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Chapter 13. Aromatic compounds

 

作者: J. W. Barton,  

 

期刊: Annual Reports Section "B" (Organic Chemistry)  (RSC Available online 1973)
卷期: Volume 70, issue 1  

页码: 386-430

 

ISSN:0069-3030

 

年代: 1973

 

DOI:10.1039/OC9737000386

 

出版商: RSC

 

数据来源: RSC

 

摘要:

13 Aromatic Compounds By J. W. BARTON School of Chemistry University of Bristol. CantockS Close Bristol BS8 1 TS 1 General Hiickel and non-Huckel systems have been discussed in a short review on antiaromatic effects.' A recent ab initio valence bond calculation of the benzene structure gives energy expectation values for the Kekule and Dewar forms which are closer than those resulting from semi-empirical treatments ; it also appears that charge-separated forms are more important than was thought hitherto.2 The flexibility of aromatic rings has been discussed. On the basis of accrued theoretical and experimental evidence it is suggested that mono- and poly- nuclear hydrocarbons are capable of 5-20' deviations from planarity in the ground state.3 The effects of substituents on rotation about the phenykarbon bond in substituted toluenes have been e~amined.~ X-Ray crystal analyses of peri-substituted naphthalenes have shown the 1,8-dimethyl derivative to be planar non-bonded interactions of the methyl groups being reduced mainly by bond-angle distortion at the junctions between the methyl groups and the nu- cle~s.~ In contrast there is little angle distortion in 1,8-bisdimethylaminonaph-thalene which is twisted about the C-4a-C-8a axis so that the dimethylamino- groups lie on either side of the mean plane of the nucleus;6 the barrier to change from one such conformation to its mirror image is at least 7.5 kcal mol- Values found for the dipole moments of 2,3,4,5-tetra- and 2,3,4,5,6-penta-fluorotoluenes are higher than expected possibly owing to hyperconjugation in the methyl groups.' Attempts to use 3Cn.m.r.data as criteria of aromaticity in potentially aromatic systems have given conflicting results ;'" ring-current effects play a ' R. Breslow Accounts Chem. Res. 1973 6 393. J. M. Norbeck and G. A. Gallup J. Amer. Chem. SOC. 1973 95,4460. H. Wynberg W. C. Niewport and H. T. Jonkman Tetrahedron Letters 1973 4623. J. E. Anderson H. Pearson and D. I. Rawson J.C.S. Chem. Comm. 1973,95. ' D. Bright I. E. Maxwell and J. de Boer J.C.S. Perkin 11 1973 2101. E. Einspahr J. B. Robert R. E. Marsh and J. D. Roberts Actu Cryst. 1973 B29 161 1. ' R. W. Alder and J. E. Anderson J.C.S. Perkin 11 1973,2086. * H. H. Huang J.C.S. Chem. Comm. 1973,723. (a) A. J.Jones P. J. Garratt and K. P. C. Vollhardt Angew. Chem. Internat. Edn. 1973 12 241; (b) A. V. Kemp-Jones A. J. Jones M. Sakai C. P. Beeman and S. Masamune Cu~d J. Chem. 1973 51 767; (c) H. Gunther H. Schmickler. H. Konigshofen K. Recker and E. Vogel Angew. Chem. Internat. Edn. 1973 12 243; (4E. Wenkert E. W. Hagaman L. A. Paquette R. E. Wingard and R. K. Russell J.C.S. Chem. Comm. 1973 135; (e) R. H. Levin and J. D. Roberts Tetrahedron Letters 1973 135; cf) H. Gunther H. Schmickler U. H. Brinker K. Nachtkamp J. Wassen and E. Vogel Angew. Chem. Internat. Edn. 1973 12 760. 386 Aromatic Compounds minor role in determining the 13Cresonance frequency compared with stereo- chemical factors such as ring size and ring train.^^'^'^ Rearrangements involving intramolecular hydrogen transfer in the mass spectra of aromatics have been reviewed;" further studies on benzyl C7H7+ and tolyl C7Hs+,cations' lad and the tolyl radical cation C,Hs'+,' le in the gas phase have been reported.While C7H7+ ions from various precursors usually isomerize to a common structure within 10- 's,it is possible to form benzyl and tolyl cations which are stable for this interval.'lc'd Active carbon functions as an efficient catalyst in the racemization of 1,l'- binaphthyl.' Syntheses of chiral crown ethers derived from resolved 2,2'-dihydroxy-1,l'-binaphthylhave been described ;'3n these show chiral recognition when complexing or-phenylethylammonium hexafluorophosphate. ' The o,m'-bridged biphenyl (1) racemizes rapidly at 60 "C;I4 conformational isomers of 1,6-bis-( 1-cyano- 1-methylethyl)triptycene have been prepared which are found to be stable against thermal (tt = 115 min at 200 "C)and photochemical inter- conversion.' Further studies of the synthesis resolution and absolute con- figurations of optically active 9,10-dihydro-9,10-ethenoanthracenes'6and trip- tycenes17 have been reported; the failure of c.d.spectral analysis to assign the correct absolute configurations to certain derivatives of these systems' is attributed to error in the calculation of transition rnoment~.'~ lo J. T. Bursey M. M. Bursey and D. G. I. Kingston Chem. Rev. 1973 73 191. I' (a)R. C. Dunbar J. Amer. Chem. SOC.,1973,95,472; (b)R. C. Dunbar and E. W. Fu ibid p. 2716; (c)J. Winkler and F.W. McLafferty ibid. p. 7533; (4M. K. Hoffmann and J. C. Wallace ibid. p. 5064; (e) K. Levson F. W. McLafferty and D. M. Jerina ibid. p. 6332. R. E. Pincock W. M. Johnson K. R. Wilson and J. H. Farmer J. Amer. Chem. SOC. 1973,95,6477. I' (a) E. P. Kyba M. G. Siegel L. R. Sousa G. D. Y. Sogah and D. J. Cram J. Amer. Chem. SOC.,1973 95 2691; (b) E. P. Kyba K. Koga L. R. Sousa M. G. Siegel and D. J. Cram ibid.,p. 2692. l4 E. W. Warnhoff and P. Reynolds-Warnhoff Canad. J. Chem. 1973 51 2338. l5 H. Iwamura J.C.S. Chem. Comm. 1973,232. l6 Y. Sakata H. Tatemitsu F. Ogura and M. Nakagawa J.C.S. Chem. Comm. 1973 22; H. Tatemitsu F. Ogura and M. Nakagawa Bull. Chem. SOC.Japan 1973,46,915. M. Kuritani Y. Sakata F. Ogura and M. Nakagawa Bull. Chem. SOC.Japan 1973 46 605; Y.Sakata F. Ogura and M. Nakagawa ibid. p. 611; F. Ogura and M. Nakagawa ibid. p. 651; Y. Shimizu T. Naito F. Ogura and M. Nakagawa ibid. p. 1520. J. Tanaka C. Katayama F. Ogura H. Tatemitsu and M. Nakagawa J.C.S. Chem. Comm. 1973,21. l9 s.F. Mason J.C.S. Chem. Comm. 1973 239; A. M. F. Hezemans and M. P. Groen- wege Tetrahedron 1973 29 1223. 388 J. W. Barton Homo- and Pseudo-aromaticity.-An alternative MO-based model has been put forward to account for the unusual stability of homoaromatic systems.20 For example with the homotropylium ion it involves treating the external rnethylene group together with its two CH neighbours as a cyclopropane ring. There is evidence of homoaromatic stabilization of the dianion (2) from 2,4-diphenyl- bicyclo[3,2,1]oct-6-en-3-one.21Attempts to use polarography to assess homo- aromatic stabilization of the radical anions from cis-bicyclo[6,1,O]nona-2,4,6-triene and its 2,3-benzo-derivative were unsu~cessful.~ There has been conflict of opinion over the suggestion that there is homoaromatic stabilization in the pentaene (3) which could exist as a 67t (or lOn)-electron homoaromatic system (4);23a*b n.m.r.studies of this and related bridged annulenes provide strong evidence that there is not.23c Bishomocyclopropenium cations such as (5) generated by additions to hexameth~lDewarbenzene,~~" are further protonated in strong acids at low temperature to give the stable symmetrical dication (6),24b,cwhich passes irreversibly into the hexamethylbenzenium cation at 40"C.Me (5) X = C1or Br (6) Further studies of the protonation of cis-bicyclo[6,l,0]nona-2,4,6-triene and some derivatives by 'C n.m.r. spectroscopy have been reported. In superacidic media there appears to be initial formation of transoid 1,3-bishomotropylium ions such as (7) which subsequently undergo conformational inversion of a 2o W. J. Hehre J. Amer. Chem. SOC., 1973 95 5808. " G. B. Trimitsis E. W. Crowe G. Slomp and T. L. Helle J. Amer. Chem. SOC.,1973 95 4333. 22 L. A. Anderson M. J. Broadhurst and L. A. Paquette J. Amer. Chem. SOC.,1973 95 2 198. 23 (a)L. A. Paquette R. E. Wingard and R. K. Russell J. Amer. Chem. SOC., 1972 94 4739; (b) G. P. Ceasar J. Green L. A. Paquette and R. E. Wingard Tetrahedron Letters 1973 1721; (c) E.Vogel U. H. Brinker K. Nachtkamp J. Wassen and K. Mullen Angew. Chem. Internat. Edn. 1973 12 758. 24 (a) H. Hogeveen and P. W. Kwant Tetrahedron Letters 1973 423; (b) H. Hogeveen and P. W. Kwant ibid. p. 1665; (c) H. T. Jonkman and W. C. Niewport ibid. p. 1671. Aromatic Compounds methylene bridge to give their cisoid counterpart^.^^ Isomerization of the bridged ion (8) to give 2-deuterioindene takes place by a process which is thought to involve the bishomotropylium ion (9) resulting from interaction of the cationic D D centre at C-9 with the C-7-C-8 ene function rather than the other ion which would result from C-9 interaction with the diene bridge.26 The term pseudoaromatic (cf. ref. 1) has been applied to the dication (lo) generated from 1,4-dichlorobicyclo[2,2,2]octanein superacidic media at -78 “C.The ion which is isoelectronic with the cyclobutadiene dication exhibits unusual stability and gives rise to unrearranged products on quenching.” Benzene Isomersand Benzene Oxides.-Prismane (12) has been obtained in low yield by photolysis of the azo-compound (11). It is a colourless liquid stable at room temperature but rearranging at 90°C to give benzene (t+ = 11 h).28 Photolysis of 1,2,4,5-tetrakis(trimethylsilyl)benzenehas given the 1,2,3,5-isomer together with fulvenes and benzvalenes ; no prismanes or Dewarbenzenes were obtained.*’ The first examples of this type of isomerization in the naphthalene ” L. A. Paquette M. J. Broadhurst P. Warner G. A. Olah and G.Liang J. Amer. Chem. SOC.,1973,95 3386. 26 D. C. Sanders and H. Schecter J. Amer. Chem. Soc. 1973,95 6858. 27 G. A. Olah G. Liang P. von R. Schleyer E. M. Engler M. J. S. Dewar and R.C. Bingham J. Amer. Chem. SOC.,1973,95 6829. T. J. Katz and N. Acton J. Amer. Chem. SOC.,1973 95 2738. 29 R. West M. Furne and M. N. M. Rao Tetrahedron Letters 1973 91 1. 390 J. W. Barton series have been reported with peri-di-t-butyl derivatives ; 1,3,6,8-tetra-t-butyl-naphthalene affords a photostationary state in which the Dewar isomer (13) is present in 94% yield.30 There is further evidence that the bicyclopropenyl re- arrangement proceeds via Dewarbenzene rather than prismane intermediates. Thermal rearrangement of (14) at 45 "Cgives rise to the benzene derivatives (16) and (17) the former being formed via the Dewar isomer (15).31 The presence of Me phPxph Ph Ph Ph Ph (17) (15) was demonstrated spectroscopically and when silver(1) catalysis was em- ployed it could be isolated ;a reaction sequence initiated by retrocarbene cleavage of one of the cyclopropene rings is suggested.This rearrangement is markedly influenced by the donor or acceptor properties of the bridge substituents ;under silver(1) catalysis the corresponding monocyanobicyclopropenyl shows no tendency to rearrange whereas the monomethoxy-derivative gives almost exclusively the Dewar isomer corresponding to (15) in a few minutes at room temperature. Thermolysis of the tetramethylhomofulvene (18) gives pentamethyl- benzene exclusively ;the main products from the corresponding endo-and exo-pentamethyl compounds are the three isomeric ethyltetramethylbenzenes formed by a radical chain process.32 30 W.L. Mandella and R. W. Franck J. Amer. Chem. Suc. 1973 95 971. 31 R. Weiss and S. Andrae Angew. Chem. Internat. Edn. 1973 12 150 152. 32 R. Criegee D. Schonleber R. Huber C. Schweickhardt R. Wolf and R. Ramirez Chem. Ber. 1973,106 857. Aromatic Compounds 39 1 The synthesis of anti-benzene dioxide (19) has been reported; unlike the syn- isomer it is thermally stable and does not equilibrate with 1,4-dio~ocin.~~ Com-parison of the vicinal coupling constant J4.5in the n.m.r. spectrum of (19) with that of the syn-isomer and the corresponding one in the recently isolated anti- biotic (20)34indicates that the latter should be assigned the syn-benzene dioxide structure.Nucleophilic substitutions of benzene trioxide (21 ;X = 0)have been studied,35 certain of which have led to a synthesis of the tri-imine (21 ;X = NH). Me Me (18) Kinetic studies of the dienol-benzene rearrangement36 and of the aromatization of indane 8,g-oxide (22)3’have been reported. In the latter it has been shown that 33 E. Vogel H. J. Altenbach and E. Schmidbauer Angew. Chem. Internal. Edn. 1973 12 838. 34 D. B. Borders P. Shu and J. E. Lancaster J. Amer. Chem. SOC.,1972 94 2540. 35 R. Schwesinger and H. Prinzbach Angew. Chem. Internat. Edn. 1973 12 989; R. Schwesinger H. Fritz and H. Prinzbach ibid. pp. 993 994. 36 V. P. Vitullo and M.J. Cashen Tetrahedron Letters 1973 4823. 37 G.J. Kasperek P. Y. Bruice T. C. Bruice H. Yagi and D. M. Jerina J. Amer. Chem. SOC.,1973 95 1673 6041. 392 J. W. Barton 5-hydroxyindane the main product formed in acidic solutions results from allylic hydration of and subsequent elimination from the cation (23) whereas in neutral and alkaline solutions the observed product 4-hydroxyindane is formed mainly through an 'oxygen walk' process uia indane 4,8-oxide (24). The formation of rearranged arene oxides has also been observed on halogen elimination from the bridged structures (25).38 X B$k? X (25) X = CN or C0,Me 2 Benzene and its Derivatives Application of the perturbation theory treatment of chemical reactivity to aro- matic substitution has been disc~ssed.~' Recent reviews have dealt with anodic aromatic ~ubstitution,~' the reactivity and stability of arenediazonium ions,4' and the Zinin reduction of nitroarenes ;42 accounts of the acyl~xylation~~ and arninati~n~~ of aromatics and of carbocations derived from aromatic have been included in reviews of a wider nature.The ambident nature of the triphenylmethyl cation has been established in certain hydrogen-transfer reactions.46 Doubts as to the correctness of the accepted value for the rate of protodetritiation of benzene at 70 "C(9.5 x s-') com-monly used as a standard for comparing partial rate factors were unjustified as shown by a recent study;47 a quantitative correlation between hydrogen exchange rates and charge distribution in the benzenium ion has been estab- li~hed.~* Criticism has been levelled at the way in which the Hammett equation has been employed for structure-reactivity correlations in aromatic substitution reaction^.^' A second example of steric hindrance to acid-catalysed hydrogen exchange has been encountered with the ortho-positions in tetraphenylmethane.'' It is found that rn-phenylenediamines undergo uncatalysed deuterium exchange 38 F.G. Klarner and E. Vogel Angew. Chem. Internat. Edn. 1973 12 840. 39 R. F. Hudson Angew. Chem. Internat. Edn. 1973 12 36. 40 L. Eberson and K. Nyberg Accounts Chem. Res. 1973 6 106. 41 H. Zollinger Accounts Chem. Res. 1973 6 335. 42 H. K. Porter Org. Reactions 1973 20 455. 43 D. J. Rawlinson and G.Sosnovsky Synthesis 1973 567. 44 F. Minisci Synthesis 1973 1. " G. A. Olah Angew. Chem. Internat. Edn. 1973 12 173. 46 G. A. Olah and J. J. Svoboda J. Amer. Chem. SOC. 1973,95 3794. 4' H. V. Ansell and R. Taylor J.C.S. Chem. Comm. 1973,952. 48 H. V. Ansell J. Le Guen and R. Taylor Tetrahedron Letters 1973 13. 49 C. D. Johnson and K. Schofield J. Amer. Chem. SOC.,1973,95 270. 50 H. V. Ansell and R. Taylor J.C.S. Chem. Comm. 1973 936. Aromatic Compounds at positions ortho and para to the amino-groups whereas o-and p-phenylene- diamines do not ; a mechanism involving direct attack by a deuterium cation is suggested.' Further studies of the protonation of aromatic hydrocarbon^,'^" fluoroaro-ma tic^,^^^ phenols and phenol ethers52c in superacidic media have been reported ; the reaction of methoxybenzenes with alkylfluoroantimonates in sulphuryl chlorofluoride at -70 "C has given dialkylaryloxonium salts which are stable at that temperature but which are transformed into ring-alkylated alkoxy- benzenes on warming to O"C.53The methylation of anisole with ['H,]methyl chloroformate and silver hexafluoroantimonate at 30 "C gives a mixture of o- rn- and p-methyl and -[2H3]methyl anisoles consistent with a principal process involving formation of the methyl-[2H,]methyl-phenyloxonium ion (26) and its subsequent intermolecular reaction with ani~ole.'~ Methoxycarbenium hexafluoroantimonate (27) proves to be an effective methylating agent for aro- matics;" arylations by means of aryl cations have also been reported.56 Gas- phase methylenation of aromatic substrates occurs in the presence of methoxy- methyl cations produced by the fragmentation of dimethyl ether ;" activated aromatics are rapidly alkylated by t-butyl trifluoroacetate in trifluoroacetic acid 51 J.C. Grivas J. Org. Chem. 1973 38 1204. '' (a) G. A. Olah and Y. K. Mo J. Amer. Chem. SOC., 1973,95,6827;(6) G. A. Olah and Y. K. Mo J. Org. Chem. 1973,38,3212; (c)G. A. Olah and Y. K. Mo J. Amer. Chem. SOC.,1972 94 5341 ; J. Org. Chem. 1973 38 2212. 53 G. A. Olah and E. G. Melby J. Amer. Chem. SOC.,1973 95,4971. 54 P. Beak J. T. Adams P. D. Klein P. A. Szczepanik D. A. Simpson and S. G. Smith J. Amer. Chem. SOC.,1973 95 6027. 55 G. A. Olah and J. J. Svoboda Synthesis 1973 52. 56 H.Bottcher H. G. C. Becker V. L. Ivanov and M. G. Kusmin Chimia (Switz.),1973 27 437; P. Burri and H. Zollinger Helu. Chim. Acfa 1973 56 2204; N. Kamigata R. Hisada H. Minata and M. Kobayashi Bull. Chem. SOC.Japan 1973 46 1016. 57 R. C. Dunbar J. Shen E. Melby and G. A. Olah J. Amer. Chem. SOC.,1973,95,7200. 394 J. W. Barton at room tem~erature.~~ confor-A detailed investigation of the synthe~is,~~" mati~n,~'~ and electrophilic substitution59c of cyclopropylbenzenes has been reported. In 1-methylcyclopropylbenzene the symmetrical conformation (28) is preferred owing to steric requirements thus the 1-methylcylopropyl group is unfavourably placed electronically and is less effective in stabilizing positive charge in the transition states of electrophilic substitutions than is a cyclopropyl group.H. Titanium(rv)-catalysed electrophilic bromination and formylation of 2-carbonyl-substituted phenols shows a marked preference for attack at the vacant position ortho to the hydroxyl function possibly owing to the formation of cyclic titanium complexes.60 Bridged ions such as (29) have been postulated as inter- mediates in electrophilic nitrations ;61 variations in the rates and isomer distri- butions for the competitive nitration of benzene and toluene in several organic solvents have been investigated.62 Nitrations of aromatics with dinitrogen tetr~xide,~~ titanium(1v) nitrate,64 and nitronium triflu~romethanesulphonate~~ have been studied and polyalkylbenzenes have been selectively mononitrated using methyl nitrate-boron trifluoride in nitromethane.66 Following studies of the ipso-nitration of o-xylene discussed in last year's Report (p.570),it is found that ipso-nitration of toluene giving rise to the diastereomers of (30) occurs to the extent of 3-4 % in acetic anhydride at -30 0C.67Similarly the action of acetyl nitrate on benzo[a]cyclopropa[c]cycloheptenegives up to 60%of the stereoisomers of (31) one of which has been shown to undergo nitro-group migration in acidic media.68 In 2,3-and 3,4-dimethylbenzonitrilessome ips0 attack takes place at the carbon atom bearing a methyl group meta to the cyano substituent giving 58 U. Svanholm and V. D. Parker J. C.S. Perkin Z 1973 562. 59 (a) W. Kurtz and F. Effenberger Chem. Ber.1973 106 511 560; (b) P. Fischer W. Kurtz and F. Effenberger ibid. p. 549; (c) W. Kurtz P. Fischer and F. Effenberger ibid. p. 525. 6o T. M. Cresp M. V. Sargent J. A. Elix and D. P. H. Murphy J.C.S. Perkin Z 1973 340. 61 F. Bernardi and W. J. Hehre J. Amer. Chem. SOC.,1973,95 3078. 62 S. Sekiguchi A. Hirose S. Kato and K. Matsui Bull. Chem. Sue. Japan 1973 46 646. 63 G. R. Underwood R. S. Silverman and A. Vanderwalde J.C.S. Perkin Z 1973 1177. 64 D. W. Amos D. A. Baines and G. W. Flewett Tetrahedron Letters 1973 3191. 65 C. L. Coon W. G. Blucher and M. E. Hill J. Org. Chem. 1973 38 4243. 66 G. A. Olah and H. C. Lin Synthesis 1973 488. 6' A. Fischer and J. N. Ramsay J.C.S. Perkin I 1973 237. 68 R. C. Hahn and M. B. Groen J. Amer. Chem. SOC.,1973,95 6128.Aromatic Compounds 395 rise to adducts such as (32),69" whereas 3,4-dimethylanisole gives (33 ;R = OAc) and the ketal(33 ;R = OMe) resulting from attack para to the metho~y-group.~~' Isomer distributions in electrophilic cyanation have been determined for a range of aromatic compounds and compared with those from other direct cyanation reactions anodic photo etc7' Friedel-Crafts-type s~lphonylation~ and aminati~n~~ have been further studied ;certain aromatics are arylaminated to give diphenylamine derivatives by N-arylhydroxylamines in a reaction which has the characteristics of an electrophilic substitution and possibly involves attack by nitrenium ions.73 Oxidative substitution reactions to receive attention include those promoted by Ce'v,74 Pd" ,'' and CO'",~~ salts.There is e.s.r. evidence that radical cations are readily formed under thallation condition^,^' and mechanistic studies of the reaction of benzene with cobalt(II1) trifluoro- acetate indicate the formation of radical cations which subsequently react with nu~leophiles.~ Rate studies of the base-catalysed deuteriation of 1,3,5-trinitrobenzene in NN-dimethylformamide4euterium oxide mixtures show that there is competi- tion between carbanion formation leading to proton exchange and Meisenheimer complex formati~n.~~ Meisenheimer complexes as intermediates in nucleophilic substitution continue to attract attention ;79 in particular several studies of the more stable spiro 0-C-O8' and 0-C-N" types have been reported.The formation of a gem-di(alky1thio) analogue of a Meisenheimer complex has been observed in solution,82 as has the formation of both cis-and trans-forms of 69 (a) A. Fischer and C. C. Greig J.C.S. Chem. Comm. 1973 300; (b) A. Fischer and D. R. A. Leonard ibid. p. 396. 70 S. Nilsson Acra Chem. Scand. 1973 27 329. " G. A. Olah S. Kobayashi and J. Nishimura J. Amer. Chem. Soc. 1973 95 564. 72 J. W. Strand and P. Kovacic J. Amer. Chem. SOC.,1973 95 2977. 73 K. Shudo and T. Okamoto Tetrahedron Letters 1973 1839. 74 M. E. Kurz E. S. Steele and R. L. Vecchio J.C.S. Chem. Comm. 1973 109. 75 G. G. Arzoumanidis and F. C. Rauch J. Ore. Chem. 1973,38 4443; L. Eberson and L. Gomez-Gonzales Acta Chem. Scand. 1973 27 1162 1249 1255. 76 J. K.Kochi R. T. Tang and T. Bernath J. Amer. Chem. SOC.,1973,95 71 14. 77 I. H. Elson and J. K. Kochi J. Amer. Chem. Soc. 1973,95 5060. 78 E. Buncel and E. A. Symons J. Org. Chem. 1973 38 1201. '' C. A. Fyfe M. Cocivera and S. W. H. Damji J.C.S. Chem. Comm. 1973 743; M. R. Crampton and H. A. Khan J.C.S. Perkin fi 1973 710 1103. M. R. Crampton J.C.S. Perkin fi 1973 2157. (a)C. F. Bernasconi R. H. De Rossi and C. L. Gehriger J. Org. Chem. 1973,38 500 2838; (6)S. Sekiguchi T. Itagaki T. Hirose K. Matsui and K. Sekine Tetrahedron 1973,29 3527; (c)S. Sekiguchi and T. Shiojima Bull. Chem. SOC.Japan 1973,46 693. 82 G. Biggi and F. Pietra J.C.S. Chem. Comm. 1973 229. 396 J. W.Barton complex (34)by addition of sulphite ion to 1,3,5-trinitroben~ene.~~ Nucleophilic substitutions of hexacyanobenzene including Meisenheimer complex formation have been described;84 the compound reacts with water to give the highly acidic pentacyanophenol (pK = -2.9).Full details of copper-catalysed sub- stitutions of aryl halides by phthalimide ion have been published,* and indirect nucleophilic displacements with carbanions on aryl halides have been achieved in the presence of tetrakis(triphenylphosphine)nickel(O)(Scheme 1);86 in a related LiCH,COPh PhBr + Ni(PPh,) + PhNi(PPh,),Br [PhNi(PPh,),CH,COPh] + PhCOCH,Ph Scheme 1 reaction replacement of halogen by methyl has been brought about by methyl- tris(triphenylphosphine)rhodium(~).~’ Amine copper(1) perchlorates are effective in promoting homolytic cleavage of aryldiazonium salts in neutral media ;’* rate studies of the homolytic phenyl- ation of 4-substituted pyridines in acidic and non-acidic media indicate that the phenyl radical has some nucleophilic ~haracter.~~ Irradiation of chlorobenzene at 2537 has given a high-energy species n-chlorobenzene (39,which behaves as a biradical.” The thermal isomerization reactions of phenylcarbene dis- cussed in last year’s Report (p.572) have now been published in full.9’ The end product of these rearrangements fulveneallene (37) has been obtained in pre- parative quantities by the vacuum thermolysis of phthalide at 7G750oC.92a,b 83 C. F. Bernasconi and R. G. Bergstrom J. Amer. Chem. SOC.,1973 95 3603; M. J. Strauss and S. P. B. Taylor ibid. p. 3813. 84 K. Friedrich and S.Oeckl Chem. Ber. 1973 106 2361 3796 3803. R. G. R. Bacon and A. Karim. J.C.S. Perkin I 1973 272. 86 M. F. Semmelhack R. D. Stauffer and T. D. Rogerson Tetrahedron Letters 1973 4519. M. F. Semmelhack and L. Ryono Tetrahedron Letters 1973 2967. A. H. Lewin and R. J. Michl J. Org. Chem. 1973,38 1126. 89 A. Clerici F. Minisci and 0.Porta Gazzetta 1973 103 171. 90 M. A. Fox W. C. Nicholls and D. M. Lemal J. Amer. Chem. SOC.,1973,95 8164. 91 W. D. Crow and M. N. Paddon-Row Austral. J. Chem. 1973 26 1705. 92 (a) U. E. Wiersum and T. Nieuwenhuis Tetrahedron Letters 1973 258 1 ;(b)C. Wentrup and P. Muller ibid. p. 2915. Aromatic Compounds 397 It is suggested that an extrusion process leads to the carbene (36) which subse- quently undergoes a Wolff-type rearrangement.Ethynylcyclopentadiene toluene ‘0 (37) and benzene are also formed in minor quantities ; the thermolysis of benzocyclo-propene gives similar products.92b The formation of benzocyclobutene and styrene in the vacuum thermolysis of methyl p-tolylacetate indicates the inter- mediacy of p-tolylcarbene ;93 the corresponding reaction of p-ethyltoluene may be mechanistically similar. although only styrene could be isolated in this case. There is recent evidence that benzonitrile oxide (38a) which is known to undergo f-Ph-CEN-0 ++ Ph-C-N=O (384 (38b) 1,3-~ycloadditions with dipolarophiles can also behave as phenylnitrosocarbene (38b) and attack olefinic bonds.94 7-Ethylcyclohepta- 1,3,5-trienes have been obtained by ring expansion of alkylbenzenes with the carbenoid reagent from diethylzinc and i~doform.~~ Cyclopentadienylcarbenes from the photolysis of diazocyclopentadienes react with arenes to form derivatives of the spironorcaradiene-spirocycloheptatriene system (39a) d(39b) the dynamics of which have been investigated ; the corresponding reactions of carbenes from diazocyclohexadienones (40) with 93 W.J. Baron and M. R. Decamp Tetrahedron Letters 1973 4225. 94 G. Lo Vecchio G. Grassi F. Risitano and F. Foti Tetrahedron Letters 1973 3777. ” S. Miyano and H. Hashimoto J.C.S. Chem. Comm. 1973 216; Bull. Chem. SOC. Japan 1973 46 3257. 398 J. W.Barton benzene give biphenyl derivatives (4l)dire~tly.’~ The action of phthalimidonitrene on 1,3-dimethoxybenzene in benzene solution gives the 3H-azepine (42) but if acetic acid is present the insertion product (43) is formed at the expense of (42).” OH VHNY YNf=Jle OMe QoMe OMe (43) Whereas arenes are unreactive in photoadditions to acrylonitrile it is found that irradiation of acrylonitrile-arene-zinc chloride complexes brings about the formation of 1,2-cycloadducts to a much greater e~tent.’~ The photoaddition of cyclopentene to benzene gives the endo-cycloadduct (44),together with a 1 (44) smaller amount of the corresponding exo-isomer ;99a in parallel reactions of 0-,rn- and p-xylenes a methyl group is oriented specifically at C-1 ;99b further studies of the photoaddition of other 1,3-dienes to benzene have also been re- port ed.’O0 96 H. Durr and H. Kober Chem. Ber. 1973 106 1565. 97 D. W. Jones J.C.S. Chem. Comm. 1973 67. 98 M. Ohashi A. Yoshino K. Yamazaki and T. Yonezawa Tetrahedron Letters 1973 3395. 99 (a)V. Y. Merritt J. Cornelisse and R. Srinivasan J. Amer. Chem. SOC.,1973,95 8250; (b) V. Y. Merritt J. Cornelisse and R. Srinivasan ibid. p. 6197. loo N. C. Yang and J. Libman Tetrahedron Letters 1973 1409. Aromatic Compounds Molecular Rearrangements.-Rearrangemen ts which have received further study include the Fischer-Hepp,"' 0-'O2 and N-Clai~en,"~ and the Smiles full details of the rearrangement of acetophenones to methyl arylacetates by thallium(w) nitrate have been published. 'O5 The reversibility of certain acid- catalysed Fries rearrangements has been demonstrated '06' and several other studies of the reaction lo6-and of its photo-induced counterpart 106e~'07a,b have been reported ; CIDNP evidence points to the operation of a radical-pair mechanism in the photorearrangement of p-cresyl p-chlorobenzoate.'07b There have been further examples of the photo-Fries-type rearrangement of N-acylaryl-amines' O8 and of the photorearrangement of azoxyarenes to o-hydroxyazo- compounds.'O9 In this connection the rearrangement of o-nitrobenzanilide to the o-hydroxyazobenzenecarboxylic acid (46) may be mentioned ; the process % a'''" d N H P h +hv ' NO N=NPh I 0- (45) (46) is probably initiated by abstraction of the amide N-proton by the excited nitro- group leading to the azoxy-derivative (45) which undergoes further photo- rearrangement to give the product.'lo The formation and rearrangement of ylides such as (47)is a useful method for the ortho-methylation of primary aromatic amines (Scheme 2):' 'la a mechanis- tically similar sequence has been employed to introduce formyl groups ortho to a methyl substituent.' lb Preferential ortho attack by sulphonyl oxygen has been observed in the rearrangement of 0-(arenesulphony1)phenylhydroxyl-amines ;l '' the effects of temperature solvent etc.,are consistent with heterolysis Io1 T. D. B. Morgan D. L. H. Williams and J. A. Wilson J.C.S. Perkin II 1973 473. lo* N. Sardvic T. Zsindely and H. Schmid Helu. Chim. Acta 1973 56 1457. M. Schmid H. J. Hansen and H. Schmid Helu.Chim. Acra 1973,56 105; H. Scheurer T. Zsindely and H. Schmid ibid p. 478. Io4 N. W. Gilman P. Levitan and L. H. Sternbach J. Org. Chem. 1973 38 373. lo' A. McKillop B. P. Swann and E. C. Taylor. J. Amer. Chem. SOC. 1973 95 3340. '06 (a) F. Effenberger H. Klenk and P. L. Reiter Angew. Chem. Inrernat. Edn. 1973 12 775; (b)J. R. Norelle J. Org. Chem. 1973 38 1924; (c)R. Martin J. M. Betoux and G. Coton Bull. SOC. chim. France 1973 1438 1442; (d)R. Martin ibid. p. 3087; (e) H. T. J. Chan and J. A. Elix Austral. J. Chem. 1973 26 1442. 107 (a) A. S. Kende J. L. Belletire and E. L. Hume Terrahedron Letters 1973 2935; (6) W. Adam J. A. De Sanabia and H. Fischer J. Org. Chem. 1973 38 2571. lo' Y. Katsuhara H. Murayama Y. Shigemitsu and Y. Odaira Tetrahedron Letters 1973 1323.Io9 R. H. Squire and H. H. Jaffe J. Amer. Chem. SOC. 1973 95 8188; D. J. W. Goon N. G. Murray J. P. Schoch and N. J. Bunce Cunad. J. Chem. 1973,51 3827. 'lo B. C. Gunn and M. F. G. Stevens J.C.S. Chem. Comm. 1972 835. 'I1 (a)P. G. Gassman and G. Gruetzmacher J. Amer. Chem. Soc. 1973 95 588; (6)C. Huyn S. Julia R. Lorne and D. Michelot Bull. SOC.chim. France 1972 4057. D. Gutsche and A. Heesing Chem. Ber. 1973 106 2379. 400 J. W. Barton Bu'OCI NaOMePhNH -PhNHCl % PhNHS+Me2C1--+ (47)1 Scheme 2 to give an intimate arylnitrenium-tosylate ion pair which recombines rapidly. Periodate oxidation of o-hydroxymethylphenols having at least one bulky ring substituent gives isolable monomeric spiroepoxycyclohexa-2,4-dienones.''3a When o-hydroxydiarylcarbinolsare oxidized in the same way the resulting epox- ides (48) undergo spontaneous rearrangement to catechol acetals (49).'36 A R' R2 = H alkyl or halogen (49) R3 = H or Ph similar spiro intermediate is possibly involved in the conversion of o-hydroxy- aldehydes and -ketones into o-hydroxy-anilides by reaction of their sodium salts with chloramine (Scheme 3).lI4 Ylides such as (50; R = CH,Ph) derived from 1 R=HorMe Scheme 3 'I3 (a) H.Becker T. Bremholt and E. Adler Tetrahedron Lerrers 1972 4205; (6) H. Becker and T. Bremholt ibid. 1973 197. 'I4 R. A. Crochet and P. Kovacic J.C.S. Chem. Comm. 1973 716. Aromatic Compounds 401 o-dimethylaminophenol are isolable whereas the corresponding p-isomers are unstable above 0°C.On heating (50; R = CH,Ph) gives mainly the ether (51 ;R = CH,Ph) formed by an intramolecular 1,4-sigmatropic rearrangement ; the corresponding ally1 derivative (50; R = CH,CH=CH,) gives in addition to (51 ;R = CH,CH=CH,) the phenol (52) formed in a sequence of 2,3-and 3,3-rearrangements.' l5 Biaryk-The UHman synthesis of biaryls has been reviewed.' l6 Oxidative coupling of phenols has received further study,"' as have coupling reactions of other aromatics in the presence of PbIVll l8 Pd",' ' and Vv' 2o salts and by anodic oxidation.' The mechanism of biaryl formation by the thermolysis of benzoyl peroxide in hexafluorobenzene has been investigated ;'22 pentafluorobiphenyl is formed in a reaction which may not involve free CF radicals when a mixture of benzene and hexafluorobenzene is photoly~ed.'~~ It may be mentioned here that photocyclizations of o-methoxybenzanilides such as (53),to phenanthridones (53) OMe take place by elimination of methanol ;'24 oxidative photocyclization with retention of the o-methoxy-group which is the usual reaction with cis-stilbenes and related compounds was not observed.I" S. Mageswaran W. D. Ollis I. 0.Sutherland and Y. Thebtaranonth J.C.S. Chem. Comm. 1973 651,653 654. M. Goshaev 0.S. Ostroshchenko and A. S. Sadykov Russ. Chem. Rev. 1972 41 2198 (English translation p. 1046). M. A. Schwartz B. F. Rose and B. Vishuvajjala. J. Amer. Chem. Soc. 1973 95 612; S. M. Kupchan and A. J. Liepa ibid. p. 4062; P. D. McDonald and G. A. Hamilton ibid.p. 7752. 'I8 R. 0.C. Norman. C. B. Thomas and J. S. Willson J.C.S. Perkin I 1973. 325. '" H. Yoshimoto and H. Itatani Bull. Chem. Sac. Japan 1973 46 2490; J. Org. Chem. 1973 38 76. Izo S. M. Kupchan A. J. Liepa V. Kameswaran and R. F. Bryan J. Amer. Chem. Suc. 1973 95,6861. K. Nyberg Acta Chem. Scand. 1973 27 503. lz2 R. Bolton and J. P. B. Sandall J.C.S. Chem. Comm. 1973 286. D. Bryce-Smith A. Gilbert and P. J. Twitchett J.C.S. Chem. Comm. 1973 457. lZ4 Y. Kanaoka and K. Itoh J.C.S. Chem. Comm. 1973 647. 402 J. W. Barton Arynes and Aryne Precursors.-The synthesis and chemistry of 1,Qdehydrobenz-enes has been reviewed.'25 Irradiation of phthaloyl peroxide in an argon matrix at 8 K results in decarboxylation to give benzopropiolactone (54) and the keto- keten (59 the two being interconvertible photochemically.' 26a Prolonged irradiation of (54) gives benzyne the i.r.spectrum of which has now been recorded. Irradiation of benzocyclobutenedione under similar conditions also gives benzyne and when acetone is included in the matrix as an internal filter there appears an i.r. spectral band at 1838 cm-' which is tentatively assigned to benzocyclopropenone (56).lZ6* When a matrix of free benzyne was allowed to \ -% @o + co \ warm triphenylene was the isolable product while with a matrix containing furan the known [4 + 21 cycloadduct was obtained. Biphenylenes from aryne dimerization are formed in vacuum pyrolyses of lH-2,3-benzoxazin- 1-ones.I2 + Iz5 R. G. Bergman Accounts Chem.Res. 1973 6 25. (a)0.L. Chapman C. L. McIntosh J. Pacansky G. V. Calder and G. Orr J. Arner. Chem. Soc. 1973.95,4061; (b)0.L. Chapman K. Mattes C. L. McIntosh J. Pacansky G. V. Calder and G. Orr ibid. p. 61 34. lz7 M. P. David and J. F. W. McOmie Tetrahedron Letters 1973 1361. Aromatic Compounds In the reaction of ortho-deuteriated benzenediazonium acetate with anthracene which gives both radical- and aryne-derived products there is extensive deuterium removal before the diazonium ions decompose ;the finding lends support to the previous suggestion that the betaine (57)is an intermediate.' 28 The cleavage of ethers by benzyne has been re~0rted.I~' Substituted naph- thalenes have been obtained from [2 + 41 cycloadditions of benzynes with dienolate anions (Scheme 4),' 30 while condensations of bromoarenes' with diethyl 0-M+ R' R2 OH R' R2 R' R' R' R' = H R2 = OH R' = OMe R2 = OH R' = OMe RZ = Me Scheme 4 malonate in the presence of sodamide have given monoesters of homophthalic acid (59)together with homophthalimides.' ' In the latter reaction it is probable that benzocyclobutenones (58) result from interaction of an aryne with diethyl malonate and that these undergo ring-opening to (59) under the strongly basic R (58) R = H or OMe conditions.The reaction of tetrachlorobenzyne with 1,2,3,4-tetramethoxy-naphthalene gives rise to the semibullvalene (60),together with the expected 1,6adduct;'32 2,3-dehydrobiphenylene (61) generated by the thermal decompo- sition of biphenylene-2-diazonium-3-carboxylate, gives [2 + 41 cycloadducts with tetracyclone and with benzene (1% yield) but apparently shows no tendency to dimerize.' 33 12* P.C. Buxton and H. Heaney J.C.S. Chem. Comm. 1973 545. G. D. Richmond and W. Spendel Tetrahedron Letters 1973 4557. I3O P. G. Sammes and T. W. Wallace J.C.S. Chem. Comm. 1973 524. 13' M. Guyot and D. Molho Tetrahedron Letters 1973 3433. '32 F. Serratosa and P. Sola Tezrahedron Letters 1973 821. E. N. Losey and E. LeGoff J. Org. Chern. 1973 38 3812. 404 J. W.Barton Quinone Methides Dimethides and Related Compounds.-Further studies of benzo-' 340 and na~hth0-I~~~ a-quinone methides and their dimers have been reported ; formation of the thione methide (62) on irradiation of 3H-benzo[b]- thiophen-2-one has been demonstrated by isolation of the adduct with N-phenylmaleimide in high yield.' SCF MO calculations for a number of quinone dimethides give no support to earlier predictions of appreciable electron delocalization in such non-benzenoid systems.' 36 Free o-quinone dimethide has been prepared by irradiation of 1,4-dihydrophthalazine in a matrix at -196 "C;on warming to -150 "C it is converted into the known spiro-dimer.' 37 Extrusion of carbon dioxide from isochroman-3-one (63) at 540 "C has given high yields of benzocyclobutene by ring closure of the o-quinone dimethide intermediate.'38 Base-catalysed re- arrangement of o-dipropargylbenzene (64) which involves the diallene (65) and presumably naphthalene-2,3-quinone dimethide (66) gives rise to the per- oxide (67) as well as to a mixture of the dimers of (66).It is suggested that (66) is oxidized to (67) by triplet oxygen ;the reaction of 2,3-dipropargylnaphthalene gives analogous products.'39 Further examples of [4 + 21 cycloadditions of o-quinone dimethides generated by photoenoli~ation~~~ and by eliminations from dihalides,' 41 have been reported. Sodium borohydride reduction of 134 (a) M. S. Chauhan F. M. Dean S. McDonald and M. L. Robinson J.C.S. Perkin I 1973,359; (6)M. S. Chauhan F. M. Dean D. Matkin and M. L. Robinson ibid. p. 120. 13' G. Jacqmin J. Nasielski G. Billy and M. Remy Tetrahedron Letters 1973 3655. 136 G. J. Gleicher D. D. Newkirk and J. C. Arnold J. Amer. Chem. SOC.,1973 95 2526. 13' C.R. Flynn and J. Michl J. Amer. Chem. Soc. 1973 95 5802. 13* R. J. Spangler and J. H. Kim Synthesis 1973 107. '39 C. M. Bowes D. F. Montecalvo and F. Sondheimer Tetrahedron Letters 1973 3181. I4O A. K. C. Chu and M. F. Tchir J.C.S. Chem. Comm. 1973 619; B. J. Arnold S. M. Mellows and P. G. Sammes J.C.S. Perkin I 1973 1266; M. Pfau E. W. Sarvkr and N. D. Heindel Bull. SOC.chim. France 1973 183. 14' J. M. Holland and D. W. Jones J.C.S. Perkin I 1973 927; J. F. W. McOmie and D. H. Perry Synthesis 1973 416. Aromatic Compounds 2,3-dimethyl-5,6-bisacetoxymethyl-l,6benzoquinone has given the spiroquinone (70) together with dur0quin0ne.l~~ It is likely that initial reduction gives the KOBu' -78 "C C3 quinol (68) which eliminates acetic acid spontaneously to form the dimethide (69);the latter then dimerizes or is further reduced to give the observed products.CH,OCOMe MeMe$ CH20COMe OH (68) 0 Me Me Me 0 The semibenzene derivative (72) is formed together with N-diphenylmethyl- N-phenylcarbamate when the bidentate anion (71) reacts with ethyl chloro- formate (Scheme 5).'43 Reaction of the acetate (73)with organo-lithium and -magnesium compounds gives mixtures of ethers (74)and conjugate addition products (75);when the organometallic reagent is tertiary or benzylic (75)may be formed almost ex~lusively.'~~ 14* A. J. Lin and A. C. Sartorelli J. Org. Chem. 1973 38 813. 143 J. G. Smith and G. E. F. Simpson Terrahedron Letters 1973 1947. 144 B. Miller J. Amer.Chem. Soc.. 1973. 95 8458. 406 J. W. Barton C0,Et C0,Et C0,Et I I I CIC0,Et p& H C02Et C0,Et FCO,Et IC0,Et - Ph2C-NPh C0,Et I (71) Et0,C CO2Et p6ph (72) Scheme 5 Quinones.-Black complexes formed when terminal acetylenes are irradiated in the presence of iron pentacarbonyl can be oxidatively degraded to mixtures of 2,s-and 2,6-disubstituted p-benzoquinones in good ~ie1d.l~' A synthesis of the diterpenoid quinone miltirone (76) has been described'46 and various poly- cyclic quinones have been prepared by condensations of o-dialdehydes with cyclic P-diket~nes,'~'also by direct oxidation of hydrocarbons with ceric ammonium nitrate.'48 An X-ray crystal analysis has been carried out on o-benzoquinone ; the ring adopts a slight boat conformation with the oxygen atoms displaced by 0.036 8 on either side of the mean plane of the ring.'49 13C and 'H n.m.r.i45 R. Victor R. Ben-Shoshan and S. Sarel Tetrahedron Letters 1973 421 1. 14' D. Nasipuri and A. K. Mitra J.C.S. Perkin I 1973 285. 14' A. Verine and Y.Lepage Bull. SOC.chim. France 1973. 11 54; M. Peyrot and Y. Lepage ibid. p. 2856. 14' T. L. Ho T. W. Hall and C. M. Wong Synthesis 1973 206. '49 A. L. McDonald and J. Trotter J.C.S. Perkin II 1973 476. Aromatic Compounds spectra of a-benzoquinone and its methyl derivatives have been analysed ; double-resonance experiments have shown that the previous assignments of (76) olefinic carbon resonances should be inverted.' 50 The photoreduction of p-quinones in the presence of hydrogen donors has been studied using CIDNP techniques.' '' Dimeric species formed in the autoxidation of quinone and hydro- quinone have been identified by e.s.r.spectro~copy.'~~ Quinones react with trimethylsilyl cyanide to give monosilyl ethers of cyano-hydrins which have been used to afford selective protection to one carbonyl group during reactions of the other with alkyl-lithium and -magnesium com- pounds (Scheme 6).'53 Nuclear alkylation of quinones has been effected with R = Me Bu",or Ph M = Li or MgBr Scheme 6 organoboranes.' 54 Further studies of the cyclo-oligomerization of quinones are reported' and the cyclotrimerization of 1,4-anthraquinone has been used as the starting point for a new synthesis of the ten-ring benzenoid hydrocarbon decastarphene[3,3,3].' 56 The kinetics of 0-Claisen rearrangements of allyl- oxynaphthoquinones show that different mechanisms operate in protic and aprotic solvents ;'57 reactions of certain quinone epoxides have been described.I5* 150 R.Hollenstein and W. von Philipsborn Helv. Chim. ACTU,1973 56 320. 151 K. Maruyama T. Otsuki A. Takuwa and S. Arakawa Bull. Chem. SOC.Japan 1973,46,2470. P. Ashworth and W. T. Dixon J.C.S. Perkin II 1973 2128. 15' D. A. Evans J. M. Hoffman,and L. K. Truesdale J. Amer. Chem. SOC.,1973,95,3822. G. W. Kabalka Tetrahedron 1973 29 1159. 155 H. E. Hogberg Acta Chem. Scand. 1973,27,2559 2591. 156 H. Brockman and H. Laatsch Chem. Ber. 1973,106,2058. 15' J. A. Miller and C. M.Scrimgeour J.C.S. Perkin II 1973 1 137. G. Read and V. M. Ruiz J.C.S. Perkin I 1973 235 368. 408 J. W.Barton The dione (79) is one of the products of photolysis of 2,6-di-t-butyl-1,4-benzoquinone in benzene. It is suggested that (79) is formed by closure of the initially formed biradical (77) to the strained cyclobutane derivative (78) and 0 (77) (78) (79) subsequent rearrangement.' 59 The photoaddition of p-benzoquinone to cyclo- octatetraene has been reinvestigated using argon laser excitation.'60 In non- acidic solvents the spiro-1,4-adduct (80)is formed accompanied by the peroxide (81) if oxygen is present. When (80)is warmed in acetic acid it rearranges to a mixture of (82) and (83) these being the sole products if the irradiation is carried out in this solvent.Chemical and structural evidence shows conclusively that the anion { Fe(CN),-[C,H,(NH),]) -contains o-benzoquinone di-imine (84) stabilized by co-ordination to iron(n).' '" T. J. King A. R. Forrester M. 0.Ogilvy and R.H. Thompson J.C.S. Chem. Comm. 1973 844. I6O E. J. Gardner R. H. Squire R. C. Elder and R. M. Wilson J. Amer. Chem. SOC.,1973 95 1693. G. G. Christoph and V. L. Goedken J. Amer. Chem. SOC.,1973 95 3869. Aromatic Compounds Cyc1ophanes.-The synthesis of [2,2]cyclophanes has been reviewed. ' 62 A new general method of cyclophane synthesis by the photochemical extrusion of sulphur bridges on irradiation in a trialkyl phosphite solvent e.g. (85)-+ (86) has been announced independently by two groups.' 63 [7]Paracyclophane (89) Li + N-N-TS the smallest of this class of compounds to be prepared results from rearrangement of the carbene (88)which has been generated by flash pyrolysis of the correspond- ingtoluenesulphonylhydrazonesalt (87).164[8]Paracyclophanesare now available from thermal cycloadditions of buta-1,3-dienes to dispiro[2,2,2,2]deca-4,9-diene (90).'65 An X-ray analysis of [8]paracyclophane-4-carboxylic acid has shown the aromatic ring to be boat-shaped nuclear atoms C-1 and C-4 attached to the chain being 9" out of the plane of the other four.'66 The [2,n]paracyclophanes (91; n = 3-10) have been synthesized.Reaction of bromine with the ethylenic bond of(91;n = 3)is predominantly by cis addition the proportion of trans addition increasing with n in the series.Oxidative photo- cyclizations of (91; n 2 7) give the bridged phenanthrenes (92).'67 As expected 162 F. Vogtle and P. Neumann Synthesis 1973 85. 163 V. Boekelheide I. D. Reingold and M. Tuttle J.C.S. Chem. Comm. 1973 406; J. Bruhin and W. Jenny Tetrahedron Letters 1973 1215; J. Bruhin W. Kneubuhler and W. Jenny Chimia (Switz.) 1973 27 277. 164 A. D. Wolf V. V. Kane R. H. Levin and M. Jones J. Amer. Chem. Soc. 1973 95 1680. 165 T. Tsuji and S. Nishida J. Amer. Chem. SOC.,1973 95 7519. 166 M. G. Newton T. J. Walter and N. L. Allinger J. Amer. Chem. SOC., 1973,95 5652. S. E. Potter and I. 0.Sutherland J.C.S. Chem. Comm. 1973 520. 410 J. W. Barton the naphthalenophanediene (93) readily undergoes photocyclization to coro- nene.168 Full details of the synthesis and an X-ray crystallographic study of the highly crowded [2,2,2] (1,3,5)cyclophane-1,9,17-triene(94) have been reported ;'69 n-n interactions in this and related compounds have been studied by photo- electron spectroscopy.' 70 A novel synthesis of the triply bridged cyclophane (95) @ / \ \ / 17 has been achieved by the construction of a third bridge across [2,2]paracyclophane making use of the unusual property of an acetyl group at position 4 to direct the entry of a chloromethyl group into the closest (13) position in the opposite ring.' 7' Further studies of the synthesis of triple-,' 72a~bquadruple-,' 72b and quintuple-' layered cyclophanes have been reported ; catalytic trimerization of cyclododeca-1,7-diyne in the presence of dimesitylcobalt has given the com- pletely bridged 'percyclophane-4' (96).' 74 (94) 16' J.R. Davy and J. A. Reiss J.C.S. Chem. Comm. 1973 806. 169 V. Boekelheide and R. A. Hollins J. Amer. Chem. SOC.,1973 95 3201. I7O R. Boschi and W. Schmidt Angew. Chem. Inrernat. Edn. 1973 12 402. 17' E. A. Truesdale and D. J. Cram J. Amer. Chem. SOC.,1973,95 5825. 172 (a) N. Kannen T. Umemoto T. Otsubo and S. Misumi Tetrahedron Letters 1973 4537; (b) T. Umemoto T. Otsubo Y. Sakata and S. Misumi ibid.,p. 593. 173 T. Otsubo S. Mizogami Y.Sakata and S. Misumi Terrahedron Letters 1973 2457. 174 R. D. Stephens J. Org. Chem. 1973 38 2260. Aromatic Compounds 41 1 The absolute configuration of l-oxo[2,2]metacyclophane has been deter- mined' 75 and further studies of conformational mobility in mixed para-' 76a3b and metapara-' 76c cyclophanes have been reported.The donor-acceptor cyclo-phanes (97) capable of internal charge-transfer interaction have been synthesized. Surprisingly the interaction is least in (97a) where the nuclei are closest and centrally superimposed and greatest in (97c). A synthesis of the internal quin- hydrone (98) has been described ;17* no rapid change of oxidation states involving OMe (97) a;n=m= 5 b;n=m=6 c;n=4,m=8 hydrogen transfer between the two aromatic rings could be detected in solutions of (98). Transannular coupling takes place during the hydrogenation of [2,2]-metacyclophane in acetic acid the reaction giving hexadecahydropyrene (99) stereospecifically.'79 Electrophilic formylation unlike nitration proceeds with- out transannular coupling to give 4-formy1[2,2]metacyclophane (100 ; R = CHO),'8o while homolytic benzoyloxylation in acetonitrile has given low yields 175 K.Mislow M. Brzechffa H. W. Gschwend and R. T. Puckett J. Amer. Chem. SOC. 1973,95 621. 176 (a)M. Sakamoto and M. Oki Tetrahedron Letters 1973 3989; Bull. Chem. SOC.Japan 1973,46 270; (b)J. F. Haley and P. M. Keehn Tetrahedron Letters 1973 4017 4019; (c) S. A. Sherrod and R. L. da Costa ibid. p. 2083. L. G. Schroff A. J. A. van der Weerdt D. J. H. Staalman J. W. Vehoeven and Th J. 177 de Boer Tetrahedron Letters 1973 1649. W. Rebafka and H. A. Staab Angew. Chem. Internat.Edn. 1973 12 776. 179 E. Langer and H. Lehner Tetrahedron Letters 1973 1143; Monatsh. 1973 104 1154 1484. A. Maquestian Y. Van Haverbeke R. Flammang M. Flammang-Barbieux and N. Clerbois Tetrahedron Letters 1973 3259. 412 J. W.Barton ofa mixture of the 4-benzoate (100; R = OCOPh) the 8-cyanomethyl compound pyrene and 4,5-dihydropyrene.l 81 3 Non-benzene Systems Three- and Four-membered Rings.-Measurement of pKR+ values for a series of diphenylcyclopropenium salts Ph,C 'X BF,- has given an order of stability R,N >> cyclo-C,H > OEt > Pr" -SMe > Ph > H indicating that conjuga- tive effects predominate in stabilizing these cations although to a smaller extent than with most other cations.' 82 For certain symmetrical cyclopropenium cations C +X ,which are unstable in aqueous solution the relationship between pKR+ and skeletal deformation frequency has been used to compare stabilities.' 83 Nucleophilic displacements on 1,2,3-tris(N-methylanilino)cyclopropenium per-chlorate have given the cyclopropen-one (101 ; X = 0)and -thione (101 ; X = S).'84 Salts of tris-(alky1thio)- and tris(phenylthi0)-cyclopropenium cations (102a) have been prepared ; their n.m.r.spectra suggest that 2p3d interaction Ph as in form (102b) is important in stabilizing these structure^.'^^ The previously known reaction of cyclopropenyl cations with cyclopropenes leading to benzene derivatives is paralleled by their reaction with 1-azirines which gives rise to pyridines but a different mechanistic pathway is suggested for the latter (Scheme 7).86 Attempted bimolecular reduction of cyclopropenium salts to bicyclo- propenyls with sodium dithionite has given instead the sulphones (103 ; R = H or Ph; X = SO,). On photolysis these yielded the benzene derivatives (105; R = H or Ph) in high yield probably via (104;R = H or Ph ;X = SO,) and thence a prismane intermediate;IR7 the thioketone (103; R = Ph; X = C=S) formed from triphenylcyclopropenium bromide and dimethylsulphonium methylide behaves in the same way.'88 IB' T. Sato and K. Nishiyama J.C.S. Chem. Comm. 1973 220. R. C. Kerber and C. M. Hsu J. Amer. Chem. SOC.,1973 95 3239. lB3Z. Yoshida H. Ogoshi and S. Hirota Tetrahedron Letters 1973 869. Z. Yoshida H. Konishi Y. Tawara K. Nishikawa and H.Ogoshi Tetrahedron Letters 1973 261 9. IB5 Z. Yoshida S. Miki and S. Yoneda Tetrahedron Letters 1973 4731. R. E. Moerck and M. A. Battiste Tetrahedron Letters 1973 4421. Is' R. Weiss C. Schlierf and H. Kolbl Tetrahedron Letters 1973 4827. B. M. Trost R. C. Atkins and L. Hoffman J. Amer. Chem. SOC.,1973 95 1285. Aromatic Compounds 413 R3 = Ph H or C02Et Ph R2 Ph )-4+R3-)ppVR3 R' Ph R' Ph R2 Br-Br-R' phrl~Rz -+ Ph*' R3 Ph N' RZ Ph R' H Scheme 7 X-Ray crystallographic analyses of diphenylcyclopropenone h~drate'~~",~ and of 2,3-diphenyl-4,4-dicyanotriafulvene1 89b have been reported. The former is nearly planar but the phenyl groups are slightly twisted in the same sense with respect to the three-membered ring ; the results suggest a considerable contribution from the dipolar form.The triafulvene (107) has been obtained from the reaction of di-p-tolylcyclopropenonewith bis(trifluoromethyl)keten presumably via the cycloadduct (106). It appears that the strong negative induc- tive effects of the trifluoromethyl groups favour an important contribution from the 'aromatic' dipolar form (107b) greater than in other triafulvenes studied previously.' (a) H. Tsukada H. Shimanouchi and Y. Sasada Tetrahedron Letters 1973 2455; (6) H. L. Ammon J. Amer. Chem. SOC.,1973 95 7093. I9O I. Agranat and M. R. Pick Tetrahedron Letters 1973 4079. 414 J. W.Barton The chemistry of benzocyclopropenes has been reviewed.' 91 Reaction of the adduct (108) of dichlorocarbene and 1,4-dihydronaphthalene with potassium t-butoxide has given the parent naphtho[b]cyclopropene (109) some reactions of m ( 107a) (107b) which have been described.' 920 It readily undergoes catalytic hydrogenation to a mixture of benzocycloheptene (86 %) and 2-methylnaphthalene (14 %) ; uncatalysed methanolysis is very slow but in the presence of silver(1) ions 2- methoxymethylnaphthalene is formed quantitatively in less than one minute at 25 "C.Using enthalpy changes found for the latter reaction an estimated strain energy of 65-47 kcal mol- ' was obtained in good agreement with a value of 67.8 kcal mol- from the heat of combustion ; the corresponding reaction of benzocyclopropene gave a value of 68 kcal mol- '. An X-ray crystallographic analysis of (109) while showing the 1,2- and 2,3-bonds to be short gave no evi- dence for bond localization in the direction of either limiting structure (l09a) or (1Wb).' 92b MO calculations of the electron distributions in benzocyclopropene its cation anion and radical have been carried out ;193 significant stabilization of the ions by charge delocalization is predicted the radical having a stability intermediate between the cation and anion.There is evidence that the benzo- cyclopropenium ion is formed when benzocyclopropene reacts with triphenyl- methyl fluoroborate in acetonitrile ;194n it is also suggested that the halogen- exchange reaction of 7,7-dichloro-2,5-diphenylbenzocyclopropene with silver fluoride takes place via benzocyclopropenium cations.'94b 19' B. Halton Chem. Rev. 1973 73 113. 19* (a) W. E. Billups and W. Y. Chow J. Amer. Chem. SOC.,1973 95 4099; (6) W. E. Billups W. Y.Chow K. H. Leavell E. S. Lewis J. L. Margrave R. L. Sass J. J. Shieh P. G. Werness and J. L. Wood ibid. p. 7878. 193 B. Halton and M. P. Halton Tetrahedron 1973 29 1717. 194 (a) P. Muller Helv. Chim. Acta 1973 56 500; (b) P. Miiller J.C.S. Chem. Comm. 1973,895. 195 (a) 0.L. Chapman D. De La Cruz R. Roth and J. Pacansky J. Amer. Chem. Soc. 1973 95 1337; (6) G. Maier and B. Hoppe Tetrahedron Letters 1973 861; (c) 0. L. Chapman C. L. McIntosh and J. Pacansky J. Amer. Chem. SOC.,1973 95 617; (d)A. Krantz C. Y. Lin and M. D. Newton ibid. p. 2744. Aromatic Compounds 415 Further evidence of structure of matrix-isolated cyclobutadiene has been reported analysis of its i.r.spectrum provides support for the assignment of a square geometry to the molecule. There is loss of chirality in the adducts when cyclobutadienyliron tricarbonyl complexes are oxidatively decomposed in the presence of trapping agents thus demonstrating the intermediacy of free cyclobuta- diene.'96 The hindered cyclobutadienes (111; R = H or C02Me) have been obtained by low-temperature photolysis of the diazo-compounds (110; R = H,C02Me);197"(111 ; R = H) is also formed by photolysis of the two isomeric tri-t-butylcyclopentadienones.' 976 From its n.m.r. spectrum the paramagnetic contribution to the induced ring current of (111 ;R = H) is estimated to be 1.04 p.p.m.Evidence from photoelectron spectroscopy suggests that the stability of donor-acceptor cyclobutadienes such as (112)may be due to strong second-order bond fixation rather than to the contribution of zwitterionic structures.' 98 The results of a preliminary X-ray crystallographic study of squaric acid have been reported ;19' Meerwein methylation of the squaric acid derivative (113) has given (114) the salt of a stable cyclobutenium dication.200 New syntheses of cyclobutene-20'" and benzocyclobutene-20 la*' diones have been described including (115) which is a benzologue of squaric acid and is relatively acidic Me Me Me Me Me Me 2BFi (114) L96 E. K. G. Schmidt Angew. Chem. Internat. Edn. 1973 12 777; R. H. Grubbs and R. A. Grey J. Amer. Chem.SOC.,1973 95 5765. 19' (a) S. Masamune N. Nakamura M. Suda and H. Ona J. Amer. Chem. SOC.,1973 95 8481; (b)G. Maier and A. Alzerreca Angew. Chem. Internat. Edn. 1973 12 1015. 19* R. Gompper F. Holsboer W. Schmidt and G. Seybold J. Amer. Chem. SOC.,1973 95,8479. 199 D. Semmingsen Tetrahedron Letters 1973 807. zoo S. Hunig and H. Putter Angew. Chem. Internat. Edn. 1973 12 149. (a) T. Kowar and E. LeGoff Synthesis 1973 212; (b)J. F. W. McOmie and D. H. Perry J.C.S. Chem. Comm. 1973 248. 416 J. W.Barton (pK = 4.48; pK2 = 8.05).2016 Flow pyrolysis of (116) in nitrogen at 250°C gives small yields of the thienocyclobutadiene (1 17 ;X = S) which like the furan analogue (1 17;X = 0)discussed in last year's Report (p. 584) is highly reactive and dimerizes in solution to the bisthienocyclo-octatetraene(1 18).202 Partial catalytic reduction of (117; X = 0) gives (119) which shows properties of a rather reactive 3,4-dialkylfuran ; the striking difference in properties between these two compounds lends support to the view that (117; X = 0) should be regarded as a truly antiaromatic system.203 HO Homo Five-and Seven-membered Rings.-The antiaromatic cyclopentadienyl cation has been generated at -78 0C;204 the e.p.r.spectrum shows it to have a triplet ground state as predicted. Sulphonium cyclopentadienylides are formed by the photolysis of diazocyclopentadiene in dialkyl sulphides ;'OS preparations of iodonium cyclopentadienylidesZo6 and of the tripolar mesomeric salt (1 20)207 + (121a) (121b) have been reported.From bond-length data obtained in an X-ray crystallo- graphic analysis of triphenylphosphonium cyclopentadienylide (121)' and from the phosphorus photoelectron spectrum the relative contributions of forms '02 K. P. C. Vollhardt and R. G. Bergman J. Amer. Chem. Soc. 1973,95 7538. '03 R. G. Bergman and K. P. C. Vollhardt J.C.S. Chem. Comm. 1973 214. '04 M. Saunders R. Berger A. Jaffe J. M. McBride J. O'Neill R. Breslow J. M. Hoffman C. Perchonock E. Wasserman R. S. Hutton and V. J. Kuck J. Amer. Chem. Sor. 1973,95,3017. '05 W. Ando J. Suzuki Y. Saiki and T. Migita J.C.S. Chem. Comm. 1973 365. '06 K. Friedrich and W. Amann Tetrahedron Letters 1973 3689. '07 Z. Yoshida S. Yoneda T. Yato and M. Hazama Tetrahedron Letrers 1973 873.Aromatic Compounds 41 7 (121a) and (121 b) are estimated to be 20 and 80% respectively,208 in good agree- ment with previous MO calculations. Reactions of (121) with electrophiles and dienophiles have been Vacuum thermolysis of a-coumarone (122) at 750 "C has given fulvene (5.5 %) benzene (22 %) and a trimer of the presumed quinone methide intermediate (123).92b The bromination of 6,6-diphenylfulvene (124) a; R = Me b; R = Ph has been re-investigated ;21 nucleophilic displacement reactions of certain 1- and 6-substituted fulvenes have been reported,2' as has the cycloaddition of 6,6-disubstituted fulvenes to dienes2' The isobenzofulvenes(l24) have been obtained as transient intermediates ;21 trapping with reagents such as N-phenylmaleimide gave 1,3-cycloadducts and (124a) gave the 1,8-cycloadduct with tropone.The quaternary salt (125) undergoes Hofmann elimination at 20 "C to give a mixture of the pentalene dimers (126) and (127) which on photolysis in a matrix at -196 "C are converted into monomeric pentalene ; the latter conversion is reversed by warming the matrix to 20 0C.2140 Fission of the dimer (126) has also QMe "6 'O* H. L. Ammon G. L. Wheeler and P. H. Watts J. Amer. Chem. Soc. 1973 95 6158. *09 Z. Yoshida S. Yoneda and Y. Murata J. Org. Chem. 1973 38 3537. 'lo P. T. Cheng P. A. Gwinner S. C. Nyberg R. k.Stanforth and P. Yates Tetrahedron 1973 29 2699; K. Hafner and F. Schmidt Tetrahedron Letters 1973 5101. 2'1 K. Hafner and F. Schmidt Tetrahedron Letters 1973 5105; D.Copocasale L. Di Nunno S. Florio and F. Naso J.C.S. Perkin 11 1973 2078. 'I2 K. N. Houk and L. J. Luskus J. Org. Chem. 1973,38 3836. 'I3 H. Tanida T. Irie and K. Tori Bull. Chem. SOC.Japan 1972 45 1999; P. L. Watson and R. N. Warrender Austral. J. Chem. 1973 26 1725. *I4 (a)K. Hafner R. Donges E. Goedecke and R. Kaiser Angew. Chem. Internat. Edn. 1973 12 337; (6) W. Weidemuller and K. Hafner ibid. p. 925. 418 J. W. Barton been brought about by iron enneacarbonyl at 50 “C,when the pentalene complex (128) was isolated ;’14’ a comparable bis(trimethylgermyldicarbony1ruthenium) complex has recently been obtained by dehydrogenative transannular cyclization I1 (CO),Fe Fe(CO) \/ C JI 0 of cyclo-octatetraene.21 1,3,5-Tri-t-butylpentalene (129) which is too sterically hindered to dimerize readily has been isolated ;preliminary analysis of the 3C and ‘H n.m.r.spectra rules out the existence of a localized bond system in (129) and indicates the presence of a paramagnetic ring current.’16 Convenient preparations of tropylium trifluoroacetate and other salts from cycloheptatriene have been described.2 The dissociation equilibrium of tropy- lium isothiocyanate has been determined,218 and the reaction of tropylium ion with cycloheptatriene has been in~estigated.~” Further reactions of tropo-thione (130) have been reported,’” including the formation of 8,8-dicyanohepta-fulvene (131; R = CN) from the reaction with tetracyanoethylene;220b there appears to be very little contribution from the 6n-electron dipolar form towards the structure of (130).220dDibenzo[c,e]tropone (132) has been synthesized ;221 as expected it behaves as a reactive 6z-electron component in thermal [6 + 41-cycloaddition reactions.Using 13Cn.m.r. spectroscopy it has been shown that ’I5 A. Brookes J. Howard S. A. R. Knox F. G. A. Stone and P. Woodward J.C.S. Chem. Comm. 1973 587. ’I6 K. Hafner and H. U. Suss Angew. Chem. Internat. Edn. 1973 12 575. *I7 J. V. Crivello Syntheric Cornrn. 1973 3 9. ’18 H. Kessler and A. Walter Angew. Chem. Internat. Edn. 1973 12 773. ’ S. It& A. Mori I. Saito K. Sakan H. Ishiyama and K. Sasaki Tetrahedron Letters 1973,2737. ’” (a)T. Machiguchi M. Hoshino S. Ebine and Y. Kitahara J.C.S. Chem. Comm. 1973 196; (6)T. Machiguchi K.Okuma M. Hoshino and Y. Kitahara Tetrahedron Letters 1973 201 1 ;(c) T. Machiguchi Y. Yamamoto M. Hoshino and Y. Kitahara ibid. p. 2627; (4T. Machiguchi T. Hoshi J. Yoshino and Y. Kitahara ibid. p. 3873. ’” C. E. Hudson and N. L. Bauld J. Amer. Chem. Soc. 1973,95 3822. Aromatic Compounds 419 tropolone acetate undergoes rapid degenerate rearrangement at low tempera- tures ;222 there is spectroscopic evidence of Meisenheimer-type complex (1 33) formation in the reaction of 2-methoxy-5-nitrotropone with sodi~rnrnethoxide.~~~ Syntheses of heptafulvene (131 ;R = H) and pentaheptafulvene have been des- ~ribed,~’~ as has a synthesis of the higher homologue 8,8’-biheptafulvenyl ;225 S 0 iron carbonyl complexes of (131 ; R = H) have also been isolated.226 Stable phenazulene derivatives (1 35) have been obtained from cycloadditions of 8,9-dicyanosesquifulvalene (134) and the method has been extended to prepare acepleiadylene derivatives.” The 8-cycloheptatrienylheptafulvenylcation (136) has been generated ;228 it is one of the most stable hydrocarbon cations yet known. Treatment of either 1,2- or R’ & -R2 02yJo OMe OMe R’-R2 = -(CH2)4-(133) R’ = Ph R2 = H ”* S. Masamune A. V. Kemp-Jones J. Green D. L. Rabenstein M. Yasunami K. Takase and T. Nozoe J.C.S. Chem. Comm. 1973,283. 223 T. Abe and T. Asao Tetrahedron Letters 1973 1327. 224 M. Nuenschwander and W. K. Schenk Chimia (Switz.) 1972 26 194. 225 S. Kuroda M. Oda and Y. Kitahara Angew. Chem. Inrernar.Edn. 1973 12 76. 226 R. C. Kerber and D. J. Ehntholt J. Amer. Chem. SOC.,1973 95 2927. 227 H. Prinzbach and H. W. Schneider Angew. Chem. Internat. Edn. 1973 12 1007; H. Prinzbach L. Knothe and H. W. Schneider ibid. p. 1009. ’” I. Fleming J.C.S. Perkin I 1973 1019. 420 J. W.Barton 3,4-benzocyclohepta-1,3,5-trienewith potassium amide in liquid ammonia affords a red-brown solution of benzocycloheptatriene mon~anion.~~’ The H n.m.r. spectrum of this ion shows it to be strongly paratropic and the proton coupling constants indicate first-order bond fixation as in (137),which will tend to decrease the antiaromaticity of the seven-membered ring. H The copper(1)-catalysed decomposition of diazo-ketones derived from dihydro- cinnamic acids forms the basis of a recent azulene synthesis (Scheme 8).230A novel ferrocene-catalysed photoalkoxycarbonylation of azulene takes place in R’,RZ = H or Me Scheme 8 carbon tetrachloride-alcohol solutions ;23 the reaction is unaffected by dissolved oxygen or by radical scavengers and possibly takes place via an azulene-iron complex.Reactions of diethyl azulene-1,3-dicarboxylateswith Grignard re-agents proceed by nuclear rather than by carbonyl addition the products giving mixtures of 2- 4- and 6-substituted azulenes on deh~drogenation.~~~ Annu1enes.-The anions (1 38)and (1 39)have been generated at low temperature and characterized by ‘Hn.m.r. spectroscopy.233 Both ions appear to be more or less planar and the spectrum of (139)suggests that there is substantial polarization 229 S.W. Staley and A. W. Orvedai J. Amer. Chem. SOC.,1973 95 3382. 230 L. T. Scott J.C.S. Chem. Comm. 1973 882. 231 T. Ishigami T. Akiyami H. Watanabe T. Kato and A. Sugimori J.C.S. Chem. Comm. 1973 871. 232 N. Abe T. Morita and K. Takase Tetrahedron Letters 1973 3883 4739. 233 S. W. Staley and G. M. Cramer J. Amer. Chem. SOC.,1973,95 5051 ;S. W. Staley and W. G. Kingsley ibid. p. 5805. Aromatic Compounds 42 1 of electron density out of the cyclopropyl ring by spirocyclopropyl conjugation ; thus the eight-membered ring of (139) supports a diamagnetic ring-current whereas that of (138) is an atropic (4n +1) system. Recent e.s.r. data on the benzocyclo-octatetraene radical anion are best interpreted in terms of a planar or near-planar structure with strong n-n interaction in the eight-membered ring.234 Reduction of [18]annulene with potassium at -110 "C gives an equi- librium mixture of two conformers of the dianion probably (140) and (141).Both CGG \ \\ \ species exhibit n-bond localization and are non-planar having six intra- and twelve extra-annular protons.23 Charged Huckel (4n +2)-electron species which have been studied include the [16]annulenediyl dication (142)236 and the [17lannulenyl anion (143),237 generation of the former being the first example of formation of a dication of this type from a [Qnlannulene; cations from oxygen- bridged annulenes have also been ~haracterized.~ 234 J. R. Dodd Tetrahedron Letters 1973 3943. 235 J. F. M.Oth E. P. Woo and F. Sondheimer J. Amer. Chem. SOC.,1973 95 7337. 236 J. F. M. Oth D. M. Smith U. Prange and G. Schroder Angew. Chem. Znternat. Edn. 1973 12 327. 237 G. Schroder G. Plinke D. M. Smith and J. F. M. Oth Angew. Chem. Znternat. Edn. 1973 12 325. 238 H. Ogawa I. Tabushi H. Kato and Y. Taniguchi Tetrahedron Letters 1973 5065; H. Ogawa and M. Kubo Tetrahedron 1973 29 809. 422 .I. W. Burton Syntheses of the bridged [14]annulene (1#)239 and of the [18]annuleno- phenanthrene (145)240 have been reported ;in both cases the macrocyclic system G sustains a diamagnetic ring-current. It appears that the upper limit for diatropic character in [4n + 2lannulenes is higher than has been predicted ;it is exhibited by 3,15,18,30-tetra-t-buty1-1,16-bisdehydro[30]annulene, the synthesis of which was described recently.241 Fluxional behaviour (146a) S(146b) has been observed with certain 1,6-methano[ 101ann~lenes.~~~ Generation of the arylcarbene (147) by heating the sodium salt of the corres- ponding toluene-p-sulphonylhydrazone in diglyme at 135 "C results in re-arrangement to the l0n-electron aromatic carbene (148),which dimerizes to give a mixture of (149) and (150); similar results are obtained if (148) is generated The mode of formation of (149) and (150) is unknown it possibly involves electrocyclic ring-closure of undecafulvene intermediates.The chemistry 239 W. Flitsch and H. Peeters Chem. Ber. 1973 106 1731. 240 U. Meissner B. Meissner and H. A. Staab Angew. Chem. Internat.Edn. 1973,12,916. 241 M. Iyoda and M. Nakagawa Tetrahedron Letters 1973 4743. 242 H. Giinther H. Schmickler W. Bremser F. A. Straube and E. Vogel Angew. Chem. Internat. Edn. 1973 12 570. 243 (a) P. H. Gebert R. W. King R. A. LaBar and W. M. Jones J. Amer. Chem. SOC. 1973 95 2357; (b)R. A. LaBar and W. M. Jones ibid. p. 2359. Aromatic Compounds 423 a:> //--‘ A/ of carbene (151) has also been investigated ;in the absence of acceptors it dimerizes to the fulvene (152).243b An X-ray crystallographic analysis of the tropolone analogue (153) discussed in last year’s Report (p. 590),has been carried The molecule shows near- mirror symmetry perturbed only by the hydroxy-group; it appears that there is more delocalization in the eleven-membered ring than in the corresponding tropone analogue.Experiments are in progress to obtain information as to possible quinonoid character in the annulenedione (154) the synthesis of which has been 4 Polycyclic Compounds Using MO methods a ‘Kekule Index’ placing valence bond structures quantita- tively in their relative order of importance has been compiled for a number of 244 D. W. J. Cruickshank G. Filippini and 0.S. Mills Angew. Chem. internat. Edn. 1973 12 855. 245 K. Yamamoto and F. Sondheimer Angew. Chem. internat. Edn. 1973 12 68. 424 J. W.Barton polycyclic benzenoid and non-benzenoid aromatic hydrocarbons.246 Photo- cyclizations of 2-vinylbiphenyl 4-~inylphenanthrene,~~~" and 2-styrylphenanth- rene247b have been studied ;the last-named cyclizes exclusively at position 3 of the phenanthrene nucleus.Syntheses of arene oxides of polycyclic benzenoid hydrocarbons have been reported ;2480 the 9,lO-oxide of phenanthrene isomerizes to dibenzo[b,d]oxepin (155) on photolysi~.~~~~ The structure of lamellicolic anhydride a heptaketide from Verticilliurn larnellicola has been established as (156).249 Surprising selectivity is observed in the formation of naphthalene derivatives from P-he~a-ketones,~~' for example treatment of (157) with silica gel at pH 8 gave (158) whereas cyclization with aqueous potassium hydroxide gave the resorcinol (159) which could be further cyclized to (160) on treatment with potassium carbonate or trifluoroacetic acid. Ph(COCH,),COPh "O2 &COPh (1 57) HO Ph 4 (158) aq.KOH I 246 A. Graovac I. Gutman M. Randid and N. Trinajstic J. Amer. Chem. SOC.,1973 95 6267. 247 (a)S. W. Horgan D. D. Morgan and M. Orchin J. Org. Chem. 1973 38 3801; (6) G. Snatzke and K. Kunde Chem. Ber. 1973,106 1341. 248 (a)S. H. Goh R. G. Harvey H. Yagi and D. M. Jerina J. Amer. Chem. SOC.,1973 95 242 243; (6)N. E. Brightwell and G. W. Griffin J.C.S. Chem. Comm. 1973 37. 249 N. J. McCorkindale A. McRitchie and S. A. Hutchinson J.C.S. Chem. Comm. 1973 108. 250 P. J. Wittek and T. M. Harris J. Amer. Chem. SOC.,1973 95 6865. A romatic Compounds (163) R' RZ = H,Me Ph or alkoxycarbonyl ( 165) (164) R' R2 = C0,Me R' = C02Et,R2 = H R' = Ph R2 = H Highly substituted naphthalenes (164) have been obtained from thermal reactions of the diyne (161) with alkyne~.~~'" It is suggested that (16l)first isomerizes to the benzocyclobutadiene (162) followed by cycloaddition and rearrangement of the adduct (163).When tris(triphenylphosphine)rhodium(I)chloride is included in the reaction mixture addition takes place in a linear mode to give the naphtha- lenes (165).25lb Various pericyclic naphthalenes have been synthesized and their derived radical anions examined.' The protonation of naphthalenes in super- acidic media has been studied ;253 rates of normal and photo-induced hydrogen- deuterium exchange of naphthalene in sulphuric acid solutions have been deter- mined.254 The reversibility of intramolecular Friedel-Crafts acylation at the a-position in the naphthalene nucleus of (166) has been demonstrated.255 2,2'-Binaphthyl undergoes a high-temperature diene addition with maleic anhydride at positions 1 and 3' rather than giving a 1,l'-adduct which might be expected from bond-order consideration^.'^^ Photochemical reactions of naphthalene continue to evoke interest.Primary and secondary products arising from [2 + 2]photocycloadditions to the nuclei of l-'57aand 2-257b naphthonitriles and of methyl 2-naphth0ate~~~' have been 251 (a) E. Muller and A. Huth Tetrahedron Letters 1972 4359; (b) H. Straub A. Huth and E. Muller Synthesis 1973 783. 252 S. F. Nelsen and J. P. Gillespie J. Amer. Chem. SOC.,1973 95 1874 2940; J. Org. Chem. 1973 38 3592. 253 G. A. Olah G. D. Mateescu and Y.K. Mo J. Amer. Chem. SOC. 1973 95 1865. 254 C. G. Stevens and S. J. Strickler. J. Amer. Chem. SOC.,1973 95,3918 3922. 255 I. Agranat and D. Avnir J.C.S. Chem. Comm. 1973 362. 256 E. Clar and F. Clar Tetrahedron 1973 29 3267. 257 (a)C. Pac T. Sugioka K. Mizuno and H. Sakurai Bull. Chem. SOC. Japan 1973,46 238; (6) K. Mizuno C. Pac and H. Sakurai J.C.S. Chem. Comm. 1973 219; (c) G. Sugowdz P. J. Collin and W. H. F. Sasse Austral. J. Chem. 1973 26 147. 426 J. w.Burton characterized ;displacement of fluorine in photosubstitution reactions of fluoro- nitronaphthalenes has been reported.258 1-Acenaphthenium ions have been observed spectroscopically.259 The dianion of acenaphthylene (167) a 14n-electron system undergoes protonation to give (168) quantitatively;260" however the main product of carbonation is the di- carboxylic acid (169) formed together with a smaller amount of the acenaphthene derivative (170).260b In contrast the dianion from pyracyclene (171) reacts at C-1 and C-2 exclusively.261 CO,H (169) ( 1 70) (171) 258 J.G. Lammers and J. Lugtenburg Tetrahedron Letters 1973 1777. 259 G. A. Olah G. Liang and P. Westerman J. Amer. Chem. SOC.,1973 95 3698. 260 (a)C. V. Ristagno and R. G. Lawler Tetrahedron Letters 1973 159; (b)T. S. Cantrell ibid.,p. 1803. 261 B. M. Trost D. Buhner and G. M. Bright Tetrahedron Letters 1973 2787. Aromatic Compounds 427 Full details of a study of the electrochemical potentials of cyclobutadieno- naphthoquinone derivatives have been published.262 The formation of phenan-throcyclobutenes by [2 + 2]photocycloaddition of olefins to phenanthrene has been further investigated.263 Phenanthro[lJcyclobutadiene (1 72) has been gener- ated and characterized as its iron tricarbonyl complex ;its reactions with dienes and with tetracyanoethylene have been reported.264 The bridged benzocyclo- butadiene derivative (173) which may be regarded as a biphenylene analogue (172) (1 73) possessing an oxepin ring has been synthesi~ed;'~~ solutions of (173) are stable for a few hours at -78 "C,but it rapidly forms a linear [2 + 21 dimer at room temperature.Thermolysis of the 1-diazoindene-benzyne cycloadduct (1 74) gives high yields of 2H-cyclopent[ j,k]fluorene (175); fluoradene derivatives may be obtained in the same way from 9-diazofluorene.266 240 "C ___, g \ N / Nucleophilic attack on 9-benzoylanthracene and related derivatives by cyanide ion in dimethylformamide under mild oxidizing conditions gives 9,lO-dicyano- anthracene and thence the 2,3,9,1O-tetra~yano-derivative.~~' Photonucleophilic substitution by ammonia has been observed with 1- and 2-methoxyanthra-9,lO- quinone2680 and with sodium anthra-9,10-quinone-2-sulphonate ;268b on present 262 R.Breslow D. R. Murayama S. Murahashi and R. Grubbs J. Amer. Chem. Soc. 1973,95,6688. 263 G. Kaupp Angew. Chem. Znternat. Edn. 1973 12 765. 264 T. Miyamoto and Y.Odaira Tetrahedron Letters 1973 43; T. Miyamoto S. Tanaka and Y.Odaira J.C.S. Perkin I 1973 138. 265 M. P. Cava and K.T. Buck J. Amer. Chem. Soc. 1973,95 5805. 266 C. Tuchscherer M. Bruch and D. Rewicki Tetrahedron Letters 1973 865. 267 N. A. Goeckner and H. R. Snyder J. Org. Chem. 1973,38 481. 268 (a)J. Griffiths and C. Hawkins J.C.S. Chem. Comm. 1973 11 1 ;(6)G. G. Wubbels D. M. Tollefsen R. S. Meridith and L. A. Herewaldt J. Amer. Chem. Soc. 1973 95 3820. 428 J. W.Barton evidence a radical mechanism appears unlikely in the case of the methoxyl displacement. Photochemical addition of cycloheptatriene to anthracene gives the [6 + 41 and [4 + 41 cycloadducts (176) and (177) the former predominating; ( 176) (1 77) the corresponding thermal reaction affords only a [2 + 41 adduct in low yield.269 Other studies involving exciplex formation between anthracenes and secondary amine~,~"" 1,3-diene~,~~'~ have been reported the last- and aromati~s~~~'*~ named being those where the participants were held together by a trimethylene chain.In the case of 1-(9-anthry1)-3-( 1-naphthy1)propane the adduct (178) was formed in a reversible process ;270d intramolecular [4 + 41 photocycloadditions have also been observed with 1,l'-and 2,2'-linked anthra~enes.~~' Full details of syntheses leading to azupyrene (179) have been published.272 The ketone (180) has been synthesized and its spectra in acidic solution indicate formation of a delocalized cation with substantial contribution from (181).273 26q T. Sasaki K. Kanematsu and K. Hayakawa J. Amer. Chem. SOC.,1973,95 5632. 270 (a) N. C. Yang and J. Libman J. Amer.Chem. SOC.,1973 95 5783; (b)J. Saltiel and D. E. Townsend ibid. p. 6141; (c) M. Itoh T. Mimura H. Usui and T. Okamoto ibid. p. 4388; (d) E. A. Chandross and A. H. Schiebel ibid. p. 61 I. 2" F. C. De Schryver M. D. Brackeleire S. Toppet and M. Van Schoor Tetrahedron Letters 1973 1253. 272 A. G. Anderson G. M. Masada and A. F. Montana J. Org. Chem. 1973,38 1439; A. G. Anderson A. F. Montana A. A. McDonald and G. M. Masada ibid. p. 1445. 273 N. Abe T. Morita and K. Takase Tetrahedron Letters 1973 4755. Aromatic Compounds The tetrafluoroborate salt of cation (182) has been prepared ;attempts to convert it into a dication or into the 16n-electron system (183) have so far proved un- ~uccessfu1.~~~ Several studiesofthechemistry ofphenalenes have been reported.275 The reaction of phenalene with dichloromethane and n-butyl-lithium gives rise to the naphthobicyclobutane (184) together with a smaller amount of the pleia- dene (185);2750,b the latter is fairly stable thermally but (184) isomerizes at 150 "C to the cyclobutene (186).275b Irradiation at 2537 8 brings about rearrangement of (184) to (185) as does catalysis by silver(1) ions;275' other isomerizations of (184) promoted by transition metals have been E.s.r.spectral studies of the radical anions of pleiadenes and related compounds including (184) and (185) have been reported.252 Cycloaddition of benzyne to acenaphthy- lene has given the cyclobutene (187) which is converted into the 'biradicaloid' pleiadene (188) on low-temperature photolysis in a matrix.276 Similar prepara- tions from 1,2- and 2,3-naphthalynes gave benzologues of (188) of which only the angularly annelated derivative (189) survived briefly in solution at room temperature.(187) (188) 274 J. Beeby and P. J. Garratt J. Org. Chem. 1973 38 3051. 275 (a) I. Murata and K. Nakasuji Tetrahedron Letters 1973 47; (b) R. M. Pagni and C. R. Watson ibid. p. 59; (c) I. Murata and K. Nakasuji ibid. p. 1591; (d)I. Murata K. Nakasuji and H. Kurne ibid. p. 3405; (e) T. T. Coburn and W. M. Jones ibid. p. 3903. 276 J. Kolc and J. Michl J. Amer. Chem. SOC.,1973 95 7391. 430 J. W.Barton The subject of circulenes was mentioned in last year’s Report (p. 596). Another example of this class of compound the thiacoronene (191) has been obtained by oxidative cyclization of the bridged [18lannulene (190).277 277 J.Lawson R. DuVernet and V. Boekelheide J. Amer. Chem. SOC.,1973,95 956.

 



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