11 Aromatic Compounds By T. J. TEWSON Department of Chemistry University of Manchester Institute of Science and Technology Sackville Street Manchester 1 General Ah initio and semi-empirical INDO methods have been applied to benzene Dewar benzene benzvalene and prismane and gave values for equilibrium geometries dipole moments and spin-spin coupling constants in good agreement with known values.' A full report of the non-empirical ab initio valence-bond treatment of benzene shows greater contribution from polar wavefunctions than has been shown before and gives good correlation for resonance energy2 which previous valence-bond treatments have failed to do. The vaiue of the diamagnetic ring current as a measure of aromaticity has been q~estioned,~ out-of-plane magnetic susceptibility being dependent on delocaliza- tion but not necessarily on aromaticity thus reviving the whole problem of defining aromaticity.X-Ray crystal analysis of 1,8-(dibromomethy1)naphthaleneshows that the hydrogens and bromine approach closer than the van der Waals radius4 and some strain is relieved by bending substituents out of plane and distorting the nucleus. N.m.r. measurements of rotation in substituted 1,3,5-trineopentyl-benzenes establish AG' and relative sizes of hydrogen fluorine chlorine bromine methyl and i~dine.~ Variations in 'through-space' fluorine-fluorine coupling in substituted 1,8- difluoronaphthalenes have been attributed to variations in distance between fluorines caused by the substituent.6 The synthesis and conformational inversions of a series of hindered unsym- metrically and symmetrically substituted triarylmethanes have been rep~rted.~ ' M.D. Newton J. M. Schulman and M. M. Manus J. Amer. Chcm. SOC..1974,96 17. J. M. Nabeck and G. A. Gallup J. Amer. Chem. SOC.,1974 96,3386. T. G. Schmatz T. D. Gierke P. Beak and W. H. Flygare Terrahedron Letters 1974 2885. J. R. Robert J. S. Sherfinski R. E. Marsh and J. D. Roberts J. Org. Chem. 1974 39 11 52. B. Nilsson P. Marlinson K. Oisson and R. Carter J. Amer. Chem. Soc. 1974 96 3 190. F. B. Mailory C. W. Mallory and M.-C. Fedarko J. Amer. Chem. Soc. 1974,96 3536. P. Finocchiaro D. Gust and K. Mislow J. Amer. Chem. Soc. 1974 96,2165 3198 3205. 281 282 T. J. Tewson Enantiomers invert by a 'two-ring flip' mechanism which is comparatively slow at room temperature (AG = -21.9 kcal mol- for trimesitylmethane) but di- astereoisomers invert by a 'one-ring flip' which is considerably slower.Theoret- ical calculations using full relaxation empirical force field methods' confirm the propeller-like conformations and show that the central carbon+arbon bond is stretched and the central CCC angle expanded to 117.7" to accommodate the strain. The calculations also agreed with the 'two-ring flip' mechanism of in-version. N.m.r. studies of the conformations of o-substituted diphenyl-ethers -sulphides -methanes -ketones -sulphoxides and -sulphones9 have been per- formed and the conformations of p-fluoro o-substituted-acetophenones a-methylstyrenes and am-dimethylbenzyl alcohols studied by the effect of con- jugation on the 19Fchemical shifts." The free energy difference of axial and equatorial benzyl groups has been estimated'' by n.m.r.methods as 1.81 kcal mol-' in favour of the equatorial substituent. Collisional activation energy spectra of C,H,+ ions have been obtained12 and these can be tropylium benzyl o-tolyl m-tolyl p-tolyl and norbornadienyl ions which do not interconvert in the time sequence of the technique s). The same technique applied to carbocations from ethylbenzene showed that a /? and spiro ions (1 )-43) are all stable,' although (2)does rearrange to (3). Benzyl + or spiro-cations formed in strong acids from aromatics containing electron- donating groups show an e.s.r.signal corresponding to ca. 5 :d of cation concen- tration. The signal intensity is reversibly temperature dependent disappears in the presence of oxygen and is suggested to be due to a tri~1et.I~ C6F6+AsF6-has been prepared in tungsten hexafluoride ~olution'~ and is a paramagnetic species presumably a triplet. Photolysis of hexachlorobenzene in the presence of antimony pentafluoride containing chlorine gave C6C16' +,16 which is also a triplet. Protonation of phenols and alkoxybenzenes in superacid shows that 8 J. D. Andose and K. Mislow J. Amer. Chem. SOC.,1974,96 2168. 9 H. Benjamins and W. D. Chandler Canad. J. Chem. 1974,52 597. LO M. G. Belsham A. R. Muir M. Kinns L. Phillips and Li-Ming Twanmoh J.C.S. Perkin 11 1974 119. I1 J. E.Anderson J.C.S. Perkin II 1974 10. 12 F. W. McLafferty and J. Winkler J. Amer. Chem. SOC.,1974 96 5182. 13 N. M. Nibbering T. Nishishita C. C. Van der Sande and F. W. McLafferty J. Amer. Chem. SOC.,1974 96 5668. 14 M. Ya. Zarubin A. M. Kutnevich and A. P. Lukashenko Zhur. org. Khim. 1974 10 400. 15 T. J. Richardson and N. Bartlett J.C.S. Chem. Comm. 1974,427. 16 E. Wasserman R. S. Hutton V. J. Kuck and E. A. Chandross J. Amer. Chem. Soc. 1974 96 1966. Aromatic Compounh 283 oxygen and carbon protonation follow different acidity functions' and both are solvent dependent. The ion (4)is irreversibly transformed into (5) on heating to 40 "C as the charge is stabilized by the methyl group." Homoaromaticity.-Molecular orbital treatment" of tropylium anions and cations with respect to homoaromaticity nonhomoaromaticity antihomoaro- maticity and dihomoaromaticity shows that the opened cyclopropyl ring is favoured in all forms including the dihomotropylium ion (6).Ab initio molecular orbital treatment of circumambulatory degenerate rearrangements of bicyclo- [3,l,O]hexenyl and homotropylium cations shows that the former goes with inversion as has been found experimentally and is antiaromatic and so de-stabilized with respect to the transition state whilst the latter should go with retention but is aromatic and so stabilized with respect to the transition state.20 Homocyclopropenyl cation (7) the simplest homoaromatic system possible has been prepared.21 Benzene Oxides Episulphides and Cyclopropa-Aromatics.-Low-temperature photolysis of benzene oxide naphthalene 1,2-oxide and phenanthrene 9,lO-oxide shows oxygen migration and formation of keto-phenols and ketones.22 syn-Benzene bisepisulphide does not isomerize to the 1On system (8) although this is an allowed process.23 The biphenylene oxide (9) has been ~ynthesized~~ " J.W. Larsen and M. Eckert-Maksic J. Amer. Chem. SOC.,1974 96 431 1. T. V. Chuikova. A. A. Shtark. and V. D. Shteingarts Zhur. org. Khim. 1974 10 132. R.C. Haddon Tetrahedron Letters 1974 2797. *' W. J. Helrre J. Amer. Chem. SOC.,1974 96 5207. G. A. Olah J. Starral and G. Liang J. Amer. Chem. Suc. 1974 96 6233. 22 D. M.Jerima B. Witkop C. L. McIntosh and 0. L. Chapman J. Amer. Chem. SOC. 1974,% 5579. 23 E. Vogel E.Schmidbauer and H.-J. Altenbach Angew. Chem. Internat. Edn. 1974 13 736. 24 G. Jikeli and H. Gunther Angew. Chem. Internat. Edn. 1974 13 277. 284 T.J. Tewson and is quite stable. o-Bromobenzyl methyl ether gives benzocyclopropene on treatment with n-butyl-lithium but attempted Birch reduction of the product gives only ring-opened material.” The structure of the product from p-quinone dibenzenesulphonimide and diphenyldiazomethane has been reassigned*‘ and is (10)rather than a benzene derivative. Two reactions suggest the formation of dibenzobicyclo[4,1,0]heptatriene (11) as an intermediate trapping experiments with dienes2’” and thi01s~’~ giving products derived from the cyclopropene compound. 2 Benzene and its Derivatives The n-complex uersus a-complex or ‘early’ uersus ‘late’ transition-state argument for electrophilic substitution with extremely active electrophiles continues.Competitive rates for boron-trifluoride-catalysed nitration with methyl nitrate in nitromethane show better correlation with n-complex than a-complex mechanism,**“ although neither correlation coefficient is very good. This method has the advantage that the possibility of mixing control is removed. On the other hand nitration with NOz+BF,- and NOz+PF,-gives normal substrate selec- tivities and o :rn :p ratios with deactivated aromatics such as nitrobenzene and nitrotoluene.28h A long study of the additivity principle in bromination and nitration reactions29 concludes that in nitration the toluene to benzene rate ratio should be 79 rather than 20 as is found by direct measurement suggesting that even in ‘normal’ nitration either a n-complex mechanism or diffusion con- trol is involved.Nitration of 1,2,4-trimethylbenzene with sulphuric-nitric acid mixtures shows large variation in the ratio of 5 to 6 substitution with sulphuric acid ~trength.~’ This suggests that ipso-attack and subsequent rearrangement is important and that this rather than a n-complex mechanism can explain the anomalous rate ratios. Tetranitrotitanium(1v) nitrates aromatic hydrocarbons in high yield,31 but competitive reactions show a low toluene to benzene ratio 25 P. Radlick and H. T. Crawford J.C.S. Chem. Comm. 1974 127. 26 A. G. Pinkins and J. Tsuji J. Org. Chem. 1974 39 497. *’ (a) W.E. Billups L. P. Win and W. Y. Chow J. Amer. Chem. SOC.,1974 96 4026; (b)T. T. Coburn and W. M. Jones J. Amer. Chem. SOC.,1974 96 5218. 28 (a) G. A. Olah and H. C. Lin J. Amer. Chem. SOC.,1974 96 2892; (b)G. A. Olah and H. C. Lin ibid. p. 549. 29 R. Daneli A. Ricci H. M. Gilow and J. H. Ridd J.C.S. Perkin If 1974 1477. ’* R. B. Moodie K.Schofield and J. B. Weston J.C.S. Chem. Comm. 1974 382. ’’ R. G. Coombes and L. W. Russell J.C.S. Perkin fI 1974 830. Aromatic Compounds of cu. 4 with normal o:p substitution suggesting that a n-complex is the rate- determining step. Nitrato-complexes of zirconium(1v) and iron(Ir1) give the same o :p ratios for aromatic hydrocarbons but different amounts of 3- and 4-sub- stituted products with pyridine and q~inoline,~~ suggesting that n-complexes are involved.Electrophilic substitution reactions which give cyclohexadiene intermediates have been reviewed33 and the reaction of 26 different phenols in the solid state with gaseous chlorine has been to give high yields of substitution products but often with isolatable cyclohexadienones as intermediates. Anomal- ously high amounts of p-substituted products in the bromination of phenols with N-bromosuccinimide and 2,4,6,6-tetrabromocyclohexadienonehave been shown to be due to electrophilic addition of HBr either in 1,2 or 1,4 fashion.35 The 1,2-addition compound rearranges to give the 1,4-product which then gives p-bromophenol. Nitrations in acetic acid or acetic anhydride of methyl-benzenes often give side-chain substitution.This has been shown to be due to elimination from the 1,4-addition product (12) to give the methylenecyclo- hexadiene( 13) which can react further with the reagents.36 I-Chloro-2,3-dimethyl- benzene gives a similar addition pr~duct,~’ but in strong acid this eliminates CI OAc CH ’’NO (1 <\ acetic acid to give the benzenonium ion (14) which in the presence of mesitylene gives the biphenyl (15). 2,3- and 2,4-Dimethylbenzonitriles also give 1,4-addition in nitric-acetic acid mixtures but in this case strong acid gives phenyl acetates rather than the benzenonium ion.38 Measurement of ionization and appearance potentials of alkyl-substituted benzenes to determine whether the Nathan-Baker order is due to solvation gave inconclusive results but definitely established that bulky groups affect conjugative interaction^.^' Hydrogen exchange on 9,10-dihydro-9,10-(trans-ll-amino-12-32 R.G. Coombes and L. W. Russell J.C.S. Perkin I 1974 1751. 33 P. B. de la Mare Accounts Chem. Res. 1974 7 361. 34 R. Lamarfine and R. Perrin J. Org. Chem. 1974 39 1744. V. Cato L. Lopez G. Pesco C. and P. E. Todesco J.C.S. Perkin ZZ 1974 1 189 I 192. 36 A. J. Fischer and J. N. Ramsay J. Amer. Chem. Soc. 1974 96 1616. 37 A. Fisher and C. C. Greig J.C.S. Chem. Comm. 1974 50. 38 A. Fischer and C. C. Greig Cunud. J. Chem. 1974 52 1231. 3g D. A. Ponomarev V. V. Takhistov M. E. Akopyan and Yu. L. Sergeev Zhur. org. Khim.,1974 10 403. 286 T. J. Tewson methy1ethano)anthracene (16) shows no difference in reactivities of the two rings in spite of the predicted field effect of the protonated nitr~gen.~' Anilinium ions in general showed a marked deviation from the addivity principle in nitration reactions:l owing to independent directing effects not shown in monosubstituted benzenes.Increasing the sulphuric acid concentration in nitric-sulphuric acid nitrating mixtures leads to the rate of nitration of toluene changing from first- to zero-~rder.~~ This is interpreted as establishing that formation of the nitron- ium ion becomes the rate-limiting step but the same result in nitric acid-acetic anhydride mixtures is shown to be a medium effect43 and not due to formation of the electrophile. Friedel-Crafts acylation of bromotoluenes and xylenes has been reported to give anomalous products but careful examination of partial rate factors shows that the unexpected products are in fact as expected !44 Friedelxrafts alkylation of benzene with optically active 2-chloro- 1-phenylpropane at low temperature gives 1,2-diphenylpropane with almost complete retention of optical presumably through the concerted formation of the ion (17).Alkyl chloro- sulphites arenesulphinates chloro- and fluoro-sulphates and sulphones react with aromatic hydrocarbons in the presence of aluminium chloride or antimony pentafluoride to give alkylated rather than sulphonated product~.~~'*~ The reaction is highly selective and toluene-benzene rate ratios in competitive re- actions correlate well with Brown's g+,giving a positive p value.46' However aromatic sulphoxides undergo deoxygenation on treatment with thionyl chloride 40 A.J. Layton J. H. Rees and J. H. Ridd J.C.S. Chem. Comm. 1974 518. 41 R.S. Cook R. Phillips and J. H. Ridd J.C.S. Perkin ZZ 1974 1 166. 42 J. W. Chapman and A. N. Strachan J.C.S. Chem. Comm. 1974,293. 43 N. C. Marziano J. H. Rees and J. H. Ridd J.C.S. Perkin IZ 1974 600. 44 T. A. Elwood W. R. Flack K. J. Inman and P. W. Rabideau Tetrahedron 1974 30 535. 45 S. Masuda T. Nakajima and S. Suga J.C.S. Chem. Comm. 1974 954. 46 (a)G. A. Olah J. Nishimura and Y.Yanada J. Org. Chem. 1974,39,2430; (b)G. A. Olah and J. Nishimura J. Amer. Chem. SOC. 1974 96 2214; (c) G. A. Olah and J. Nishimura J. Org. Chem. 1974 39 1203. Aromatic Compounds 287 and Friedel-Crafts catalysts47 and chlorosulphonylbenzoyl chlorides acylate rather than sulphonate in the presence of aluminium tri~hloride.~' Tetra- chlorocyclopropene reacts with aromatic hydrocarbons in the presence of aluminium chloride to give initially aryltrichlorocyclopropenes,49which react further with the catalyst to give arylcyclopropenium salts.Substituent effects are transmitted across the cyclopropene ring. Substituted 1,2,4,5-tetrafluorobenzene reacts with sulphur sulphur monochloride sulphur dichloride and pentafluoro- phenylsulphenyl chloride to give diary1 sulphides in good yield.50 Reaction of olefins with aromatics using tungsten hexachlorideeethylaluminium dichloride catalyst depends upon the intermediate complex formed with the catalyst.An olefin-aromatic complex gives alkylation whilst a bisolefin complex leads to metathesis of the olefin? The intermediate complexes formed in Friedel- Crafts acylations have been reviewed.'* Nitration studies on p-~ymene~,~ show that ipso-attack at the isopropyl group is the predominant reaction and the intermediate can either rearrange to give nitro-p-cymenes or be substituted with loss of the isopropyl group to give nitrotoluene whilst in compounds (18a-c; n = 2 3 or 4) the amount of ips0 attack increases with ring size.536 1,2-Dihydrobenzocyclobutenereacts with sulphur trioxide complexes to give 2(o-sulphophenyl)ethanol from ips0 @KH21" '\ (18) a;n = 2 b:n=3 c I1 = 4 attack and 3-and 4-sulphonic acids from conventional substit~tion,~~" the ratios depending upon the SO complex and the solvent used.Partial rate factors for sulphonation of alkyl benzenes show that fo decreases with increasing size of the alkyl group owing either to retardation of formation of the o-complex or to its collapse to the sulphonic acid; the isomer distribution for 5-and 6-substitution in the sulphonation of 3-substituted benzenesulphonic acid parallels conjugative electron release over the acid strength 104-1 15% H2S04,54C although the reaction is complicated by formation of sulphonic anhydrides. The discrepancy between p values for chlorination of 2-substituted thiophens and substituted benzenes with chlorine in acetic acid has been shown to be due to the 47 I. Granoth J.C.S.Perkin I 1974 2166. 48 E. C. Dart and G. Holt J.C.S. Perkin I 1974 1403. 49 J. S. Chickos E. Patton and R. West J. Org. Chem. 1974 39 1647. G. C. Yakobson G. C. Furin and T. V. Terent'eva Zhur. org. Khim. 1974 10 799. H. L. Hocks A. J. Hubert and Ph. Teyssie Terrahedron Lerrers 1974 874. s2 B. Chevrier and R. Weiss Angew. Chem. Internat. Edn. 1974 13 1. 53 (a)R. C. Hahn and D. L. Stack J. Amer. Chem. SOC.,1974 % 4335; (b)M. W. Galley and R. C. Hahn. ihid. p. 4337. 54 (a) A. Koeberg-Telder and H. Cerfontain J.C.S. Perkin I/ 1974 1200; (6) H. Cerfontain and Z. R. H. Schaasberg-Nienhus ibid. p. 536; (c) A. Koeberg-Telder C. Ris and H. Cerfontain ibid. p. 98. 288 T. J. Tewson use of incorrect data,55 and the values are in fact the same.Partial rate factors for molecular chlorination of methyl phenyl and diphenyl sulphoxides show the sulphoxide group to be activating whilst for protiodesilylation it is deactivating ; this is explained by interactions of the sulphoxide group with the reagents and solvent.56 Rates of nitration of methyl phenyl sulphoxide show that an equilib- rium of protonated and unprotonated sulphoxides is in~olved.~ ' Alkyl-aromatics adsorbed on silica are cleanly substituted by halogens with isomer distribution suggesting electrophilic sub~titution.~~ Chlorine or t-butyl hypochlorite in carbon tetrachloride chlorinate phenols giving high yields of ortho-products apparently by an ionic me~hanism.'~ Low-temperature chlorina- tion of anisole in the dark produces 1,3,4,5,6-pentachloromethoxycyclohexane via initial formation of 4-chloroani~ole.~~ Electrophilic substitution of aryl gem-dichlorocyclopropanesshows that the dichlorocyclopropyl group is largely para-directing unlike the cyclopropyl group.6 The nitrosyl complex [Ru(bipy),(NO)XI2 nitrosates activated aromatics in + good yield.62 Iodine tris(trifluor0acetate) gives aryl bis(trifluoroacetoxy)iodo- compounds the positional selectivity indicating an electrophilic reaction.63 A series of papers has been published on the preparation of o-substituted amines phenols and thiophenols via intermediates formed on the heteroatoms.Thus N-aryl nitrones give o-chloro-imines on treatment with thionyl chloride or phosgene,6Q and o-hydroxy-amines on treatment with oxalyl followed by hydrolysis ; o-formylation of phenol^^^".^ and arnine~~~'~ is achieved via formation of sulphonium salts (19) ylide formation and a Sommelet-Hauser rearrangement.+/ z-s c'"R (19) Z =NHorO 55 R. N. McDonald and J. M. Richmond J.C.S. Chem. Comm. 1974 333. 56 A. C. Boicelli R. Danieli A. Mangini A. Ricci and G. Pirazzini J.C.S. Perkin II 1974 1343. 57 N. C. Marziano E. Maccarone C. M. Cunino and R. G. Passerini J. Org. Chem. 1974 39 1098. '' C. Yaroslavsky Tetrahedron Letters 1974 3395. 59 W. D. Watson J. Org. Chem. 1974 39 1160. 'O W. D. Watson and J. P. Heeschen Tetrahedron Letters 1974 695. '' 0. M. Nefedov and R. N. Shafran Zhur. org. Khim. 1974 10 477. 62 W. L. Bowden W. F. Little and T.J. Meyer J. Amer. Chem. SOC.,1974 96 5605. 63 I. I. Maletina V.V. Orda and L. M. Yagupol'skii Zhur. org. Khim. 1974 10 296. 64 (a)D. Liotta A. D. Baker S. Goldstein N. L. Goldman F. Wienstein-Lame D. Felsen- Rhengold and R. Engel J. Org. Chem. 1974 39 2718; (6) D. Liotta A. D. Baker N. L. Goldman and R. Engel ibid. p. 1975. 65 (a) P. G. Gassman and D. R. Amick Tetrahedron Letters 1974 3463; (6) P. G. Gassman and D. R. Amick ibid.,p. 889; (c) P. G. Gassman and H. R. Drewes J. Amer. Chem. SOC.,1974,96,3003;(d)P. G. Gassman and G. D. Gruetzmacher ibid. p. 5487; (e)P. G. Gassman G. Gruetzmacher and T. J. Van Bergen ibid. p. 5512. Aromatic Compounds Electrophilic displacement reactions have been used to prepare isomers that would be otherwise inaccessible.Thus treatment of aryltrimethylstannanes with nitrosyl chloride followed by oxidation gives nitro-compounds66 and of aryltrimethylsilanes with thallium trifluoroacetate gives arylthallium bis-(trifluoroacetates).67 Electrophilic displacement of the diazonium cation from o-aryl azophenols has been observed68 and it appears to be a better leaving group than Brt Cl' or NO,+ although the mechanism of the displacement is not clear. Aryl-lead trifluoroacetates on treatment with trifluoroacetic acid give aryl trifluoroacetates ;69 the reaction apparently goes through a radical cation although if an aromatic solvent is used biphenyls are obtained with substitution patterns suggestive of an electrophilic reaction. Hypobromous acid brominates acetophenone in the ring" rather than in the side chain.t-Butyl hypobromite bromination of 1,3,5-tribromobenzene is very slow in the absence of potassium t-butoxide7' but faster than that of 1,3,5-trimethoxybenzene in its presence suggesting (20) as an intermediate. Gas-phase halogenation of aromatics using Br+ and I+ produced by nuclear decay Br using high moderator concentrations shows very low ~electivity~~ and a large amount of substituent replacement. The extent of replacement and increased o-substitution in going from fluoro- to iodo-benzene suggests that aryldihalo genonium ions are formed. Pyrolysis of methanesulphonyl azide produces a nitrene and in aromatic solvents the singlet inserts but the triplet behaves as an ele~trophile.~~"~~ Rate studies of the reactions between dimethylamine and 4-flUOrO- or 4-chloro-nitrobenzenes show that the former reaction but not the latter has a large salt effect which is interpreted as electrophilic catalysis of the breakdown of the intermediate.74 Arrhenius parameters for nucleophilic displacement on picryl chloride by 3-and 3,hubstituted anilines show that the disubstituted bh C.Eaborn I. D. Jenkins and D. R. M. Walton J.C.S. Perkin I 1974 870. 67 H. C. Bell J. R. Kalman J. T. Pinhey and S. S. Sternhell Tetrahedron Letters 1974 3391. 68 N. J. Bunce J.C.S. Perkin I 1974 942. 69 H. C. Bell J. R. Kalman J. T. Pinhey and S. S. Sternhell Tetrahedron Letrers 1974 853 857. 70 T. L. Broxton L. W. Deady J. D. McCormack L. C. Kaun and S. H. Toh J.C.S. Perkin I 1974 1769.71 M. H. Mach and J. F. Bunnett J. Amer. Chem. SOC.,1974 96,936. 12 E. J. Knust A. Halpern. and G. Stocklin J. Amer. Chem. SOC.,1974 96 3733. 73 (a)R. A. Abramovitch T. D. Bailey T. Takaya and V. Una J. Org. Chem. 1974 39 340; (6)R. A. Abramovitch G. N. Knaus and V. Una ibid. 1974 p. 1101. 74 D. Ayediran T. 0.Bamkole and J. Hirst J.C.S. Perkin 11 1974 1013. 290 T.J. Tewson compounds follow an isokinetic relationship and that the rates are governed by a -I effect but that relative rates for the monosubstituted compound are temperature dependent.75 Rates of ionization of aromatic hydrocarbons as measured by detritiation with ethoxide ion vary considerably from the equilib- rium a~idities.'~ Nitrobenzene undergoes reversible hydrogen exchange with sodium borohydride as shown by tritium labelling presumably through the nitro-cyclohexadienyl anion (21).Methoxide ion displacement on polyfluoro- benzenes shows that the order of displacement is rn > o >> p which is explained by the inductive effect.77 (21) NO. (22) Enthalpic stabilities of carbanionic a-complexes between acetone or cyclo- pentanone and poly(nitro)aromatics show them to be as stable as the oxygen analogue^.^' The a-complexes between 1,3,5-trinitrobenzene and substituted anilines have been characterized by n.m.r. and visible and it has been confirmed that in the presence of potassium methoxide a a-complex of structure (22) is formed.79b The isopropoxide ion reacts with 2,4,6-trinitrotoluene to give both a a-complex and the anion with proton transfer being the rate-determining step for anion formation."" Sodium and potassium t-butoxide form only the anion although with a fully deuteriated methyl group the o-complex is formed as well.''" Rate' lo and equilibrium constants for the formation of 1 1 a-complexes between cyanide ion and 1,3,5-trinitrobenzene in alcoholic solvents and equilibrium constants for the cyanide complexes with 2,4,6-trinitrotoluene and 2,4,6-trinitro- anisole'l' have been determined.The rate and equilibrium constants for the formation of the a-complexes between methoxide and picryl chloride' have also been determined. The 2,4,6-trinitrophenyl ether of catechol with sodium meth- oxide gave'* a Meisenheimer complex (23) and the Meisenheimer complex 75 S.I. Ette and J. Hirst J.C.S. Perkin 11 1974 76. '' A. Albagli J. R. Jones and R. Stewart Canad. J. Chem. 1974 52 1059. 77 R. D. Chambers W. K. R. Musgrave J. S. Waterhouse D. Lyn H. Williams J. Burden W. B. Hollyhead and J. C. Tatlow J.C.S. Chem. Comm. 1974 240. 78 R. M. Murphy C. A. Wulf and M. J. Straus J. Amer. Chem. SOC.,1974 96 2678. 79 (a)E. Buncel and J. G. K. Webb Canad. J. Chem. 1974 52 630; (b) E. Buncel H. Jarrell H. W. Leung and J. G. K. Webb J. Org. Chem. 1974 39 272. (a) E. Buncel A. R. Norris K. E. Russell P. Sheridan and H. Wilson Canad. J. Chem. 1974 52 1750; (b) E. Buncel A. R. Norris K. E. Russell P. Sheridan and H. Wilson ibid. p. 2306. (a)L. H. Gan and A. R. Norris Canad. J. Chem. 1974,52 1; (b)L.H. Gan and A. R. Norris ibid. p. 8; (c)L. H. Gan and A. R. Norris ibid. p. 18. V. N. Drozd V. N. Knyazev and A. A. Klimov Zhur. org. Khim. 1974 10 828. Aromatic Compounds 29 1 n n from l-(fi-hydroxyethoxy)-2,4-dinitrobenzene (24) is more stable than that (25) from N-fi-hydroxyethyl-N-methyl-2,4-dinitrobenzene because of the greater ground-state stability of the latter c~mpound.~2-Picrylthioethane-1-thiol gave a complex (26) on treatment with base but with the n-propyl compound nucleophilic displacement of an o-nitro-group occurred.84 Nucleophilic displacement reactions of benzenediazonium salts in the absence of strong base light or reducing agents proceeds via the phenyl cation formation of which is the rate-determining step.85 The cation reacts with gaseous nitrogen.86 Synthesis of o-substituted benzonitriles has been achieved by nucleophilic dis- placement from o-nitrobenzonitriles,87 and photolysis of 2-allyloxyacetophenone in methanol gave methoxyacetophenone by a nucleophilic displacement reaction and 3-methyl-2-vinylbenzofuranby hydrogen abstraction from the acetophenone Cleavage of aryl-substituent bonds with potassium in liquid ammonia has been studied in the presence of acetone thus permitting distinction between ionic and radical cleavage.Electronegative substituents (F C1 Br I 0,and S) undergo radical cleavage whilst if the substituent is phosphorus arsenic antimony or bismuth anionic cleavage occurs ; aryl-selenium bonds are cleaved uia both routes.89 Reductive dehalogenation of aryl bromides with lithium di-n-propyl- amide has been studied in the presence of a large excess of the amine to suppress aryne formation and showng0 to involve the transition state (27).For iodo- anisoles however reductive dehalogenation probably proceeds by amide ion u3 C. F. Bernasconi and H. S. Cross J. Org. Chem. 1974,39 1054. 84 E. Farina C. A. Veracini and F. Pietra J.C.S. Chem. Comm. 1974 672. 85 K. G. Harbison R. J. Rogers C. G. Swan J. E. Sheals and D. G. Gorenstein Tetra-hedron Letters 1974 2913. 86 R. G. Bergstrom G. H. Wahl jun. and H. Zollinger Tetrahedron Letters 1974 2974. 87 J. R. Beck R. L. Sobczak R. G.Suhr and J. A. Yahner J. Org. Chem. 1974,39,1839. 88 F. R. Sullivan and L. B. Jones J.C.S. Chem. Comm.1974 312. 89 R. A. Rossi and J. F. Bunnett J. Amer. Chem. SOC.,1974,% 112. 90 E. R. Biehl S. Lapis and P. C. Reeves J. Org. Chem. 1974 39 1900. 292 T. J. Tewson attack at the halogen to give the carbanion. Metal-ammonia reduction of bi- phenyls and of methoxybiphenyls in the absence of a proton source forms dianions which give 1,6dihydrobiphenyls on work-up; in the presence of a proton source reduction goes further to give isomeric phenylcycl~hexenes.~ o- m-,and p-Dibenzoylbenzenes all gave radical anions with alkali metals in liquid ammonia; the o-isomer gave (28) with two equivalents of potassium whereas two equivalents of lithium gave (29).92 Hydrogen abstraction from phenols has been correlated with quantum mechan- ical indices which shows that over a wide range of reactivities the relationship is far more complex than a simple Hammett relati~nship.~~ Partial rate factors for amination with ammonium radical cations establish that the reaction shows the same selectivities as electrophilic substitution and is sensitive to steric and polar but not conjugative effects.94 The authors suggest that the inductive order for electrophilic substitution is due to reactions involving electron transfer and that the Nathan-Baker order is followed by reactions involving the Wheland intermediate.E.s.r. studies of 1,l-di-t-butylbenzyl radical (30) in which the radical is at 90" to the aromatic ring show that the ~-a delocalization is much smaller than expected.95" Other e.s.r. studies confirm that the 2,4,6-tri-t-butylphenyl radical is a o-radi~al.~~' 2-Hydroxy- and 2-methoxy-phenyl radicals generated by photo- lysis of the related iodo-compounds at low temperature are a-radicals which rearrange to phenoxy radicals on further photolysis or warming.96 Rates of 91 A.J. Birch and G. Nadamuni J.C.S. Perkin I 1974 545. 92 J. A. Campbell R. W. Koch J. V. Hay M. A. Ogliaruso and J. F. Wolfe J. Org. Chem. 1974 39 146. 93 I. Luskovits J. Kardos and M. Simonyi Tetrahedron Letters 1974 2085. 94 A. Clerici F. Minisci and 0.Porta J.C.S. Perkin I 1974 416. 95 (a) K. Schreiner and A. Bernelt Angew. Chem. Internat. Edn. 1974 144; (6)L. R. C. Barclay D. Griller and K. V. Ingold J. Amer. Chem. SOC.,1974 96 3011. Q6 P. H. Kasai and D. McLeod jun.J. Amer. Chem. SOC.,1974 96 2338. Aromatic Compounds 293 aromatic cyclohexylation by cyclohexyl radicals show a marked dependence on the polarity of the medium; an initial reversible n-complex which rearranges to a a-complex and then collapses to the product is ~uggested.~' The reactions of cyclopropyl radicals with aromatics for both substitution and hydrogen- abstraction processes show that the radicals have very little polar character.98 Phenyl radicals react with p-xylene to give 2,5-dimethylbiphenyl and 4,4-di- methylbibenzyl; the proportion of the latter compound increases with tem- perature which is taken to indicate reversible formation of the o-complex (31).99 Pyrolysis of phenyl acetate to phenol and keten has been established as a radical not a concerted reaction ;other products are also formed.'oo"*b Dimerization of benzyl radicals containing methyl ethyl and isopropyl groups gave'" significant amounts of o-and p-semibenzene dimers e.g.(32). Ph IH CR'R' C R( 'R' (32) (34) Decomposition of benzoyl peroxide in the presence of nitrogen dioxide has been examined quantitatively and the proposed mechanism confirmed."' Pentafluorobenzoyl peroxide and hexafluorobenzene at 200 "C give a mixture from which (33) can be isolated in poor yield but defluorination of the mixture gave (34) in good yield suggesting a mixture of isomeric cyclohexadiene structures formed by migration of o-radical~."~ The phenol (35) gives (36) on oxidation Bu' D..I OMe J5U' y -OMe OH (35) 97 J.R. Shelton and A. L. Lipman jun. J. Org. Chem. 1974,39 2386. 98 T. Shono and I. Nishiguchi Tetrahedron 1974 30 2183. 99 R. Henriquez A. R. Morgan P. Mulholland D. C. Nonhebel and G. G. Smith J.C.S. Chem. Comm. 1974,987. 100 (a)A. C. Barefoot and F. A. Carroll J.C.S. Chem. Comm. 1974,357; (b) C. E. Kahnus and D. M. Hercules J. Amer. Chem. SOC.,1974 % 449. I01 K. J. Skinner H. S. Hochster. and J. M. McBride J. Amer. Chem. SOC.,1974,% 4301. 102 Y.Rees and G. H. Williams J.C.S. Perkin I 1974 2266. 103 L. V. Vlasova L. S. Korbrina and G. C. Yakobson Zhur. org. Khim. 1974 10 787. 294 T. J. Tewson with one-electron oxidants presumably uia a secondary radical formation on the methoxyl carbon.lo4 The formation of aromatic a-radicals postulated in the electrochemical reduction of aryl halides has been confirmed by the electro- chemical reduction of (37),where the second aromatic ring acts as an internal radical trap.' O5 Electrochemical reduction of aryltrimethyl-silanes and -germanes produces silyl- and germyl-substituted cyclohexa- 1,4-dienes with the products being the same as predicted from a Birch reduction.lo6 Perchlorobenzyl- and perchlorophenyl-aminyl radicals are extremely stable and in solution the former exists in equilibrium with its dimer.lo' Tetraphenylethylene radical cations cyclize to 9,lO-diphenylphenanthrenevia disproportionation to the dication and tetraphenylethylene cyclization and not disproportionation being the rate-determining step.'08 Analysis of the e.s.r.and CIDNP spectra obtained from a study of the decomposition of benzenediazonium salts suggests that the azo-benzene radical cation is responsible for the spectra but that this is not a major reaction path~ay.'~' y-Irradiation of bromobenzene and p-bromophenols gives hydrogen radical addition to the carbon bearing bromine and no sign of a n-complex radical is detectable by e.s.r. spectroscopy. ' The y-induced radical chain reduction of aryl diazonium salts shows two classes of kinetics one which is proportional to the hydrogen source but independent of dose rate and another which is indepen- dent of the hydrogen source but dependent on the dose. A mechanism is proposed' ' to explain this. Theoretical studies using semi-empirical INDO methods of phenylcarbene cycloheptatrienylidene and cycloheptatetraene and the benzo-annelated analogues show that the allene isomer should be more stable than the carbene in the parent compounds but not in benzo-analogues,' l2and to' support this view the carbene (38) the dimerization of which was reported in last year's Annual I04 R.C. Eckert Hou-Ming Chang and W. P. Tucker J. Org. Chem. 1974 39 718. 105 J. Grimshaw and J. Trocha-Grimshaw Tetrahedron Letters 1974 993. 106 C. Eaborn R. Jackson and R. Pearce J.C.S. Perkin I 1974 2055. I07 (a)S. Olivetta M. Ballester and J. Castafier Tetrahedron Letters 1974 587 615. 108 U. Svanholm A. Roulan and V. D. Parker J. Amer. Chem. Soc. 1974,96 5108. 109 J. Bargon and K.-G. Seifert Tetrahedron Letters 1974 2265.I10 J. Edwards D. J. Hills S. P. Mistra and M. C. R. Symons J.C.S. Chem. Comm. 1974 556. Ill J. E. Packer R. K. Richardson P. J. Spoole and D. R. Webster J.C.S. Perkin 11 1974 1472. 112 R. L. Tyner W. M. Jones Y. Ohm and J. R. Sabin J. Amer. Chem. SOC.,1974 96 3765. Aromatic Compounds Reports (p. 422) was generated from a chiral precursor which gave only one of the two dimers obtained previously suggesting that a stereospecific cyclo- addition from the allene form is responsible for the formation of the dimers. ' ' 3a Photolysis of phenol in chloroform effects a photo-Reimer-Tiemann reaction giving the same products as in the base-catalysed reaction. Such photoreactions can be performed on dihydroxybenzenes and anilines for which the base- catalysed reaction does not work ;it is presumed that the reaction goes through an aromatic radical or radical cation.' 3b Photochemical addition of olefins to benzene gives 1,Zaddition if the olefin has donor or acceptor properties but 1,3-addition if it has neither; with donors the addition is specifically endo but with acceptors it is exo.' 13' These results parallel the behaviour of liquid mixtures of olefins with benzene as shown by n.m.r. where the average orientation of the olefin is endo to the aromatic nucleus when it is a donor and exo when it is an acceptor.' '3d Furan undergoes photo- (39) H-(40) chemical 2,5- 1',4'-cycloaddition with benzene to give (39) which isomerizes further to (40)on further irradiation or heating.' l4 Molecular Rearrangements.-The allyl ether (41 ; R = H) prepared from phloroacetophenone and propargyl bromide followed by reduction gave deoxyhumulones (42 ;R = H) on thermal rearrangement but the attempted synthesis of the natural product (41 ; R = Me) gave only products of C-alkyla-tion.' '' The y-chloro-y-methylallyl ether (43) under either thermal or catalytic forcing conditions gave the m-substituted phenol (44)by an intermolecular process.' l6 Rates of Claisen rearrangement of allyl aryl ethers in trifluoroacetic 'I3 (a)R.A. LaBar and W. M. Jones J. Amer. Chem. SOC.,1974 96 3646; (b) K. Hirao M. Ikegame and 0. Yonemitsu Tetrahedron 1974 30 2301; (c) D. Bryce-Smith A. Gilbert B. Orger and H. M. Tyrrell J.C.S. Chem. Comm. 1974 334; (d)D. Bryce-Smith A.Gilbert and H. M. Tyrrell ibid. p. 699. "* J. Berridge D. Bryce-Smith and A. Gilbert J.C.S. Chem. Comm. 1974 964. E. Collins and P. Shannon J.C.S. Perkin I 1974 944. E. K. Aleksandrova L. I. Bunina-Krwornkova Kh. V. Bal'yan and V. M. Feoktishov Zhur. org. Khim.,1974 10 825. 296 T. J. Tewson R H OH R*R acid show good correlation with (ap+ om)/2 indicating a polar transition state. Large salt and isotope effects confirm a polar mechanism and indicate that proton transfer is involved in the rate-determining step.' ' Rearrangement of cin- namylphenyl ether gives both 0-and p-substituted products. The ratio is depen- dent on the acidity of the solvents used and there is no abrupt change of rate in liquid-crystal solvents on going from the nematic to isotropic phase all contrary to previous reports establishing that alignment of the molecule in the liquid crystal is not important in the formation of transition states.' '' Base-catalysed rearrangement of catechol monoallyl ethers gives different products from the thermal reaction and involves successive sigmatropic rearrangements of the anion.' l9 Claisen rearrangement of the allylic amine (45)proceeds without migration of the double bond suggesting that the reaction is unlikely to be con- cer ted.''' Pure o-ally1 thiophenol has been isolated and shown to undergo the Claisen- type rearrangement which is catalysed by nucleophiles. It is suggested that nucleophilic attack at the allylic carbon triggers a concerted process ;I2 ' 2-methylallyl phenyl sulphide when passed over y-alumina at 300 "C gives 2,2-dimethyl-2,3-dihydrobenzothiophenin a Claisen-type rearrangement.22 3-Phenylprop-2-ynyl ally1 ethers (46) isomerize to the allene on treatment with base and this undergoes [,4 + ,2] cycloaddition to give dihydronaphthalenes (47).' 2-Methoxyallyl bromide gives bicyclo[3,2,2]nona-4,7-dien-3-one(48) ' * U. Svanholm and V. D. Parker J.C.S. Perkin 11 1974 169. M. J. S. Dewar and B. Nahlovsky J. Amer. Chem. SOC.,1974 96,460. W. D. Ollis R. Somanathan and I. 0. Sutherland J.c.S. Chem. Comm. 1974 494. lZo G. de Saqui-Sannes M. Riviere and A. Lattes Tetrahedron Letters 1974 2073. "' H. Kwart and J. L. Schwartz J. Amer. Chem. SOC.,1974 % 1575. G. Dzhamatova T. A. Dunilova and E. A. Viktorova Zhur.org. Khim. 1974,10 76. A. J. Bartlett T. Laird and W. D. Ollis J.C.S. Chem. Comm. 1974 496. Aromatic Compounds in low yield on treatment with silver salts the absence of dihydroindanones suggesting that a concerted cycloaddition is involved. 24 The benzidine rearrangement is implicated in the photolysis of 1,4-diethyl- 1,4-diphenyl-2-tetrazene as NN-diethylaminobenzene-N-ethylaniline (49)is obtained from the rea~ti0n.I~’ The phenylhydrazones from a-substituted acetones rearrange in acidic conditions to give p-substituted anilines (50),also apparently (48) (49) through the benzidine rearrangement. ’ The photo-Fries rearrangement of aryl benzoates is shown to be a singlet reaction both by CIDNP and the in- effectivenessof naphthalene on altering the path of the rea~ti0n.I~’ The Wallach rearrangement of phenylnaphthyl and naphthylnaphthyl azoxybenzenes gives the product with the hydroxy-group on the naphthyl ring regardless of the initial position of the oxygen of the azoxy-group.12* A mechanism has been proposed for the rearrangement and denitrosation of N-methyl-N-nitrosoaniline in hydro- chloric acid (Scheme l).’29 o-Substituted nitrosobenzenes in very dilute solution H H k I PhN-NO Ph-7!JkNO-PhNCH, I I CH CH + p2 NOCl P-NOC~H~NHCH 3 Scheme 1 in concentrated sulphuric acid give quinone oximes presumably by way of the nitroso cation rather than the self-condensation products which are obtained in more concentrated solutions.’ 30 124 H.M. R. Hoffman and A.E. Hill Angew. Chem. Internat. Edn. 1974 13 136. 12’ J.-D. Cheng and H. J. Shine J. Org. Chem. 1974 39 336. 126 F. Sparatoge V. Boido and G. Pirisiono Tetrahedron Letters 1974 2371. 12’ W. Adam J.C.S. Chem. Comm. 1974,289. 12* A. Dolenko and E. Buncel Canad. J. Chem. 1974 52,623. D. Lyn H. Williams and J. A. Wilson J.C.S. Perkin II 1974 13. I3O E. Yu. Balyaev L. M. Gornosfaev M. S. Tabis and E. L. Borina Zhur. obshchei Khim. 1974 44 633. 298 T.J. Tewson Solvolysis of 3,3-diaryltricyclo[3,2,1,1,2*4]oct-8-yl tosylates (51) to the bicyclo- octenes (52) shows anchimeric participation of the aryl group but the low p-value of -1.68 points to the rearrangement being concerted.' 31 The photo-induced rearrangement of 1,1,5,5-tetraphenyl-3,3-dimethylpenta-1,4-diene yields a cyclo- propane product.This may involve either a di-n-methane rearrangement or a [,2 + ,2,](or [,2 + n2s])process. If the latter mechanism is correct then irradiation of 1,1,5,5-tetrapheny1-3,3-dimethylpen t-1 -ene should give a cyclo- propane derivative. This does not occur and 1,4,5,5-tetraphenyl-3,3-dimethyl-pent-1-ene is formed via a novel 1,Qphenyl migration.'32 Photolysis of triptycene is shown by trapping experiments to proceed through the carbene (53) rather than by the di-n-methane rearrangement as had been previously proposed. ' Arynes.-MIND0/3 calculations on bisdehydrobenzenes (54a-c) show that the o-and p-isomers should have a singlet ground state but the result with the rn-isomer is not clear.Also the rn-isomer should have a ground-state energy similar to the o-isomer although no accounts of its attempted preparation have yet appeared.'34 Ene addition of benzyne to cyclic olefins is shown to be a concerted reaction rather than a radical one,'35 but the [2 + 21 and [2 + 2 + 21 reactions of tetrachlorobenzene and norbornadiene are very little affected by high pressure and the authors conclude that pressure studies on concerted re- actions are only meaningful when a great deal is known about the transition states of the alternative reaction modes.' 36 Cycloaddition of benzyne to +unsaturated 131 J. W. Wilt T. P. Mallory P. K. Mookerjee and D. R. Sullivan. J. Org. Chem. 1974 39 1327. 13' H. E. Zimmerman and R. D. Little J. Amer. Chem. SOC.,1974 96,5143.H. Iwamura and K. Yoshimura J. Amer. Chem. SOC.,1974 % 2654. 134 M. J. S. Dewar and W.-K. Li J. Amer. Chem. SOC., 1974 96 5569. 135 G. Mehta and B. Palsingh Tetrahedron 1974 30,2409. I 36 W. J. Le Noble and R. Mukhtar J. Amer. Chem. SOC.,1974 96,6191. Aromatic Compounds carbonyl compounds gives 1,Zaddition to both the carbon-oxygen and carbon- carbon double bonds the ratio of which depends upon the reactivity of the car- bony1 group and not upon the formation of intermediate radicals.' 37 The formation of benzyne- from N-nitrosoacetanilide and benzenediazonium acetate has been studied by isotope labelling. It was shown that a 'pre-equilib- rium' Elcb mechanism is not involved but a reversible Elcb mechanism cannot be distinguished by this method from a concerted E2 mechanism.'38 Benzyne from 1-aminobenzotriazole in carbon disulphide reacts with the solvent to give 39 benzo-1,3-dithiolium carbene (55) initially which can either dimerize or react with other substrates.2-Polychloroarylethanolsdo not react with base to give furans by nucleophilic displacement but lithiation gives an aryl lithio-compound which on reflux eliminates to a benzyne and then reacts with the alcohol to give the furan in good ~ie1d.I~' However the cyclizations of o-halogeno-stilbenes and a-phenylcinnamic acids to phenanthrenes by potassium-liquid ammonia do not go through benzynes but involve radical anions.141 Quinone Methides Dimethides and Related Compounds.-A full report on the formation of o-xylylene by the photolysis of 1,4-dihydrophthalazine has been published together with details of the further photolysis to benzocyclobutane and the preparation of o-xylylene from five other l-Phenyl-1-tolyl on photolysis with maleic anhydride gives products that are suggestive of the formation of o-xylylene intermediates.143 1,8-Naphthoquinodimethide 13' A. T. Browne and R. H. Levin Tetrahedron Letters 1974 2043. 138 J. I. G. Cadogan C. D. Murray and J. T. Sharp J.C.S. Perkin I 1974 1321. '39 J. Tdakayama J.C.S. Chem. Comm. 1974 166. I4O N. J. Foulgar and B. J. Wakefield J.C.S. Perkin I 1974 871 S. V. Kessar S. Narula S. S. Gandhi and U. K. Nadir Tetrahedron Letters 1974 2905. 14' C. R. Flynn and J. Michl J. Amer. Chem. SOC.,1974 96 3281.14' A. C. Pratt J.C.S. Chem. Comm. 1974 183. 300 T. J. Tewson (55b) has been synthesized from (55a) and e.s.r. studies show that the triplet is only 200 cal rnol-' above the singlet and thus is thermally accessible.'44 Non-photochemical formation of o-xylylene apparently occurs when o-xylene di- halides are heated with copper(0)-t-butyl isocyanide as trapping experiments give products suggestive of o-xylylene formation. 145 Photolysis of o-tolualdehyde gives the dimeric hemi-acetal by way of the photo- enol (56),and benzoin from hydrogen abstraction by the tri~1et.l~~" The same enol has been trapped with dienophiles and the stereochemistry confirmed as being the (E)-isomer none of the (2)-isomer being formed; ring-closure to cyclobutenols occurs in dilute solution.146b Thermolysis of benzocyclobutenols gives the same enol ;146c vinyl and phenyl substituents assist the reaction.'46d Photolysis of l-(o-tolyl)propane-l,2-dioneproduces a similar enol (57) as was shown by trapping experiment^,'^^" but ring-closure was not reported for this compound. Annelated benzocyclobutenols (58) are reversibly photolysed to the cyclic ketones (59),the forward reaction requiring 2537 8,light and the backward 3000 8,;the reaction was presumed to go through an o-xylyleqe photo-en01 of the same type. 146 Thermolysis of vinylbenzocyclobutenes gives the o-xylylenes (60) which either undergo 1,7-hydrogen shifts to o-tolylbutadienes or ring-closure to 1,2-dihydronaphthalenes depending on the nature of R' and R2.14' (58) (59) 44 R.M. Pagni C. R. Watson jun. and J. E. Boor J. Amer. Chem. SOC.,1974 % 4064. 145 Y. Ito K. Yonezawa andT. Saegusa J. Org. Chem. 1974 39 2769. 146 (a)D. M. Findlay and M. F. Tehir J.C.S. Chem. Comm. 1974 514; (b)B. J. Arnold S. M. Mellows P. G. Sammes and T. W. Wallace J.C.S. Perkin I 1974 401 ; (c) B. J. Arnold P. G. Sammes and T. Wallace ibid. p. 409; (d)B. J. Arnold P. G. Sammes and T. Wallace ibid. p. 405; (e) Y. Ogata and K. Takagi J. Org. Chem. 1974 39 1385; (f)M. L. Viriot-Villaume C. Carre and P. Caubere Tetrahedron Letters 1974 3301. 14' M. R. Camp R. H. Levin and M. Jones jun. Tetrahedron Letters 1974 3575. Aromatic Compounds 301 80"C ___* (62) (63) 1-Methoxymethyl-2-naphthol in glacial acetic acid gives the quinone methide (61) which dimerizes to (62) the product of kinetic control; above 80°C this isomerizes to (63).14* In the equilibria of aryl azo-1-and 2-naphthols (64) and (65) the 1-naphthol exists as a 1 1 mixture of the phenol and quinone imine Ar Ar N//N ,N-H N Ar Ar I I N N' 'H whilst the 2-naphthol derivative is almost entirely in the phenol form presumably stabilized by more favourable hydrogen bonding.149 Quinones.-A molecular orbital study of 36 quinones by self-consistent-field methods gave good general correlations with observed physical data except for the carbonyl stretching frequencies. l5 Oxidation of 1,4-diphenylnaphthalene-2,3-diols with lead tetra-acetate gave trimers from 1;4-diphenyl-2,3-naph-thaqinone (66) and low-temperature oxidation with trapping reagents also gave products from the quinone f~rmation.'~ p-Alkylphenols gave good yields of lJ8 G.Catteral J.C.S. Chem. Comm. 1974 41. 14' S. Millefori F. Zuccarrello A. Millefori and F. Guerrera Teetrahedron 1974 30 735. G. J. Gleicher D. F. Church and J. C. Arnold J. Amer. Chem. SOC.,1974 96 2403. '" D.W. Jones and R. L. Wife J.C.S. Perkin I 1974 1. 302 T.J. Tewson Ph Ph (66) p-quinols on oxidation with thallium triperchlorate.' 52 Oxidation of phenol by peracetic acid has shown that 0-and p-hydroxylation first occur with the o-dihydroxybenzene then being oxidized to hexa-2,4-dienoic acid whilst the p- compound is oxidized to p-quinone. 2-Azido-3-vinyl-l,4-quinonesgive indole quinones on heating 54a photolysis of 2-azido-1,4-quinones with dienes gives 2-alkenyl-2,3-dihydroindole-4,7-diones,' 54b and the condensation of hydro-quinones with halogenated maleic anhydrides gives polyhydroxylated naph- thoquinones in excellent yield.1s5 Cyclophanes.~6lParacyclophane (67) has been prepared the aromatic ring apparently being bent 20" out of the plane as measured from the U.V.spectrum although the n.m.r. spectrum still shows a ring current.' 56 3-Carboxy[7]para-cyclophane has been prepared and its U.V. spectrum shows a general red shift as expected. One proton is forced into the n-electron cloud giving a very low-field signal in the n.m.r. and a limited accuracy X-ray analysis shows the para-carbons are 17" and the benzylic carbons 24" out of the plane.lS7 (67) Force-field calculations of the conformations of [n]paracyclophanes have been performed and the results are in good agreement with experimental data in so far as these are known.ls8 The conformation and geometry of the aromatic rings in [2,2]metacyclophanes are affected by substituents in the bridges.' 59 (S)-4-Deuterio[2,2]paracyclophanehas been prepared'60" and its c.d.spectrum obtained and successfully described theoretically. 160b Flipping of [2,2]meta- paracyclophane (68) requires that the 1-proton of the meta aromatic ring has to 152 Y. Yamada K. Hosaka H. Sanjoh and M. Suzuki J.C.S. Chem. Comm. 1974,661. ' 53 R. A. G. Marshall and R. Naylor J.C.S. Perkin II 1974 1242. '54 (a) P. Germeraad and H. W. Moore J. Org.Chem. 1974 39 774; (b)P. Germeraad and H. W. Moore ibid. p. 781. R. Huot and P. Brassard Cunad.J. Chem. 1974,52 838. 156 V. V. Kane A. D. Wolf and M. Jones jun. J. Amet. Chem. SOC.,1974 96 2643. Is' N. L. Allinger T. J. Waller and M. G. Newton J. Amer. Chem. SOC.,1974 96 4588. 58 N. L. Allinger J. T. Sprague and T. Liljefors J. Amer. Chem. SOC., 1974 96 5100. 15' E. Langer and H. Lehner Tetrahedron Letters. 1974 1357. 16' (a)P. H. Hoffman E. C. Ong 0.E. Weigang,jun. and M. J. Nugent J. Amer. Chem. SOC.,1974 96,2620; (b)M. A. Hassloch M. J. Nugent and 0.E. Weigang jun. ibidl p. 2619. Aromatic Compounds (68) X = H or D (69) X = H F or CN pass through the n-cloud of the other ring and the rate of inversion as measured by the n.m.r. spectrum is affected by deuterium substitution with KdK = 1.20 +_ 0.04 Substitution at the 4-position also affects the rate of inversion but correlation with Hammett values gives curves rather than a straight line; this is attributed to bond-length changes caused by substitution.'6'" The diene (69) can flip more easily than the saturated compound if X = H but fluorine or cyanide substitution completely stops the inversion below 140 "C.161b [2,2]-(2,6)-Pyridinoparacyclophane-1,g-diene(70)and the related saturated compound have been prepared; the saturated compound flips on the n.m.r.time-scale but the diene does not and an X-ray crystal structure of the diene shows the pyridine ring to be at right angles to the benzene ring. The authors speculate that in the boron trifluoride complex (71) bonding occurs .through the benzene ring as flipping does not take place on the n.m.r.time-scale.'62'*b Coupling of 2,6-dibromomethyltoluene with 2,6-dimethylthiotoluene gives both syn-and anti- dithiametacyclophanes. Stevens rearrangement on the anti-compound followed by Hofmann elimination gives the anti-[2,2]dimethylmetacyclophane-lg-diene (72) which is in equilibrium both thermal and photolytic with the pyrene (73) but the syn-isomer gives only the pyrene (74) which is not in equilibrium with the cyclophane.' Three-and four-layered [2,2,2]metacyclophanes have been 16' (a)S. A. Sherrad R. L. Costa. R. A. Barnes and V. A. Bockelheide J. Amer. Chem. SOC. 1974 96 1565; (b) V. Bockelheide P. H. Anderson and T. A. Hylton ibid.p. 1558. 16' (a)V. Bockelheide K. Galuszko and K. S. Szeto J. Amer. Chem. SOC.,1974 96 1578; (6) V. Bockelheide K. Galuszko K. S. Szeto L. H. Weaver and B. W. Mathews ibid. p. 1585. '63 R. H. Mitchell and V. Bockelheide J. Amer. Chem. Soc. 1974,96 1547. 304 T.J. Tewson (74) (75) n U (82) X = Br or OTs prepared and form both syn- and anti-isomers the anti-compounds being con- verted into the syn-isomers on heating (75) +(76).'64 [2,2]-(2,5)-( 1,4)-Furano- and thiopheno-naphthophanes have been synthesized and the naphthothio- phenophanes isolated in both syn- and anti- forms (77) and (78).16' Synthesis of both chiral and achiral [2,2]-( 1,5)-naphthalenophanes has been achieved'66 and [9]metacyclophane with a hydroxy-group in position 16has been synthesized ; the bridge lies on one side of the ring and cannot invert and Reimer-Tiemann reaction gives the appropriate troponecyclophane in good yield.' 67 Syntheses of [2,6]para~yclophane-1,6-diene'~~ (79) l-phenyl-12-oxo[ 131- paracyclophan- 1-en-1 3-one [8]-(3,6)-pyridazinophane(8l) and its mono- N-~xide'~' have been described.Neither em-nor endo-[10]-(2,4)-quinoline-cyclophane 1-bromide or tosylate (82) undergoes bimolecular nucleophilic or '64 T. Umenoto T. Otsuko and S. Misumi Tetrahedron Letters 1974 1523. 16' S. Mizogami N. Osaka T. Otsubo Y. Sakata and S. Misumi Tetrahedron Letters 1974 799. M. W. Haenel Tetrahedron Letters 1974 3053. 16' T. Hiyama Y.Ozaki and H. H. Nozaki Tetrahedron 1974 30 2661.L. G. Kaufman and D. T. Longone Tetrahedron Letters 1974 3229. 16' D. Bichan and M. Winnik Tetrahedron Letters 1974 3857. T. Hiyama S. Hirano and H. Nozaki J. Amer. Chem. SOC.,1974 96 5287. Aromatic Compounds (84) (85) X = 0 or CH ionization reactions establishing the rigidity of bridging hydrocarbon chains. Photochemical reaction of [10]-(9,1O)-anthracenopha-4,6-diyne(83) in benzene gives the dimer (84) and in the presence of furan or cyclopentadiene gives the addition product (85).17 Birch reduction of [2,2]paracyclophane gives a tetra- hydro-(dl) compound in agreement with CNDO calculations on the likely inter- mediate~,'~~ and substitution of [2,2]metacyclophanes in positions 4 and 8 occurs using radical cation conditions whereas normal electrophilic conditions cause transannular reactions.' 74 3 Non-benzene System! Dissolution of l,l-dichloro-2,5-diphenylcyclopropabenzene(86) in fluorosul-phonic acid gives the stable cation (87) an aromatic system as shown by its n.m.r.spectrum,' but the 2,2,5,5-tetramethylbicyclo[4,1 ,O]hepta- 1(6)-en-6-one (88) is unstable toward both acid and base. 0 Ph Ph w W. E. Parham P E. Olson K. R. Reddy and K. B. Sloan J. Org. Chem. 1974 39 172. 17' T. Inoue T. Kaneda and S. Misumi Tetrahedron Letters 1974 2969. 173 J. L. Marshall and B.-H. Song J. Org. Chem. 1974 39 1342. K. Nishiyama K. Hata and T. Sato J.C.S. Perkin Zi 1974 577. 175 B. Halton A. D. Woolhouse H. M. Hugel and D. P. Kelly J.C.S. Chem. Comm. 1974 247. 306 T.J.Tewson Cyclobutadiene chemistry has been reviewed' 76 and two further stable cycls- butadienes (89) and (90) have been synthesized. Compound (89) is stable in the solid state below 80°C'77and (90) does not react with either dienophiles or dienes but does undergo addition with bromine and hydrogen.178 The synthesis of and X-ray studies on 172-dithiosquaric acid (91) show it to be a stable flat com- pound. 79 Preparation of the cyclobutadiene iron tricarbonyl complex (92) containing an intramolecular trap has been reported. Photolylic generation of the cyclobutadiene gives the Dewar benzene derivative (93) which then re- arranges to (94).'8o CH,-0-CH,-CrCMe N.m.r. studies of the reaction of 2-chlorotropone with methoxide ion show that the 7-methoxy-compound (95)is first formed; this rearranges rapidly to the geminal methoxy compound (96).' 81 Ethanethiolate reacts with tropone to give the mono-addition product at C-7 and the gem-adduct is not formed.'82 OMe (95) (96) Annulenes as aromatic compounds have been reviewed.183 A crystal structure analysis of bis(potassium dig1yme)- 1,3,5,7-tetramethylcyclo-octatetraeneshowed G. Maier Angew. Chem. Internat. Edn. 1974 13 425. I" H. Straub Angew. Chem. Internat. Edn. 1974 13 405. 17' M. P. Cava H. Fironzabadi and M. K. Kreiger J. Org. Chem. 1974 39 40. 179 D. Coucouvanis F. J. Hollander R. West and D. Eggerding J. Amer. Chem. Suc. 1974 96 3006. lE0R. H. Grubbs T. A. Pancoast and R. A. Grey Tetrahedron Letters 1974 2425. "' F. Pietra J.C.S.Chem. Cumm. 1974 544. ''' C. A. Veracini and F. Pietra J.C.S. Chem. Cumm. 1974 623. F. Sondheimer Chimiu (Switz.) 1974 28 163. Aromatic Compounds 307 it to be flat with equal bond lengths and definitely an aromatic systern.lg4 sym-Dibenzo-1,5-cyclo-octadiene-3,5-diyne(97) and sym-dibenzo-1,3,5-cyclo-octad-ien-7-yne (98) show paramagnetic ring currents and are easily reduced to 10n systems.lS5 Bicyclo[3,3,2]decatrienyl dianion (99) is the longicyclic homologue of the cyclo-octatetraene dianion and as such is a stable 1k system.186 The cis-benzocyclononatetraenyl dianion isomerizes to the trans-compound on standing at room ternperature.lg7 Analysis of the crystal structure of 1,6-methano[l0]annulen-ll-oneshows it to be virtually the same as those of the other 1,6-rnethano[lO]annulenes,with no interactions between the carbonyl group and the aromatic system.188 Various derivatives of 1,6-methano[ lolannulene can be prepared from lH-3,8-methano- cyclopropa[ lolannulene (100) by opening the cyclopropane ring with nucleo- philes ;' 89 the bridged annulenes are generally photo-oxidized initially to 1,4-endoperoxides which rearrange to diepoxides.190 Two reports of the synthesis and structure of 8b,8c-diazocyclopent[f,gl-acenaphthylene (101) establish that it is a planar 1277 antiaromatic compound with no tendency to form the 107c monocyclic system,191a*b and comparison of its molecular diamagnetic susceptibility with the proton magnetic resonance of (102) shows that it is a 4n system with a paramagnetic ring current.The prepara- I 84 S. Z. Goldberg K. N. Raymond C. A. Harmon and D. H. Templeton J. Amer. Chem. SOC.,1974 % 1348. Ia5 H. W. C.Wong P. J. Gcrratt and F. Sondheimer J. Amer. Chem. SOC.,1974 % 5604. IB6 M. J. Goldstein S. Tomada and G. Whittaker J. Amer. Chem. SOC.,1974 % 3676. la7 A. G. Anastassiou and E. Reichmans Angew. Chem. Internat. Edn. 1974,13. 728. lS8 S. It6 and Y. Fukazawa Tetrahedron Letters 1974 1045. E. Vogel and J. Sombreck Tetrahedron Letters 1974 1627. lg0 E. Vogel A. Alscher and K. Wihus Angew. Chem. Internat. Edn. 1974,13 398. lgl (a) J. L. Alwood D. C. Hrucir C. Wong and W. W. Pandler J. Amer. Chem. SOC. 1974 96 6132; (6)W. Flitsch and H. Lerner Tetrahedron Letters 1974 1677. 308 T.J.Tewson tion and n.m.r. tudies of 1,7-methano[l2]annulene (103) and 1,6-methano[ 121- annulene (104) show both 10 be paratropic; both are easily reduced to 14n dianions and (103) but not (104) reveals rapid degenerate n-bond shift in the low-temperaturcs 3C n.m.r. lH-Aza[l3]annulene and its N-acylated derivatsves have been prepared none of which are particularly stable but the parent compound shows a diamagnetic ring current whilst the N-sub- stituted compounds do not.192d Ill I1 C C (106) (107) The three didehydro[ 14lannulenes (105H107)have been synthesized and although the diamagnetic ring current increases with conjugation the stability decreases.Ig3 The two furano[l4]annulenes (108) and (109) and the benzo[ 141- *''(a) E. Vogel H. Konigshofen K.Mullen and J. M. F. Oth Angew. Chem. Internat. Edn. 1974 13 281; (b) E. Vogel M. Mann Y.Sakata K. Miillen and J. M. F. Oth ibid. p. 283; (c) J. M. F. Oth K. Mulien H. Konigshofen M. Mann Y. Sakata and E. Vogel ibid. p. 284; (d) A. G. Anastassiou and R. L. Elliott J. Amer. Chem. Soc. 1974 96,5257. M. Iyoda M. Morigaki and M. Nakagawa Tetrahedron Letters 1974 1817 3677. Aromatic Compounds 309 (1 14) (115) (118) a; X = N-H b; X = N-1R = H Me,or Et c;x=o d;X = S,R = HorEt \ e; X = S=O R = H or Et \\/ CrC-C~C \/ No (116) X = 0 f;X= S ,R=HorEt (117) X = H / \o annulenes (110) and (111) all show a diamagnetic ring current although this is decreased in the benzo cases and the furano-compounds react with dimethyl acetylenedicarboxylate to give conformationally mobile ad cts.194 The [15]annulenone 4,7 :10,lZdioxides (1 12H115)have been prepared all of which give stable 14z systems with acid particularly (1 13).Ig5 The [15]annulenone (116) and [15]annuIene (1 17) also form stable 14n systems (1 16dd~ith trifluoro- acetic acid and (1 17) with trityl tetrafluoroborate.196 The didehydrohetero[l7]- annulenes (118a-f) have all been synthesized ;the nitrogen oxygen and uulphur 194 P. J. Beeby R. T. Weavers and F. Sondheirner Agnew. Chrm. Internat. Edn.. 1974. 13. 138; R. T. Weavers and F. Sondheimer ibid. pp. 139 141. lY5H. Oagawa N. Shimojo H. Kato and H. Saikachi Terrahrdron 1974 30 1033. ‘96 H. Ogawa H. Kato N. Ibii T. M. Cresp and M. V. Sargent Tetrahedron Letters 1974 3889.310 T. J. Tewson C C c C Ill Ill 111 111 C C Po c C C C Ill 111 Ill 111 mo0u compounds are all diatropic but the syn-ethyl sulphoxide and the sulphone are paratropic whilst the anti-ethyl sulphoxide is atropic.’ 97 The authors speculate that the axial oxygen has a 2p overlap that allows an 18n Mobius configuration; the syn-compound cannot do this and so is paratropic. MIND0/3 and MIND0/2’ studies of [18]annulene give an alternating bond structure and the authors suggest that the X-ray crystal structure which gives an equal bond length structure is due to a non-centrosymmetric structure with an equal proportion of the two alternating forms present in the cry~ta1.I~~ The tetradehydro[ 18lannulones (1 19)-(122) all undergo electrochemical reduction to the phenolic compounds and (121) and (122) require a lower potential than ben~oquin0ne.I~~ Triepoxyr 19Jannulenone (123) and triepoxy[2l]annulenone (124) have been prepared ;(123) shows a diamagnetic ring current but (124) shows 19’ P.J. Beeby J. M. Brown P. J. Garratt and F. Sondheimer Tetrahedron Letters 1974 599; J. M. Brown and F. Sondheimer Angew. Chem. Internat. Edn. 1974 13 339 377. 19* M. J. S. Dewar R. C. Haddon and P. J. Student J.C.S. Chem. Comm. 1974 569. N. Darby K. Yamamoto and F. Sondheimer J. Amer. Chem. SOC.,1974 96 248. Aromatic Compounds 31 1 0 0 (123) no ring current and is not paratropic suggesting that in this series Hiickel's (4n + 2) rule breaks down when n = 5.200,201 4 Condensed Systems Local aromatic properties of polycyclic benzenoid hydrocarbons have been assessed by a numerically simple extension of Clar's valence formula using the number of complete aromatic sextets that each n-electron can participate in which gives good results in predicting reactivities and structures.202 The second triplet state of naphthalene has been prepared by intermolecular energy transfer and its lifetime measured as -1.5 x 10-s which is an order of magnitude less than that for anthra~ene.~'~ An attempt to prepare the 2,3- dideh ydronaphthalene (1 25) by pyrolysis of 2,3-diazidonaphthalene gave trans- 1,2-dicyano- 1 ,Zdih ydro benzocyclobutene in~tead.~ 1,2-Dihydroxy- 1,2-di h yd- O4 ro- and 1,4-dihydroxy- 1,4-dihydro-naphthaleneshave been synthesized.20s The disproportionation of 1,2-dihydro- and 1,4-dihydro-naphthaleneshas also been studied ; the 1,2-compound undergoes a thermal concerted reaction to naph- thalene and tetralin but the 1,4-compound rearranges and disproportionates in a reaction that is catalysed by the walls of the reaction Synthetic studies of polynitro-1,5- and -1,8-dimethylnaphthaleneshave been reported.207 Oxidation of 'k-region' dihydropolycyclic aromatics with sodium dichromate gives 'k-region' o-quinones which on reduction and treatment with dimethyl 2oo T.M. Crespand M. V. Sargent J.C.S. Chem. Comm. 1974 101. 201 T. M. Cresp and M. V. Sargent J.C.S. Perkin I 1974 2145. 202 M. Randic Tetrahedron 1974 30 2067. '03 C. C. Ladwig and R.S. H. Liu J. Amer. Chem. SOC.,1974,96 6210. '04 M. E. Peeks C. W. Rees and R. C. Storr J.C.S. Perkin I 1974 1260. '05 A. M. Jeffrey H. J. C. Yeh and D. M. Jerina J. Org. Chem. 1974 39 1405. '06 G. B. Gill S. Hawkins and P. H. Gore J.C.S. Chem. Comm. 1974 742. *07 S. R. Robinson B. C. Webb and C. H. J. Wells J.C.S. Pcrkin I 1974 2239. 312 T. J. Tewson acetal give 'k-region' arene oxides in good yield.208 Anthracene ancl phenanth- rene are fluorinated over potassium tetrafluorocobaltate followed by defluorina- tion to give the perfluoroaromatic compounds in a yield which is modest but none the less a considerable improvement over previous achicd ement~.~'~ Substituted anthracenes can be prepared in high yield by sodiLdn bdrohydride reduction of the appropriate anthraquinones,2 lo and 9,lO-dihydroanthracenes are synthesized by reduction of anthraquinones with phosphorus iodine and hydrogen iodide.2 9-Methyl- and 9,lO-dimethyl-anthracene are sulphonated on the methyl groups by reaction with the sulphur trioxide-dioxan The cis-and trans-isomers of 9,1O-dihydro-9,1O-diphenylphenanthrene have been reassigned on the basis of the ex.spectra of the appropriate radical anions.21 Thioanthracene radical cation perchlorates undergo substitution reactions in excellent yields.214 The kinetics of addition of the trichoromethyl radical to 9-substituted anthracenes correlate well with Brown's oP+substituent parameters with a pt = -0.83.2l5 1-Methoxyanthraquinones undergo photo- chemical nucleophilic substitution with replacement of the methoxy-group.2 l6 Photocycloaddition of olefins to 9-cyanophenanthrene proceeds either through a singlet exciplex or a triplet state depending upon the olefin,2 7a and the exciplex involved in the photoaddition of or-methylstyrene and 9-cyanophenanthrene has been An attempt to repeat the synthesis of (126) gave instead the photolysis product (127) when the reaction was performed in daylight.However when light was excluded work-up gave (126). The authors who worked in Colorado suggest that the ambient light in Oxford where the reaction was originally performed was too dim to effect the transformation !218 '08 H. Cho and R. G. Harvey Tetrahedron Leffers 1974 1491. 209 J. Burdon J. R. Knights I. W. Parsons and J.C. Tatlow Tetrahedron 1974,30 3499. 210 T. R. Criswell and B. Klanderman J. Org. Chem. 1974 39 70. 2' I R. N. Renaud and J. C. Stephens Cunud. J. Chem. 1974,52 1229. 212 A.-K. Telder and H. Cerfontain Tetrahedron Letters 1974 3535. 'I3 N. L. Bauld and .I.D. Young Tetrahedron Letters 1974 3143. 2'4 K. Kim V. J. Hull and H. J. Shine J. Org. Chem. 1974 39 2534. 'I5 J. C. Arnold G. J. Gleicher and J. D. Unruh J. Amer. Chem. SOC.,1974 96 787. 'I6 J. Griffiths and C. Hawkins J.C.S. Perkin I 1974 2283. 'I' (a)K. Mizimo C. Pac and H. Sakurai J. Amer. Chem. Soc. 1974 96 2993; (6) R. Caldwell and L. Smith ibid. p. 2994. 'I8 S. J. Cristol and J. S. Perry Tetrahedron Letters 1974 1921. Aromatic Compounds The odd-alternant hydrocarbon benzo[cd]pyrenyl anion (128) has been prepared and its n.m.r.spectrum shows that the charge is carried on alternate carbon atoms.2 l9 (128) The kinetics of protiodetritiation of hexahelicene benzo[c]phenanthrene in all six positions correlate well with Huckel localization energies with no evidence that puckering in the chain is localized in one position.220 However synthesis of several dimethylhexahelicenes shows that as the steric interactions increase the torsional strain in the molecule becomes more uniformly distributed over the molecule.221 Two double helicenes diphenanthro[4,3-a ; 3’,4’-o]picene(1 29) and benzo[s]diphenanthro[4,3-a ; 3’,4’-olpicene ( 1301 have been synthesized ; (129) (130) was isolated as exclusively d1,222a but the optically active forms racemize at 220 “C with t+= 20 min which is very similar to the behaviour of the hexaheli- cenes ; the meso-form is not involved in the racemization.222b ’19 I.Murata K. Yamamoto and 0.Hara Trirrihedron Letters 1974. 2047. ’lo J. Le Guen and R. Taylor J.C.S. Perkin II 1974 1274. 22 W. H. Laarhoven and Th. J. M. Cupper Tetrahedron 1974 30 1101. ”’ (a) R. H. Martin Ch. Eyndels and N. Defay Tetrahedron 1974 30 3339; (6) W. H. Laarhoven Th. J. M. Cupper and R. J. F. Nivard ibid. p. 3343. 314 T. J. Tewson (131) Photo-dehydrocyclization of 8-phenyl-di-p-naphthylethylenegives 42 yd ben-zocorene (131) as well as the expected products 1-phenylpentahelicene and 10-phenyl[ 1,2-a]anthracene the corene being a photo-oxidation product of the anthra~ene,~~~‘ and the same reaction on 4,5-diphenyltriphenyleneand 43- diphenylphenanthrene gives 1 ,Zphenyl shifts rather than cyclization although some benzo[e]naphtho[ 1,2,3,4-ghi]perylene was also isolated in the case of the triphenylene.223b Photolysis of trans-5,5’-dimethoxy-2,2’,4,4’-tetramethylstilbene gave 4,7-di- methoxy-1,3,6-trimethylphenanthreneby loss of a methyl group as well as the expected product 4,7-dimetho~y-l,3,6,8-tetramethylphenanthrene.~~“ al-An ternative synthesis for polycyclic aromatics has been reported :dibenzyl aromatics can give quinonoid-type compounds which can undergo Diels-Alder reactions with maleic anhydride to give more condensed compounds.Thus 3,8-diphenyl- pyrene was synthesized from 1,5-dibenzylnaphthalene ; 1,6-diphenylcoronene was also synthesized.225 Azulene and methylazulene react with strong nucleophilic bases to give either nucleophilic addition or methylene-azulenate anions,226 and 2-chloroazulene- 1,3-dicarboxylate reacts with alkali-metal acetylides to give 4-and 6-substituted azulene-1,3-dicarboxylates, presumably by addition and elimination.227 Polaro- graphic reduction potentials of (132)-(136) show considerable deviation from (133) (134) R = H (135) R = Me 223 (a) A.H. Tinnemans and W. H. Laarhoven J. Amer. Chem. Soc. 1974 96 4611; (b) A. H. Tinnemans and W. H. Laarhoven ibid. p. 4617. M. S. Newman and H. M. Chung J. Org. Chem. 1974,39 1036. 224 225 E. Clar M. M. Lovat and W. Simpson Tetrahedron 1974 30 3293.226 R. N. McDonald H. E. Petty N. L. Wolfe and J. V. Pankstehs J. Org. Chem. 1974 39 1877. 227 T. Fujita T. Morita and K. Takase Tetrahedron Letters 1974 2585. Aromatic Compounds the energy of the lowest HMO orbital unlike benzenoid compounds. This may be caused by the radical anion forming a 6x-electron system in the five-membered ring228 (137). Synthesis of indeno[2,1-a]azulene (138) and of indeno[ 1,2-a]-azulene (139) has been achieved by an extremely elegant route.229 Synthesis of 6-hydroxy-7H-naphth[3,2,1-cd]azulene-7-one(140) and the study of its tauto- merism have been reported.230 A new convenient synthesis of heptalene (141)has been reported and its 13C n.m.r. spectrum shows that it undergoes a rapid r-bond shift with AE of -3.5 kcalmol-' in a similar fashion to the [12]annulene (103).23* An elegant study of the photochemical conversion of 6b,l2~-dihydrocyclobuta[ 1,241:3,4-a']-bisacenaphthylene (142) into dinaphth[de- 1,2,3 :d'e'-5,6,7]azulene (143) shows 228 A.G. Anderson jun. and G. M. Masda J. Org. Chem. 1974,39 512. 229 A. Chen M. Yasunami and K. Takase Tetrahedron Letters 1974 2581. 230 N. Abe T. Morita and K. Takase Tetrahedron Letters 1974 3621. 23' E. Vogel H. Konigshofen J. Wassen K. Miillen and J. M. Oth Angew. Chem. Internat. Edn. 1974 13 732. 316 T. J. Tewson H 0aa. I 6 OH that light of A = 277 nm is required to achieve the singlet -triplet conversion of the starting material and that light of A = 360 nm converts triplet (142) into the product (143).Light of A = 214nm can effect the conversions of (142) into (143) and (144) into (144a) in one step although in the case of (144) the con- version cannot be accomplished with two photons.232 Synthesis of the 1,2-dihydroxybenzocycloheptenes(145) and (146) has been reported but they are stable only in solution.233 However synthesis of cyclo-hepta[cd]phenalen-6-one (147) and the cyclohepta[cd]phenalenium cation (148) ”‘ J. M. Labrum J. Kolc and J. Michl J. Amer. Chem. SOC.,1974 96 2636. 233 P. D. Carpenter D. J. Humphreys and G. R. Proctor J.C.S. PerkinI 1974 1527. Aromatic Compounds shows them both to be stable the cation being the weakest base of this type ye^ dis~overed.~~" The syntheses of bisbenzo[4,5]cyclohepta[ 1,2-a:2' 1'-albenzene-5.7-dione (149) and bisbenzo[4,5]cyclohepta[ 1,2-a:1',2'-d]benzene-5,7-dione (150) have also been reported.235 234 1.Murata K. Yamamoto and Y. Kayane Angew. Chem. Intrrnat. Edn. 1974 13 807 808. 23J I. Agranat and D. Avnir J.C.S. Perkin I 1974 1155.