17 Aromatic Compounds By H. HEANEY Department of Chemistry The University of Technology Loughborough Leicestershire. LEI 7 3TU 1 General The concept of aromaticity has been discussed again.' Is it an outmoded concept or can one still conveniently classify compounds usefully in this way? The invited lectures at the international symposium on non-benzenoid aromatic compounds held in Sendai have been published,2 as have the proceedings of symposia held in Jer~salem,~ Aro-and at the I.U.P.A.C. congress in B~ston.~ maticity and the relevance to pericyclic reactions has been re~iewed,~ as has the Mobius-Hiickel concept.6 Hindered rotation about the sp2-sp3 carbonsarbon bonds in a number of bisdichloromethylbenzenes has been reported. The barrier (AG * = 17.7 kcal mol-') was particularly high in the case of the octachloro-o-xylene derivative (l).7For the rneta-isomer' three conformers were indicated by the low-tempera- ture n.m.r.spectra and two conformers for the para-is~rner.~ Relatively high energy barriers to rotation also exist in compounds such as (2)." While space- filling models suggest that severe hindrance to the rotation of the t-butyl groups in (3) should be observed no evidence was found in the n.m.r. spectrum even H ' J. F. Labarre and F. Crasnier Fortschr. Chem. Forsch. 1971 24 33. ' Papers in Pure Appl. Chem. 197 1 28 pp. 11 1-398. ' 'Aromaticity Pseudo-Aromaticity and Anti-Aromaticity,' Israel Academy of Sciences and Humanities Jerusalem 1971. Papers in Pure Appl. Chem.1971 28 supplement. M. J. S. Dewar Angew. Chem. Internat. Edn. 1971 10 761. H. E. Zimmerman Accounts Chem. Res. 1971,4 272. V. Mark and V. A. Pattison Chem. Comm. 1971 553. J. Peeling B. W. Goodwin T. Schaefer and C. Wong Canad. J. Chem. 1971,49 1489. B. H. Barber and T. Schaefer Canad. J. Chem. 1971,49 789. lo A. Mannschreck and L. Ernst Chem. Ber. 1971 104,228. 515 516 H. Heaney at -80 "C.l1 This result was ascribed to an in-plane bending of the t-butyl groups away from the phenyl substituent. The energy barrier to ring inversion in 2-(1-hydroxy-1-methylethy1)tetraphenylene has been studied and is very low compared with the barrier in cyclo-octatetraene. l2 The result was interpreted as indicating a decrease in the anti-aromaticity of the planar transition state involved in the inversion compared with the anti-aromaticity in planar cyclo- octatetraene.Protonation of aromatic aldehydes by HS0,F-SbF substantially increases the barrier to rotation about the aryl-to-carbonyl carbon bond versus that observed in the boron trifluoride c~mplexes.'~ Similar effects have also been observed in related system^.'^ Results of other studies of inversions and rotations at nitrogen' and in carbon-carbon systems16 have also appeared. The asymmetric syntheses of hexa-' and octa- and nona-helicene18 have been reported by the photocyclization of the appropriate diarylethylenes using circularly polarized light. It was shown that the optical activity did not result from partial asymmetric photodestruction.The spontaneous resolution of racemic 1,l'-binaphthyl has been achieved by heating the solid at temperatures between 105-1 50 "C. Partial resolution was also achieved during the solidifi- cation of molten samples." The chiral binaphthyl derivative (4) is readily resolved and has been used with bases some of which are normally difficult to I' B. Miller and K.-H. Lai Tetrahedron Letters 1971 2957. H. P. Figeys and A. Dralants Tetrahedron Letters 1971 3901. l3 R. Jost P. Rimmelin and J. M. Sommer Chem. Comm. 1971 879. l4 M. Rabinovitzand A. Ellencweig Tetrahedron Letters 197 1,4439; R.Jost P. Rimmelin and J. M. Sommer ibid. p. 3005. W. J. Deloughry and I. 0. Sutherland Chem. Comm. 1971 1104; M. J. S. Dewar and W. B. Jennings J. Amer. Chem.Soc. 1971 93 401 ; C. H. Bushweller J. W. O'Neil and H. S. Bilotsky ibid. p. 543; C. H. Bushweller and J. W. O'Neil Tetrahedron Letters 1971 347 1. I6 G. Markl F. Lieb and C. Martin Tetrahedron Letters 1971 1249; D. Y. Curtin P. E. Bender and D. S. Hetzel J. Org. Chem. 1971 36 565; M. Oki and M. Suda Bull. Chem. SOC.Japan 1971,44 1876; M. Oki and N. Nakamura ibid. p. 1880. A. Moradpour J. F. Nicoud G. Balavoine H. Kagan and G. Tsoucaris J. Amer. Chem. Soc. 1971,93 2353. l8 H. Kagan A. Moradpour J. F. Nicoud G. Balavoine R. H. Martin and J. P. Cosyn Tetrahedron Letters 197 1 2479. l9 R. E. Pincock and K. R. Wilson J. Amer. Chem. Soc. 1971,93 1291. 2o J. Jacques C. Fouquey and R. Viterbo Tetrahedron Letters 1971 4617. Aromatic Compounds 2 Benzene and Derivatives Mechanistic aspects of electrophilic substitutions which are of current interest have been reviewed.2 Fluorine hyperconjugation in aromatic systems has been reviewed22 and the major conclusion is reached that it is unimportant as a primary factor.A model based on polar (inductive) effects best describes sub- stituent effects of perfluoroalkyl groups. Spirodiene rearrangement^^^ and the synthesis of quinones which have a heterocyclic ring directly fused to the quinone moiety24 have been reviewed. The deuteriation of the aromatic ring of benzyldicarbonyl-n-cyclopentadienyl-iron occurs more readily than the deuteriation of anisole under comparable conditions and this suggests that the group -CH2-Fe(CO),-n-C,H is more electron releasing than is the methoxy-gro~p.~~ Partial rate data have been reported for the nitration of p-halogenoanisoles.In acetic anhydride attack para to the methoxy-group occurs to the extent of 40 31 and 28% of total attack in the series p-iodo- p-bromo- and p-chloro-anisole.26 The so-called ips0 partial rate factors for iodine bromine and chlorine are 0.18 0.07, and 0.06,. Evidence for a field effect in aromatic nitration has been adduced from the rates of nitration of 3,8-diaza[ lO]cyclophane and a related open-chain compound. The rate for the cyclophane is lower by a factor of 200.27 Except for alkylation sulphonation and iodination electrophilic substitution in aro- matic compounds is normally regarded as being irreversible ; however the bromination of NN-dialkylanilines has been shown to be reversible.Thus o-bromo-NN-dimethylaniline hydrobromide gave a mixture of products including NN-dimethylaniline and p-bromo-NN-dimethylaniline when heated at 120 "C in chloroform.28 The debromination step presumably involves the ion (5) as shown. (5) Electrophilic substitutions of aromatic compounds which proceed by way of addition-elimination reactions were mentioned in last year's report.29 Thus 5-substituted-hemimellitenesand 4-substituted-o-xylenes react with nitric acid- acetic anhydride to give 4-nitrocyclohexa-2,5-dienones in addition to normal 21 G. A. Olah Accounts Chern. Res. 1971 4 240; J. H. Ridd ibid. p. 248. 22 D. Holtz Chem. Rev. 1971 71 139. 23 D. H. Hey Quarr. Rev. 1971 25 483.24 I. Baxter and B. A. Davis Quart. Rev. 1971 25 239. 25 S. N. Anderson D. H. Ballard and M. D. Johnson Chern. Comm. 1971 779. 26 C. L. Perrin and G. A. Skinner J. Amer. Chem. SOC.,1871,93 3389. 27 G. Mossa A. Ricci and J. H. Ridd Chern. Comm. 1971 332. '* F. Effenberger and P. Menzel Angew. Chem. Internat. Edn. 1971 10,493. 29 H. Heaney Ann. Reports (B) 1970 67 331. 518 H. Heaney substitution product^.^' For example the dienone (7) was isolated in 73% yield from (6). The nitration of polyalkylbenzenes with fuming nitric acid leads to ring and side-chain substitution products together with small amounts of dinitrocyclohexenones ; thus ethylmesitylene affords (8) as a minor (2-4 %) prod~ct.~The chlorination of 3,4-dimethylphenolY 3,4-dimethylphenyl acetate (7) or 3,4-dimethylphenyl methyl ether in acetic acid gives the enone (9) which decomposes first to the dienone (10) and then to the phenols (11) and (12).32 Aromatic compounds undergo methylthiolation by treatment with methyl methanethiosulphonate in the presence of aluminium chloride.However since the introduction of an RS group activates the product to further electrophilic substitution di- and poly-substitution occurs readily.33 0 c1 Me Me Me Me C1 Me C1 Me (9) Reactions of aromatic compounds with thallium salts continue to attract attention.34 Arylthallium(II1) compounds have been shown to form biaryls when allowed to react with PdCl in acetic acid containing sodium acetate.35 The role of the sodium acetate may involve the formation of Pd" species which is more efficient than PdCl in the coupling reaction.Acetophenone and a number of its derivatives have been converted in good yield into methyl phenylacetate 30 D. J. Blackstock M. P. Hartshorn A. J. Lewis K. E. Richards J. Vaughan and G. J. Wright J. Chem. SOC.(B) 1971 1212. 31 H. Suzuki M. Sawaki and R. Sakimoto Chem. Comm. 1971 1509. 32 P. B. D. de la Mare and B. N. B. Hannan Chem. Comm. 1971 1324. 33 J. K. Bosscher E. W. A. Kraak and H. Kloosterziel Chem. Comm. 1971 1365. 34 K. Ichikawa S. Uemura T. Nakano and E. Uegaki Bull. Chem. SOC.Japan 1971 44,545; S. Uemura K. Sohma M. Okano and K. Ichikawa ibid. p. 2490; A. McKillop J. D. Hunt M. J. Zelesko J. S. Fowler E. C. Taylor G. McGillivray and F. Kienzle J.Amer.Chem.SOC., 197 1,93,484 1 ;E. C. Taylor F. Kienzle R. L. Robey A. McKillop and J. D. Hunt ibid.,p. 4841 ;A. McKillop 0.H. Oldenziel B. P. Swann E. C. Taylor and R. L. Robey ibid. p. 7331 ; K. L. Erickson and H. W. Barowsky Chem. Comm. 1971 1596. 35 S. Uemura Y. Ikeda and K. Ichikawa Chem. Comm. 1971 390. Aromatic Compounds 519 (or derivatives) using thallium(rI1) nitrate in acidic methanol.36 1,2-Aryl migra- tion occurs in an intermediate such as (13) which is formed by the oxythallation of the enol form of the initial ketone. OMe o-Quinone methide has been generated by the photolysis of the compounds (14) and (15),37 and is stable at -196 0C.38The nucleophilic cyclization of an enol ether unit on to an o-quinone methide has been used in the formation of carpanone (18).39 The required precursor (17) was obtained by the phenolic coupling of (16) using palladium dichloride and led to the direct isolation Me HI M.p7 of (18).This brilliant synthesis results in the generation of five contiguous asym- metric centres. Cyclization of the quinone methide (20) has been suggested to account for the base-catalysed formation of (21)from (19)."' Similarly the forma- tion of (25) at 250 "Cfrom (22) proceeds as shown.41 36 A. McKillop B. P. Swann and E. C. Taylor J. Amer. Chem. SOC.,1971 93 4919. 37 0.L. Chapman and C. L. McIntosh Chem. Comm. 1971 383. 38 C. L. McIntosh and 0.L. Chapman Chem. Comm. 1971,771. 39 0. L. Chapman M. R. Engel J. P. Springer and J. C. Clardy J.Amer. Chem. SOC. 197 1,93,6696. 40 E. E. Schweizer T. Minami and D. M. Crouse J. Org. Chem. 1971 36 4028. 41 R. Hug Gy. Frater H.-J. Hansen and H. Schmid Hefu. Chim. Acta 1971 54 306. 520 H. Heaney O-(CH,),-$R Br Me Me 25 + rapid 1 CIAR& R2 OR2 R' R2 (24) Intramolecular cycloadditions to o-quinodimethanes also proceed in high yield. Thus after heating the benzocyclobutene derivative (26) in toluene at 190 "C the product (28) was isolated in 85 % yield. The results obtained in a number of reactions support the view that for example the intermediate (27) is involved in the formation of (28);42this principle has been applied to the The full account of the generation and synthesis of racemic ~helidonine.~~ reactions of 1,3-diphenylisoindenone has appeared.44 o-Benzoquinone 0-phenylene sulphite and o-phenylene carbonate are known to afford the dimer of cyclopentadienone on pyrolysis.45 The deposition of the pyrolysis products 42 W.Oppolzer J. Amer. Chem. SOC.,1971 93 3833 3834. 43 W. Oppolzer and K. Keller J. Amer. Chem. SOC. 1971 93 3836. 44 J. M. Holland and D. W. Jones J. Chem. Suc. (0,1971 608. 45 D. C. De Jongh R. Y. Van Fossen and C. F. Bourgeois Tetrahedron Letters 1967 271. Aromatic Compounds 521 on an i.r. plate at -196°C has enabled the monomer to be observed.46 3,4,6- Trimethyl-1,2-benzoquinoneforms the dimer (30) when a chloroform solution is left at room temperat~re.~~ It is presumably formed via the quinone methide (29). The isomerization of hindered quinone methides such as (31) to alkenyl phenols e.g.(32) can be achieved rapidly in quantitative yield on neutral alu- mina.48 Stable 0-and p-naphthoquinone methides have been isolated and are 0 0 0 OH Me Me Me present as glucosides in the insect Aphis nerii4’ The synthesis of compounds in the triquinocyclopropane series was reported last year. The tetraquinocyclo- butane (34) has now been prepared by the thermal dimerization of the diquino- ethylene (33).” 0 C II C 0 Rearrangements of methylene cyclohexadienes bearing allyl or benzyl groups at the quaternary carbons should be capable of proceeding by symmetry-allowed concerted pathways. However the deuteriated compound (35) gave (36) in which complete equilibration of the ends of the allyl group had taken place and strongly suggesting a radical chain mechanism in which the allyl radical 4h 0.L. Chapman and C. L. McIntosh Chem. Comm. 1971 770. 47 M. F. Ansell and A. J. Bignold Chem. Comm. 1971 1562. 48 D. Braun and B. Meier Angew. Chem. Internar. Edn. 1971 10 566. 49 K. S. Brown and U. Weiss Tetrahedron Letters 1971 3501; K. S. Brown and P. M. Baker ibid. p. 3505. S. Koster and R. West Chem. Comm. 1971 1380. 522 H. Heaney MebMe Me Me\ Me Me D' (35) (37) is the chain carrier.51 The benzyl analogue (37) could only be observed by n.m.r. spectroscopy and it rearranges very rapidly to (38) also by a radical mechanism. Reaction of either the dienol (39) or the semibenzene (40) with 1% sulphuric acid in ahetic acid for 10 min gave the normal ally1 migration product (41).52 However over an extended period (20 h) using 10 % sulphuric acid the compounds (39) (40) and (41) each gave identical mixtures of (42H45).The & Mea Me Me Me (42) (43) Me Me (44) (45) surprising conclusion concerning these rearrangements is that migration of the poorest migrating group occurs. Initial protonation must occur predominantly on the carbon flanked by two methyl groups and molecular models indicate that steric strain is most effectively relieved by this process. The tosyl hydrazones (46; R = H or Me) rearrange in the presence of acids to (47; R = H or Me). The [3~,3s]-sigrnatropic shift is analogous to the dienimine-aniline type.53 51 B. Miller and K.-H. Lai Tetrahedron Letters 1971 1617. 52 K.-H. Lai and B. Miller Tetrahedron Letters 1971 3575. 53 M. Schmid H.-J. Hansen and H. Schmid Helv. Chim.Acta 1971 54 937. Aromatic Compounds ,NHTs IdNHTs HN R Me (46) (47) The monoethers of hydroquinone and catechol which are hindered towards aromatic electrophilic substitution are efficiently cleaved to the corresponding quinones and alcohols on treatment with nitrous acid.54 Thus 4-benzyloxy-2,6-di-t-butylphenol is converted smoothly into benzyl alcohol and 2.6-di-t-butylbenzoquinone. "0-Labelling experiments showed that the intermediate (48) fragments to the cation (49) which affords the quinone in the aqueous II (48) 0 (49) medium. The preparation of substituted 2,5-diamino-p-benzoquinonesby established methods in good yield is not easy.It has now been reported55that the oxidative amination of p-hydroquinones using sodium iodate in the presence of the appropriate amine gives very good yields. Indane-5,6-quinone tetrahydronaphtho-2,3-quinone, and 4,5-dimethylbenzo-1,2-quinone each react with cyclopentadiene to afford adducts in which the diene behaves as the dien~phile.~~ With a number of other o-benzoquinonesand cyclo-pentadiene the quinone acted as both the diene and the dien~phile,~' and the two products underwent intramolecular Cope interconversions. With acyclic dienes the quinone always acts as a dienophile. Using tetrachloro-or tetrabromo-o-ben~oquinone~~' acyclic dienes add to one of the carbonyl groups.For example with 2,3-dimethylbuta-l13-diene the spirodihydropyran (50) was obtained. In benzene at 80 "C (50)was converted as expected into (51) whereas in the pre-sence of 2,3-dimethylbuta-1,3-dienethe bis-adduct (52) was obtained. Treatment of the p-nitrobenzenediazonium ion with sodium methoxide in methanol affords nitrobenzene in high yield. Evidence has been presented5' 54 D. H. R. Barton P. G. Gordon and D. G. Hewitt J. Chem. Soc. (C) 1971 1206. " W. Schafer and A. Agnado Angew. Chem. Internat. Edn. 1971 10 405. 56 W. M. Horspool P. Smith and J. M. Tedder J. Chem. Soc. (C) 1971 1638. 57 (a)M. F. Ansell A. F. Gosden V. J. Leslie and R. A. Murray J. Chem. SOC.(C),1971 1401; (b) M. F. Ansell A. J. Bignold A. F. Gosden V.J. Leslie and R. A. Murray ibid. p. 1414; (c) M. F. Ansell and V. J. Leslie ibid. p. 1423. 58 W. J. Boyle T. J. Broxton and J. F. Bunnett Chem. Comm. 1971 1469. 524 H. Heaney Me c1 Me Me which supports the view that the initial product is the cis-p-nitrophenylazo- methyl ether which reacts further by a free-radical mechanism to form the nitro- benzene. The reduction of aryl diazonium salts by means of borohydride has been shown to proceed by way of aryldia~enes.~~ The diazotization of 2-amino- tetrafluorophenol in 70 % aqueous sulphuric acid gave l-diazotetrafluoro-benzene-2-oxide(53) in virtually quantitative yield.60 The decomposition of the diazo-oxide in the presence of dipolarophiles leads to the formation of products derived from the dipolar keto-carbene (54).Thus with benzonitrile the benzo- xazole (55) was obtained in 51% yield. The decomposition of the diazonium salt from 3-amino-4-t-butyl-5-nitrobenzoic acid (56) remarkably affords the benzocyclobutene (57) in good yield.61 The mechanism of this reaction is obscure C02H C02H O,N @NH2 02Nq \ but will undoubtedly be studied further. The decomposition of N-nitrosoace- tanilide in a mixture of 2,Sdimethylfuran and benzene gives rise to 2-benzyl-5- methylfuran. It was suggested that this product arises by acetate ion deprotona- 59 C. E. McKenna and J. G. Traylor J. Amer. Chem. SOC.,1971 93 2313. 6o J. M. Birchall R. N. Haszeldine J. Nikokavouras and E. S. Wilks J. Chem. SOC.(C) 1971 562. 61 M. H. Knight T. Putkey and H.S. Mosher J. Org. Chem. 1971 36 1483. Aromatic Compounds tion of the charge-transfer complex (58).62 The decomposition of N-nitroso- N-exo-bicyclo[3,1,0]hex-2-en-6-ylurea (59) in the presence of sodium carbonate results in the formation of benzene in 90% yield.63 It was suggested that the intermediates (60H62)are involved. In less-basic media bi- and tri-cyclic products were obtained in addition to benzene. The norbornenone derivative (63)is converted exclusively into 1,2,3,4-tetraphenylbenzeneunder mild alkaline condition^.^^ This reaction does not appear to involve decarbonylation and may well involve the loss of two molecules of carbon dioxide as shown in (64) NO H HI wN-coNH2 (59) Ph 'H followed by the loss of water.2-Aryl-6-oxocyclohex-1 -enylacetic esters undergo dehydrogenation to phenols with simultaneous loss of the acetate side-chain when heated at 100°Cin DMF in the presence of sodium hydride.6' The reaction of diphenylcyclobutenedione with an excess of diazomethane gives a mixture of (65) and (66). The formation of (66) from (65) occurs on heating in toluene whereas in xylene the phenol (67)was obtained.66 There is a pronounced tem- perature effect on the reaction of diazomethane with 1,3,5-trinitrobenzene. At 0 "C the product is (68),whereas at -80 "C(69) was obtained.67 62 J. I. G. Cadogan M. J. P. Harger J. R. Mitchell and J. T. Sharp Chem. Comm. 1971 1432. " W. Kirmse and F. Scheidt Angew. Chem. Internat. Edn. 1971 10 263. 64 E. A. Harrison Chem.Comm. 1971 1090. 65 D. Nasipuri A. Bhattacharyya and B. G. Hazra Chem. Comm. 1971 660. 66 W. Ried W. Kuhn and A. H. Schmidt Angew. Chem. Internat. Edn. 1971 10 736. 67 J. C. Van Velzen C. Kruk and Th. J. De Boer Rec. Trau. chim. 1971 90 842. 526 H Heaney PhB Me0 \ '"rH Me0 The full account of the reactions of organolithium compounds with aryl sulphonium salts which were reported previously68 has now been published. The ligand coupling reaction requires both units to possess a 7c-system and proceeds with the retention of configuration at carbon.69 The evidence supports the view that intermediate sulphuranes are involved. The location of the metal ion in certain aromatic carbanion systems has been studied. In for example fluorenyl-lithium 7Li n.m.r.suggests that the lithium ion is located above the n-cl~ud.~~ The n.m.r. spectrum of [3,5-2H2]phenylmagnesiumbromide has been studied7' and an extended Schlenk equilibrium used to account for the species present. Diborane has been shown to react with arylmercury halides in tetrahydrofuran to form intermediates which can be oxidized to phenols in high yield.72 A number of reports of reactions of sodium-naphthalene with organic halides have appeared. Different views have been reported for reactions with aryl halides.73 A radical coupling mechanism was suggested for reactions of alkyl halides and the observation of a CIDNP effect in the reactions of p-fluorobenzyl chloride or iodide74 suggests that the radical-radical-anion pair (70) is involved." H. Heaney Ann. Reports (B) 1969 66 329. 69 R. W. LaRochelle and B. M. Trost J. Amer. Chem. SOC.,1971,93 6077. 'O R. H. Cox H. W. Terry and L. W. Harrison J. Amer. Chem. SOC.,1971 93 3297. 71 D. F. Evans and G. V. Fazakerley J. Chem. SOC.(A) 1971 184; G. Fraenkel D. G. Adams and R. R. Dean J. Phys. Chem. 1968,72,944. 72 S. W. Breuer M. J. Leatham and F. G. Thorpe Chem. Comm. 1971 1475. 73 T. C. Cheng L. Headley and A. F. Halasa J. Amer. Chem. SOC.,1971 93 1502; G. D. Sargent Tetrahedron Letters 1971 3279. 74 J. W. Rakshys Tetrahedron Letters 1971 4745. Aromatic Compounds The cerium(1v)-catalysed decomposition of phenyldiazomethane leads to a mixture of cis- and trans-stilbene in which the cis-isomer predominate^.^^ It was suggested that radical-cation intermediates are involved although an expla- nation for the formation of the cis-isomer in high yield is obscure.The benzo- phenone ketyl radical can be generated thermally in for example decalin. a-Diketones can be reduced efficiently by this system to the a-hydroxyketone ; for example benzoin is obtained in 85 % yield from ben~il.~~ Aromatic ketones such as a-tetralone are reduced to the corresponding hydrocarbons by lithium in ammonia in a two-step process in which the benzylic alcoholate ion is formed first and this is then further reduced by excess of metal after protonation with ammonium chloride.77 Catalysis by trace quantities of cobalt was also noted. Vinyl esters of aromatic acids have been converted in high yields into diaroyl- methanes in the presence of aluminium chloride.These reactions may proceed via the diaroylacetaldehydes. '' Deuterium and tritium labelling studies have shown that the formyl proton in salicylaldehyde formed in the Reimer-Tiemann reaction is not derived from the aryl residue.79 Thus protonation of the anion (71) must occur before re-aromatization. Phthalaldehyde reacts with phenyliso- cyanate to form N-phenylphthalamidine quantitatively." It was suggested that the reaction proceeds via the iminoaldehyde (72). The oxidation of various araldehyde hydrazones with mercuric oxide in a number of solvents such as benzene gives rise to the diazoalkane. It has now been shown that arylnitriles are formed in solvents such as 1,2-dimetho~yethane.~l The reaction is thought to involve a tautomeric equilibrium between the diazoalkane and the imine.A number of very interesting sulphur trioxide oxidations of suitably protected substituted arenes have been reported." Thus for example pentachlorotoluene affords the betaine (73) from which the benzyl alcohol can be isolated. Prolonged reaction leads to (74) from which pentachlorobenzaldehyde can be isolated. Stilbene ozonides react with a number of bases including dimethylsulphoxide to afford quantitative yields of benzaldehydes and benzoic acids. Thus the 75 W. S. Trahanovsky M. D. Robbins and D. Smick J. Amer. Chem. SOC.,1971 93 2086. 76 M. B. Rubin and J. M. Ben-Bassat Tetrahedron Letters 1971 3403. 77 S. S. Hall S. D. Lipsky F.J. McEnroe and A. P. Bartels J. Org. Chem. 1971 36 2588. 78 Y. S. Rao and R. Filler J. Org. Chem. 1971 36 1447. 19 D. S. Kemp J. Org. Chem. 1971 36 202. 80 I. Yamamoto Y. Tabo and H. Gotoh Tetrahedron Letters 1971 2295. 81 D. B. Mobbs and H. Suschitzky Tetrahedron Letters 1971 361. 82 V. Mark L. Zengierski V. A. Pattison and L. E. Walker J. Amer. Chem. Sac. 1971 93 3538. 528 H. Heaney SO H / so; +o\ so; +/ 1 C,CI CH -0 C,CI -CH / \ ,so; SOJH +s (73) SO3H (74) ozonide derived from trans-2,4-dinitrostilbene gives benzaldehyde and 2,4-dinitrobenzoic acid.8 Treatment of for example benzaldehyde dimethylacetal with boron trifluoride in deuteriochloroform at room temperature results in the formation of the stable delocalized carbonium ion (75).84 The advantages of using tetra-alkylammonium salts in reactions which traditionally use metal salts have been pointed out.This has been used to good effect in the benzoin condensati~n.~~ c1 A new route to biaryls involves the elimination of hydrogen chloride from the charge-transfer complexes formed between n-excessive arenes and aryl halides which contain electron-withdrawing groups. Thus using (76)and (77) the corres- ponding biaryl was obtained in 79 % yield.86 The prediction87 that NO-diaryl- hydroxylamines should undergo benzidine-type rearrangements has been verified.88 Benzyl-N-(o-nitrophen0xy)carbonate was treated with base followed by o-nitrofluorobenzene and gave the compound (78). Attempted removal of 83 R.M. Ellam and J. M. Padbury Chem. Comm. 1971 1094. 84 M. Rabinovitz and D. Bruck Tetrahedron Letters 1971 245. J. Solodar Tetrahedron Letters 1971 287. 86 F. Effenberger K. Nagel and W. Agster Angew. Chem. Internat. Edn.. 1971 10 566. *’ M. J. S. Dewar in ‘Molecular Rearrangements’ ed. P. de Mayo Interscience New York 1963 vol. 1 p. 344. 88 T. Sheradsky and G. Salemnick Tetrahedron Letters 1971 645. Aromatic Compounds the protecting group with hydrobromic acid resulted in the rearrangement to (79). The trifluoromethyl group is frequently hydrolysed by strong bases particu- larly in arenes containing hydroxy- or amino-substituents in the para-position. Good yield conversions of trifluoromethylnitrochlorobenzenes into the phenols without hydrolysis of the trifluoromethyl group have been reported using powdered sodium hydroxide in dimethyl ~ulphoxide.~~ Reductive dehalogena- tions which occur during nucleophilic aromatic substitutions are more common than was previously thought particularly when attempting to replace iodine activated by a nitro-group with a bulky amine.” Whereas a-chloronaphthalene is not converted into a-ethoxynaphthalene with ethoxide ion in refluxing ethanol 5-chloroacenaphthylene is converted into 5-ethoxyacenaphthylene (80).Stabili-zation of the intermediate (81) was suggested to account for the change in reac- tivity.” The chemistry of Meisenheimer complexes continues to attract considerable attention.92 The complex derived by the reaction of methoxide ion with 3,5,6,8-tetranitroacenaphthenewas formulated as (82).93The potassium salt of trans-4-t-butylcyclohexanol reacts with picryl chloride to afford the styphnate (84),presumably via hydride ion abstraction from the Meisenheimer adduct (S3).94 Triarylnitrones are produced in the reactions between diphenyl- acetonitrile and certain nitrobenzenes carried out in the presence of for example OEt EtO CI OC,H Bu‘ OC,H,,Bu’ (83) *’ R.L. Jacobs J. Org. Chem. 1971,36 242. 90 F. Pietra M. Bartolozzi and F. Del Cima Chem. Cornm. 1971 1232. 91 M. J. Perkins Chem. Comm. 1971 231. 92 M. Nilsson C. Ullenius and 0. Wennerstrom Tetrahedron Letters 1971 2713; 0. Wennerstrom Acta Chem. Scand. 1971 25 789,2341 ;F. Terrier and M.-P. Simonnin Bull.Soc. chim. France 1971 677; E. J. Fendler W. Ernsberger and J. H. Fendler J. Org. Chem. 1971 36 2333; E. J. Fendler D. M. Camaioni and J. H. Fendler ibid. p. 1544; J. H. Fendler E. J. Fendler and L. M. Casilio ibid. p. 1749; F. Terrier F. Millot and M.-P. Simonnin Tetrahedron Letters 1971 2933; M. J. Straws and H. Schran ibid. 1971 2349; M. R. Crampton M. A. El Ghariani and H. A. Khan Chem. Comm. 1971 834. ’’ C. H. J. Wells and J. A. Wilson Tetrahedron Letters 1971 4521. 94 M. L. Sinnott and M. C. Whiting J. Chem. SOC.(B) 1971 965. 530 H. Heaney sodium methoxide in methanol.95 Nucleophilic displacement of hydride ion is apparently involved in the first step. The chlorination of aromatic amines by reagents such as N-chlorosuccinimide is known to proceed via the N-chloro- amine.A kinetic study has now shown that heterolytic cleavage leads to chloride ion and a nitrenium cation and hence to product.96 In the presence of alcoholic solvents varying amounts of cyclohexa-2,5-dienone derivatives for example (85) were also isolated. Bu‘ Me OMe The reactions of polymethylhalogenobenzenes which do not have an ortho-hydrogen with potassium t-butoxide at 225°C lead to products derived by dehydrobr~mination.’~ In the case of bromodurene the products show that the hydrogen is removed from an ortho-methyl group ;for example (86)was formed in the presence of cyclohexene. Full accounts of the amide-ion catalysed re- arrangements of trihalogenobenzenes in liquid ammonia have appeared.98 The so-called ‘halogen-dance’ proceeds by a positive halogen transfer.Thus for example 1,2,4-tribromobenzene rearranges in the presence of potassium anilide to give 1,3,5-tribromobenzene and disproportionates to di- and tetra- bromobenzenes. The evidence points strongly to a ‘seven-halogen’ syster- in which 1,2,3,5-tetrabromobenzeneacts as a co-catalyst. An interesting method of dichloromethylating nitroarenes involves the reaction of trichloromethyl-lithium with the nitro-compound in the presence of a trace of lithium n-butoxide. Substitution occurs ortho to the nitro-group and may involve intermediates such as (87) and (88).99 Intramolecular nucleophilic (87) (88) 95 M. Jawdosiuk B. Ostrowska and M. Makosza Chem. Comm. 1971 548. 96 P.G. Gassman and G. A. Campbell J. Amer. Chem. SOC.,1971,93,2567. 97 J. I. G. Cadogan J. K. A. Hall J. T. Sharp and A. K. Robertson Chem. Comm. 1971 1273. J. F. Bunnett and C. E. Moyer J. Amer. Chem. SOC., 1971,93 1183; J. F. Bunnett and G. Scorrano ibid. p. 1190; D. J. McLennan and J. F. Bunnett ibid. p. 1198; J. F. Bunnett and I. Feit ibid. p. 1201. 99 E. T. McBee E. P. Wesseler and T. Hodgins J. Org. Chem. 1971 36 2907. Aromatic Compounds 531 substitution in highly fluorinated compounds has been used in the synthesis of five-membered heterocyclic systems. loo Nucleophilic substitution in 1,2,3,4- tetrafluoronaphthalene occurs at the 2-position," ' and in decafluorophenan- threne at positions 2 and 7,'02 not as had been tentatively predicted at positions 9 and 10.Benzene Isomers and Homoaromatic Systems.-Full papers which describe the now well-known initial approach to the synthesis of Dewar-benzenes have appeared together with an account of non-aromatization reaction^."^ A very efficient synthesis of benzvalene and naph thvalene involves the interaction of cyclopentadienyl-or indenyl-lithium with dichloromethane and an alkyl-lithium reagent.'04 Large quantities of these two arene isomers are thus poten- tially available although benzvalene is thermodynamically very unstable. The full account of some Diels-Alder reactions of Dewar-hexafluorobenzene has appeared.'" The spectroscopic data are in accord with exo-addition and this was rationalized in terms of steric effects which operate in the transition states.Full papers have also appeared on cis-and trans-9,lO-dihydronaphthal-ene. O6 Labelling experiments have shown that the homocyclo-octatetraene dianion is protonated in polar media with a high selectivity and results in the formation of all-cis cyclonona-l,3,6-triene (89).lo7 Similarly reactions with oxygen permanganate or methyl iodide result in the formation of 5-substituted all-cis- cyclonona-l,3,6-triene derivatives."* A monocyclic bishomotropylium ion has been reported to result from the protonation of cis-bicyclo[6,1,O]nona-2,4,6-triene. The n.m.r. spectrum is consistent only with protonation at position 3 which results in the formation of the 1,3-bishomotropylium ion (9O).lo9 Metal-catalysed reactions of homotropylium ions have been discussed.''' loo G. M. Brooke W. K. R. Musgrave R. J. D. Rutherford andT. W. Smith Tetrahedron 1971 27 5653; G. M. Brooke W. K. R. Musgrave and T. R. Thomas J. Chem. SOC. (C) 1971 3596. lol P. L. Coe G. M. Pearl and J. C. Tatlow J. Chem. SOC.(C) 1971 604. O2 J. Burdon B. L. Kane and J. C. Tatlow J. Chem. SOC.(C) 1971 1601. lo3 E. E. van Tamelen S. P. Pappas and K. L. Kirk J. Amer. Chem. SOC.,1971,93,6092; E. E. van Tamelen and D. Carty ibid. p. 6102. lo4 T. J. Katz E. J. Wang and N. Acton J. Amer. Chem. SOC.,1971 93 3782. Io5 M. G. Barlow R. N. Haszeldine and R. Hubbard J. Chem. SOC.(0,1971 90. O6 E. E. van Tamelen and B. C. T. Pappas J. Amer. Chem. SOC.,1971,93,6111;E. E. van Tamelen T. L. Burkoth and R. H. Greeley ibid.p. 6120. lo' W. H. Okamura T. I. Ito and P. M. Kellett Chem. Comm. 1971 1317. lo8 T. I. Ito F. C. Baldwin and W. H. Okamura Chem. Comm. 1971 1440. lo9 P. Warner and S. Winstein J. Amer. Chem. SOC.,1971 93 1284. 'lo P. Warner Tetrahedron Letters 1971 723; L. A. Paquette Chem. Comm. 1971 1076. 532 H. Heaney 3 Thermal Elimination and Rearrangement Reactions The pyrolyses of tetrachloro-o-phenylene carbonate- and tetrachloro-o-benzo- quinone show qualitative similarities to the mass spectral fragmentations. '' ' Thus the quinone gives (91) at 650 "C whereas at 720 "C tetrachlorobut-l-ene-3-yne is the major product and presumably arises by decarbonylation of tetra- chlorocyclopentadienone. The major product obtained in the flash-vacuum- thermolysis of p-benzoquinone at 850 "Cis vinylacetylene ;(92) is the most likely intermediate ;'12' phenyl p-benzoquinone has also been studied.' 12* Pyrolysis coupled with mass spectrometry has been used to study the fragmentation of 3-bromotropolone.In the presence of methanol two major products were obtained 2-bromophenol and dimethyldicyclopentadiene dicarboxylate.' ' 0 0 0 (92) (91) The first product arises by the loss of carbon monoxide whereas the second also involves the loss of hydrogen bromide and rearrangement to the keten (93). The pyrolysis of trans-pentafluorocinnamic acid at 400 "C affords 5,6,7,8-tetrafluorocoumarin,' whereas the pyrolysis of pentafluorophenyl ally1 ether results in the formation of the stable cyclohexadienone (94).' ' The gas-phase pyrolysis of (94a) at 295 "C gave a quantitative yield of acetic acid and dimethyl isophthalate.l6 Deuterium-labelling experiments demon- strated the intramolecularity of the rearrangement and that a [1,5] or two successive [1,3] migrations occur. The thermal dimerization of phenylallene 111 D. C. De Jongh D. A. Brent and R. Y.Van Fossen J. Org. Chem. 1971 36 1469. 112 (a) H. J. Hageman and U. E. Wiersum Tetrahedron Letters 1971 4329; (b) Chem. Comm. 1971 497. 113 H. F. Grutzmacher and J. Hiibner Tetrahedron Letters 1971 1455. 11a H. Heaney and A. P. Price Chem. Comm. 1971 894. 115 G. M. Brooke Tetrahedron Letters 1971 2377. 116 J. A. Berson and R. G. Salomon J. Amer. Chem. Soc. 1971,93,4620; R. A. Baylouny ibid.p. 462 1. Aromatic Compounds results in the formation of 2,3-dimethyl- 1-phenylnaphthalene possibly via (95).' l7 A number of other interesting thermal rearrangements and extrusions which result in the formation of aromatic compounds have been reported.l18 C0,Me C0,Me QJ OAc PhH Although NNDO calculations predict that the polyene geometry of pentalene is preferred to the aromatic geometry there are indications from the calculated bond lengths and AH that there is a slight degree of aromaticity associated with pentalene (96).'19 The preparation of the fulvene derivative (97) was the key step in an attempted preparation of a derivative of pentalene.l2' Two isomeric products together with cyclopentadiene were obtained from pyrolysis of (97) at 600 "C.The flash thermolysis and collection of the products at -196 "C gave a mixture which is believed to contain (98) the first simple pentalene derivative. The vapour-phase pyrolysis of 6-vinylfulvene at 110 "C afforded a mixture of which the dihydropentalene (99) was a major product. 12' The flash thermolysis of o-nitroanisole at 900 "Cgives benzaldehyde together with a number of other products.122 The intermediacy of the phenoxymethyl and spiro-oxiran (100)radicals was suggested. (100) 'I7 J. E. Baldwin and L. E. Walker J. Org. Chem. 1971 36 1440. R. Weiss and C. Schlierf Angew. Chem. Internat. Edn. 1971 10 811; D. L. Coffen Y. C. Poon and M. L. Lee J. Amer. Chem. Soc. 1971,93,4627; R. Maruca J. Org. Chem. 1971 36 1626; W. S.Trahanovsky and P. W. Mullen Chem. Comm. 1971 102; L. F. Miller and R. F. Boyer J. Amer. Chem. Soc. 1971 93 650; M. Pomerantz T. H. Witherup and W. C. Schumann J. Org. Chem. 1971 36 2080; M. Kato T. Sawa and T. Miwa Chem. Comm. 1971 1635; R. S. Atkinson A. J. Clark and R. E. Overill ibid. p. 535. 'I9 N. C. Baird and R. M. West J. Amer. Chem. Soc. 1971 93 3072. lZo R. Bloch R. A. Marty and P. de Mayo J. Amer. Chem. SOC.,1971,93 3071. "' J. J. Gajewski and C. J. Cavender Tetrahedron Letters 1971 1057. lZ2 R. A. Marty and P. de Mayo Chem. Comm. 1971 127. 534 H. Heaney The flash-vacuum-pyrolyses of the isomeric tolyldiazomethanes all give rise to styrene and benzocyclobutene in ca. 50 % yield.123 l3C-Label1ing experiments using formyl-labelled p-tolualdehyde have confirmed the previously suggested mechanism.'24 Other pyrolytic reactions have also led to benzocyclobutene derivatives.'25 4 Non-benzene Systems Three-and Four-membered Rings.-The reaction of an excess of dimethylamine with tetrachlorocyclopropene surprisingly generates the trisdimethylamino-cyclopropenium ion (101) rather than ring-opened products in almost quanti- tative yield.' 26 Other secondary amines with the exception of diethylamine react similarly.The intermediacy of the tri-t-butylcyclopropenium ion is impli- cated in the reaction of rn-chloroperoxybenzoic acid with 1,2,3-tri-t-butylcyclo- propene,'27 which leads to di-t-butylacetylene and the mixed anhydride (102) as ..-. if? x2 Me,N NMe Ph (101) primary products.The condensation of cyanoacetic acid with diphenylcyclo- propenone leads unexpectedly to the triafulvene (103). 28 7,7-Dichlorobicyclo-[4,1,0]hept-3-ene (104) reacts with potassium t-butoxide in dimethyl sulphoxide and forms benzocyclopropene( 105)in ca.40 %yield.'29 The dehydrohalogenation of (106)provides another route to a benzocyclopropene derivative 7,7-dichloro- 2,5-diphenylbenzocyclopropene.'30 The hydrolysis of the photoadduct (107) leads to cyclobutenedione which is reasonably stable.' ' H Ph 123 B. G. Odell Ann. Reports (B) 1970 67 173. 124 E. Hedaya and M. E. Kent J. Amer. Chem. SOC.,1971 93 3283. 125 D. L. Forster T. L. Gilchrist C. W. Rees and E. Stanton Chem. Comm. 1971 695; T. L. Gilchrist C. W. Rees and E. Stanton ibid.,p.801; A. Roedig V. Kimmel and W. Lippert Tetrahedron Letters 1971 12 19. '26 Z.-i. Yoshida and Y.Tawara J. Amer. Chem. SOC.,1971 93 2573. J. Ciabattoni and J. P. Kocienski J. Amer. Chem. SOC.,1971 93 4902. E. D. Bergmann and I. Agranat J. Chem. SOC.(0,1971 1541. W. E. Billups A. J. Bakeney and W. Y.Chow Chem. Comm. 1971 1461. B. Halton and P. J. Milsom Chem. Comm. 1971 814. 13' J. C. Hinshaw Chem. Comm. 1971 630. Aromatic Compounds 535 Five- Seven- and Nhe-membered Rhgs.-Cyclopentadiene reacts with dichloro- carbene generated from chloroform using potassium t-butoxide giving as one of the products 6-chlorof~lvene.~~~ This may prove to be a new general route to 6-substituted fulvenes. The condensation of sodium cyclopentadienide with acetoxychloroalkanes such as (108) followed by the elimination of acetic acid with triethylamme affords fulvenes [(109) in this case] in good yield.133 Vilsmeier formylation of 6,6-bisdimethylaminofulveneyields the bisaldiminium salt (1 10) which on hydrolysis with sodium hydroxide affords (lll) (112) or (113) de- pending on the concentration of the base.’34 The fungal metabolite Illudin S Q AcO C1 OHC N Me OHCEHNMe2 H H (114) has been converted into the fulvenes (115) and (1 16) on brief treatment with cold sulphuric acid.The formation of dimethyl 4,5-azulenedicarboxylate (1 18) may occur by the .8 + r2scycloaddition of dimethyl acetylenedicarboxylate ”’ M. B. D’Amore and R. G. Bergman Chem. Comm. 1971,461. 133 R. Kyburz H. Schaltegger and M.Neuenschwander Helv. Chim. Acta 1971 54 1037. 134 K. Hafner and F. Schmidt Tetrahedron Letters 1971 2237. 135 S. M. Weinreb T. C. McMorris and M. Anchel Tetrahedron Letters 1971 3489. 536 H. Heaney HO-0 with (117) followed by the loss of dimethylamine.' 36 The synthesis of azulene derivatives from tropolones has been described :'37 thus 7-isopropyl-2,4-di- methylazulene was prepared from 4-isopropyltropolone. Reactions of tropone with electron-rich olefins in inverse-electron-demand Diels-Alder reactions have been re~0rted.l~' Thus (119) was formed with acenaphthylene. Reactions of a,cc'-dibromoketones with di-iron nonacarbonyl in the presence of 1,3-dienes lead to the formation of cyclohept-3-enones. Bro- mination and dehydrobromination leads to tropone derivatives.39 The mechanism of the thermal rearrangement of (120) to the tropone derivative (122) via (121) has been studied by kinetic and deuterium-labelling methods R. W. Alder and G. Whittaker Chem. Comm. 1971 776. T. Nozoe K. Takase and S. Fukuda Bull. Chem. SOC.Japan 1971,44 2210 2215. 138 T. Uyehara and Y. Kitahara Chem. and Znd.,1971 354. 13' R. Noyori S. Makino and H. Takaya J. Amer. Chem. SOC.,1971 93 1272. Aromatic Compounds and supports the view that an antara-antara [3,3]-sigmatropic process is in- v~lved.'~~ The rearrangement of tropones to m-hydroxybenzaldehydes is not confined to substrates carrying nitro-groups. The tropone derivative (123) rearranges to m-hydroxybenzaldehyde in the presence of aqueous piperidine probably via (124).14' The base-catalysed hydrolysis of 7-acetoxynorbornadiene leads to tropyl derivative^.'^^ In the presence of methanol methyl tropyl ether was obtained in 57 % yield and no deuterium incorporation was observed in the presence of methan[2H]ol and sodium deuteroxide.The suggested mechanism involves the [1,3]-sigmatropic shift of C-7 to the norcaradiene derivative (125). Heptatriafulvalene has been predicted to be polyolefinic rather than aro- rnati~.'~~ Stable salts of the type (126) have now been prepared and their spectral data are consistent with the existence of aromatic ~haracter.'~~ The reaction of tropylium perchlorate with cyclopentadiene in aqueous dioxan affords a complex mixture of alcohols.'45 However only .4 + ,2 cycloaddition occurs to form the allylic cation (127) and all of the products are derived from this ion or ions of the type (128).The reaction of antimony pentachloride with heptafulvalene results in the formation of the ditropylium salt (129) in high yield.'46 8-Cyano- 8-cycloheptatrienylheptafulvenylium fluoroborate has been prepared by the ..H, 0' 140 T. Miyashi M. Nitta and T. Mukai J. Amer. Chem. SOC.,1971 93 3441; see also J. E. Baldwin and M. S. Kaplan ibid. p. 3969. 141 G. Biggi F. Del Cima and F. Pietra Chem. Comm. 1971 1627. 142 B. Franzus W. C. Baird R. E. Felty J. C. Smith and M. L. Scheinbaum Tetrahedron Letters 1971 295. 143 H. Yamaguchi and T. Nakajima Theor. Chim. Acra 1968,12 349. 144 K. Takahashi T.Fujita and K. Takase Tetrahedron Letters 1971 4507. 145 S. It6 and I. Itoh Tetrahedron Letters 1971 2969. 146 H. Volz and M. Volz-de Lecea Annafen 1971 750 136. 538 H. Heaney abstraction of hydride ion from (130).14' Although 8-cyanoheptafulvene is unstable to acids a number of electrophilic substitution reactions have been carried out in the presence of weak bases. Thus the Vilsmeier reaction results in formylation at C-8 in 47% yield.'48 Conformational aspects of the chemistry of the 2-carboxytribenzotropylium ion (131) have been discussed assuming a chiral rapidly inverting boat-shaped ion. 149 Two tetrabenzoheptanonafulvalenes,(132) and (1 33) have been syn- thesized but both appear to be non-planar non-aromatic compounds. 50 8) -& 147 T.Otomo M. Oda and Y. Kitahara Chem. Comm. 1971 114. 14* M. Oda and Y. Kitahara Bull. Chem. SOC.Japan 1971,44,296. 14' W. Tochtermann and G. H. Schmidt Annalen 1971 754 90. lSo P. J. Garratt and K. A. Knapp Chem. Comm. 1971 1084. Aromatic Compounds 5 Cyclophanes and Annulenes The chemistry of cyclophanes has been reviewed. 51 Syntheses of layered cyclophanes' 52 and of the bridged metacyclophane' 53 (134) have been described. In the latter example extrusion of the methylamino-bridge occurs at about 200 "Cto afford (135). Full accounts of studies of ring rotations of rn-phenylene units in nietaparacyclophanes have appeared.' The solvolyses of I-tosyl-oxy[2,2]paracyclophane proceed with complete retention of configuration and are somewhat faster than those of aliphatic secondary tosylates.The results were tentatively interpreted as involving a bridged ion in which positive charge is distributed to both rings.'55 The acid-catalysed rearrangement of (+)-(S)-4-methyl[2,2]paracyclophane leads to optically pure (+)-(S)-12-methyl[2,2]-metaparacyclophane. The requirement of a fully chiral reaction co-ordinate to explain the result suggests that the intermediate (or possibly transition state) (136) is involved. '56 At relatively high temperatures all positions in metapara- cyclophane undergo hydrogen exchange at roughly the same rate with the excep- tion of that at the strongly hindered 8-position. '57 Acetylation with acetyl chloride and aluminium chloride in dichloromethane at -25 "C results in the formation of four monoacetylated derivatives of which (139) is the major product and presumably arises via the ions (137) and (138).'57 l5 ' D.J. Cram and J. M. Cram Accounts Chem. Res. 1971 4 204. 152 S. Mizogami T. Otsubo Y. Sakata and S. Misumi Tetrahedron Letters 1971 2791 ; T. Otsubo S. Mizogami Y.Sakata and S. Misumi ibid. p. 4803. 15' V. Boekelheide and R. A. Hollins J. Org. Chem. 1971 36 2437. 154 D. T. Hefelfinger and D. J. Cram J. Amer. Chem. SOC.,1971 93 4767; S. Akabori K. Shiomi and T. Sato Bull. Chem. SOC.Japan 1971 44 1346. 155 R. E. Singler and D. J. Cram J. Amer. Chem. SOC.,1971 93 4443; R. E. Singler R. C. Helgeson and D. J. Cram ibid. 1970 92 7625. 156 M. H. Delton R. E. Gilman and D. J. Cram J. Amer. Chem.SOC.,1971,93 2329. 15' D. T. Hefelfinger and D. J. Cram J. Amer. Chem. Soc. 1971 93 4754. 540 H. Heaney The n.m.r. spectroscopy of annulenes has been reviewed. 58 Dibenzocyclo-nonatetraenone does not sustain a paramagnetic ring current.lS9 Two [lo]- annulenes (140) and (141) have been prepared and are crystalline below -60 0C.160The automerization of (141) has been studied by variable-tempera- ture I3C n.m.r. spectroscopy. Neither of these substances should be regarded as aromatic compounds. Attempts to prepare quinone-like bridged [10]annu- lenes have shown that whereas the 2,5-dione exists as the norcaradiene (142) the 11,ll-difluoro-derivativedoes exist in the bicyclic forrn,l6' as does the 2,7-dione (143).162 The resolution of a number of chiral 1,6-methano[lO]-annulene derivatives has been reported.'63 An attempted synthesis of the 1,5- didehydro[lO]annulene (144) resulted in the formation of the compound (145) possibly via a Cope-like rearrangement.' 64 Similarly an attempted reaction to form (146) resulted in the formation of anthracene. The synthesis of compound 0 0 (142) (143) 15' R. C. Haddon V. R. Haddon and L. M. Jackman Forschr. Chem. Forsch. 1970/1971 16 103. Is9 M. Rabinovitz E. D. Bergmann and A. Gazit Tetrahedron Letters 1971 2671. 160 S. Masamune K. Hojo K. Hojo G. Bigam and D. L. Rabenstein J. Amer. Chem. SOC.,1971 93,4966. E. Vogel E. Lohmar W. A. Boll B. Sohngen K. Miillen and H. Giinther Angew. Chem. Internat. Edn. 1971 10 398. 162 E. Vogel W. A. Boll and E.Lohmar Angew. Chem. Internat. Edn. 1971 10 399. 163 U. Kuffner and K. Schlogl Tetrahedron Letters 1971 1773. 164 N. Darby C. U. Kim J. A. Salaiin K. W. Shelton S. Takada and S. Masamune Chem. Comm. 1971 1516. Aromatic Compounds 54 1 (147) in which one of the benzene rings in biphenylene is formally replaced by a bridged [lOIannulene ring has been re~0rted.l~~ N.m.r. data suggest "F that the unsaturated system in (148) is planar and sustains a diamagnetic ring current. 166 The synthesis and properties of the bridged methano[ lolannulene (147) analogue of phenalenone (149) has been de~cribed.'~' The annulene portion appears to be only slightly perturbed by the enone bridge. The oxidative- photocyclization of 1-(9'-anthryl)-4-phenylbuta-1,3-dieneaffords 3,4 :8,9-di-benzopyrene.It was suggested that this reaction involves the [101annulene (150).168 The full account of the synthesis of pyracylene (151) has been pub- 1i~hed.l~' In accord with predictions the peripheral 12n system sustains an induced paramagnetic ring current. Similarly the polarography of the quinone (1 52) and the e.s.r. spectrum of the semiquinone radical-anion (1 53) support the description of this [12lannulene as being antiaromatic. Other [12lannulene 165 P. J. Garratt and K. P. C. Vollhardt Angew. Chem. Internat. Edn. 1971 10 125. 166 M. 0.Riley and J. D. Park Tetrahedron Letters 1971 2871. 167 I. Murata T. Nakazawa and T. Tatsuoka Tetrahedron Letters 1971 1789. 168 R. J. Hayward and C. C. Leznoff Tetrahedron 1971 27 2085.169 B. M. Trost G. M. Bright C. Frihart and D. Britelli J. Amer. Chem. SOC.,1971 93 737. 170 P. S. Kinson and B. M. Trost J. Amer. Chem. SOC.,1971 93 3823. 542 H. Heaney systems have been rep~rted,'~' including non-planar systems. 172 Dehydro-[12]ann~lenes,'~~ have been reduced to the dianions. The and [12]ann~lene'~~ dianion from [12]annulene sustains a diamagnetic ring current is stable at + 30 "C,and does not undergo any dynamic processes of the type observed in [12]annulene it~e1f.l~~ Despite the non-planarity of the ring which is due to the presence of the inner protons the resonance energy associated with the 14 n-electrons is at least 8 kcal mol-' greater than that of the isoelectronic [14]annulene. A number of [lSlannulene derivatives have been prepared in order to study the derived cation^.'^' The annulenone (154) is best regarded as a polyenone in its ground state.However in concentrated sulphuric acid the U.V.spectrum suggests a contribution from the 14 n-electron system (155). 76 A number of [161- and [181-annulenes have been prepared,' and [181annulene undergoes an isodynamic conformational process whereby the outer and inner protons exchange their magnetic environments and become equivalent above +41 OC.17* [20]Ann~lene'~~ does show evidence for a paramagnetic ring current at -105"C and [22]ann~lene'~' a strong diamagnetic ring current in the n.m.r. spectrum. The exact limit for aromaticity in [4n + 2lannulenes 171 G. M. Pilling and F. Sondheimer J.Amer. Chem. SOC.,1971 93 1970 1977. 172 H. A. Staab F. Graf K. Doerner and A. Nissen Chem. Ber. 1971 104 11 59; A. B. Holmes and F. Sondheimer Chem. Comm. 1971 1434. 173 P. J. Garratt N. E. Rowland and F. Sondheimer Tetrahedron 1971 27 3157. 174 J. F. M. 0th and G. Schroder J. Chem. SOC.(B) 1971,904. 175 G. P. Cotterrell G. H. Mitchell F. Sondheimer and G. M. Pilling J. Amer. Chem. SOC.,1971 93 259; H. Ogawa N. Shimojo and M. Yoshida Tetrahedron Letters 1971 2013; H. Ogawa M. Kubo and H. Saikachi ibid. p. 4859. 176 H. Ogawa H. Kato and M. Yoshida Tetrahedron Letters 1971 1793. 177 T. M. Cresp and M. V. Sargent Chem. Comm. 1971 1454; K. Endo Y. Sakata and S. Misumi Bull. Chem. SOC.Japan 1971 44 2465; K. Fukui T. Okamoto and M. Nakagawa Tetrahedron Letters 197 1 3 121.178 J.-M. Gilles J. F. M. Oth F. Sondheimer and E. P. Woo J. Chem. SOC.(B) 1971 2177. 179 B. W. Metcalf and F. Sondheimer J. Amer. Chem. SOC.,1971 93 6675. 180 R. M. McQuilkin B. W. Metcalf and F. Sondheimer Chem. Comm. 1971 338. Aromatic Compounds has been calculated as being between the 22- and the 26-membered rings. Tride- hydro[26]annulene the only previously known [26]annulene derivative shows no ring current but this could be due to the presence of the three acetylenic residues. Monodehydro[26]annulene has now been prepared and is capable of sustaining an induced diamagnetic ring current."' 6 Polycyclic Compounds Full papers have appeared which describe the preparation and reactions of compounds having parallel triple bonds.'82 The reactions of a number of rhodium-complexed bisacetylenes for example from (1 56) with acetylenes yield annelated products under mild conditions :'83 thus diphenylacetylene gives (157) in 80 % yield.The norbiphenylene anion was reported recently,'84 and a benzo-derivative of the corresponding cation has been reported this year. 185 A Wittig reaction between (158) and homophthalaldehyde gave (159) in low yield and hydride abstraction gave (160). The macrocyclic compound (162) was on the other hand prepared in surprisingly good yield by the interaction of the ylide (161) with isophthalaldehyde.'86 The introduction of substituents either on the double bond or in the ortho-position of trans-stilbene reduces the melting points of the compounds to the extent that a number of them are room-tempera- ture nematic materials.'87 The /?-0x0-sulphoxide (163) undergoes rearrangement at room temperature in the presence of toluene-p-sulphonic acid to give even- tually a mixture of naphthalene derivatives.'88 In ethyl acetate solution the '" B. W. Metcalf and F. Sondheimer J. Ainer. Chem. SOC.,1971,93 5271. "* H. A. Staab and J. Ipaktschi Chem. Ber. 1971 104 1170 H. A. Staab J. Ipaktschi and A. Nissen ibid. p. 1182; A. Nissen and H. A. Staab ibid. p. 1191. lS3 E. Muller R. Thomas M. Sauerbier E. Langer and D. Streichfuss Tetrahedron Letters 197 1 52 1. H. Heaney Ann. Reports (B) 1969 66 346. P. J. Garratt and K. P. C. Vollhardt Chem. Comm. 1971 1143. C. D. Tulloch and W. Kemp Chem.Comm. 1971 747. W. R. Young A. Aviram and R. J. Cox Angew. Chem. Internat. Edn. 1971 10 410. "' Y. Oikawa and 0. Yonemitsu Chem. Comm. 1971 555. 544 H. Heaney CH CH I1 II PPh PPh compounds (165 ;XR = OEt OH and SMe) are formed possibly via the inter- mediate (164). 1,5-Dimethoxycarbonylbiphenylenehas been prepared in extremely good yield (75 %) when methyl 2,3-di-iodobenzoate was heated with copper bronze in DMF.ls9 The reduction of a number of polycyclic hydrocarbons with lithium in liquid ammonia produces anions which are alkylated by methyl iodide to afford cyclohexadiene derivatives. These cyclohexadienes are rearranged by the trityl cation. Thus 9,lO-dihydrophenanthreneaffords (166) which is rearranged to (167).I9' The abstraction of hydride ion by the trityl ion is well known and has been used to remove protecting groups from alcohols.191 Hydride ion is ab-stracted from benzyl benzyloxycarbonyl tetrahydropyranyl and bismethylene- dioxy-derivatives of alcohols.The perchlorodiphenylmethyl carbonium ion is also capable of abstracting hydride ion. However the perchlorotriphenylmethyl ion although able to convert cycloheptatriene into the tropylium ion is itself converted into the perchlorotriphenylmethyl radical. 192 This suggests that the hydride shift is a two-step process in this reaction. The 13Cn.m.r. spectrum of lS9 M. S. Newman and M. W. Logue J. Org. Chem. 1971,36 1398. I9O D. F. Lindow and R. G. Harvey J. Amer. Chem. SOC.,1971 93 3786. 19' D. H. R. Barton P. D. Magnus G.Streckert and D. Zurr Chem. Comm. 1971 1109. 192 M. Ballester J. Riera-Figueras J. Castaiier and A. Rodriguez-Siurana Tetrahedron Letters 197 1 2079. Aromatic Compounds 545 the dimer of 9-phenyl[9-' 3C]fluorenyl shows it to have the hexa-arylethane structure (168).193 The anodic methoxylation of for example 9,lO-diethyl- anthracene results in the formation of an almost 1 1 mixture of the cis-and trans-dimethoxy-compounds. It was argued that neither possible boat con-formers adequately explains the spectral data. 194 (168) Azulene derivatives are obtained by the reaction of 2H-cyclohepta[b]furan- 2-one with enamines. Thus the compound (169) gave the azulene (171 ;n = 3) with 1 -N-pyrrolidinylcyclohept-1-ene.'95 Using pyrrolidine cyclopentene the intermediate (170) was isolated and readily converted into (171 ; n = 1).The reactions of diarylketens with ethoxyacetylene lead to dihydroazulenones.' 96 a- (1 70) Thus (172) forms (173). The hydrocarbon (174) can be converted into the corresponding relatively unstable 12n-electron anion using methyl-lithi~m.'~~ High electron-density resides at position 1 in the anion since the hydrocarbon (174) is regenerated on protonation. Similarly the reaction of the anion with (172) (173) 193 H. A. Staab K. S. Rao and H. Brunner Chem. Ber. 1971 104,2634. 194 V. D. Parker J. P. Dirlam and L. Eberson Acta Chem. Scand. 1971 25 341. 195 P.-W. Yang M. Yasunami and K. Takase Tetrahedron Letters 1971 4275. 196 H. Teufel and E. F. Jenny Tetrahedron Letters 1971 1769.19' P. Eilbracht and K. Hafner Angew. Chem. Internat. Edn. 1971 10 751. 546 H. Heaney benzophenone and loss of lithium hydroxide leads to the stable compound (175). Two routes to the synthesis of benzo[4,5]cyclohepta[1,2,3-de]naphthalene (176) have been reported.'98 The carbinol (177) undergoes a Wagner-Meerwein rearrangement to the ion (178) whichcyclizes to the propellane( 179).199 Electrophilic additions to dehydro- janusene (180) give mixtures of rearranged and non-rearranged products as do the ring-opening reactions of epoxyjanusenes.200 Carbonium ion rearrange- ments occur during solvolyses of halogenojanusenes and related compounds.20 It is of interest to note that two series of doubly rearranged derivatives exist which are related by way of the achiral trans-ketone (181).202 Solvolyses of various benzobicyclanyl p-bromobenzenesulphonates have been reported.203 The rearrangement of (182) in sulphuric acid-acetic acid leads to (183).204 Rearrangements of 1,4-dihydro- 1,4-epoxynaphthalene occur during lg8 J.F. Muller D. Cagniant and P. Cagniant Tetrahedron Lerrers 1971 45; J. T. Craig K. W. Tan and A. D. Woolhouse ibid. 1971 3209. 199 G. Wittig and W. Schoch Annulen 1971 749 38. 2oo S. J. Cristol and M. A. Imhoff J. Org. Chem. 1971 36 1849. 201 S. J. Cristol and M. A. Imhoff J. Org. Chem. 1971 36 1854. *02 W. M. Macintyre M. A. Imhoff and S. J. Cristol J. Org. Chem. 1971 36 1865. 203 H. Tanida and S. Miyazaki J. Org. Chem. 1971 36 425; H. Tanida and T.hie ibid. p. 2777. 204 R. Caple G. M.-S. Chen and J. D. Nelson J. Org. Chem. 1971,36 2870. Aromatic Compounds /\ Ph 1 Ph certain cycloaddition rea~tions.~'' Thus cycloaddition with N-phenyltriazoline- dione occurs by a stepwise mechanism and aryl migration to the carbonium ion (184) results in the formation of the stabilized ion (185) which gives the final product (186). The rearrangement reactions of l-methoxybenzo barrelenes (187) are similar and give rise to a number of different product and equilibria between various products have been demonstrated in a highly alkylated 205 T. Sasaki K. Kanematsu and M. Uchide Tetrahedron Letters 1971 4855. 206 H. Heaney and S. V. Ley Chem. Comm. 1971 224; I. F. Mikhailova and V. A. Barkhash J.Org. Chem. (U.S.S.R.) 1970 6 2335. 548 H. Heaney example.207 The rearrangement of (188)in sulphuric acid leads to a quantitative yield of the lactone (189).208The reaction of (190) with palladium(I1) chloride- copper(r1)chloride in acetic acid containing sodium acetate results in the formation Me of (192) as the major product. It was suggested that the intermediate (191) is involved.209 Other examples of rearrangements in systems such as (193)210and (194)2l1 have been reported. O*O & &BPdC1 J HH 2 207 H. Hart and G. M. Love Tetrahedron Letters 1971 1342; J. Amer. Chem. SOC.,1971 73 6265. 208 H. Heaney and S. V. Ley Chem. Comm. 1971 1342. 209 C. J. R. Adderley J. W. Nebzydoski M. A. Battiste R. Baker and D. E. Halliday Tetrahedron Letters 197 1 3545.210 R. Baker and T. J. Mason J. Chem. SOC.(B),1971 1144. 211 M. A. Battiste P. F. Ranken and R. Edelman J. Amer. Chem. SOC.,1971 93 6276. Aromatic Compounds The chromium complex obtained from biphenylenyl-2,2’-dilithium and chromic chloride reacts with a number of transition-metal halides to afford two types of o-hexaphenylene one of which is screw-shaped and can be resolved.2 Dibenzo[g,p]chrysene reacts with lithium and yields the dianion (195); cis-and trans-isomers of the dihydro-derivative can be i~olated.”~ The synthesis of the interesting polycyclic hydrocarbon dibenzo[ghi,mno]fluoranthene (196) (Corannulene) has been described in full.’14 The molecule is bowl-shaped as a resuk of distortions.Low yield but simple syntheses of pyraceheptylene (197) and benzo[a]pyraceheptylene (198) have been reported.215 The heat of hydrogenation of acepleiadylene indicates that the ‘conjugation’ energy of the three non-naphthalene double bonds is approximately 18.9kcal mol-l .216 5,10-Dimethylene-5,1O-dihydroacepleiadene (1 99) and the analogue 212 G. W‘ittig and K.-D. Rumpler Annafen 1971 751 1. 213 G. W’ittig E. Barendt and W. Schoch Annalen 1971 749 24. 214 W. E. Barth and R. G. Lawton J. Amer. Chem. Soc. 1971,93 1730. C. Jutz and E. Schweiger Angew. Chem. Internat. Edn. 1971 10 808. 216 R. B. Turner W. S. Lindsay and V. Boekelheide Tetrahedron 1971 27 3341. 550 H. Heaney (200) have been prepared.217 They are readily hydrated to bridged epoxides which suggests that they are non-planar.Evidence was presented which suggested that an 18-n-electron periphery is obtained from (199) in the presence of base. *” J. W. Lown and A. S. K. Aidoo Canad. J. Chem. 1971,49 1861.