of mixed clusters of copper, zinc, and lithium which are gentle enough to tolerate the presence of esters, nitriles, and chlorideP2 The method is illustrated (Scheme 19) by the regio- and stereo-selective addition of the cuprate 46 to 1 -( methylthio )- 1 -hexyne leading to alkenylcopper derivative 47 which reacted with electrophiles such as water, iodine, allylic halides, and trimethyltin chloride to provide stereochemically pure tri- and tetra-substituted olefins in good yields (67-92%). Copper-zinc reagents such as 48 harbouring simple alkyl ligands are more reactive than their functionalized counterparts and add at lower temperature. I n Et02C CU (CN ) Li.ZnM+*Li I allyl bromide (3 eq.) -60 + 0 "C, 1 h (7996) I C I Scheme 19 Addition of the Gilman reagent EtCu to 1 -ethoxy- 1 -hexyne and 1 -diphenylamino- 1 -propyne, catalysed by magnesium bromide, illustrates the influence of mesomeric electron-donation on the regioselectivity of carbocupration. In the case of 1-ethoxy- 1 -hexyne, the reaction is not regioselective due to the conflicting inductive effect of the P-alkyl substituent and the mesomeric effect of the 0 atom (Scheme 20) whereas the analogous reaction with 1 -diphenylamino- 1 -propyne is dominated by the donor properties of the amine substituent, giving rise to exclusive p-metallation (Scheme 2 1).Configurational stability at reflux in THF was observed for alkenylcuprates possessing a S heteroatom and at 20°C for the corresponding N intermediates. Alkoxyalkenyl cuprates, however, undergo facile trans elimination above - 20°C (Scheme 2 1 ). Notwithstanding the less favourable regiocontrol and configurational stability exhibited by alkoxyalkynes compared to the sulfur and nitrogen analogues, Normant and co-workers6s were able to utilize vinylcuprates, prepared via the syn-addition of ' H + Scheme 20 (I) EtCu, MgBr2 (1 eq.) THFEt20, 4 + O ° C , 1 h HO,C (ii) HMPT, P(OEt)3 c r2 -40+20°C,4h Me (72% overall) (Iii) IN HCI, 10 min. Scheme 21 lithium derived dialkylcuprates to ethoxyethyne, in the synthesis of stereochemically pure allylic sulfides as shown in Scheme 22.hCuLi c EtCuLi (0.5 eq.) E t P EtO -50-+-25"C H (I) CICHZSCH, (1.Oeq.) Et2O/THF. -30 "c r.t., 4 h (ii) 5N HCI, -10 OC 76 96 Scheme 22 L Nakamura and co-workers studied the addition of MeLi, MeCu, and Me,CuLi to heteroalkynes using ab initio molecular orbital calculations and found an excellent correlation between experimental regioselectivity and the calculated energies of the regioisomeric transition structures, indicating that the activation enthalpy is an important determinant of regioselecti~ityP~(~) They concluded that a heteroatom substituent controls the regiochemistry of carbometallation mainly by affecting the electron population of the alkyne fragment in the transition state. The addition of MeLi and MeCu to the alkyne were found to proceed through two stages involving the x-complex 49 and the transition structure 50 to the product 5 1 (Scheme 23).No indication of coordination between the heteroatom and the metal was found in any of the transition states, whereas some coordination was found in the products. In addition to their regiochemical influence, heteroatoms increased the rate of carbometallation while alkyl groups retarded the reaction. Casson and Kocienski: The hydrometallation, carbometallation, and metallometallation of heteroalkynes 251- 1 2- RMn WCuBr 1 .o 10.1 1.010.5 1.013.0 Scheme 23 ( E ) (2) 75 25 88 12 99 1 The enhanced reactivity of 1-heteroalkynes allows addition of alkenyl cuprates which are generally less reactive than alkyl cuprates (Schemes 24 and 25).65 Protonolysis of adduct 52 was accompanied by hydrolysis of the enol ether and isomerization of the double bond gave ketone 53 in 75% overall yield whereas protonolysis of adduct 54 gave the acid-stable 1-alkylthio- 1,3-butadiene 55.+ $Lcuu hle (0.5 eq.) Scheme 24 A (0.5 eq.) EtO \ hCuLi THF, 0 "c, 1 h 40+-5"C THF -5 "C, 30 mln. US E> EtS 55 Scheme 25 Carbocupration of 1 -( pheny1thio)ethyne is the first step in a new stereoselective synthesis of trisubstituted alkenes (Scheme 26)."6 Addition of BuLi (2 eq.) to a-( pheny1thio)alkenyl cuprate 56 generated a putative higher order cuprate 57 whose 172-metallate rearrangement occurred with inversion of configuration, leading to the alkenylcuprate 58 and thence to a variety of trisubstituted alkenes via reaction with electrophiles such as iodine, methyl propiolate, and ally1 bromide.Vermeer6' and Truce68 described the easy reaction of 1-alkynyl sulfoxides with organocopper( I) reagents. Reaction of Pr'Cu-prepared from the corresponding 56 57 1- Iu+ 58 Scheme 26 Grignard reagent and 1 eq. of copper( I ) bromide-with 1 -propynylsulfoxide 59 provided syn-adduct 60 in almost quantitative yield (Scheme 27). Attack at sulfur rather than the triple bond occurs with some lithium dialkylcuprates. For example, lithium dimethylcuprate adds normally but the more reactive lithium di-n-butylcuprate gives appreciable quantities of n-butyl ethyl sulfoxide. Similarly, treatment of 1-alkynyl sulfoxides with Grignard reagents in THF at - 70°C results in attack on the sulfur at0rn.6~ S(O)Ph I! (ii) NH,CVNaCN (i) (i 4&H7)Cu (2 eq.YMgBr THF.-70% 15 min. + X3H7 H 95 % Me 59 60 Scheme 27 Mainly polymeric products are formed by the slow reaction of 1-alkynyl sulfones with Grignard reagents in THF at O°C;69 however, Vermeer and co-w~rkers~~ found that Cur-catalyses addition to Grignard reagents to 1-alkynyl sulfones. The stereochemistry depends on the ratio of Grignard reagent to Cu' with high concentrations of Cu' forming the (E)-isomer-Le., syn-addition (Scheme 28). Similar results were observed for methylthioethyne. Discrepancies were also reported in the stereocontrol exhibited in the addition of monoalkylcopper( I ) reagents and lithium dialkylcuprates to 1 -alkynyl sulfones. Lithium di-n-butylcuprate provided an 8 1 O/O yield of the trans-adduct when reacted with ethyl 1-propynyl sulfone whereas n-butylcopper gave a 90% yield of the cis-adduct.6x Scheme 28 26 Contemporary Organic SynthesisNaso and co-workers7' observed that the stereochemistry of the addition of dialkyl- and diphenyl-cuprates to benzenesulfonylethyne depended on temperature, time allowed for equilibration, and the size of the ligands on the cuprates (Scheme 29).Up to 30% of the (2)-isomer was isolated from the reaction of dimethyl- and diphenyl-cuprates at 0°C when the reaction was quenched immediately after mixing of the reagents (entry 2). Equilibration for 30 minutes provided the (E)-isomer exclusively (entry 1). With di-n-butyl and di-sec-butylcuprates 5-20% of the (Z)-isomer was isolated even after equilibration at 0°C. At - 78°C almost no stereoselectivity was observed (entry 4).Absolute stereocontrol was achieved with di-t-butylcuprate to form the (2)-isomer even at lower temperatures (entries 5,6). Two possible explanations were cited for the inconsistent stereochemistry: the presence of two different reaction pathways with two different activation energies and/or isomerization of the two intermediates. 1 2 3 4 5 6 c R-CU - Me 0 30 100 Me 0 a 20-30 80-70 Blf 0 0.5 5 95 Blf -78 0.5 42 58 100 But -30 10 But -78 0.5 100 - - PhSOp HH H R R-CU ] i4 PhSOp HR H H Entry I R T "C Time(min.) (Z) (0 Scheme 29 Eisch and co-workers14 were able to effect the syn-carbocupration of phenyl trimethylsilylethyl sulfone in high yield using lithium dialkylcuprates (LiCuR,, R = Me, Ph, allyl) as illustrated in Scheme 30.(i) Me&uLi (1.25 eq.) THF. -78 "c, 1.5 h Me3si)fPh Me (ii) MeOH. -78 "c. NH4CI SiMes 95% Scheme 30 Treatment of phospha- and thiophospha-alkynes with an excess of alkyl Grignard reagent in the presence of an equimolar amount of copper( I ) chloride provides alkenylphosphine sulfides with excellent regio- and stereo-~ontrol.~~ (Scheme 3 1). E Me2P+s (i) EtMgBr (%7 eq.) - Me2pHEt CU2cI2 (1 eq.) EtzO. d U X . 4 4 h '1' (ii) NH4CW0 H Ph Ph 95 % Scheme 31 Recently, a similar protocol was applied to a,b-alkynylphosphonates to form the corresponding disubstituted vinyl phosphonates in accordance with the well established syn-selectivity of addition and p-placement of the alkyl s~bstituent~~ (Scheme 32). ( EtO)2P50 111 C3H7 Scheme 32 (i) PhMgBr (5 eq.) cu2c12 (1 ea.1 88% 8 (Et0)2pHc3H7 H Ph Vermeer and co-workers investigated the behaviour of 1 -alkynyldiphenylphosphines towards organocopper( I ) compounds in THF and found that addition of 6 1 occurred in the presence of R,Cu.MgBr or RCwMgBr, (Scheme 33):' Exclusive syn addition and high regiocontrol (exclusive attack of the R group at the p-C) was obtained.The transfer of only one of the two R groups from the homocuprate R,Cu.MgBr to the alkynylphosphine is notable because, in similar additions to l-alkynyl sulfides, both R groups are transferrable. PPh2 I 'I' the 61 EtCuMgBr2 (1.25 eq.) THF, 20-25 "C, 60 dn. 100% EtfiuMgBr (I .1 eq.) MF,-60+20"c 30 min. 100% t + Ph2 Et CuMgBr2 MeB: Et Scheme 33 The vicinal difunctionalization of acetylenes bearing an organoseleno group has recently been reported by Braga and co-worker~.~~ Reaction of lithium Casson and Kocienski: The hydrometallation, carbometallation, and metallometallation of heteroalkynes 27butylcyanocuprate with 62 (Scheme 34), followed by capture of the intermediate alkenyl cuprate with several electrophiles led to di- and tri-substituted vinylic selenides in acceptable yields.In all the cases studied, only one regioisomer was obtained-a consequence of carbanion stabilization by the selenium atom. The major stereoisomer corresponded to syn addition of the organocuprate, although in some cases, an example of which is shown in Scheme 34, the product 63 derived from the anti-adduct could be detected. B",N/\- 1 - 62 63 Scheme 34 BuLi (4.2 rnml) THF,-78%,1 h 3.4 Metallacycles The formation of metallabicycles via intramolecular reductive coupling of enynes has received much attention in recent years.7s Low-valent metallocenes (MPc,, where M = Ti, Zr, Hf) form titana-, zircona- and hafna-cycles respectively. These metallabicycles are versatile intermediates which can be elaborated into a wide range of mono-and bi-cyclic organic compounds via protonolysis, iodinolysis, and carbonylation.Efficient cyclization is enhanced by the presence of a substituent boosting the alkene nucleophilicity, the most common being the silyl group, although tin, germanium, carbon, and hydrogen have been employed. Both electronic and steric effects control the regiochemistry of the reaction but insertion often occurs at the more sterically-hindered position, which highlights electronic control as being the dominant factor.76 3.4.1 Zirconium-alkyne complexes Alkyne autodimerization, a significant side-reaction in metallocylizations, is limited by the use of 1 -trimethylsilylacetylenes, but additional difficulties arise from competitive displacement of the bulky silyl ligand prior to coupling.77 Van Wagenen and Livingh~use~~ found that the complexation of strongly ligating 1-methylthioalkynes, e.g. 64 (Scheme 35), led SMe MeS / C6H13 65 I (L=THFO~ -1 PhNCO, THF -20+25"C.l2h 51 % I 66 Scheme 35 to the generation of zirconacyclopropene 65 with a minimum ( < 3%) of dimer formation. Insertion of electrophiles, an example of which is shown in Scheme 36, followed by protonation provided the adduct 66 in good yield.The regiochemistry of the insertion is consistent with a transition state involving internal MeS -+ Zr complexation. Whitby and co-workers recently reported a zirconocene-mediated synthesis of 3,4-disubstituted piperidines and reduced isoquinolines using a methylthio activated alkyne (Scheme 36).78 Reductive coupling of the diyne 67 and protolytic workup formed the piperidine 68 containing an (E,E)-exocyclic diene moiety which was further elaborated via cycloaddition chemistry to form 69. Cp&Clp (2.1 mmol) Bn b- ' -78 %+r.t., 3 h -BuH, -- 67 69 SMe -Me Scheme 36 3.4.2 Tantalum-alkyne complexes Unsymmetrical tantalum-alkyne complexes react with carbonyl compounds to produce two regioisomeric allylic alcohols in varying ratio depending on which tantalum-carbon bond of the tantalacyclopropene inserts the carbonyl compound (Scheme 37).75-76 The enhanced electron density imparted by the methylthio moiety gave exclusive reaction at the P-position of the methylthio substituent (entry a).In contrast, the reaction between the zirconocene- 1 -( methy1thio)- 1 -alkyne complex and carbonyl compounds produced a 1 : 1 regioisomeric mixture.77 The resonance effect of the phenyl group in phenylthioalkynes weakens the influence of the sulfur on regioselectivity (entry b). The proportion of a-adducts also increased when sulfonyl-substituted acetylenes were employed (entry c). Reactivity of alkynes toward the low-valent tantalum in the formation of tantalum-alkyne complexes was directly proportional to the electron density of the triple bond and decreased in the order: R'C = CSR2 > R'C = CR2 > R'C = CS0,R2 - R'C = CC0,R2.3.4.3 Titanium-alkyne complexes The cyclization of several heteroatom-containing diynes was investigated by Nugent and co-workers using both titanium and zirconium based reagents.'' 28 Contemporary Organic SynthesisC10H21-R (9 Tact5 Zn, DME PhH. 25 %, t (h) (ii) THF.pyr. (a9 Ph(CH2)&HO I 25 %, 30 min. Ph x A NaOH. H@ 25%. 1 h I + c'oH=e, H B Ph Entrv R t fhl A:B Yiild f%\ a SMe 0.2 99: 1 73 b SPh 0.5 77 : 23 85 c SO#e 2.5 54 : 46 54 Scheme 37 Noteworthy, differences in selectivity were observed in the nominally isoelectronic reagents. In the case of the bis-alkoxyalkyne 70 (Scheme 38), the titanium reagent was found to be superior to the zirconium reagent with the desired cyclized product 7 1 produced in 63% yield.(i) cp2Tci (1.3 q.1 PP hpMe (1.6 eq.) Na(0.596 Hg) (3.4 eq.) ?Et ( Y o E t [THF,457-25%. 15min.! (ii) -25 "c, 3 h - OEt (iii) 10% H,SO, 63% 70 OEt 71 Scheme 38 4 Metallometallation Metallometallation of alkynes introduces two carbon-metal bonds in a single step thereby creating the opportunity for selective chain extension on adjacent carbons. Metallometallations usually involve bimetallic reagents of the type R3Si-MR,7 or R,Sn-MR, in which M = B, Al, Mg, Mn, Cu, Zn, Si, or Sn. A noteworthy feature of these reagents is their low basicity. In many cases metallometallations can be performed on substrates which contain functional groups such as hydroxyl, ester, amine, and halide. Metallometallation reactions can be divided into four categories depending on the nature of the bimetallic reagent: (i) stoichiometric metallo-cuprations: Ge-Cu26 Sn-Cu80-97 si_cu;84,~2,~4,~6.~8- 102 (ii) metallometallations with Cur catalysis: sn-zn103- 10s Sn-A182, 103,104,106- 108 Sn-Mg82,103,104,108 Sn-B 108- I 10 Si-BI 10 Si-Al4 1,106 Si-Zn41.106 Si-Mg;4 1,1 I I (iii) metallometallations with other transition metal catalysts: Si-B/Co"' Sn-B/Co1I0 Si-Si/Mnl SnSn/MnIo3 Sn-Mg/Pd123 Sn-A1/PdIo3 Sn-Zn/Pd lo3 Sn-Sn/Pd82,106,1 13-117 Si-Mg/PdlOh,l I1,117 Si-Al/Pd106,1 I ] , I 17 Sn-Si/pd82,1 15.1 18.1 19 Si-Si/Pd31,36,120- I26 Ge-Ge/Pd36 B-B/Pt; I 27 (iv) uncatalysed metallometallations: Te-Te 1 2 8- 1 3 1 Si-Ti.132 Although terminal alkynes metallometallate with a high degree of regio- and stereo-control,' 33 internal alkynes usually require the presence of some activating group such as C02R, to achieve useful control.87J 16~134 In addition to the inherent bias in the bimetallic reagent, the regio- and stereo-chemical outcome of the reaction may be influenced by the catalyst employed, reaction conditions, solvents, Lewis acids, and the presence of suitable functional groups on the substrate.I,l l6 Unsymmetrical alkynes in which one of the substituents is a heteroatom (Si, 0, S, N) present a potentially valuable method for controlling the regioselectivity of metallometallations through mesomeric, inductive, or coordination effects.A particularly attractive feature of the metallometallation of heteroalkynes is the opportunity for further elaboration to synthetically valuable heteroalkenes provided (a) the addition is regioselectivs and (b) the two C-metal bonds can be selectively and sequentially replaced by electrophiles as depicted in Scheme 39.In the following sections the relatively small amount of data which describes the influence of Si, 0, S, and N substituents on the regiochemistry of various metallometallation reactions are examined. Casson and Kocienski: The hydrometallation, carbometallation, and metallometallation of heteroalkynes 29R2 a H 1w:O 78% b n-C6HI3 1w:o 58% c CH2OH 0:lOo 75% d CH2CH20H 0:loo 44% o CH2CH20THP 1w:O 72% 1 f CH2CH2CH20H 1w:o 74% R ' i m8H17 Hwm8H'7+ 4 + Bu3Sn-SnBu3 H SnBu3 80 Scheme 39 f 4.1 1-Trimethylsilyl-1-alkynes Oshima et al. investigated the Cut-catalysed reaction of 1 -trimethylsilyl- 1 -alkynes with the silylzinc reagent (PhMe,Si),Zn (Scheme 4O).lo6 The reaction was highly regioselective and invariably gave 1,2-disilyl- 1-alkenes regardless of the alkyne substituent.However, the stereochemistry depended on the presence of proximate hydroxyl groups. 1-(Trimethylsily1)-1 -octyne 72b and 4-( 2-tetrahydropyrany1oxy)- 1-( trimethylsily1)- 1 - butyne 72e gave syn-adducts which afforded the ( E ) - 1,2-disilyl- 1-alkenes 73b,e on workup. However, 3-( trimethylsilyl)-2-propyn- 1-01 72c and 4-( trimethylsilyl)-3-butyn- 1-01 72d provided the anti-adducts which protonated to give the (2)-isomers 74c,d. The authors postulated that the initial addition proceeds with syn-stereochemistry but that isomerization later occurs driven by intramolecular coordination of the hydroxyl group to the zinc atom.The chelation effect disappeared when the hydroxy group was separated from the alkyne by three carbons, 72f leading to the expected syn-adduct exclusively. 72 t+f ( E ) : ( Z ) Yield I I R Scheme 40 4.2 1-Alkoxy- 1-alkynes Scheme 4 1 outlines the stannylcupration of 1 -alkoxy- 1-alkynes which draws attention to one of its major limitations: reversibility. In principle the adducts 79 and 77 could be trapped in situ by a suitable electrophile, giving trisubstituted alkenyl stannanes as products. However, in practice, most electrophiles react preferentially with the bimetallic reagent rather than the adduct. Extensive chemical and NMR studies by Cabezas and Oehlschlagerx5 on the stannylcupration of terminal alkoxyalkynes has finally H -0C8H 17 75 ( BU~S~)~CU(CN) U2 + 30 Contemporary Organic Synthesisprovided conclusive evidence for the mechanism of the reaction, as well as an explanation for the presence of a number of by-products in the reaction.Reaction of 75 with 76 in THF at - 40°C followed by warming to 0°C and methanolysis gave a mixture of regioisomers 78 and 80 in a 4:6 ratio in 42% yield. The kinetic product of addition at - 78°C corresponds to intermediate 79 which rapidly equilibrates with 77. Addition of the alkoxyalkyne 75 in the presence of a protic source such as MeOH, to the higher order cuprate 76 at - 78°C results in protonolysis of intermediate 79 before equilibration with 77 is possible, thus providing regioisomer 80 in 95% yield.Selective protonation of the alkenylcopper intermediates 79 and 77 occurs because they are more basic than Me,Sn(L)CuLi thereby forcing the equilibrium to the right. Cox and WudP' estimate the CuH conjugate acid of a stannylcuprate has a pK, of about 5. When the reaction is performed at 0°C in the presence of HMPA and the absence of a proton source, a mixture of 78 and 80 were isolated in 94% yield with a regioselectivity of 95:5 in favour of 78. Similar results were obtained in the reaction of (Bu,Sn)Cu( CN)Li with alkoxyalkynes, although the presence of HMPA was necessary to prevent decomposition of the copper reagent at 0°C. The regioselective formation of 7 7 under these conditions is presumed to be favoured by intramolecular interaction between the oxygen and the copper. In contrast, the reaction of the dithiane derivative 8 1 (Scheme 42) under kinetic conditions, provided 82 and 83 in a ratio of (41 :59) in favour of 83. The anomalous regioselectivity was attributed to coordination between Cu and S leading to preferential formation of regioisomer 83.81 \ (Bu$n)&u(CN)LI2 -78 "c, THF 89 % I 82 41 :59 83 Scheme 42 Despite the complexity of the stannylcupration reaction, the regiochemistry of the reaction can be tuned by deft manipulation of reaction conditions as illustrated in Scheme 43. In order to avoid the problem of regioisomeric mixtures in reversible metallocupration reaction^,^^ Casson' 3s investigated the irreversible Pdo-catalysed stannylstannylation of 1 -alkoxy- 1 -alkynes under conditions which had already been established for H-O--(CH~)SOTBS condition5 + (4 or @I ( BU~S~)~CU(CN)L~ HHO-(CH2J50TBS H SnBu3 A + Bu3Sn Hw:-(cHd50m B ..=ondltlons I Batia I Ymld(%) I T("C.1 solvent A:B (a) 0 THFRiMPA 10 : 90 91 (b) -78 TH F Scheme 43 simple terminal alkynes.82,' l4 Stannylstannylation of 1-alkoxy- 1-alkynes 84 (Scheme 44), for example, readily occurred on reaction with Me,Sn-SnMe, in benzene in the presence of 2 mol% Pd(PPh,), and galvinoxyl (added to retard radical-induced isomerization) at ambient temperature to give syn-adduct 85 in good yield. Me PdlPPhh ( 2 d %) ~ Y" galvinoxyl (cat.) 12 (1.1 e9.1 * I .SnMe3 PhH. 3 h. r.t. Y '0' 'SnMe, n I fie& I 84 A 85 Scheme 44 The regioselectivity of silylstannylation was then examined in the hope that any regiochemical differentials could be amplified with more dissimilar metals.Surprisingly, alkoxyalkyne 86 (Scheme 45) reacts very easily with Me,%-SnMe, in benzene using Pd( PPh,), as the catalyst to give syn-adduct 87 as a single regioisomer in 90% yield in which the tin atom is located on the a-carbon adjacent to the oxygen substituent. * c6H13KsiMe3 PdPPh,], Me&i-SnM& galvinoxyl (cat.) PhH. 3 h, r.t. EtO SnMe3 OEt 9 w o 86 87 Scheme 45 The results of Casson described above contrast sharply with those of Ito and co-workers136 who showed that 1-ethoxy- 1-propyne undergoes silylstannylation using Pd( OAc), and 1 , 1,3,3-tetrarnethylbuty1 isocyanide (Scheme 46) to give syn-adduct 88, in which the tin atom is located on Casson and Kocienski: The hydrometallation, carbometallation, and metallometallation of heteroalkynes 31the B-carbon remote from the oxygen substituent, as the major product.Regioselectivity in excess of 95:5 is typical of reactions involving the bulky reagent t-BuMe,Si-SnMe, whereas Me,%-SnMe, added with poor regiocontrol. The a-silylated enol ethers are amenable to further chemical manipulation as illustrated in Scheme 46. The complementary results observed by Ito and Casson suggests that the regioselectivity of other metallometallations might be tuned by simply varying the catalyst. I ~R Yield 90 H-OEt Pd(0AC)Z (0.04 q.) Bu'Me$ISnM* (1.3 eq.) Bu'CH&(M~)~NC (0.3 eq.) toluene. 24 h. r.t. 99% w Me3SnYH ' + eutMeaiYH Suh2Si AOEt Me3SnAOEt 88 95:5 PhCOCl 1 eq.) PdCI&H&N)2 (5 m ~ l % ) UCI*H20 (5 eq.) MeCN.70 "c, 30 rnln. 89% - 0 0 H,O Ph uSiMe2But 74 % Ph Scheme 46 4.3 1 -(Phenylthio)- 1 -alkynes Silylstannylation of 1 -phenylthio- 1-alkynes 89a-f with Me&-SnMe, in the presence of Pd(PPh,), occurs with the same regioselectivity as the alkoxy series described above but the reaction is more sluggish (Scheme 47).135 Up to 30 h at reflux is required to produce the R L S i M e 3 89 90 Scheme 47 OTHP 80% OH 77% OMe 78% P f 62% pPhCGH4C02 76% (CH212OH say0 silylstannanes in yields of 1 1-58%. A substantial improvement can be obtained without sacrifice of regioselectivity by using Pd,(dba), (2 mol%) in the presence of tri-2-furylphosphine (4 mol%) in Now the reactions only require 2 h at r.t. and give the silylstannane adducts in 56430% yield.4.4 1-Amino- 1-alkynes (ynamines) Ricci and co-workerslo2 recently described a highly regioselective silylcupration of N,N-diphenylaminoethyne 9 1 (Scheme 48) in which the copper atom is placed at the a-position next to the heteroatom-a result which appears to be opposite to the trend set by alkoxyalkynes. However, in this case it is likely that the regiochemistry is governed by internal coordination of the copper by the amino group in adduct 92. Ph2N -H ... 91 Scheme 48 92 (0 Me1 (1 eq.) -23OC.3h (ii) NH&I I NH3 Ph2NYe H ~ H 5 Conclusion In this review we have shown that heteroatoms both activate and control the regiochemistry of a wide variety of additions to alkynes leading to synthetically valuable heteroalkenylmetal derivatives. 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ISSN:1350-4894    

DOI:10.1039/CO9950200019

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

Contemporary Organic Synthesis Editorial Board Professor G. Pattenden, FRS (Chairman), University of Nottingham Professor P. D. Bailey, Heriot- Watt University Dr S. E. Gibson (nee Thomas), Imperial College of Science, Technology, and Medicine Professor P. J. Kocienski, University of Southampton Professor C. J. Moody, Loughborough University of Technology Professor E. J. Thomas, University of Manchester International Advisory Board Professor E. J. Corey, Harvard University Professor S. Hanessian, Universiti de Montrial Professor M. Julia, Universiti de Paris XI (Paris-Sud) Professor P. D. Magnus, University of Texas at Austin Professor G. Mehta, University of Hyderabad Professor K. C. Nicolaou, The Scripps Research Institute and University of Professor R. Noyori, Nagoya University Professor L.E. Overman, University of California, Irvine Professor L. F. Tietze, University of Gottingen California at Sun Diego, La Jolla Contemporary Organic Synthesis is a bimonthly journal which aims to review and provide perspective in all aspects of methodology, selectivity and efficiency in contemporary synthesis. As well as covering all the principles and methods in functional group chemistry and interconversions, organometallic chemistry and asymmetric synthesis will feature prominently; so too will modern aspects of strategy and computer aided design, biotransformations and protecting group protocols. Special methods and techniques, such as sonochemistry, FVP, electroorganic synthesis and supported catalysis will be included as occasional articles, and the manner in which synthesis addresses problems and provides solutions in biology, medicine, agriculture, the environment and new materials, will also be encompassed.Contemporary Organic Synthesis aims to be proactive, drawing attention to new opportunities and new directions, providing timely information to the synthetic chemist who needs to keep abreast of developments in the field. Although the majority of articles are intended to be specially commissioned, the Society is always prepared to consider offers of articles for publication. In such cases a short synopsis, rather than the completed article, should be submitted to Dr S. R. Buxton, Managing Editor, Organic Publications, The Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge CB4 4WF, UK.Members of The Royal Society of Chemistry may subscribe to Contemporary Organic Synthesis by placing their orders on the Annual Subscription renewal forms in the usual way. All other orders accompanied with payment should be sent directly to The Royal Society of Chemistry, The Distribution Centre, Blackhorse Road, Letchworth, Herts SG6 ZHN, England. 1995 subscription rate: EEA &165, USA $303, Canada El73 (plus GST), Rest of the World f173. Contemporary Organic Synthesis is published 6 times a year in February, April, June, August, October, December. Airfreight and mailing in the USA by Mercury Airfreight International Ltd, 2323 Randolph Avenue, Avenel, New Jersey, NJ 07001, USA and at additional mailing offices. Second class postage is paid at Rahway, NJ.USA Postmaster: Send address changes to Contemporary Organic Synthesis, c/o Mercury Airfreight International Ltd, 2323 Randolph Avenue, Avenel, New Jersey 07001. All other dispatches outside the UK are by Bulk Airmail within Europe and Accelerated Surface Post outside Europe. 0 The Royal Society of Chemistry, 1995 All rights reserved No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form, or by any means, electronic, mechanical, photographic, recording or otherwise, without the prior permission of the publishers. Typeset in Great Britain by Unicus Graphics Ltd Printed in Great Britain by Whitstable Litho LtdContemporary Organic Synthesis Editorial Board Professor G. Pattenden, FRS (Chairman), University of Nottingham Professor P.D. Bailey, Heriot- Watt University Dr S. E. Gibson (ne'e Thomas), Imperial College of Science, Technology, and Medicine Professor P. J. Kocienski, University of Southampton Professor C. J. Moody, Loughborough University of Technology Professor E. J. Thomas, University of Manchester International Advisory Board Professor E. J. Corey, Haward University Professor S. Hanessian, Universiti de Montrial Professor M. Julia, Universiti de Paris X I (Paris-Sud) Professor P. D. Magnus, University of Texas at Austin Professor G. Mehta, University of Hyderabad Professor K. C. Nicolaou, The Scripps Research Institute and University of Professor R. Noyori, Nagoya University Professor L. E. Overman, University of California, Iwine Professor L.F. Tietze, University of Gottingen California at San Diego, La Jolla Contemporary Organic Synthesis is a bimonthly journal which aims to review and provide perspective in all aspects of methodology, selectivity and efficiency in contemporary synthesis. As well as covering all the principles and methods in functional group chemistry and interconversions, organometallic chemistry and asymmetric synthesis will feature prominently; so too will modern aspects of strategy and computer aided design, biotransformations and protecting group protocols. Special methods and techniques, such as sonochemistry, FVP, electroorganic synthesis and supported catalysis will be included as occasional articles, and the manner in which synthesis addresses problems and provides solutions in biology, medicine, agriculture, the environment and new materials, will also be encompassed.Contemporary Organic Synthesis aims to be proactive, drawing attention to new opportunities and new directions, providing timely information to the synthetic chemist who needs to keep abreast of developments in the field. Although the majority of articles are intended to be specially commissioned, the Society is always prepared to consider offers of articles for publication. In such cases a short synopsis, rather than the completed article, should be submitted to Dr S. R. Buxton, Managing Editor, Organic Publications, The Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge CB4 4WF, UK. Members of The Royal Society of Chemistry may subscribe to Contemporary Organic Synthesis by placing their orders on the Annual Subscription renewal forms in the usual way.All other orders accompanied with payment should be sent directly to The Royal Society of Chemistry, The Distribution Centre, Blackhorse Road, Letchworth, Herts SG6 lHN, England. 1996 subscription rates: EEA &185, USA $350, Canada El90 (plus GST), Rest of the World E190. Contemporary Organic Synthesis is published 6 times a year in February, April, June, August, October and December. Airfreight and mailing in the USA by Mercury Airfreight International Ltd, 2323 Randolph Avenue, Avenel, New Jersey, NJ 07001, USA and at additional mailing offices. Second class postage is paid at Rahway, NJ. USA Postmaster: Send address changes to Contemporary Organic Synthesis, c/o Mercury Airfreight International Ltd, 2323 Randolph Avenue, Avenel, New Jersey 07001. All other dispatches outside the UK are by Bulk Airmail within Europe and Accelerated Surface Post outside Europe. + 0 The Royal Society of Chemistry, 1996 All rights reserved No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form, or by any means, electronic, mechanical, photographic, recording or otherwise, without the prior permission of the publishers. Typeset in Great Britain by Unicus Graphics Ltd Printed in Great Britain by Whitstable Litho Ltd

ISSN:1350-4894    

DOI:10.1039/CO99502FX033

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

ISSN 1350-4894 COGSE6 2 1-1-1-40 (1995) Contemporary Organic Synthesis A journal of current developments in Organic Synthesis V O L U M E 2 I N D E X E S C O N T E N T S ... 111 Contents of volume 2 iv Contributors to volume 2 V Journal details 1-1 Index of authors cited 1-25 Subject index Notice to librarians: Journal binding Preliminary pages iii-vi are designed to be bound at the beginning of volume 2, and the Indexes bound at the end.ISSN 1350-4894 COGSE6 2 1-1-1-40 (1995) Contemporary Organic Synthesis A journal of current developments in Organic Synthesis V O L U M E 2 I N D E X E S C O N T E N T S ... 111 Contents of volume 2 iv Contributors to volume 2 V Journal details 1-1 Index of authors cited 1-25 Subject index Notice to librarians: Journal binding Preliminary pages iii-vi are designed to be bound at the beginning of volume 2, and the Indexes bound at the end.ISSN 1350-4894 COGSE6 2 1-462,I-1-1-40 (1995) Contemporary Organic Synthesis A journal of current developments in Organic Synthesis VOLUME 2 CONTENTS 1 19 35 43 65 85 107 121 133 151 173 189 209 225 25 1 Aromatic heterocycles as intermediates in natural product synthesis Michael Shipman Reviewing the literature published up to the end of 1993 The hydrometallation, carbometallation, and metallometallation of heteroalkynes Sharon Casson and Philip Kocienski Reviewing the literature published up to the end of July 1994 Serotonin, sumatriptan, and the management of migraine Alexander W.Oxford Stoichiometric organotransition metal complexes in organic synthesis Julian Blagg Reviewing the literature published between 1 September I993 and 31 August 1994 Catalytic applications of transition metals in organic synthesis Christopher G.Frost and Jonathan M. J. Williams Reviewing the literature published between 1 September 1993 and 31 August 1994 Organic halides Peter L. Spargo Reviewing the literature published between 1 July 1993 and 30 June 1994 Carboxylic acids and esters T. Harrison and T. Laduwahetty Reviewing the literature published between 1 January 1993 and 31 July 1994 Hypervalent iodine in organic synthesis: a-functionalization of carbonyl compounds Om Prakash, Neena Saini, Madan I? Tanwar and Robert M. Moriarty Reviewing the literature published up to February 1995 Saturated and unsaturated lactones T. Laduwahetty Reviewing the literature published between 1 January 1993 and 31 July 1994 Aldehydes and ketones Patrick G.Steel Reviewing the literature published between July 1993 and September 1994 a-Cation equivalents of amino acids Patrick D. Bailey, Joanne Clayson, and Andrew N. Boa Reviewing the literature published up to the end of 1994 Saturated oxygen heterocycles Christopher J. Burns Reviewing the literature published between 1 April 1993 and 30 September 1994 Saturated nitrogen heterocycles Timothy Hamson Reviewing the literature published between June 1993 and December 1994 Synthesis and use of cyclic peroxides K. J. McCullough Reviewing the literature published between January 1992 and January 1995 Recent advances in organofluorine chemistry Jonathan M.Percy Reviewing the literature published between January 1992 and April 1995269 289 315 337 357 365 393 409 441 I- 1 1-25 Amines and amides Michael North Reviewing the literature published in 1994 Synthetic developments in host-guest chemistry James Dowden, Jeremy D. Kilburn, and Paul Wright Reviewing the literature published in 1994 Protecting groups Krzysztof Jarowicki and Philip Kocienski Reviewing the literature published in 1994 Synthesis of aromatic heterocycles Thomas L. Gilchrist Reviewing the literature published between July 1993 and February 1995 Nitro and related compounds Graeme Robertson Reviewing the literature published between December 1993 and May 1995 Dispiroketals: A new functional group for organic synthesis Steven V. Ley, Robert Downham, Paul J.Edwards, Jean E. Innes and Martin Woods Methods for the asymmetric preparation of amines Anders Johansson Reviewing the literature published up to January I995 Synthesis of thiols, sulfides, sulfoxides and sulfones Christopher M. Rayner Reviewing the literature published between October 1993 and February 1995 Saturated and unsaturated hydrocarbons Richard €? C. Cousins Reviewing the literature published between September 1993 and December 1994 Index of authors cited Subject index Contributors to Volume 2 Bailey, Patrick D., 173 Blagg, Julian, 43 Boa, Andrew N., 173 Burns, Christopher J., 189 Casson, Sharon, 19 Clayson, Joanne, 173 Cousins, Richard P. C., 441 Dowden, James, 289 Downham, Robert, 365 Edwards, Paul J., 365 Frost, Christopher G., 65 Gilchrist, Thomas L., 337 Harrison, Timothy, 107, 209 Innes, Jean E., 365 Jarowicki, Krzysztof, 315 Johansson, Anders, 393 Kilburn, Jeremy D., 289 Kocienski, Philip, 19, 315 Laduwahetty, T., 107, 133 Ley, Steven V., 365 McCullough, K.J., 225 Moriarty, Robert M., 121 North, Michael, 269 Oxford, Alexander W., 35 Percy, Jonathan M., 251 Prakash, Om, 121 Rayner, Christopher M., 409 Robertson, Graeme, 357 Saini, Neena, 121 Shipman, Michael, 1 Spargo, Peter L., 85 Steel, Patrick G., 151 Tanwar, Madan P., 121 Williams, Jonathan M. J., 65 Woods, Martin, 365 Wright, Paul, 289~~~~~~~~~~~ ~ Contemporary Organic Synthesis Editorial Board Professor G. Pattenden, FRS (Chairman), University of Nottingham Professor P. D. Bailey, Heriot- Watt University Dr S. E. Gibson (nee Thomas), Imperial College of Science, Echnoloa, and Medicine Professor P.J. Kocienski, University of Southampton Professor C. J. Moody, Loughborough University of Technology Professor E. J. Thomas, University of Manchester International Advisory Board Professor E. J. Corey, Harvard University Professor S. Hanessian, Universitk de Montrkal Professor M. Julia, Universitk de Paris XI (Paris-Sud) Professor P. D. Magnus, University of Texas at Austin Professor G. Mehta, University of Hyderabad Professor K. C. Nicolaou, The Scripps Research Institute and University of Professor R. Noyori, Nagoya University Professor L. E. Overman, University of California, Irvine Professor L. F. Tietze, University of Gottingen California at San Diego, La Jolla Contemporary Organic Synthesis is a bimonthly journal which aims to review and provide perspective in all aspects of methodology, selectivity and efficiency in contemporary synthesis.As well as covering all the principles and methods in functional group chemistry and interconversions, organometallic chemistry and asymmetric synthesis will feature prominently; so too will modern aspects of strategy and computer aided design, biotransformations and protecting group protocols. Special methods and techniques, such as sonochemistry, FVP, electroorganic synthesis and supported catalysis will be included as occasional articles, and the manner in which synthesis addresses problems and provides solutions in biology, medicine, agriculture, the environment and new materials, will also be encompassed.Contemporary Organic Synthesis aims to be proactive, drawing attention to new opportunities and new directions, providing timely information to the synthetic chemist who needs to keep abreast of developments in the field. Although the majority of articles are intended to be specially commissioned, the Society is always prepared to consider offers of articles for publication. In such cases a short synopsis, rather than the completed article, should be submitted to Dr S. R. Buxton, Managing Editor, Organic Publications, The Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge CB4 4WF, UK. Members of The Royal Society of Chemistry may subscribe to Contemporary Organic Synthesis by placing their orders on the Annual Subscription renewal forms in the usual way.All other orders accompanied with payment should be sent directly to The Royal Society of Chemistry, The Distribution Centre, Blackhorse Road, Letchworth, Herts SG6 lHN, England. 1996 subscription rates: EEA 1185, USA $350, Canada 1190 (plus GST), Rest of the World E190. Contemporary Organic Synthesis is published 6 times a year in February, April, June, August, October and December. Airfreight and mailing in the USA by Mercury Airfreight International Ltd, 2323 Randolph Avenue, Avenel, New Jersey, NJ 07001, USA and at additional mailing offices. Second class postage is paid at Rahway, NJ. USA Postmaster: Send address changes to Contemporary Organic Synthesis, c/o Mercury Airfreight International Ltd, 2323 Randolph Avenue, Avenel, New Jersey 07001.All other dispatches outside the UK are by Bulk Airmail within Europe and Accelerated Surface Post outside Europe. 0 The Royal Society of Chemistry, 1996 All rights reserved No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form, or by any means, electronic, mechanical, photographic, recording or otherwise, without the prior permission of the publishers. Typeset in Great Britain by Unicus Graphics Ltd Printed in Great Britain by Whitstable Litho Ltd~~~~~~~~~~~ ~ Contemporary Organic Synthesis Editorial Board Professor G. Pattenden, FRS (Chairman), University of Nottingham Professor P. D. Bailey, Heriot- Watt University Dr S. E. Gibson (nee Thomas), Imperial College of Science, Echnoloa, and Medicine Professor P.J. Kocienski, University of Southampton Professor C. J. Moody, Loughborough University of Technology Professor E. J. Thomas, University of Manchester International Advisory Board Professor E. J. Corey, Harvard University Professor S. Hanessian, Universitk de Montrkal Professor M. Julia, Universitk de Paris XI (Paris-Sud) Professor P. D. Magnus, University of Texas at Austin Professor G. Mehta, University of Hyderabad Professor K. C. Nicolaou, The Scripps Research Institute and University of Professor R. Noyori, Nagoya University Professor L. E. Overman, University of California, Irvine Professor L. F. Tietze, University of Gottingen California at San Diego, La Jolla Contemporary Organic Synthesis is a bimonthly journal which aims to review and provide perspective in all aspects of methodology, selectivity and efficiency in contemporary synthesis.As well as covering all the principles and methods in functional group chemistry and interconversions, organometallic chemistry and asymmetric synthesis will feature prominently; so too will modern aspects of strategy and computer aided design, biotransformations and protecting group protocols. Special methods and techniques, such as sonochemistry, FVP, electroorganic synthesis and supported catalysis will be included as occasional articles, and the manner in which synthesis addresses problems and provides solutions in biology, medicine, agriculture, the environment and new materials, will also be encompassed. Contemporary Organic Synthesis aims to be proactive, drawing attention to new opportunities and new directions, providing timely information to the synthetic chemist who needs to keep abreast of developments in the field. Although the majority of articles are intended to be specially commissioned, the Society is always prepared to consider offers of articles for publication. In such cases a short synopsis, rather than the completed article, should be submitted to Dr S.R. Buxton, Managing Editor, Organic Publications, The Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge CB4 4WF, UK. Members of The Royal Society of Chemistry may subscribe to Contemporary Organic Synthesis by placing their orders on the Annual Subscription renewal forms in the usual way. All other orders accompanied with payment should be sent directly to The Royal Society of Chemistry, The Distribution Centre, Blackhorse Road, Letchworth, Herts SG6 lHN, England. 1996 subscription rates: EEA 1185, USA $350, Canada 1190 (plus GST), Rest of the World E190. Contemporary Organic Synthesis is published 6 times a year in February, April, June, August, October and December. Airfreight and mailing in the USA by Mercury Airfreight International Ltd, 2323 Randolph Avenue, Avenel, New Jersey, NJ 07001, USA and at additional mailing offices. Second class postage is paid at Rahway, NJ. USA Postmaster: Send address changes to Contemporary Organic Synthesis, c/o Mercury Airfreight International Ltd, 2323 Randolph Avenue, Avenel, New Jersey 07001. All other dispatches outside the UK are by Bulk Airmail within Europe and Accelerated Surface Post outside Europe. 0 The Royal Society of Chemistry, 1996 All rights reserved No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form, or by any means, electronic, mechanical, photographic, recording or otherwise, without the prior permission of the publishers. Typeset in Great Britain by Unicus Graphics Ltd Printed in Great Britain by Whitstable Litho Ltd

ISSN:1350-4894    

DOI:10.1039/CO99502FP035

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

128 G. Handke and N. Krause, Tetrahedron Lett., 1993,34, 129 C. Darcel, S. Bartsch, C. Bruneau and P.H. Dixeuf, 130 T. Moriya, N. Miyaura and A. Suzuki, Synlett, 1994, 131 H. Bienaym6, Tetrahedron Lett., 1994,35,7387. 132 Y.S. Lee, K.H. Nam, S.H. Jung and H. Park, 133 P. Rochet, J-M. Vatkle and J. Go&, Synthesis, 1994, 134 H-F. Chow, X-P. Cao and M. Leung, J. Chem. SOC., 135 F. Toda, K. Tanaka and H. Nawata, J. Chem. SOC., 136 B.J.L. Royles and D.M. Smith, J. Chem. SOC., Perkin 137 V. Ratovelomanana, Y. Rollin, C. GCbkhenne, 6037. Synlett, 1994, 457. 149. Synthesis, 1994, 792. 795. Chem. Commun., 1994,2121. Perkin Trans. 1, 1994, 2043. Trans. 1, 1994, 355. C. Gosmini and J. Perichon, Tetrahedron Lett., 1994, 35, 4777. 138 D. Grandjean, P. Pale and J. Chuche, Tetrahedron Lett., 1994,35, 3529.139 K. Kusuda, K. Kawamura, Y. Ueno and T. Toru, Tetrahedron Lett., 1993, 34, 6587. 140 K. Miwa, T. Aoyama and T. Shioiri, Synlett, 1994, 107. 141 G.G. Melikyan, R.C. Combs, J. Lamirand, M. Khan and K.M. Nicholas, Tetrahedron Lett., 1994, 35, 363. 142 K. Iida and M. Hirama, J. Am. Chem. SOC., 1994,116, 10310. 143 M. Yoshimatsu, H. Yamada, H. Shimizu and T. Kataoka, J. Chem. SOC., Chem. Commun., 1994, 2107. Lett., 1993, 34, 5403. Tetrahedron Lett., 1994,35, 7615. 5975. 59, 6877. SOC., Chem. Commun., 1994, 1845. 1829. 4738. 713. 144 M. Alami, F. Ferri and G. Linstrumelle, Tetrahedron 145 T. Mandai, Y. Tsujiguchi, S. Matsuoka and J. Tsuji, 146 S. Ikeda and Y. Sato, J. Am. Chem. SOC., 1994, 116, 147 S. Ikeda, D.-M. Cui and Y. Sato, J. 0 ~ .Chem., 1994, 148 C. Darcel, C. Bruneau and P.H. Dixeuf, J. Chem. 149 K.K. Wang and Z. Wang, Tetrahedron Lett., 1994,35, 150 Z. Wang and K.K. Wang, J. 0%. Chem., 1994,59, 151 M.E. Maier and D. Langenbacher, Synlett, 1994, 152 J. Isihara, N. Kanoh, A. Fukuzawa and A. Murai, 153 K.K. Wang, Z. Wang and Y.G. Gu, Tetrahedron Lett., 154 H. Hopf and M. Theurig,Angew. Chem., Znt. Ed. 155 M. Moniatte, M. Eckhardt, K. Brickmann, Chem. Lett., 1994, 1563. 1993,34,8391. Engl., 1994,33, 1099. R. Bruckner and J. Suffert, Tetrahedron Lett., 1994, 35, 1965. Tetrahedron Lett., 1994, 35, 5689. Tetrahedron Lett., 1994, 35, 5645. 50,5335. 156 M. Yamaguchi, K. Omata and M. Hirama, 157 C. Meyer, I. Marek, J-F. Normant and N. Platzer, 158 D. Chemin and G. Linstrumelle, Tetrahedron, 1994, 159 S.A.Hitchcock, S.H. Boyer, M.Y. Chu-Moyer, S.H. Olson and S. J. Danishefsky, Angew. Chem., Znt. Ed. Engl., 1994, 33, 858. 160 T. Brandstetter and M.E. Maier, Tetrahedron, 1994, 50, 1435. 161 H. Audrain, T. Skrydstrup, G. Ulibarri, C. Riche, A. Chiaroni and D.S. Grierson, Tetrahedron, 1994, 50, 1469. K.M. Pham, D.M. Vyas and M.D. Wittman, Tetrahedron, 1994, 50, 1519. 482. 35, 37. 35, 2655. Tetrahedron Lett., 1994,35, 7997. R.A. Fairhurst, J. Chem. SOC., Chem. Commun., 1994, 1543. Danishefsky, Angew. Chem., Znt. Ed. Engl., 1994,33, 2477. 169 M.D. Shair, T. Yoon and S.J. Danishefsky, J. 0%. Chem., 1994,59,3755. 170 M.F. Braiia, M. Moran, M.J.P. de Vega and I. Pita- Romero, Tetrahedron Lett., 1994,35, 8655. 171 K. Toshima, K. Yanagawa, K. Ohta, T. Kano and M.Nakata, Tetrahedron Lett., 1994, 35, 1573. 172 P. Magnus, Tetrahedron, 1994,50, 1397. 173 D. Elbaum, T.B. Nguyen, W.L. Jorgensen and S.L. 162 J.F. Kadow, D.J. Cook, T.W. Doyle, D.R. Langley, 163 T. Nishikawa, S. Shibuya and M. Isobe, Synlett, 1994, 164 J.M. Nuss and M.M. Murphy, Tetrahedron Lett., 1994, 165 R.S. Huber and G.B. Jones, Tetrahedron Lett., 1994, 166 T. Nishikawa, M. Yoshikai, K. Obi and M. Isobe, 167 P. Magnus, D. Parry, T. Iliadis, S.A. Eisenbeis and 168 M.D. Shair, T. Yoon, T-C. Chou and S.J. Schreiber, Tetrahedron, 1994,50, 1503. Cousins: Saturated and unsaturated hydrocarbons 461128 G. Handke and N. Krause, Tetrahedron Lett., 1993,34, 129 C. Darcel, S. Bartsch, C. Bruneau and P.H. Dixeuf, 130 T. Moriya, N. Miyaura and A. Suzuki, Synlett, 1994, 131 H.Bienaym6, Tetrahedron Lett., 1994,35,7387. 132 Y.S. Lee, K.H. Nam, S.H. Jung and H. Park, 133 P. Rochet, J-M. Vatkle and J. Go&, Synthesis, 1994, 134 H-F. Chow, X-P. Cao and M. Leung, J. Chem. SOC., 135 F. Toda, K. Tanaka and H. Nawata, J. Chem. SOC., 136 B.J.L. Royles and D.M. Smith, J. Chem. SOC., Perkin 137 V. Ratovelomanana, Y. Rollin, C. GCbkhenne, 6037. Synlett, 1994, 457. 149. Synthesis, 1994, 792. 795. Chem. Commun., 1994,2121. Perkin Trans. 1, 1994, 2043. Trans. 1, 1994, 355. C. Gosmini and J. Perichon, Tetrahedron Lett., 1994, 35, 4777. 138 D. Grandjean, P. Pale and J. Chuche, Tetrahedron Lett., 1994,35, 3529. 139 K. Kusuda, K. Kawamura, Y. Ueno and T. Toru, Tetrahedron Lett., 1993, 34, 6587. 140 K. Miwa, T. Aoyama and T. Shioiri, Synlett, 1994, 107.141 G.G. Melikyan, R.C. Combs, J. Lamirand, M. Khan and K.M. Nicholas, Tetrahedron Lett., 1994, 35, 363. 142 K. Iida and M. Hirama, J. Am. Chem. SOC., 1994,116, 10310. 143 M. Yoshimatsu, H. Yamada, H. Shimizu and T. Kataoka, J. Chem. SOC., Chem. Commun., 1994, 2107. Lett., 1993, 34, 5403. Tetrahedron Lett., 1994,35, 7615. 5975. 59, 6877. SOC., Chem. Commun., 1994, 1845. 1829. 4738. 713. 144 M. Alami, F. Ferri and G. Linstrumelle, Tetrahedron 145 T. Mandai, Y. Tsujiguchi, S. Matsuoka and J. Tsuji, 146 S. Ikeda and Y. Sato, J. Am. Chem. SOC., 1994, 116, 147 S. Ikeda, D.-M. Cui and Y. Sato, J. 0 ~ . Chem., 1994, 148 C. Darcel, C. Bruneau and P.H. Dixeuf, J. Chem. 149 K.K. Wang and Z. Wang, Tetrahedron Lett., 1994,35, 150 Z. Wang and K.K. Wang, J. 0%. Chem., 1994,59, 151 M.E.Maier and D. Langenbacher, Synlett, 1994, 152 J. Isihara, N. Kanoh, A. Fukuzawa and A. Murai, 153 K.K. Wang, Z. Wang and Y.G. Gu, Tetrahedron Lett., 154 H. Hopf and M. Theurig,Angew. Chem., Znt. Ed. 155 M. Moniatte, M. Eckhardt, K. Brickmann, Chem. Lett., 1994, 1563. 1993,34,8391. Engl., 1994,33, 1099. R. Bruckner and J. Suffert, Tetrahedron Lett., 1994, 35, 1965. Tetrahedron Lett., 1994, 35, 5689. Tetrahedron Lett., 1994, 35, 5645. 50,5335. 156 M. Yamaguchi, K. Omata and M. Hirama, 157 C. Meyer, I. Marek, J-F. Normant and N. Platzer, 158 D. Chemin and G. Linstrumelle, Tetrahedron, 1994, 159 S.A. Hitchcock, S.H. Boyer, M.Y. Chu-Moyer, S.H. Olson and S. J. Danishefsky, Angew. Chem., Znt. Ed. Engl., 1994, 33, 858. 160 T. Brandstetter and M.E.Maier, Tetrahedron, 1994, 50, 1435. 161 H. Audrain, T. Skrydstrup, G. Ulibarri, C. Riche, A. Chiaroni and D.S. Grierson, Tetrahedron, 1994, 50, 1469. K.M. Pham, D.M. Vyas and M.D. Wittman, Tetrahedron, 1994, 50, 1519. 482. 35, 37. 35, 2655. Tetrahedron Lett., 1994,35, 7997. R.A. Fairhurst, J. Chem. SOC., Chem. Commun., 1994, 1543. Danishefsky, Angew. Chem., Znt. Ed. Engl., 1994,33, 2477. 169 M.D. Shair, T. Yoon and S.J. Danishefsky, J. 0%. Chem., 1994,59,3755. 170 M.F. Braiia, M. Moran, M.J.P. de Vega and I. Pita- Romero, Tetrahedron Lett., 1994,35, 8655. 171 K. Toshima, K. Yanagawa, K. Ohta, T. Kano and M. Nakata, Tetrahedron Lett., 1994, 35, 1573. 172 P. Magnus, Tetrahedron, 1994,50, 1397. 173 D. Elbaum, T.B. Nguyen, W.L. Jorgensen and S.L. 162 J.F. Kadow, D.J. Cook, T.W. Doyle, D.R. Langley, 163 T. Nishikawa, S. Shibuya and M. Isobe, Synlett, 1994, 164 J.M. Nuss and M.M. Murphy, Tetrahedron Lett., 1994, 165 R.S. Huber and G.B. Jones, Tetrahedron Lett., 1994, 166 T. Nishikawa, M. Yoshikai, K. Obi and M. Isobe, 167 P. Magnus, D. Parry, T. Iliadis, S.A. Eisenbeis and 168 M.D. Shair, T. Yoon, T-C. Chou and S.J. Schreiber, Tetrahedron, 1994,50, 1503. Cousins: Saturated and unsaturated hydrocarbons 461

ISSN:1350-4894    

DOI:10.1039/CO99502BP041

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

~~ Stoichiometric organotransition metal complexes in organic synthesis JULIAN BLAGG Pfizer Central Research, Sandwich, Kent, CT13 9NJ Reviewing the literature published between 1 September 1993 and 31 August 1994 1 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 3 3.1 3.2 3.3 3.4 3.5 3.6 4 4.1 4.2 4.3 4.4 5. 6 6.1 6.2 6.3 7 8 8.1 8.2 9 9.1 9.2 9.3 9.4 10 Introduction Transition metal alkyl, allyl, alkenyl, alkynyl and acyl complexes in organic synthesis Hydrozirconation methodology Ally1 zirconium species Alkyl, allyl, alkenyl and alkynyl chromium species in synthesis Alkyl and alkenyl cobalt species in synthesis Acyl transition metal complexes in synthesis Chiral rhenium complexes in synthesis Manganese enolates Group 6 transition metal carbene complexes in synthesis Annulation reactions Spirocycle synthesis Vinyl carbene complexes Amino acid and peptide synthesis Carbene-mediated cycloadditions Cleavage of transition metal carbene complexes q2-Complexes in organic synthesis q2-Alkyne dicobalt hexacarbonyl complexes q2-Complexes of zirconocene q2-Complexes of osmium y2-Complexes of manganese y3-Complexes in organic synthesis q4-Complexes of iron tricarbonyl in organic synthesis Acyclic complexes Cyclic complexes q4-Azadiene tricarbonyl iron complexes q5-Complexes in organic synthesis $'-Complexes in organic synthesis y6-Arene chromium tricarbonyl complexes in synthesis @-Arene manganese tricarbonyl cations and q6-arene ruthenium cyclopentadienyl cations in organic synthesis Transition metal mediated cycloadditions in organic synthesis The Pauson-Khand and related cycloadditions Titanium- and zirconium-mediated cycloadditions Cobalt-mediated cyclotrimerizations Rhenium promoted cycloadditions References 1 Introduction This review covers the literature from 1 September 1993 to 3 1 August 1994 and is a selective account of recent developments in the application of stoichiometric organotransition metal chemistry to organic synthesis.The format is similar to last year's review' although the section on carbene complexes has been further subdivided. New areas which have come to the fore in the last year include the use of manganese enolates for regioselective ketone alkylation (Section 2.7), the use of y2-osmium complexes to control the reactivity of aromatic systems (Section 4.3) and the synthesis of peptides containing unnatural amino acids using chromium carbene complexes (Section 3.4).Notable synthetic applications of y4-diene tricarbonyl iron complexes (Section 6.1) and the intramolecular Pauson-Khand reaction (Section 9.1) have been published. Several general reviews have appeared covering organozirconium chemistry,2 higher order transition metal promoted cycl~additions~ and organonickel chemi~try;~ an interesting account of the relative electrophilicity and nucleophilicity of organometallic complexes has also a~peared.~ Other reviews relevant to a particular area are cited in the text. 2 Transition metal alkyl, allyl, alkenyl, alkynyl, and acyl complexes in organic synthesis 2.1 Hydrozirconation methodology New and useful extensions to the classical hydrozirconation methodology originally developed by Schwartz6 have continued to be published this year. A simple but noteworthy example is the preparation of tritiated Schwartz reagent which should prove useful for the regioselective radiolabelling of molecules undergoing metabolic ~tudies.~ Of particular interest to the synthetic organic chemist are methods to elaborate the C-Zr bond formed in hydrozirconation reactions. Lipshutz has developed a catalytic version of his earlier work on the copper-mediated transfer of vinyl groups from zirconium to the P-position of enones.8 Key to this advance was the addition of Me,ZnLi which regenerates the copper species Me,Cu(CN)Li in situ without reacting with the enone.The zinc enolate 1 formed in this procedure may be trapped by an aldehyde in a remarkable six step one-pot synthesis of the prostanoid skeleton (Scheme 1).This work should Blagg: Stoichiometric organotransition metal complexes in organic synthesis 431 74% Scheme 1 be compared with that of Wipf who has published a similar process whereby alkylzirconium species add to the P-position of enones in the presence of 3-10 mol% CuBr.SMe, or CuCN. Here the resulting zirconium enolate may be trapped with an aldehyde; the addition of alkylzincs to regenerate the catalytic copper( I ) species is not necessary.9 Wipf has also published an efficient synthesis of allylic alcohols via dialkylzinc-mediated transmetallation of alkyne hydrozirconation products and aldehyde trapping.”) An important aspect of this work is the stereoselective addition to a-substituted aldehydes to give predominantly the syn-isomer (Scheme 2).This is an improvement over the non-selective AgC10,-mediated coupling of alkenylzirconates with aldehydes developed by Suzuki. J Scheme 2 In another synthetically useful procedure involving copper catalysis, Takahashi has prepared a variety of dienes or 1,4,7-trienes.l I Trapping of an alkyne hydrozirconation product 2 with ally1 chloride in the presence of catalytic CuCN gives the skipped diene 3 accompanied by a small amount of dimerization product. Use of the previously reported allylation of zirconacycles12 followed by a copper-catalysed allylation gives the 1,4,7-trienes 4 (Scheme 3). LEI (2e4.) 2 3 (75%) Blf BunY A 4 (81%) Scheme 3 Chemoselective hydrozirconation of alkenes or alkynes in molecules containing reactive carbonyl groups has been achieved by the simple expedient of protecting the carbonyl as the acyl silane.I3 This prevents both hydride addition to the carbonyl and intramolecular chelation of the carbonyl oxygen to the coordinatively unsaturated zirconium, thereby rendering it unreactive under transmetallation conditions.Following his work on the hydrozirconation of allenylstannanes to give terminal dienes,’, Suzuki has reported the hydrozirconation of an isolated terminal allene and subsequent trapping of the allylzirconium species 5 with aldehydes and ketones to give homoallylic alcohols in a highly regio- and stereo-selective manner (Scheme 4).* Low temperatures and the use of dichloromethane as solvent are crucial to the success of these reactions.Wipf has published an interesting series of reactions which further exploit the AgC10,-mediated epoxide rearrangements published last year.16 Treatment of the succinate 6 with hexenylzirconocene in the presence of 5 mol% AgClO, initially generates the cationic intermediate 7 which undergoes a chelation-controlled attack of the alkenyl zirconium reagent to give the acetal8 (Scheme 4).” A version of this reaction catalytic in zirconium ( 10 mol%) and AgClO, ( 10 mol%) was also reported in the same paper. Srebnik has continued his elegant work on the hydrozirconation of vinylboranes18 to give a-haloboranes which are valuable intermediates for aminoboronic acid synthesis.19 This provides a useful 44 Contemporary Organic SynthesisJ 0 HO' 7 Scheme 4 84% (96% d.e.) 0 8 PPTS. Hfl 80 "c.4h 100% acetone R0J-+k/-- 0 alternative to the methodology of Matteson.20 Of particular note is the use of optically pure vinylboranes bearing a chiral ligand on boron which undergo diastereoselective hydrozirconation (Scheme 5).21 The hydrozirconation of alkenylzincs to give the 1, l-bimetallic of Zn and Zr has been published by Knochel; trapping with aldehydes give (E)-alkenes in a highly selective manner (Scheme 5).22 2.2 Ally1 zirconium species Taguchi, Takahashi, and co-workers have pioneered the generation of allylzirconium species by p-elimination of an alkoxy group in the zirconocene complex of an allylic ether.23 This methodology has now been applied to a highly diastereoselective ring-contraction process.24 For example, treatment of the homochiral vinylmorpholine 9 with 'Cp2Zr' gave the pyrrolidine 10 via an intermediate allyl zirconium species (Scheme 6).25 The stereochemistry of the product depends only on the configuration of the amino acid used to prepare the vinylmorpholine. This method was used to prepare the pyrrolidizine alkaloid c-hexCHO 83% (98% E ) Via Scheme 5 9 Scheme 6 Ph 10 (90% d.e.) ( - )-macronecine in five steps ( 10% overall yield) from N-Boc-L-proline methyl ester.Taguchi has also used this type of ring-contraction to prepare cyclobutanes from 4-vinylf~ranosides.~~ 2.3 Alkyl, allyl, alkenyl, and alkynyl chromium species in synthesis This topic has recently been the subject of an excellent review by H~dgson;*~ however, several subsequent publications have extended the synthetic applicability of alkyl, allyl, alkenyl, and alkynyl chromium reagents.Wipf has developed a low-temperature version of the Nozaki-Hiyama coupling reaction which allows the addition of organochromium reagents to sensitive molecules.2x Hodgson has recently reported an efficient homologation of aldehydes to the corresponding methyl ketones via Cr"-mediated addition of Me,SiCBr,.29 Also of note, Taddei has used a classical Nozaki coupling to prepare hydroxyethylene isosteres of peptidic linkages30 and Kibayashi has used the coupling as the key step in a synthesis of allopumiliotoxins 267A and 339A.,' Blagg: Stoichiometric organotransition metal complexes in organic synthesis 452.4 AIkyl and alkenyl cobalt species in synthesis Most of the chemistry associated with these species has involved the use of alkylbis( dimethylg1yoximato)cobalt complexes as radical-trapping and radical-generating reagents.In particular, the mild homolytic functionalization of the organic ligand has been applied to organic synthesis.32 However, a recent publication from Orsini dealt with the application of Coo species to C-C bond formation in a cobalt version of the Reformatski-reaction.”” The active species Co[PMe,], was generated in situ from CoC1, and PMe,. This method has the advantage of mild reaction conditions and higher yields when compared with the zinc-mediated Reformatski-reaction; moreover, only 1,2 addition is observed with enones. The disadvantage is the use of PMe,; however, in the same paper Orsini also demonstrated that the reaction proceeds with catalytic amounts of CoClJPMe, as long as magnesium turnings are added to the reaction (magnesium alone does not mediate the coupling).An interesting paper from Welker has highlighted the use of ql-cobalt substituted butadiene complexes in Diels-Alder cycl~additions.~~ The diene complexes are prepared in high yield from the corresponding allene 11 and a stabilized cobalt anion 12 (Scheme 7). A bulky cobalt ligand at the 2-position of the diene serves to enforce a predominantly s-cis diene conformation such that Diels-Alder reactions occur under mild conditions; moreover, the reaction of dienophiles with complex 13 proceeds in an exo-selective manner in contrast to standard Lewis acid or thermal Diels-Alder reactions.The cobalt-containing products may be functionalized in a variety of ways with maintainance of stereochemical integrity. 0 (Pyr) (dmg)2 Co-Na’ I 0 - 25 %, 6h 0 n 13 92% 0 11 L3 = PYr) (dmg)2 dmg = dimethylglyoximato Scheme 7 2.5 Acyl transition metal complexes in synthesis Davies has published an efficient method for the kinetic resolution of the widely used chiral auxiliary CpFe( CO)PPh,COMe via aldol reaction of the lithium enolate with ( 1 R)-( + )-camphor,35 whilst Brunner has used the auxiliary in an asymmetric synthesis of a precursor to erap pa mil.^^ Marson has published an interesting application of molybdenum acyl complexes to the synthesis of hydroxymethyl lactones and spiroketals (Scheme S).37 The key to this process is the SnC1,-mediated intramolecular cyclization of the acyl oxygen of 14 onto a pendent epoxide.=--/ -Mo- \ Na* (ii) PPhs MeCN Ph3P’ - - / Mo- \ 0 co co co co 14 (i) SnCI, CH,CI, (ii) Hfi (iii) NaBPh,, MeOH 1 51 % overall Scheme 8 2.6 Chiral rhenium complexes in synthesis Gladysz has published an interesting procedure for the synthesis of optically pure 1-substituted or 1,4-disubstituted tetrahydroisoquinolines via coordination of isoquinoline to the chiral auxiliary CpReNO( PPh,) to give the homochiral ( + )-( S)-cation 15 (Scheme 9).38 This cation, on treatment with Me,SiCH,Li at - 55”C, generates the enamine 16 (88% d.e.) which can subsequently be alkylated at the 4-position (also 88% d.e.). Reduction of the iminium salt and removal of the auxiliary gives the optically pure tetrahydroisoquinoline 17 in good yield.The same chiral auxiliary has been used by Gladysz for the enantioselective synthesis of sulfides via a [2,3] sigmatropic rearrangement of the ylid derived from the coordinated diallyl sulfonium salt 18 (Scheme 9).34, 2.7 Manganese enolates Several papers have appeared over the last year which highlight the use of manganese enolates for the regioselective monoalkylation of ketones. This chemistry represents a significant advantage over the corresponding lithium enolates which often give non-regioselective or polyalkylated by-products. Manganese enolates are efficiently obtained by reaction of ketones with Mn-amides [ e.g. PH(Me)NMnCl] at - 10°C to 20°C in THF; subsequent alkylations are greatly facilitated by the addition of a polar solvent such as DMSO.,O Trapping of the enolates with Me3SiC1 gives silyl enol ethers in a highly regioselective manner.4 Alternatively, manganese enolates may be obtained by transmetallation of the corresponding lithium en~lates.,~ 3 Group 6 transition metal carbene complexes in synthesis A large volume of work has been published in this area over the last year, particularly in the field of chromium 46 Contemporary Organic SynthesisI B HOTf loO%to-55% @ -0Tf I Re: ON' I 'PPh3 Me Me BU'OK (+)-( S )-15 U -80% (> 98% e.e.) 79% v 17 (88% d.e.) I 18 hie Scheme 9 carbene chemistry and readers are referred to a good short review by S ~ h m a l z ~ ~ which highlights the major developments in chromium carbene complexes as applied to organic synthesis.3.1 Annulation reactions Group 6 transition metal carbene mediated reactions have been the subject of intense mechanistic study; W ~ l f f ~ ~ and Harvey45 have published papers which allow rational predictions of reactivity and reaction pathways to be made in this complicated area and their results, coupled with further understanding of the processes involved, will allow optimization of synthetically useful carbene-mediated reactions. last year; for example, a simple and efficient new preparation of alkoxycarbene complexes containing functional groups in the alkoxy moiety has been reported which involves the alkylation of tetramethylammonium alkoxide salts with alkyldiphenylsulfonium salts.46 Treatment of the vinylcarbene complex 19 (Scheme 10) with alkynes to produce phenols has not proven synthetically useful; however, Wulff has demonstrated that the a- or Key synthetic advances have also been made in the (ii) EtN' CN, CH&12 91% (i) MeOTf, - 80 % ~- (ii) Et4N+ C N 16 (88% d.e.) Q I ON-*~.pph3-oTf SiMe3 "'3- (88% d.e.) de > 98°/0 8.8.P-silylvinylcarbene complexes 20 or 2 1 are useful synthons, stable enough to undergo annulation reacti0ns.4~ In 20 the silicon moiety migrates to the phenolic oxygen, rendering the products stable and isolable while for 2 1 the silicon is incorporated in the product aromatic ring and may be replaced (e.g. by proteodesilylation as illustrated). The regiochemistry of the alkyne insertion is of note; the larger alkyne substituent is incorporated adjacent to the phenolic oxygen.For stannyl substituted alkynes this regiochemistry is reversed thereby placing tin meta to the phenolic oxygen. For stannyl substituted alkynes this regiochemistry is reversed thereby placing tin meta to the phenolic oxygen (Scheme can subsequently be exchanged with lithium or substituted using palladium-mediated couplings. Chan has used silyl substituted alkynes in an approach to regioselective quinone synthesis; as observed for the stannyl group above, the silyl is incorporated meta to the phenolic oxygen and can be converted into iodide to allow subsequent palladium-catalysed reaction^.^' Following on from his earlier work:' Merlic has published an efficient photochemical benzannulation of biarylcarbene complexes which proceeds with particularly good chemoselectivity with fury1 and the tin residue Blagg: Stoic h io rn etric organ otra nsition meta 1 complexes in organic synthesis 47R 1 9 R = H 20 R = SiMe,Bu' 40 % OMe ( i ) H e S n B u 3 (ii) TBSOTf,Et3N (0c)5cf=5d Me& H OSiM+BU' I Scheme 10 OH (ii) CF3C02H, air 60% 0)Me naphthalene substituted substrates (Scheme 1 1).51 Synthesis of the biaryl carbene precursor 22 is accomplished in high overall yield using a palladium-catalysed cross-coupling. Wulff has recently published a stereoselective synthesis of an arene Cr( CO), complex in which benzannulation of the propenyl complex 23 with the homochiral alkyne 24 leads to 25 with remarkably high diastereoselectivity ( > 92%).The propargylic oxygen appears to play a key stereoelectronic directing role (Scheme 1 1 ).52 22 OCPh3 -?-H 23 25 (68 9'0 yield, > 92 % d.e.) Scheme 11 3.2 Spirocycle synthesis Two papers have been published which explore the chromium-mediated cyclization of 1 -alkyn-4-ols.Quayle has prepared a variety of spirocyclic carbene complexes 26 via exposure of the alkynols to THF.Cr( CO), generated from photolysis of Cr( CO), in THF (Scheme 1 2 y 3 Oxidative removal of the chromium reveals the target y-lactones. Similarly, McDonald has found that chromium, tungsten, or preferably molybdenum hexacarbonyl can be used to cyclize 1 -alkyn-4-ols to the corresponding 2,3-dihydrofurans in the presence of trimethylamine-N-oxide (TMNO), which induces the loss of one CO ligand;54 note that less than one equivalent of metal is required since molybdenum is lost from the intermediate 27 under the reaction conditions to generate a catalytically active species.This should be compared with the requirement for oxidative removal of the metal in the work of Q~ayle.~, 78% U Mo(C0)6 0.5 q. TMNO(0.5 eq), Et$l * E t a . 60h Ph ii% 27 phYo> + Me3Ni, Mo(CO)s Scheme 12 3.3 Vinyl carbene complexes A simple and efficient procedure for the preparation of alkylidenepyrrolidinocarbenes of chromium has been published by Maiorana and Papagni using the base-catalysed elimination of the previously precedented aldol products 28 (Scheme 13).55 The reaction of these alkylidene complexes with LDA at low temperature and trapping with electrophiles gives predominantly the a-substituted products 29 (Scheme 1 3).56 Of particular interest is the stereoselective tandem Michael addition-alkylation of ketone enolates to vinylalkoxycarbene complexes published by Nakamura (Scheme 1 3).57 The high yields in most of these reactions offer advantages over the corresponding Michael addition of ketone enolates to a,p-unsaturated esters which are less efficient. Particularly noteworthy are the high syn stereoselectivity and the options for subsequent functionalization of the carbenoid products 30.A useful example of the Michael addition of imines to alkynylcarbene complexes of chromium leading to an efficient three-step synthesis of 2H-pyrroles has also been published.58 48 Contemporary Organic Synthesis3.5 Carbene-mediated cycloadditions I ., , (i) MsCI, E t d . 0 "c, 2h 7 1' (ill NaOH, EOH, r.t.. 5 rnin.- 'ww'5w' (48 - 70%) --R 28 0 0 (I)LDA.- 78 "c, 20 min. (Oc)scr<~ (ii) MeL - 74% 78 "c to 0 "c * Me Me 29 (U : y = 84 : 1 6) OLi 30 [84% (87 : lS)] E t o 2 c ~ Scheme 13 3.4 Amino acid and peptide synthesis Hegedus has continued his elegant work on stereoselective peptide synthesis via photolytic coupling of chromium aminocarbene complexes.s9 Photolysis of optically pure chromium aminocarbene complexes 3 1 in the presence of peptide methyl esters gives the protected tetrapeptide esters in good yield; moreover, this reaction can be achieved with the peptide supported on Merrifield resin (Scheme 14):O The main advantages here are that the coupling is induced by visible light and that unnatural amino acid fragments may be directly incorporated into the growing peptide chain without the need to presynthesize the amino acid directly.The synthesis of homochiral unnatural amino acids has also been achieved!' I N-Val-Leu-Gly -0* Resin 0 31 (i) THF. hv, CO, 0 "c (ii) deprotection Ph I I Hegedus has published a detailed study of electronic effects on the stereochemical outcome of the [2 + 21 cycloaddition of chromium carbene complexes with imines to form p-lactams.h2 Optically active butenolides have been prepared using the photolytic [2 + 21 cycloaddition of chromium alkoxycarbene complexes 32 to homochiral ene-carbamates (Scheme 1 5).63 Although cyclobutanone formation in the above case is relatively rapid, the corresponding [2 + 21 cycloaddition of chromium alkoxycarbene complexes with aldehydes to give P-lactones is slow and only synthetically useful in an intramolecular sense (Scheme 1 5).64 Intramolecular [ 2 + 21 cycloaddition with an alkene to give a metallocyclobutane intermediate has been published by Soderberg as a route to indoles and quinolines.6' The reaction of Fischer carbene complexes with enynes (e.g.33) gives cyclobutanones via a similar intramolecular [ 2 + 21 cycloaddition; high diastereoselectivity is observed in these reactions (Scheme 15)F6 Formal [2 + 2 + 13 cycloadditions of aminocarbene complexes have been shown to give trisubstituted ~yclopentanes.6~ The corresponding alkoxycarbene complexes give cyclopropanes via [2 + 21 cycloaddition followed by reductive elimination of the metal. The aminocarbenes, however, undergo a second insertion of alkene to the metallocyclobutane intermediate, prior to reductive elimination of the metal.+ Ph.. n If NKo 0 (m)scr<CHO THF. 16h M e O - B - - H 0 72% single diastereoisomer MeCN, 70 "c, 4h Me 33 20 : 1 ratio of diastereoisomers Scheme 14 Scheme 15 Blagg: Stoichiometric organotransition metal complexes in organic synthesis 49Diels-Alder-type [4 + 21 cycloadditions of vinylcarbene complexes have been known for some time; the carbene moiety activates the dienophile to the same extent as a Lewis acid catalyst in the standard Diels-Alder reaction. Barluenga has now examined a diastereoselective [4 + 21 cycloaddition using a chiral diene with alkoxyvinyltungsten carbenes.68 These reactions give predominantly the endo products via the s-trans vinylalkoxydiene in moderate to excellent diastereoselectivity. The corresponding chromium carbenes can undergo a competing [2 + 11 cyclopropanation/tandem Cope rearrangement leading to seven-membered ring products.1,68>69 Barluenga has locked the alkoxyvinylcarbenes in an s-cis conformation via an internal boron chelate 34 such that subsequent [4 + 21 cycloaddition gives exo-selective products in high diastereoexcess (Scheme 1 6).70 An exo-selective [4 + 21 cycloaddition with alkoxyvinylcarbene complexes of tungsten has been reported where the dienophile is locked in the s-cis conformation by virtue of a bulky ligand on the THF.- 78 “c to r.t. alkoxy oxygen atom.71 p” Me P h A O w 90% 8.8. Me OMe Scheme 16 Mention was made in last year’s review’ of the Grubbs metathesis catalyst and several notable applications in synthesis have been published this year.In particular, Martin’s approach to the synthesis of manzamine A via the efficient cyclization of the tricyclic precursor 35 deserves mention (Scheme 1 7).72 Catalytic versions of the Grubbs metathesis reactions are now being developed but will not be discussed further in this review.73 3.6 Cleavage of transition metal carbene complexes A number of papers have appeared which highlight procedures for removal of the metal atom from transition metal carbene complexes. Chan has studied the insertion of organosilanes into vinylcarbene complexes to give allylsilanes (Scheme 1 8),74 whilst vinyl silanes may be formed by the addition of alkyllithiums to silyl substituted Fischer carbene complexes (Scheme 1 8).75 Sodium borohydride in trifluoroacetic acid is effective in removing the metal 35 Me Scheme 17 86%, (96 : 4, E : Z) Scheme 18 moiety from amino carbene complexes to give the free amine (Scheme 1 4 q 2-Complexes in organic synthesis 4.1 q 2-Alkyne dicobalt hexacarbonyl complexes A good review of y2-alkyne dicobalt hexacarbonyl complexes applied to the synthesis of enediyne antitumor agents has been published by mag nu^;^^ in addition, he has published a more detailed account of the y2-alkyne dicobalt hexacarbonyl mediated approach to the azabicyclo[ 7.3.llenediyne core of dynemi~in.~~ A full account of the a to #? epimerization of C- 1 -alkynyl substituted pyranose derivatives via their dicobalt hexacarbonyl derivatives has now been published by I~obe.~’ 50 Contemporary Organic SynthesisNew synthetic applications of q2-alkyne dicobalt hexacarbonyl complexes include the reaction of cobalt complexed alkynyl aldehydes with homochiral y-alkoxyallyl boranes 36 to give 3,4-dioxy-1,5-eneyne complexes in enantioselective fashion (Scheme 1 9).s0 The cobalt moiety serves to protect the alkyne and exerts a high degree of stereocontrol in the addition reaction.The Nicholas reaction of dicobalt hexacarbonyl stabilized propargylic cations has been used in an effective, high yielding route to the otherwise elusive N-unsubstituted 2-azetidinones 37 (Scheme 1 9).81 + 36 37 Scheme 19 A number of applications involving ring-closure reactions have been published in the last year. For example, Hanoaka has applied the Nicholas reaction in an intramolecular sense to give tetrahydropyrans via a 6-endo ring-closure onto an epoxide; this reaction occurs with complete retention of stereochemistry at the propargylic position due to the configurational stability imparted to the cationic intermediate by the cobalt moiety (Scheme 20).82 Tetrahydrofuran derivatives may be obtained by a similar intramolecular endo ring-closure of cobalt complexed 3,4-epoxyhex-5-yne- 1-01s (Scheme 20).83 Ring closure onto cobalt stabilized propargylic cations has been exploited by Grove in a synthesis of Ph p (99: 1, u s : trans) Ph‘ Ph’ (92 : 8, u s : trans) Scheme 20 the morphinan skeleton; the cobalt moiety facilitates kinetically controlled ring-closure to give the desired cis-fused products.84 Intramolecular fluoride and Lewis acid catalysed attack of a silyl enol ether onto a cobalt-stabilized propargylic cation has allowed Tyrrell to prepare five- to six-, and seven-membered rings.85 Unfortunately, a mixture of kinetic and thermodynamic enolates is obtained for methyl ketones resulting in a mixture of ring closed products.A new strategy has been developed for the Mn( OAc), mediated oxidative cycloaddition of enynes with 1,3-dicarbonyl compounds, involving protection of the alkyne with dicobalt hexacarbonyl and thereby directing cycloaddition to the alkene.86 Lastly, Nicholas has reported that cobalt-stabilized propargylic cations can be reduced by zinc to the corresponding radical species which then undergo efficient intermolecular coupling reactions. This methodology is particularly useful for ring closure reaction^.^^ 4.2 q *-Complexes of zirconocene Takahashi has published a detailed account of the reactions of q2-zirconocene alkene complexes with aldehydes and ketones; excellent regoselectivity in zirconacyclopentane formation can be achieved with vinylsilanes to give y-silylalcohols after hydrolytic removal of the metal (Scheme 2 1).88 Carbon-carbon bond formation occurs at the P-position of the vinyl silane.An improved procedure for functionalizing the a-position of amines via q2-zirconocene complexes of imines has been published by Whitby8’ as well as a detailed study of the kinetics and steric/electronic factors involved in the formation and trapping of y2-zirconocene complexes of imines.’O H+ I 7296 B(C6FSh the 38 cp&w Me Scheme 21 Blagg: Stoichiometric organotransition metal complexes in organic synthesis 51Jordan has extended his work on the functionalization of pyridines a-to nitrogen via the cationic q2 zirconocene pyridine complex by developing an exciting catalytic, diastereoselective version of the reaction where the zirconium catalyst bears a chiral ethylenebis( tetrahydroindenyl) ligand.” The enhanced reactivity towards insertion reactions exhibited by cationic q2-zirconocene complexes has been exploited by Jordan to activate q2-( iminoacyl) zirconocene complexes 38 (Scheme 2 1).The increased Lewis acidity of the metal centre on formation of the cationic complex enhances the rate of insertion of alkenes and alkynes such that reactions can be performed at ambient temperature in less than one hour.y2 q2-Zirconocene complexes of a variety of species have proven useful for mediating C-C bond formation a to a heteroatom. For example, formation of the q2-zirconocene complex of 3,4-dihydro-2H-pyran 39 has enabled Whitby to prepare a range of 1-substituted dihydropyrans via regioselective insertion of alkenes (Scheme 22).y3 The q2-zirconocene complexes of (i) MeLi.- 78 “c (i)Bu’Li,-2O“c (ii) Cpgr(Me)Ci (iii) 80 “c. 1%. benzene (ill PhCHO (iii) HCI 39 Ph Ph (i) Ph&O,F&.OEtz.-40 “c M@Hl (i9 MeOH 57% I 9 Ph 62% Me I y-=P2 (i) MGnLi, THF, - 78 “c ;o^. SnMe3 (11) Cp,Zr(Me)CI. 23 “C t OH OH aldehydes have recently been prepared via treatment of the zirconocene( a-stannylalkoxide) complexes 40 with methyl lithium at low temperature; these species insert aromatic aldehydes and ketones to give 1,2-diols after hydrolytic removal of the metal (Scheme 22).”4 This represents a threo-selective pinacol-type coupling process with the advantage that unsymmetrical diols may be prepared; unfortunately, aliphatic aldehydes or ketones do not insert. A more versatile vanadium-mediated pinacol-type synthesis of unsymmetric diols has been published by Pedersen which is of more general applicability in synthesis (Scheme 2 2).ys Many of the reactions of q2-zirconocene complexes involve insertion of unsaturated functionality (alkenes, alkynes, carbonyls, etc.) to generate a five-membered metallocyclic species.An important aspect of this chemistry is the subsequent functionalization of the metallocycle to give useful organic products.Although this may be achieved by, for example, chemoselective halogenation of the C-Zr bonds,’6 or heterocycle forrnati~n,~’ methods of C-C bond formation are limited. Whitby has reported work on the insertion of phenyl isocyanide into zirconacyclopentanes’ and zirconacyclopentenes;” he has also demonstrated that alkyl- and trialkyl-silylisocyanides react similarly.’y Insertion of lithium chloroallylide into zirconacyclopentanes has also been achieved; the resultant q3-allyl intermediate 4 1 may be trapped with aldehydes or ketones to give homoallylic alcohols 42 (Scheme 23).’0° Negishi has trapped simple zirconacyclopentanes and zirconacyclopentenes with aldehydeslO’ whilst Erker has trapped the simple (butadiene) zirconocene reagent with ketones, nitri1es,’O2 and W(CO),.103 Reaction of zirconacyclopentenes with allylic acetals forms the e C I , LDA - 78 “C to r.t.THF H H PPh 42 75% ‘0 Et 76% (> 20 : 1 d.e.) Scheme 22 43 44 Scheme 23 5 2 Contemporary Organic Synthesismetallocycle 43 which is irreversibly transformed into the skipped diene products 44 via cleavage of one of the acetal C-0 bonds (Scheme 23);lo4 overall this is very similar to the reaction of allyl ethers with zirconacyclopentenes reported last year by Takahashi.'>los In contrast, reaction of zirconacyclopentenes with homoallylic bromides gives cyclopropanes via a different pathway.lo6 (i) BuSJBH, 4.3 q 2-Complexes of osmium Four papers have been published in the last year from the laboratory of Harman which highlight the use of r2-complexes of osmium as a tactic for controlling the reactivity of aromatic systems. q2-Coordination of or anilines'O* to osmium localizes the n-electron density in the non-coordinated diene moiety.Subsequent treatment with Michael acceptors gives a regio- and stereo-controlled electrophilic addition para to the heteroatom substituent or ortho if the para position is blocked; moreover, the osmium moiety stabilizes the resultant diene species, thus facilitating the synthesis of substituted 3-aminocyclohexenes 45 or 4-substituted 2,5-cyclohexadienones 46 and 6-substituted 2,4-~yclohexadienones 47 (Scheme 24). q*-Coordination of furans renders the heterocycle more susceptible to electrophilic attack at the 4-position and less susceptible to polymerization such that complex 48 may be isolated from the reaction with methylvinylketone in methanol (Scheme 24).lo9 A similar tactic has been used by Harman with pyrrole to facilitate electrophilic attack at the 4-position of the v2-osmium complex.' (in CeN 5 q 3-Complexes in organic synthesis A detailed investigation of the reactions of q3-allyl iron tricarbonyl anions with electrophiles has been published by Brookhart.' l 2 Initial electrophilic attack occurs at the metal which, in the presence of PPh,, undergoes CO insertion and acyl migration to give the a$-unsaturated enone complex 50 (Scheme 26).Brookhart went on to study the effect of substituents in the allylic complex; in particular, the effect of syn and anti substituents on the regiochemistry of acyl migration.A similar class of acyl migration involving $-complexes of iron has been reported by Nakanishi. P,y-Unsaturated carboxylic ester 5 1 can be prepared via carbonyl insertion/acyl migration of ( q3-allyl)Fe)CO),NO complexes which, in turn, are easily prepared from allyl halides (Scheme 26).I I Carbonylation occurs regioselectively at the s 45 0 [&I2+ Me 47 4.4 q Womplexes of manganese q2-Complexes of manganese have been used to protect the alkene moiety of cyclic a,P-unsaturated ketones thereby allowing regioselective a '-deprotonation to form the enolate and subsequent alkylation to give 49. Good stereocontrol is observed in the case of five-membered rings with the electrophile entering away from the bulky organometallic protecting group (Scheme 25).'" OH I tie [&]2+- 4 Me' O V 0 Me * 46 Scheme 24 least-hindered terminus of the allyl ligand and is facilitated by the addition of 1,2-bis( dipheny1phosphino)ethane (DPPE).Nakanishi also demonstrated that ( $-allyl)Fe( CO),NO complexes undergo conjugate addition to a,P-unsaturated carbonyl compounds to give the corresponding d,&-unsaturated carbonyl species in good yield; use of ( q3-l or -2-trimethylsilyloxyallyl)Fe( CO),NO complexes gives 1,6-or 1,5-diketones respectively.' l4 chromium tricarbonyl complexes to impart stereocontrol in conjugate additions is well documented. New to the repertoire, however, is the use The use of q*-iron acyl complexes and arene Blagg: Stoichiometric organotransition metal complexes in organic synthesis 530 0 p +2] I co 4 0 0 63% CO 49 Scheme 25 50 (87%) Fe(CO),NO (i) DPPE.CH&i2 r.t, 18h I 51 (87%) Scheme 26 of q5-( C,H, )Mo( CO),( x-allyl) fragments as control elements in the conjugate addition; Liu has published two papers which demonstrate their potential in this process for the synthesis of substituted tetrahydrofurans. Of particular interest is the observation that the major isomer from the conjugate addition appears to arise from attack at the least-hindered Si face of the disfavoured s-trans-enone complex 52 (Scheme 27).' q3-( n-Ally1)molybdenum complexes of cyclopentenone have been used by Liebeskind to synthesize 4-substituted-2-cyclopentenones. I l6 90% (14 : 1 selectivity) (i) LiN(SiMe& -78% (ii) PhCHO I (S)-tran~ 52 69% Scheme 27 89% Two interesting papers have been published concerning the nucleophilic addition of carbanions to q3-allyl palladium complexes.Chen has demonstrated that reaction of the metal allenyl complex 53 with a soft carbanion leads to the zwitterionic complex 54. This q3-trimethylene methane species can be trapped by electron-deficient olefins to give cyclopentenoids (Scheme 28).' l 7 Hoffman has shown that q3-allyl palladium complexes 55 can be trapped with various enolate anions in the presence of TMEDA at the central carbon atom to give a general synthesis of substituted cyclopropanes. At least one aryl substituent is required at the termini of the n-ally1 system (Scheme 28).Il8 Ph3P\ A.* Pd Br' 'PPh3 Me0& C02Me Y 53 A 'T' Pd'(PPh3)p 54 Me02C C02Me ==bo 0 56 % Scheme 28 6 q *-Complexes of iron tricarbonyl in organic synthesis q4-diene tricarbonyl iron complexes have proven to be useful intermediates in organic synthesis due, in particular, to the stereocontrol exerted by the Fe( CO), moiety in addition to protecting the diene from attack.This year the range of reactions involving complexed q4-dienes has been expanded and new methods for the generation of homochiral complexes have been published. 6.1 Acyclic complexes The Fe(CO), moiety serves as both an activating group (for the acyl chloride) and protecting group (for the diene) in the allylation of cx,p-y,d-unsaturated acid chlorides (Scheme 29);"' the reaction proceeds under neutral conditions without Lewis acid catalysis except for sterically-hindered allylsilanes. Iwata has studied an interesting series of 1,2-nucleophilic additions to acyclic (Z)-dienone complexes 56; the use of organolithium or organocopper reagents gives the expected tertiary alcohols 57 via nucleophilic attack 54 Contemporary Organic Synthesisfrom the less-hindered ex0 face.However, the use of more Lewis acidic organoaluminium reagents gives stereoisomer 58 via initial (2) to ( E ) isomerization of the dienone (Scheme 29).li0 Iwata has also described the efficient stereoselective addition of organocerium reagents to 1-imino-( E, E )-diene complexes.121 60% (88 % with AC13 present) (1 : 1 mixture of isomers) y C 0 ) 3 Bu"Li 2 THF. 51 - % 78 "C Me 56 K L ( ! ! - ; H Fe(CO)3 Me 58 (100%d.e.) Scheme 29 57 (1Whd.e.) Several papers have been published in the last year on routes to hornochiral q4-diene tricarbonyl iron complexes.In particular, Uemura has extended the previously reported kinetic resolution methods using pig liver esterase or bakers yeast in aqueous sytems to the more favourable use of Lipase in organic solvents. 22 Formation of diastereomeric derivatives has been used by Howell to resolve substituted sorbaldehyde complexes' 23 whilst Nakanishi has chromatographically separated diastereomeric q4-N-substituted-2,4-hexadienamide complexes.' 24 An interesting and remarkably stereoselective complexation of a diene bearing a proximal chiral auxiliary was recently published by Pearson (Scheme 30). Diethyl ether proved the solvent of choice and a bulky chiral auxiliary to block one face of the diene is essential; the best auxiliary contained a coordinating group with the potential to direct the incoming iron. This type of reaction was also applied to the complexation of azadienes via chiral hydrazone derivative^."^ In a similar vein, Schmalz used the diastereoselective complexation of chiral dienes derived from L-arabinose to give predominantly the endo isomer 59 (Scheme 30).126 In a neat extension Schmalz was able to replace the benzyloxy group of 59 with a variety of nucleophiles to give the ex0 derivatives in a stereoselective manner (Scheme 30).127 Some elegant synthetic applications of q4-diene tricarbonyl iron complexes have appeared; for example, Donaldson has completed both the C-1 to ph%OH Ph Ph%OH Ph 42 % (> 99 : 1 d.e.) 59 OTMS I Scheme 30 C- 1 1 and C- 15 to C-24 portions of the polyene macrolide macrolactin A 60 in racemic form.Construction of both fragments relies on control of chirality by face selective reactions on y4-sorbaldehyde tricarbonyl iron (Scheme 3 1 ). ' 28 Gree has prepared the C- 15 to C-24 fragment using similar methodology but in optically pure form.129 Saalfrank and Gree have also introduced a pendent allenic residue into a functionalized $-sorbaldehyde tricarbonyl iron complex.13o Roush has completed a formal asymmetric total synthesis of ikarugamycin from the simple symmetrically functionalized diene complex 6 1 (Scheme 32).l3l The key steps include highly enantio- and diastereo-selective crotylboration of 6 1 to give the ex0 diastereoisomer 62 in 90% yield and subsequent condensation with Meldrum's acid to give the conjugated triene 63.This subsequently undergoes stereoselective ex0 face attack, away from the metal, by vinylmagnesium bromide to introduce the third chiral centre. Lastly, conversion of the a-hydroxy group into a suitable leaving group and treatment with triethylaluminium incorporates the required ethyl group with clean, iron-controlled, retention of stereochemistry to give the key intermediate 64. 6.2 Cyclic complexes Yeh has reported an interesting regio- and stereo-controlled synthesis of bridged bicyclic systems via Lewis acid catalysed conjugate addition of Blagg: Stoichiometric organotransition metal complexes in organic synthesis 5sOH (ii) Bu'MeSiOTf 2,6- Midi ne 76% (iii) LDA. CO.H+ 88% 1 HO 16 60 A B C02Me A Scheme 31 functionalized zinc-copper reagents RCu( CN)ZnI to (tropone)iron tricarbonyl65 (Scheme 33).13* The iron tricarbonyl moiety protects the diene functionality in the Michael addition but allows intramolecular closure of the enolate onto the diene in the presence of CO to give the bicyclic product 66.In a similar paper he has used the same methodology to functionalize tricarbonyltropyliumchromium tricarbonyl.133 61 Me 62 (> 98% e.e.) Meidrom's acid pyridine 92% 1 0 63 (ii) Ac@, DMAP, pyridine (iii) EtdI. CH&I, - 20 "c, 75% 64 Scheme 32 0 0 65 6.3 q 4-Azadiene tricarbonyl iron complexes Simple v4-azadiene tricarbonyl iron complexes have been prepared by direct complexation of a,@-unsaturated imines or by the condensation of amines with tetracarbonyliron complexes of a,@-unsaturated carbonyl compounds.The preparation and reactions of functionalized azadiene Scheme 33 0 'C0,Et 56 Contemporary Organic Synthesiscomplexes are only now being explored. Martelli recently reported the synthesis of the formyl complex 67 (Scheme 34) via a mild aza-Wittig r e a ~ t i 0 n . l ~ ~ Of note is the subsequent reaction with Grignard reagents on the free aldehyde. Reduction of complexed azadienes with LiAlH, gives the fully saturated amines whilst the free azadienes give allylamines under the same conditions, indicating that coordination of the azadiene activates the ligand to hydride attack.135 Lastly, Knolker has published an interesting paper which indicates that 1,4-aryl substituted azadiene complexes can act as efficient catalysts for 1,3 diene complexation via transfer of the Fe( CO), moiety.'36 1 OH Scheme 34 cAFe+( CO), qCo2Me H2N OMe MeCN.25 "c. 3d v 36% mukoeic acid 69 rearranges to the thermodynamically favoured C-alkylated arylamine 69; subsequent oxidative cyclization gives the carbazole skeleton (e.g. for mukoeic acid (Scheme 35). A similar oxidative cyclization of complexed cyclohexadienyl cations bearing a pendent alkylamine affords simple indole derivatives.13x In an extension of previous work, Genet and Stephenson have used Schiff base nucleophiles to attack q5-cyclohexadienyl tricarbonyl iron cations. This chemistry has the potential to give a general route to substituted phenylglycine derivatives (Scheme 36).'3y An interesting study on the regiochemistry of attack at disubstituted acyclic q5-cyclohexadienyl tricarbonyl iron cations has been published by Donaldson in which the classical nucleophilic attack at the terminus of the coordinated system is affected by the relative steric effects of the substituents.Shibasaki has published a novel process involving y-substitution of rs-pentadienyl chromium complexes. For example, treatment of the pentadienyl benzoate 70 with two equivalents of (naphthalene). Cr( CO), in the presence of an aldehyde gives the y-substituted product 7 1 in good yield accompanied by a small amount of the y-protonation product (Scheme 36).14' C02Me I Ph LiN(SiMe)2,3h, (i) Ph2C=NACOZMe - 78 "C -k)""='.h / MeO (ii) NHICI, H20 Me0 'Fe+(CO), 88% 70 I PhCHO, naphthalene.Cr(C0)3 (2eq.) Ph&ok OH 71 (75%) ' " X H O naphthalene.Cr(C0)3 (2 eq.) THF, 90 "C, Sh, 66% U H Scheme 35 Scheme 36 7 q 5-Complexes in organic synthesis Knolker has published two full papers on the synthesis of carbazole alkaloids via the electrophilic aromatic substitution of arylamines by tricarbonyl iron complexed cyclohexadienyl cations.137 The rapidly formed intermediate N-alkylated arylamine 68 slowly This selectivity should be contrasted with the generally poor selectivity seen with electrophilic trapping of pentadienyl alkali metal reagents.The intramolecular version of this process looks especially promising (Scheme 36). Blagg: Stoichiometric organotransition metal complexes in organic synthesis 578 q 6-Complexes in organic synthesis 5 steps 8.1 q 6-Arene chromium tricarbonyl complexes in synthesis The ready availability of homochiral ortho-substituted benzaldehyde chromium tricarbonyl complexes has prompted continued exploration of their synthetic potential.For example, Hanoaka has extended his previously published arene chromium tricarbonyl mediated synthesis of the taxol side-chain intermediate 72 to a synthesis of homochiral ( + )-goniofufurone 73 (Scheme 37).142 CH&12 (iii) hv, air 0 hn, air dH (i)TsNt MeCN, hv, air optically pure 72 P h w 0 OH 73 (+)-goniofufurone VHTs 3 Me Me R = CN, 90%. 99% 8.8. R = CO,Me, 92?k 96% 8.8. Scheme 37 Baldoli and Maiorana have prepared a series of optically pure alkynyl alcohols via attack of alkynyl lithium or magnesium species onto homochiral ortho-substituted benzaldehyde chromium tricarbonyl complexes,143 while Kundig has reported that the coordination of ortho-substituted benzaldehydes to chromium tricarbonyl accelerates the Bayliss-Hillman reaction and improves the overall stereoselectivity.*44 Kundig has also demonstrated that the Bayliss-Hillman reaction can be applied to homochiral aldimine complexes to give 74 (Scheme 37).145 Homochiral aldimine complexes have also been used by Del Butter0 and Maiorana in a [2 + 21 mediated ketene cycloaddition to give optically pure P-lactams (Scheme 38).146 By analogy with the known mode of nucleophilic attack on complexed benzaldehydes, the predominant stereoisomer is presumed to arise via ketene attack on the Si face of the amine away from the bulky Cr( CO), unit with the imine anti to the ortho substituent.In an alternative B-lactam synthesis from the same group, remarkable stereocontrol was observed in the addition of lithium ethylisobutyrate to the homochiral 2-methoxycinnamyl-p-ankidine complex 75 (Scheme 38).147 Presumably the stereocontrol is again due to nucleophilic attack away from the bulky Cr( CO), moiety on the preferred conformation of the imine. dr(co>, optically pure (+I - (S) Rp? 0 95% (> 98% e.e.) Me0 H H ' N-PMP ( i ) LDA, Me&HCO&t Me p THF, - 78 "C, 45% * , (ii) CH+12, hn, air ov ' p ~ p dr(co), 95% (abs. stereochem. unknown) 75 98% 8.8. Scheme 38 The concept of facially selective attack on the preferred conformer of an ortho-substituted benzaldehyde complex has been used by Hanoaka in 1,3-dipolar cycloadditions of nitrones (Scheme 39).14x In this case the selective formation of the cis-3,5-disubstituted isooxazolines arises from the electron-withdrawing effect of the Cr( CO), moiety coupled with an electron-rich dipolarophile; the ortho-trimethylsilyl group is not essential.The formation of homochiral isooxazolines does, however, require the ortho-trimethylsilyl group to impart planar chirality on the nitrone complex. preparation of homochiral ortho-disubstituted arene Several groups have published work on the 58 Contemporary Organic Synthesis-0, + ,Me N Ph- M~N&OH ci- aCHO CH&i2, NaHCO, R , W0C,N2,6h R = H or SiMe, (racemat e) uncomplexed ephedrine ligands.16* Schmalz has achieved the asymmetric synthesis of ( 1 S74S)-dihydroxyca1amenene via diastereoselective complexation of the homochiral alcohol 77 and subsequent control of stereochemistry at the benzylic positions by virtue of the steric control imparted by the bulky Cr(CO), moiety (Scheme 40).16' n Scheme 39 > 98% cis R = SiMe3 80% R = H 69% chromium tricarbonyl complexes via an ortho lithiation strategy.Green has used a chiral tartrate-derived ligand to direct deprotonation to one of the two prochiral ortho positions'49 whilst Sirnpkin~'~' and KundiglS1 have used chiral bases to induce modest to good enantioselectivities (up to 95% e.e.). In a similar approach, Uemura has carried out ortho lithiations in the presence of chiral diamine ligands with modest enantioselectivities (up to 82°/0).1s2 Hayashi has published further studies on his interesting palladium-catalysed asymmetric cross-coupling of meso-arene chromium tricarbonyl complexes with alkenyl and aryl boronic acids; to date up to 69% e.e.has been achieved.lS3 Uemura has used a similar palladium-mediated coupling approach to the racemic synthesis of biphenyl^'^^ whilst Wulff has carried out palladium-mediated couplings of vinylstannanes with complexed arene chromium tricarbonyl triflates.lss Thomas has introduced planar chirality into chromium tricarbonyl complexes of ortho-substituted styrenes via diasteroselective ortho-met allat ion of the c hiral a -me thy1 benzy lamine complex 76 and subsequent dimethyldioxirane-mediated oxidation of the amine and Cope elimination to give the styrene (Scheme 40).156 The dioxirane-mediated oxidation in the presence of the sensitive Cr( CO), moiety is of particular interest and has also been used to oxidize alkylthio substituted arene chromium tricarbonyl complexes to the corresponding ~ulfoxides.'~~ Use of Kagan's modified Sharpless reagent affords an asymmetric version of the oxidation reaction I s8 which, depending upon the conditions, can give the fully oxidized sulfones.Is9 Use of homochiral arene chromium tricarbonyl complexes in synthesis is exemplified by the work of Jones who has used catalytic amounts of a homochiral ephedrine complex to mediate the addition of dimethylzinc to hydroxyaldehydes in superior enantioselectivities to those obtained with the n .._ 77 t /\..= 'r--yy OMe Ci(C0)s Scheme 40 A potentially useful novel synthetic method involving the diastereoselective intramolecular hetero Diels-Alder reaction of imino arene chromium tricarbonyl complexes has been published by Laschat (Scheme 4 1).lb2 This remarkably efficient reaction gives only the trans isomer due to the steric control exerted by the Cr( CO), moiety.Lastly, Semmelhack and Goti reported a potentially useful, mild method (25"C, 1 h in ethyl acetate) for introducing the Cr( CO), moiety via arene displacement from the ( q5- 1 -methylpyrrole)tricarbonyl chromium complex. l6 Me Me y 2 C>(CO), Me Me .Me toluene 98% Me " A (oc),c~ single isomer (X-ray) Scheme 41 Blagg: Stoichiometric organotransition metal complexes in organic synthesis 598.2 q 6-Arene manganese tricarbonyl cations and q 6-arene ruthenium cyclopentadienyl cations in organic synthesis Pearson has continued to exploit the enhanced susceptibility of 7'-arene manganese tricarbonyl cations towards nucleophilic attack by application of this methodology to the synthesis of the CFG ring system of ristocetin A.1J64 He has also studied chiral auxiliary directed nucleophilic additions to @-arene manganese tricarbonyl cations with up to 90% e.e.observed with bulky nucleophiles.16s q6-Arene ruthenium cyclopentadienyl cations are similarly activated towards nucleophilic attack and Pearson has used this methodology in a formal total synthesis of the ACE inhhitor K-1 3.166 A 9 Transition metal mediated cycloadditions in organic synthesis MeCN 85% 9.1 The Pauson-Khand and related cycloadditions Significant applications of the intramolecular Pauson-Khand reaction in organic synthesis have appeared this year which demonstrate the generality of this reaction in a range of systems and in the presence of a wide variety of functional groups.For example, Clive has prepared angularly fused triquinanes in good yield and high stereoselectivity by a tandem intramolecular Pauson-Khand cyclization/radical ring-closure process (Scheme 42).'67 H ( i ) NaBH,, CeCg, 99% (ii) Bu3SnH. 78% 1 0 H Scheme 42 Krafft has prepared the CDE ring system of the pentacyclic steroid xestobergsterol A using an intramolecular Pauson-Khand ring cyclization which allows all the stereocentres to be introduced with correct relative stereochemistry. 168 In a particularly impressive sequence of reactions Schreiber has constructed ( + )-epoxydictymene via a tandem Nicholas reaction/Pauson-Khand ring-closure (Scheme 43).16' number of annulated pyranose systems via intramolecular Pauson-Khand cyclization onto carbohydrate tem~1ates.l~~ The first example of a reversal of the selectivity in an intramolecular Pauson-Khand cyclization has been reported; Marco-Contelles has prepared a Scheme 43 cyclization of one stereoisomer of 3,5-dimethyl-4-propargyl- 1,6-heptadiene gives predominantly the bicyclic product with both substituents in the more hindered endo ~ 0 s i t i o n .l ~ ~ Advances in the methodology associated with the Pauson-Khand reaction include in situ generation of the (alkyne)Co(CO), complex from CoCl, and zinc,17* and a catalytic version of the intramolecular Pauson-Khand rea~ti0n.l~~ Fe( CO), mediated Pauson-Khand-type reactions have also been explored by P e a r ~ o n l ~ ~ and Kn01ker.l~~ Asymmetric Pauson-Khand reactions have been studied by Greene using a chiral auxiliary directly attached to the complexed alkyne via an ether linkage in both the inter-176 and intra-m~lecular~~~ cyclization.De Meijere has placed the chiral auxiliary on the tether between the alkyne and alkene in intramolecular Pauson-Khand cyclizations onto methylene cycl~propanes.'~~ All of these methods give moderate induction in most cases with a few examples providing products in > 90% d.e. Higher diastereoselectivities (96 :4) could be achieved in intramolecular cyclizations using the 1 0-methylthio-isoborneol auxiliary which provides a more rigid template for the cyclization reaction by chelation of the sulfide moiety with the metal ligand (Scheme 44).17' 9.2 Titanium- and zirconium-mediated cycloadditions One of the highlights in this field has been the total synthesis of ( + )-preussin by Livinghouse who applied the previously developed imidotitanium-alkyne [2 + 21 cycloaddition to the homochiral precursor 78 in the 60 Contemporary Organic Synthesis96 : 4, diastereomeric ratio n-C7HI5COCN SMe 25 "C M F Scheme 44 presence of octanoyl cyanide (Scheme 45).lS0 In an alternative approach to CC-1065, Tietze has applied the methodology of Buchwald to perform an intramolecular zirconium-mediated cyclization of a pendant alkene onto an q2-benzyne zirconocene complex (Scheme 45).18' Following the elegant total synthesis of dendrobine last year by Mori, a more detailed account of the key zirconocene-mediated ring-closure reaction has appeared, including X-ray .OBn ,OBn 78 K i cp CI -.OBn -,OBn I Me (+)- preussin (44% overall) A NC c+15 OBn 65% overall Scheme 45 analysis of the products.lx2 Whitby has further exploited the synthetic potential of the zirconocene-mediated cyclization of enynes and diynes bearing nitrogen in the tether to synthesize a variety of piperidine and isoquinoline systems.'83 Several papers have appeared over the last year on catalytic versions of zirconocene-mediated cycloadditions of dienes which are beyond the scope of this review.IX4 9.3 Cobalt-mediated cyclotrimerizations Vollhardt has carried out a regioselective [2 + 2 + 21 cyclotrimerization of a, w-alkynenitriles with silyl substituted acetylenes to give annulated pyridines.lx5 Extension of this methodology to the construction of the C,D ring system of ergot alkaloids was also reported.Malacria has demonstrated the use of allenes as participants in the cobalt-mediated [2 + 2 + 21 cycloaddition reaction.' x6 9.4 Rhenium promoted cycloadditions In 1992 Kennedy reported the rhenium( 111) oxide promoted oxidative cycloaddition of y-hydroxyalkenes to give, for example, 2- hydroxymethyltetrahydrofurans. 87 This methodology has now been applied to spiroketal synthesis (Scheme 46) and a [3 + 21 cycloaddition mechanism has been suggested.lg8 McDonald has reported a similar PCC-mediated oxidative cyclization of hydroxy polyenes in which he proposes a [2 + 21 cycloaddition mechanism.Ix9 R e p , 2,6-lutidine OH Scheme 46 Acknowledgements. 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ISSN:1350-4894    

DOI:10.1039/CO9950200043

出版商:RSC    

年代:1995

数据来源: RSC