3 Organometallic chemistry Part (i) Palladium and nickel catalysed methods By VISUVANATHAR SRIDHARAN* and PAUL C. WOLSTENHOLME-HOGG Department of Chemistry Leeds University Leeds UK LS2 9JT 1 Introduction Pd and Ni salts/complexes are exceptionally versatile and robust catalysts for the construction of carbon–carbon and carbon–heteroatom bonds with excellent regioand stereochemical control. The discovery of new homogeneous catalysts 1–31,2 and heterogeneous catalysts,3–6 including water-soluble polymer-bound catalysts and glass bead technology,7 continues to strengthen the catalytic processes making them even more adaptable and e¶cient. Reported herein are recent developments in Pdand Ni-catalysed carbon–nitrogen and carbon–oxygen bond formations inter- and intramolecular enyne and ynyne cascade reactions concluding with miscellaneous cascade reactions.R1 R1 P R R OAc OAc R1 R1 R R P Pd PPri 2 PPri 2 TFA Pd PR2 PR2 TFA Pd Pd 1 a R = o-tolyl R1 = H b R = mesityl R1 = Me 2 3 a R = Pri b R = Bu t 2 Carbon–nitrogen bond formation Pd and Ni catalysed amination of aryl halides and triflates Aromatic amines are an important class of compounds. They are present in many natural products and continue to be exploited for their unique functionality in numer- *Corresponding author. 89 Br O Me H2N O Me NH Me Me Br H2N + DPPFPdCl2 Me Me + Pd2(dba3) BINAP HN 96% 83% Scheme 1 H R H H (BINAP)Pd ArBr (BINAP)Pd(Ar)Br A (BINAP)Pd(Ar)Br N B (BINAP)PdArNR C NaOBut NaBr ArNHR Scheme 2 ous synthetic organic materials. Buchwald’s8 and Hartwig’s groups9 have independently reported the Pd-catalysed amination (using secondary amines) of aryl iodides and bromides in the presence of a strong base such as an alkoxide or amide.Both groups have also independently developed catalytic systems which utilise DPPF [1,1@-bis(diphenylphosphino)ferrocene] or BINAP ligands for Pd- or Ni-catalysed amination processes.10–12 These catalytic systems a§ord high yields for secondary amines derived from aryl halides and primary amines (Scheme 1). A catalytic cycle for the reactions above (Scheme 1) is presented in Scheme 2 utilizing BINAP as the ligand. Oxidative addition of Pd(0) into the aryl bromide a§ords A which readily forms pentacoordinate complex B. Deprotonation of the coordinated amine by base would give C which reductively eliminates to give (BINAP)Pd and the aryl amine.Both Buchwald’s and Hartwig’s groups conclude that chelating phosphines possessing modest bite angles are important for favourable reductive elimination (C to product Scheme 2)† as opposed to the b-hydride elimination pathway (C to product Scheme 3). Use of the second generation catalytic systems minimises the b-hydride elimination product in these processes. Buchwald et al. have further developed Hayashi-type P–N and P–O ligands 4–6 to couple acyclic secondary amines with aryl halides.13 Complex formation with ligands 5 or 6 to Pd(0) in the presence of NaOBut enables †Note added in proof recent studies from Hartwig’s group shows that catalysts containing electron-rich modestly hindered bidentate phosphines with bite angles (\90°) gave the best results for the coupling of aryl bromides and primary amines.See B. C. Hamann and J. F. Harting J. Am. Chem. Soc. 1998 120 3694. 90 V. Sridharan and P.C. Wolstenholme-Hogg Pd N R1 H H PdH NH R1 + + Pd(0) Scheme 3 Br But N But + Bu Bu Bu2NH 92–97% Pd2(dba)3 ligand 6 Scheme 4 PPh2 Me NMe2 PPh2 PPh2 Me NMe2 PPh2 Me OMe Fe Fe Fe Fe Me O Me PdL P Ph2 NH R R1 4 P P 5 CF3 6 7 CF3 Fe 2 2 8 the coupling of secondary cyclic or acyclic amines to aryl halides in good yields. However this catalytic system is not e§ective for the coupling of primary amines (Scheme 4). Palladium complex 7 gives rise to a reduction in electron density around Pd due to poor r-donation of the methoxy moiety relative to the PAr 2 substituent. This in turn favours the rate of reductive elimination for the above process. Buchwald has further enhanced the scope of this process by altering the base to Cs 2 CO 3 allowing the incorporation of more labile functional groups into the system.Thus simple aryl bromides underwent coupling with secondary amines using 1.5mol% Pd 2 (dba) 3 and 4.5mol% racemic PPFOMe 6 in dioxane at 100 °C whereas electron deficient aryl 91 Organometallic chemistry Part (i) Pd and Ni catalysed methods Br MeO2C O HN MeO2C N O Br + HN N But But + 86% Pd2(dba)3 ligand 6 Cs2CO3 Pd2(dba)3 BINAP Cs2CO3 92% Scheme 5 NH CO2H I N CO2H Me I HN + Pd(0) / Cu / TEABr Me + N Pd2dba3 BINAP NaOBut 18-crown-6 85% 95% K2CO3 Scheme 6 N Cl O HN N N O N N Cl F NH2 NH O OEt N N NH F NH O OEt + + 87% Ni(COD)2,DPPF 98% Pd2(dba)3 BINAP Scheme 7 bromides underwent coupling in the presence of Pd 2 (dba) 3 and BINAP in toluene at 100 °C (Scheme 5).Aryl iodides have also been successfully coupled to both a-amino acids14 and secondary amines15,16 at room temperature using THF and 18-crown-6 (Scheme 6). Aryl chlorides17,18 have been converted to aniline derivatives using a catalytic amount of Ni(COD) 2 and DPPF (or 1,10-phenanthroline) in the presence of NaOBut. Electron-rich or electron-deficient aryl chlorides can be used successfully in the above process as shown in Scheme 7. In contrast to aryl iodides and bromides neutral aryl triflates19,20 gave higher yields of aryl amines than electron-deficient aryl triflates due to the increased rate of base-promoted triflate cleavage in electron deficient triflates 92 V. Sridharan and P.C. Wolstenholme-Hogg MeO OTf H2N MeO N H OTf O Ph HN N O 64% Ph + + 42–92% Pd(OAc)2 BINAP NaOBut Pd(OAc)2 BINAP NaOBut Scheme 8 OTf Me O Ph Ph NH NH2 Me O + i ii Scheme 9 Reagents i Pd(OAc) 2 /BINAP Cs 2 CO 3 ; ii cat.HCl wet THF. Br Br H2N NH2 NH N Br n + n Pd2(dba)3 BINAP 2 n N + N N N 3 LiNPh2 Pd[P( o-tol]3)2 P( o-tol)3 84% 86% NaOBut Scheme 10 (Scheme 8). Utilising Cs 2 CO 3 as base has improved the amination of electron-deficient triflates from 42 to 92% (Scheme 8).21 Primary arylamines have also been obtained via Pd-catalysed coupling of triflates and benzophenone imine (Scheme 9).22 One particular application of the amination process is the synthesis of polyamines. Polyamines,23 together with linear and triarylamine dendrimers,24 have been obtained via Pdcatalysed coupling procedures (Scheme 10). 3 Carbon–oxygen bond formation Aryl ethers are an important class of compounds in natural products.Buchwald’s25,26 93 Organometallic chemistry Part (i) Pd and Ni catalysed methods Br NC Me Me Me OH CN O HO Br + Pd2(dba)3 TolBINAP 73% O Pd(OAc)2 DPPF 69% NaH NaH Me Me Me Scheme 11 Br PdBr PdOR OR Pd(0) NaOR NaBr Scheme 12 Pd O H R2 R1 Pd H R2 O R1 + + Pd(0) Scheme 13 and Hartwig’s27 groups have reported the use of either Pd or Ni catalysed aryl carbon–oxygen bond forming processes. Both inter- and intramolecular processes have been reported and selected examples are shown in Scheme 11. A catalytic cycle similar to the amination process is shown in Scheme 12. The catalytic cycle involves oxidative addition of Pd(0) to aryl bromide followed by substitution of the bromide with the alkoxide. Reductive elimination then a§ords the aryl ether and Pd(0) catalyst.94 V. Sridharan and P.C. Wolstenholme-Hogg NC Br NaO + NC Pd2dba3 ligand 8 74% Pd2(dba)3 DPPF 50% O Scheme 14 Br O O + Br O KN(SiMe3) 51% O Pd(PPh3)2Cl2 Cs2CO3 71% Pd2(dba)3 DPPF Scheme 15 This process can sometimes give low yields due to b-hydride elimination as shown in Scheme 13. Hartwig has developed a new ligand 8,28 for the coupling of electron-poor aryl bromides and electron-rich alkoxides (Scheme 14). Closely related Pd-catalysed processes for the a-arylation of ketones,29,30 both inter- and intramolecularly have also been reported (Scheme 15). 4 Cascade reactions Cascade reactions may be defined as multi-reaction one-pot sequences in which the first reaction creates the functionality to trigger the second reaction and so on.This section is concerned with Pd- and Ni-catalysed processes in which two or more C–C/C–heteroatom bonds are formed. Enyne and ynyne systems Intermolecular processes Yamamoto et al. have reported palladium catalysed benzannulation of conjugated enynes (Scheme 16).31 These processes are regiospecific thus 1,3-disubstituted benzene or trisubstituted arenes were not observed. Yamamoto has also investigated regiospecific Pd-catalysed [4]2] cycloadditions of enyne–diyne systems.32 These also occurred in good yields with the process believed to proceed via a pallado cycle (Scheme 17). Regiospecific Pd-catalysed cyclotrimerisation of 1,3-diyne to 1,3,5-unsymmetrically substituted benzene occurs in good yield (Scheme 18).33,34 Palladiumcatalysed reactions of disulfides with alkynes35 and addition of terminal alkynes to acceptor alkynes36 have also been reported.95 Organometallic chemistry Part (i) Pd and Ni catalysed methods R R Pd(PPh3)4 a R = n-C6H13 77% b R = Me 70% c R = Me2CHOHCH2CH2 81% R Scheme 16 R R1 R1 R R1 R1 • R R1 + R1 Pd(PPh3)4 Pd R =Me R1 = Bu n 80% R = Me R1 = Ph 99% Scheme 17 R H R R R Pd(PPh3)4 R = n-hexyl 64% R = PhCH2CH2 51% Scheme 18 Intramolecular processes Grigg et al. have developed a three component polycyclisation cascade using allene (1 atm) and sodium benzenesulfinate (Scheme 19).37 This process yields 9 as a single diastereomer via the formation of five new bonds and two stereocentres. Grigg et al.37 have also extended the cascade cyclisation anion capture methodology to ynynyne systems. Triscyclisation anion capture is illustrated in Scheme 20.Organotin reagents RSnBu 3 and RSnMe 3 comprise a valuable source of diversity and added complexity in the cascade cyclisation anion capture processes (Scheme 20). Palladium-catalysed Stille coupling reactions continue to dominate catalytic carbon–carbon bond formation. The development of fluorous tin reagents,38 new tin reagents39 and novel iminophosphine ligands40 for cross coupling are the topic of numerous papers41–60 which appeared throughout the year including Nicolaou’s application to complex 96 V. Sridharan and P.C. Wolstenholme-Hogg EtO2C EtO2C I • EtO2C EtO2C PdL • EtO2C EtO2C PdL + PhSO2Na EtO2C EtO2C + Pd(PPh3)4 SO2Ph PhSO2Na 9 66% Scheme 19 N CO2Me OCO2Me O O SnBu3 N CO2Me O • PdL N CO2Me • LPd N CO2Me O LPd N CO2Me O O Pd(0) / LiCl 74% Scheme 20 polyether frameworks.61 In the cascade theme a related biscyclisation–anion capture process has been applied to the synthesis of ([)-a-thujone (Scheme 21).62 A wide range of natural products have been synthesised utilising Pd-catalysed cyclisation processes as a key step.Such natural products include (^)-scopadulic acid B,63 ([)-pancracine,64 (])- pilocarpine,65 camptothecin analogues,66 vitamin D3,67 morphine analogues68 and cephalotoxine.69 An alternative to initiation by insertion of Pd(0) into a suitable C–X bond is to initiate a cascade process by hydropalladation. A combination of Pd 2 (dba) 3 with HOAc can be utilised as a source for the initiating palladium hydride species. This work originally pioneered by Trost,70 has been successfully applied to biscyclisation processes (Scheme 22).71 Genet et al.have reported Pd-catalysed cyclisation of an enyne system in the absence of HOAc with a mixed solvent of dioxane–water and TPPTS ligands.72 The results from their investigations showed a rather di§erent 97 Organometallic chemistry Part (i) Pd and Ni catalysed methods SO2Ph PhO2S O Me O SO2Ph PhO2S H Me Pd2(dba)3 H ii iii Me O Me3Zn i 91% Scheme 21 Reagents and conditions i PtO 2 H 2 AcOH 50 °C; ii,Al/Hg THF H 2 O; iii,LDA MoOPh. O OAc CO2Et CO2Et EtO2C EtO2C O OAc CO2Et CO2Et EtO2C EtO2C H H H H Pd2(dba)3 HOAc 50% Scheme 22 O Ph O OH Ph EtO2C CO2 Et B NMe NH SiMe2Ph EtO2C EtO2C B N Me HN SiMe2Ph MeO2C CO2 Me 85% PdCl2 / TPPS Pd(OH)2 / C MeO2C MeO2C Bu3SnH SnBu3 95% + Pd2(dba)3 85% + Scheme 23 cyclisation product (Scheme 23). Similarly Tanaka Lautens and co-workers73 have used borosilane or Bu 3 SnH as the initiator and substrate rather than HOAc in the cascade process of enyne and ynyne systems (Scheme 23).Oh et al. have recently reported the use of HCOOH (1 mol.) instead of HOAc to a§ord the reduced cascade product in good yield (Scheme 24).74 Alkenes and 1,2-dienes Intermolecular processes Yamamoto and co-workers have reported in a series of papers addition of C-pronuc- 98 V. Sridharan and P.C. Wolstenholme-Hogg OSiMe2But H XPd OSiMe2But PdX H OSiMe2But H PdCl2 / PPh3 HCOOH OSiMe2But 74% Scheme 24 H CO2Et Ph CN SnBu3 Ph CO2Et CN Ph NC EtO2C SnBu3 Cl Ph + CN CN Pd2(dba)3 51% + Ph CN + Pd(0) 91% Scheme 25 S I • S SO2Ph O OMe I + • CO (1 atm) + N (1 atm) Ts Pd(PPh3)4 H + PhSO2Na + CO (1 atm) OMe + O + N Pd(0) Ts 95% 97% Scheme 26 leophiles to alkenes,75 1,2-dienes76 and enynes77 to form carbon–carbon bonds.A typical cascade process is illustrated in Scheme 25. Pronucleophiles and vinyltin in the presence of Pd 2 (dba) 3 and DPPF a§orded the dimerisation product in good yield (Scheme 25). Grigg et al. have used the di§erence in rate for insertion of aryl Pd(II) species into CO and allenes to their advantage and devised a series of tetramolecular queuing cascades (Scheme 26).78 99 Organometallic chemistry Part (i) Pd and Ni catalysed methods OH I • O O + CO (20 atm) OH O + PdX 73% Pd(OAc)2 dppb Scheme 27 I • NH O N O O PdX O PdX O O PdX + CO O + O + PdX Pd(0) 75% Scheme 28 O H2N Me O CO2H + HN + Me O CO (60 bar) 99% (PPh3)2PdBr2 conc. H2SO4 LiBr Scheme 29 Intramolecular processes Alper and Okura have demonstrated an intramolecular version of the above process which occurred in good yield (Scheme 27).79 Grigg has further enhanced the process to pentamolecular queuing cascades and this is illustrated in Scheme 28.80 5 Miscellaneous cascade reactions Beller et al.have synthesised novel amino acids via three component cascade processes (Scheme 29).81 The above process may be modified by tuning the catalyst system to enantio/diastereoselective systems. Grigg et al. have reported the Pd-catalysed oxime 100 V. Sridharan and P.C. Wolstenholme-Hogg N HO N Pd O L L N O N O H H + Pd(II) – – + H+ – Pd(II) Scheme 30 Ph N N OH N Me O HN H H N O O Ph N Me O HN H N O O PdCl2(MeCN)2 Et3N NMM Ph + H 9 1 80% Scheme 31 OMe OMe OTf OTf B OTBPPS OMe OMe OTBDPS + 66% 82%ee Pd2(dba)3 R-BINAS Scheme 32 to metallonitrone to isoxazoline cascade in good yield (Scheme 30).82 In the aldoxime case oximes underwent a stereospecific and highly facially selective cascade under the reaction conditions above (Scheme 31) to a§ord enantiopure adducts in 80% yield (9 1).Cascade Suzuki83 cross coupling Heck reactions have been applied to the synthesis of polyfused systems in high enantioselectivity and good yield (Scheme 32). Tietz and Schirok have synthesised cephalotaxine via a Pd-catalysed cascade process (Scheme 33).69 Finally Mori has reported a nickel catalysed cascade process for the synthesis of pyrolizidine and indolizidine derivatives in good yield and high enantiomeric excess (Scheme 34). In utilizing the versatility of this process for the construction of pyrrolizidine and indolizidine skeletons Mori applied the technique to the formal total synthesis of ([)-elaeokanine C with great success.84 101 Organometallic chemistry Part (i) Pd and Ni catalysed methods O O HN AcO O O N P PdOAc oTol oTol N Pd(PPh3)4 H 85% 2 Bun 4NOAc I 80% I O O Scheme 33 N O N O H OSiPh3 N O H OSiPh3 Ni(COD)2 PPh3 Ph3SiH THF + 9.1 1 97%ee 99%ee 68% 9% Scheme 34 References 1 W.A.Hermann and B. Cornils Angew Chem. Int. Ed. Engl. 1997 36 1048; W. A. Hermann C. Brossmer C. P. Reisinger T. H. Riermeir M. Ofele and M. Beller Chem. Eu. 1997 3 1357; F. Robin F. Mercier L. Ricard F. Mathey and M. Spagnol Chem. Eu. 1997 3 1365. 2 M. Oh§ A. Oh§ M.E. Vanderboom and D. Milstein J. Am. Chem. Soc. 1997 119 11 687. 3 D. Villemin P. A. Ja§res B. Nechab and F. Courivaud Tetrahedron Lett.1997 38 6581. 4 D.E. Bergbreiter and Y. S. Liu Tetrahedron Lett. 1997 38 7843. 5 A. Hessler and O. Stelzer J. Org. Chem. 1997 62 2362. 6 C. Amatore. G. Broker A. Jutand and F. Khalil J. Am. Chem. Soc. 1997 119 5176. 7 L. Tonks M. S. Anson K. Hellgardt A. R. Mirza D. F. Thompson and M.J. Williams Tetrahedron Lett. 1997 38 4319. 8 A. S. Giuram R. A. Rennels and S. L. Buchwald Angew. Chem. Int. Ed. Engl. 1995 1348; J. P. Wolfe and S. L. Buchwald J. Org. Chem. 1996 61 1133. 9 J. Louie and J. F. Hartwig Tetrahedron Lett. 1995 36 3609; F. Paul and J. F. Hartwig Organometallics 1995 14 3030; J. F. Hartwig and F. Paul J. Am. Chem. Soc. 1995 117 5373. 10 J. F. Hartwig Synlett 1997 329; S. Driver and J. F. Hartwig J. Am. Chem. Soc. 1997 8232. 11 J. P. Wolfe S. Wagaw and S.L. Buchwald J. Am. Chem. Soc. 1996 7215. 12 J. F. Marcoux S. Wagaw and S. L. Buchwald J. Org. Chem. 1997 62 1568. 13 J. P. Wolfe and S. L. Buchwald Tetrahedron Lett. 1997 38 6359. 14 D. Ma and J. Yau Tetrahedron Asymmetry 1996 7 3075. 15 J. P. Wolfe and S.L Buchwald J. Org. Chem. 1997 62 6066. 16 J. P. Wolfe R. A. Rennels and S. L. Buchwald Tetrahedron 1996 52 7225. 17 J. P. Wolfe and S. L. Buchwald J. Am. Chem. Soc. 1997 119 6054. 18 Y. Hong G. J. Tanoury H. C. Wilkinson K. P. Bakale S. A. Wald and C. H. Senanayake Tetrahedron Lett. 1997 38 5607. 102 V. Sridharan and P.C. Wolstenholme-Hogg 19 J. P. Wolfe and S. L. Buchwald J. Org. Chem. 1997 62 1264. 20 B. C. Hamann and J. F. Hartwig J. Org. Chem. 1997 62 1268. 21 J. Ahman and S. L. Buchwald Tetrahedron Lett. 1997 38 6363.22 J. P. Wolfe J. Aham J. P. Sadighi K. A. Singer and S. L. Buchwald Tetrahedron Lett. 1997 38 6367. 23 T. Kanbara K. Izumi Y. Nakadai T. Narise and K. Haseyawa Chem. Lett. 1997 1185. 24 J. Louie and J. F. Hartwig J. Am. Chem. Soc. 1997 119 11 695. 25 M.P. John P. Wolfe and S. L. Buchwald J. Am. Chem. Soc. 1997 119 3395. 26 K. A. Widenoefer H. Annita and S. L. Buchwald J. Am. Chem. Soc. 1997 119 6787. 27 G. Mann and J. F. Hartwig J. Org. Chem. 1997 62 5413. 28 G. Mann and J. F. Hartwig Tetrahedron Lett. 1997 38 8005. 29 B. C. Hamann and J. F. Hartwig J.Am. Chem. Soc. 1997 119 12 382; M. Palucki and S. L. Buchwald J. Am. Chem. Soc. 1997 119 11 108. 30 H. Muratake and M. Natsume Tetrahedron Lett. 1997 38 7581. 31 S. Saito M. N. Salter V. Gevorgyan N. Tsuboya K. Tando and Y. Yamamoto J.Am. Chem. Soc. 1996 118 3970. 32 V. Gevorgyan A. Takeda and Y. Yamamoto J. Am. Chem. Soc. 1997 119 1313; M. Murakami K. Kenichiro and Y. Ito J. Am. Chem. Soc. 1997 119 7163. 33 A. Takeda A. Ohno I. Kadota V. Gevorgyan and Y. Yamamoto J. Am. Chem. Soc. 1997 119 4547. 34 V. Gevorgyan N. Sadayori and Y. Yamamoto Tetrahedron Lett. 1997 38 8603. 35 Y. Gareau and A. Orellana Synlett 1997 803. 36 B.M. Trost M. T. Sorum C. Chan A. E. Harms and G. Ruhter J. Am. Chem. Soc. 1997 119 698. 37 R. Grigg R. Rasul and V. Savic Tetrahedron Lett. 1997 38 1825. 38 M. Larhed M. Hoshino S. Hadida D. P. Curran and A. Hallberg J. Org. Chem. 1997 62 5583; M. Hoshino P. Degenkolb amd D. P. Curran J. Org. Chem. 1997 62 8341. 39 G. Fouquet M. Pereyre and A. L. Rodriguez J. Org. Chem. 1997 62 8341. 40 E. Shirakawa Y.Murota Y. Nakao and T. Hiyama Syn. Lett. 1997 1143. 41 E. Shirakawa H. Yoshidaand and H. Takaya Tetrahedron Lett. 1997 38 3759. 42 K.W. Stagliano and H. Malinakova Tetrahedron Lett. 1997 38 6617. 43 F. Clerici E. Erba M. L. Gelmi and M. Valle Tetrahedron 1997 53 15 859. 44 L. Lu and D. J. Burton Tetrahedron Lett. 1997 38 7673. 45 C. Chen K. Wilcoxen K. Kim and J. R. McCarthy Tetrahedron Lett. 1997 38 7677. 46 H. Tanaka H. Yamada A. Matsuda and T. Takahashi Synlett 1997 381. 47 J. Thibonnet M. Abarbri J. L. Pavrain and A. Duchene Synlett 1997 771. 48 P. A. Evans J. D. Nelson and T. Manangun Synlett 1997 968. 49 E. Wright T. Gallagher C. G. V. Sharples and S. Wonnacott Bioorg. Med. Chem. Lett. 1997 2867. 50 T. Gan G. Scott and J. M. Cook Tetrahedron Lett. 1997 38 8453. 51 G.T. Grisp Y. L. Jaing P. J. Pullman and C. DeSavi Tetrahedron Lett. 1997 38 17 489. 52 M.I. Konaklieva H. Shi and E. Turos Tetrahedron Lett. 1997 38 8647. 53 M. Suzuki H. Doi M. Bjorkman Y. Andreson B. Langstrom Y. Wantanabe and R. Noyori Chem. Eur. J. 1997 2039. 54 E. Shirakawa K. Yamasaki and T. Hiyama J. Chem. Soc. Perkin Trans. 1 1997 2449; E. Shirakawa H. Yoshida and T. Hiyama Tetrahedron Lett. 1997 38 5177. 55 T. Luker H. Heimstra H. and W. N. Speckamp J. Org. Chem. 1997 62 8131. 56 M. Benaglia S. Toyota R. Craig C. R. Woods and J. S. Siegel Tetrahedron Lett. 1997 38 4737. 57 S. H. Chen Tetrahedron Lett. 1997 38 4741. 58 G. Barbarella M. Zambianchi G. Sotgiu and A. Bongini Tetrahedron 1997 53 9401. 59 M. Iyoda M. Miura S. Sasaki S. M. Humaynkabir Y. Kuwatani and M. Yoshida Tetrahedron Lett.1997 38 4581. 60 S. Khatib A. Mamai G. Guillaumet M. Bouzoubaa and G. Coudert Tetrahedron Lett. 1997 38 5993. 61 K. C. Nicolaou G. Shi J. L. Gunzner P. Gartner and Z. Yang J. Am. Chem. Soc. 1997 119 5567. 62 W. Oppolzer A. Pimm B. Stammen and W. E. Hume Helv. Chim. Acta 1997 80 623. 63 L. E. Overman D. J. Ricca and V. D. Tran J. Am. Chem. Soc. 1997 119 1203. 64 J. Jin and S. M. Weinreb J. Am. Chem. Soc. 1997 119 5773; G. R. Friestad and B. P. Branchaud Tetrahedron Lett. 1997 38 5933. 65 Z. Wang and X. Lu Tetrahedron Lett. 1997 38 5213. 66 F. G. Frang D. D. Bankson E. M. Huie M.R. Johnson M. C. Kang and C. S. Leitouller Tetrahedron 1997 53 10 953. 67 S. Hatakeyama T. Ikeda J. Maeyama T. Esumi Y. Iwabuchi and H. Irie Bioorg. Med. Chem. Lett. 1997 7 2871; H. Yokoyama K. Miyamoto Y.Hirai and T. Takahashi Synlett 1997 187. 68 C. Y. Hong L. E. Overman and A. Romero Tetrahedron Lett. 1997 38 8439; C. Y. Chang J. P. Liou and M.J. Lee Tetrahedron Lett. 1997 38 4571. 69 L. F. Tietze and H. Schirok Angew. Chem. Int. Ed. Engl. 1997 36 1124. 70 B.M. Trost Acc. Chem. Res. 1990 23 34. 71 C.W. Holzapfel and L. Marais Tetrahedron Lett. 1997 38 8585. 103 Organometallic chemistry Part (i) Pd and Ni catalysed methods 72 J. Christophe M. Savignac and J. P. Genet Tetrahedron Lett. 1997 38 8695. 73 S. Onozawa Y. Hatanaka and M. Tanaka Chem. Commun. 1997 1229; M. Lautens N. D. Smith and D. Ostrorsky J. Org. Chem. 1997 62 8970. 74 C. H. Oh Y. Rhim and S. K. Hwang Chem. Lett. 1997 777. 75 I. Nakamura N. Tsukada M. A. Masum and Y. Yamamoto Chem. Commun. 1997 1583.76 M.A. Masum M. Meguro and Y. Yamamoto Tetrahedron Lett. 1997 38 6071. 77 V. Gevorgyan C. Kadowaki M.M. Saltzer I. Kadota S. Saito and Y. Yamamoto Tetrahedron 1997 9097. 78 R. Grigg S. Brown V. Sridharan and M.D. Uttley Tetrahedron Lett. 1997 38 5031. 79 K. Okuro and H. Alper J. Org. Chem. 1997 62 1566. 80 R. Grigg and R. Pratt Tetrahedron Lett. 1997 38 4489. 81 M. Beller M. Eckert F. Vollmuller S. Bogdanoic and H. Geissler Angew. Chem. Int. Ed. Engl. 1997 36 1494. 82 M. Frederickson R. Grigg J. Markandu M. Thornton-Pett and J. Redpath Tetrahedron Lett. 1997 38 7777. 83 A. Kojima S. Honzawa C. D. J. Boden and M. Shibasaki Tetrahedron Lett. 1997 38 3455. 84 Y. Sato N. Saito and M. Mori Tetrahedron Lett. 1997 38 3931. 104 V. Sridharan and P.C. Wolstenholme-Hogg