10 Aromatic Chemistry By R. BOLTON Department of Chemistry Bedford College London NWI 4NS 1 General A second method for generating phenyl cation has been reported involving the spontaneous p -decay of 1,4-ditritiobenzene; the product then contains the label attached to C-4.l The synthesis of such labelled phenyl cations could also be brought about by the ring-closure method reported previously.' A novel 1,2-shift of a methyl group has been found in the reaction of (1)under the influence of base as shown in reaction ( l).3 a/ -& / ButOK,THF / / (1) 0 0 (1) Contributions towards a knowledge of the properties of aromatic compounds include a report of new binuclear lanthanide n.m.r. shift reagent^.^ Theoretical aspects of aromatic chemistry have been advanced by a general theory of chemical bonding5 as well as by theoretical approaches to the Birch reduction6 and to halogenobenzenium ions.' Reactivity-selectivity relationships in the reactions of benzyl derivatives have been discussed in terms of HOMO-LUMO interactions.* Changes in the nature of the transition state with changes in the nature of the nucleophile have been suggested from a study of the reactions of benzyl bromides,' and a paper on cation-anion interactions is appropriate in this context.lo Re-assessment of sub-stituent effects has expectedly occupied a number of workers; another extension of the Hammett equation has been announced" and perturbation theory has been applied to substituent effects providing descriptions of these in terms of changes G.Angelini M. Speranza A. L. Segre and L. J. Altman J. Org. Chem. 1980,453291. * M. Hanack and U. Michel Angew. Chem. Znt. Ed. Engl. 1979,18 870. B. Miller and A. K. Bhattacharya J. Am. Chem. SOC.,1980,102,2450. T. J. Wenzel T. C. Bettes J. E. Sadlowski and R. E. Sievers J. Am. Chem. SOC., 1980 102 5903. S. Fliszar J. Am. Chem. SOC.,1980 102 6946. A. J. Birch A. L. Hinde and L. Radom J. Am. Chem. SOC.,1980,102,3370. R. C. Binning jr. and K. M. Sando J. Am. Chem. SOC., 1980,102,2948. Y. Karton and A. Pross J. Chem. SOC.,Perkin Trans. 2 1980 250. V. P. Vitullo J. Grabowski and S. Sridharan J. Am. Chem. SOC.,1980,102 6463. lo C. D. Ritchie and T. C. Hofelich J. Am. Chem. SOC.,1980 102 7039. G. Weeks and V. Horak J. Org. Chem.1980,45,2068. 158 R. Bolton in the Coulombic integral. l2Other attempts to understand and quantify theoretically such substituent effects have used a parallel between benzyl anions and phenoxide or anilide anions,13 or have studied carbo-cation~,~~ or have sought to differentiate between field and inductive effects on the basis of their non-proportionality.ls The dual-parameter substituent constant already successfully applied to benzene chemistry,16 has been extended to the naphthalene system although the correspond- ing tests have not been made." In most cases the proliferation of parameters ensures a better fit between experimental and calculated figures although the physical significance of these new parameters (as opposed to their mathematical function) is sometimes hard to envisage.Such extensions of the Hammett equation have been regularly reported but few have reached general applicability. A parallel has been reported" between o1and the effects of substituents on the fifth overtone of the aryl C-H stretching vibration. 2 Non-benzenoid Systems Among the interesting systems reported this year the preparation of a dialkoxy- (aryl)bromane(III) (2) deserves mention (Scheme 1).l9 The BrlI1 derivative shows considerable stability towards water and other weak nucleophiles and has mild oxidizing properties. The preparations of other remarkable species include the dication ether salts A;OAi2' and the stable 4n7r-system (3)*l as well as cyclo-octa[deflfluorene. This last compound was obtained from cyclopenta[deflphenanthrene; it shows para- HO Br OH (2) Reagents i Br,.CCl,; ii OH-; iii Me,CO H'; iv 2 equivalents of Bu"Li; v (CF,),CO; vi H' H,O; vii HONO HBr Cu; viii BrF, (CH,Cl) Scheme 1 l2 R. Ponec Collect. Czech. Chem. Commun. 1980 45 1646. G. Kemister A. Pross L. Radom and R. W. Taft J. Org. Chem. 1980,45 1056. D. A. Forsyth and B. B. Sandel J. Org. Chem. 1980 45 2391. W. F. Reynolds J. Chem. SOC.,Perkin Trans. 2 1980,985. I6 M. Godfrey J. Chem. SOC., Perkin Trans. 2 1978 487. l7 M. Godfrey J. Chem. SOC., Perkin Trans. 2 1980 330. Y. Mizugai and M. Katayama J. Am. Chem. SOC.,1980,102,6424. l9 T. T. Nguyen and J. C. Martin J. Am. Chem. SOC.,1980,102 7382. P.J. Stang G. Maas and T. E. Fisk J. Am. Chem. SOC.,1980,102,6361.** A. G. Anastassiou and H. S. Kasmai Angew. Chem. Int. Ed. Engl. 1980 19,43. Aromatic Compounds 159 tropic anti-aromatic properties.’* Among unusually acidic hydrocarbons octa-fluorofluorene (see below) and 5H-perfluoro-l,2,3,4,5 -pentamethylcyclopen ta- diene (4) deserve mention. The trifluoromethyl groups in the latter compound raise the acidity of the remaining proton so that a pK value of -2 is ob~erved;’~ although inferior to the effect of five cyano-substituents the effect is nonetheless considerable. (3) (4) A new synthesis of annulenones has been described.24 In essence it combines two classical reactions for the aldol condensation of a terminal acetylenic aldehyde and a methyl ketone provides the unsaturated ketone the two ‘ends’ of which may then be linked by acetylenic oxidative coupling.Dimethylbisdehydro[ nlannulen- ones may thus be obtained where n is 15 17 19 or 21. Interest is now turning towards the properties of excited states in the annulene systems or towards the aromaticity of their anions. Thus studies of the excited states of methano-bridged [lo]- [14]- and [18]-ann~lenes~~ provided strong evidence of considerable transannular interactions while other studies have been made of the radical ions of 4,5,7,8-tetramethyl-[2.2]paracyclophane26“ and of [16lannulene dianion.266 The photoelectron spectrum of [8]paracyclophane (and those of the [6]-and [7]-analogues) suggested that the observed splitting arose from the electronic effect of methyl substituents rather than from the deformation of the ring.27 Among the contributions to azulene chemistry a shorter synthesis of the parent hydrocarbon (previously reported in a note28n) has now been described.286 The process may be used to incorporate hydrogen or carbon labels at specified positions in the system.While it has yet to be shown to be able to produce bulk quantities of azulene quickly and cheaply the main obstacle appears to be the need to follow the last stage of the reaction (see Scheme 2) by t.1.c. in order to avoid losses through the acid-catalysed decomposition of azulene. The method has however considerable ___+ _I_* [-H,OI a $cH2N2 \ [97%] \ [SO%] [30-50%] I / Scheme 2 22 I. Willner and M. Rabinovitz J. Org. Chem. 1980,45 1628.23 E. D.Laganis and D. M. Lemal J. Am. Chem. SOC.,1980,102,6633. 24 J. Ojima Y. Shiroishi K. Wada and F. Sondheimer J. Org. Chem. 1980,45 3564. 2s H. J. Dewey H. Deger W. Frohlich B. Dick K. A. Klingensmith G. Hohlneicher E. Vogel and J. Michl J. Am. Chem. Soc.. 1980,102,6412. 26 (a)J. Bruhin F. Gerson and H. Ohya-Nishiguchi J. Chem. SOC.,Perkin Trans. 2 1980 1045; (b)G.R. Stevenson and B. E. Forch J. Am. Chem. SOC.,1980,102 5985. ” R. Gleiter H. Hopf M. Eckert-Maksic and K.-L. Noble Chem. Ber. 1980 113 3401. 28 (a)L. T.Scott J. Chem. SOC.,Chem. Commun. 1973 882; (b) L. T.Scott M. A. Minton and M. A. Kirms J. Am. Chem. SOC.,1980,102 6311; (c) K. Hafner Angew. Chem. 1958,70 419. 160 R. Bolton advantages over the simple Ziegler-Hafner synthesis whose success relied upon the pyrolysis of an azulene precursor in benzidine and the concomitant distillation of the azulene in a stream of superheated steam.*" The carcinogenic hazard may be removed by the use of triethanolamine in place of benzidine but the difficulties of maintaining temperature flow of steam and regular addition of the azulene precursor remain.The synthesis of bis(perfluoroacy1)azulenes and their decomposition to give azulene-1,3-dicarboxylicacid have now been achieved.29 The observation of elec-trophilic trifluoroacetylation of azupyrene (5) has confirmed the conclusions about its aromatic character that were made from spectroscopic considerations and in the face of the 4rt~-system.~~ The synthesis of 6,6'-bis(azuleny1) has been achieved by the Ziegler-Hafner method using 4,4'-bipyridyl as starting material.The fact that each pyridine system in turn could be converted into the azulene system by this route reflects considerable improvements in the yields of individual steps of this sequence.31 The dimerization of (6) forms the dihydro-derivative (7) of some 6,12-diaryl-azuleno[1,2-b]azulenes;the parent may be obtained by oxidation with molecular bromine.32 Benz[a]indeno[ 1,2,3-cd]azulene (8) has been obtained by the photolysis of 1-X-triptycenes (X =OCOPh OPh or SMe).33 @(-Jc=c/Ar \H \/ (6) (5) (7) (8) In the cyclophane series the ready formation of a rn-xylylene system led to the formation of octamethyl[2.2]metacyclophane in 20% yield.34 The Dewar isomer of [4]metacyclophane has been and so has the quinhydrone correspond- ing to the [3.3]metacyclophane The polyphenylenicenes may be con- veniently included here; triphenylenicene (benz0[2.2]metacyclophane)~~ and penta- phenylenicene3* have been prepared along with an interesting series of systems 29 L.J. MathiasandC. G. Overberger,J. Org. Chem. 1980 45 1701. 30 A. G. Anderson jr. G. M. Masada and G. L. Kao J. Org. Chem. 1980,45 1312. 31 Ch. Jutz Synthesis 1980 31. 32 T. Toda N. Shimazaki T. Mukai and C. Kabuto Tetrahedron Lett. 1980 21 4001. 33 Y. Kawada H. Tukada and H. Iwarnura Tetrahedron Lett. 1980 21 181. 34 J. J. Gajewski M. J. Chang P. J. Stang andT. E. Fisk J. Am. Chem. Soc. 1980,102 2096. 35 L. A. M. Turkenburg J. W. van Straten W.H. de Wolf and F. Bickelhaupt J. Am. Chem. Soc. 1980,102,3256. 36 H. A. Staab C. P. Herz and A. Dohling Chem. Ber. 1980,113 233. 37 E. Hammerschmidt and F. Vogtle Chem. Ber. 1980,113 1125. E. Hammerschmidt and F. Vogtle Chem. Ber. 1980,113 3550. Aroma tic Compounds 161 such as anthra~enophane.~~ Among the chemistry of cyclophanes may be included their susceptibility to Diels-Alder reagents4’ and the formation of the significant chromium complex (712-[3.3]paracyclophane)chromium(~).41The extension of these synthetic methods culminated in the synthesis of a [2]catenane containing a 2 2 -membered heterocyclic 3 Electrophilic Reactions The process has been reviewed.43 Electrophilic attack upon benzocyclopropenes demonstrates an alternative mechanism involving attack upon a u-bond.The limitations and extent of such a mechanism deserve further definiti~n.~~ Some theoretical discussions upon the electrophilic attack by protons upon the cyclopro- penium ions also deserve mention.45 The electrophilic nature of the hydroxyl radical has again been determined by studying the distribution of products arising from the attack of Cerfontain and his workers have continued their careful studies of the mechanism of s~lphonation.~’-~~ The complicated behaviour of sulphonation involving sulphur trioxide resuits partly because of changes in the nature of the rate-determining step with changes of the solvent and also from the intervention of a number of competing processes which are reflected by changes in the nature of the reaction products.The anthracene derivatives used in the most recent work are also vulner- able to coupling reactions in strongly acidic media; such polymeric species were detected in the course of the sulphonation and were major products when anthracene pyrene naphthacene or 9,lO-dimethylanthracene were treated with aluminium(II1) chloride (loo/,) in liquid antimony(II1) chloride at 100-130 0C.55 The carbonium ion which was formed by proton attachment was held to be formed through a disproportionation reaction which may be represented by reaction (2) 6ArH + 4SbCl3 + 4(ArH.H)’ + 4C1-+ $Sb + [Ar( -H)]z (2) In this way anthracene gave anthra[2,l-~]aceanthrylene;pyrene gave 1,l’-bipyrenyl and dinaphtho[2,1,8a,8,7-defg;2’,1’,8a’,8’,7‘-ijkI]pentapheneby sub-sequent ring-closure between positions 10 and 10‘of the biaryl.39 R. Wingen and F. Vogtle Chem. Ber. 1980 113 676. 40 A. F. Murad J. Kleinschroth and H. Hopf Angew. Chem. In[. Ed. Engl. 1980 19 389; A. F. S. Murad and H. Hopf Chem. Ber. 1980,113,2358;but compare the synthesis by Diels-Alder processes described by P. G. Gassman T. F. Bailey and R. C. Hoye J. Org. Chem. 1980 45 2923. 41 R. Benn N. E. Blank M. W. Haenel J. Klein A. R. Koray K. Weidenhammer and M. L. Ziegler Angew. Chem. Znt. Ed. Engl. 1980,19 44. 42 G. Schill G. Doerjer E. Logemann and W. Vetter Chem. Ber. 1980 113 3698. 43 F. Effenberger Angew. Chem. Znt. Ed. Engl. 1980,19 151. 44 L. K. Bee P. J. Garratt and M. M. Mansuri J. Am. Chem. SOC.,1980 102,7076. 45 T.Clark and R. Weiss J. Org. Chem. 1980 45 1790. 46 N. V. RaghavanandS. Steenken J. Am. Chem. SOC.,1980,102 3495. 47 F. van de Griendt and H. Cerfontain J. Chem. SOC.,Perkin Trans. 2 1980 13. 48 F. van de Griendt and H. Cerfontain J. Chem. SOC.,Perkin Trans. 2 1980 19. 49 F. van de Griendt and H. Cerfontain J. Chem. SOC.,Perkin Trans. 2 1980 23. 50 K. Lammertsma and H. Cerfontain J. Chem. SOC.,Perkin Trans. 2 1980 28. 51 R. Brogman and H. Cerfontain J. Chem. SOC.,Perkin Trans. 2 1980 33. 52 A. Koeberg-Telder F. van de Griendt and H. Cerfontain J. Chem. Soc. Perkin Trans. 2 1980 356. ” F. van de Griendt and H. Cerfontain J. Chem. SOC.,Perkin Trans. 2 1980 904. 54 F. van de Griendt C. P. Visser and H. Cerfontain J. Chem. Suc. Perkin Trans. 2 1980 911.” A. C. Buchanan 111 A. S. Dworkin and G. P. Smith J. Am. Gem. Suc. 1980,102 5262. 162 R. Bolton The sulphodeacylation of dimesityl ketone received kinetic In 89.8% (w/w) sulphuric acid the reaction could be analysed in terms of two competing processes. The first fission of the diary1 ketone provides both mesitylene and mesitoic acid (2,4,6-trimethylbenzoic acid) whose subsequent acid-catalysed decarboxyla- tion occurs readily under these conditions; 2,4,6-trimethylbenzenesulphonicacid then arises from attack upon thk arene that is provided by these two routes. It would be interesting to detect the direct sulphodecarboxylation of mesitoic acid; the recent work was interpreted in terms of protiodecarboxylation followed by rapid sulphonation but the rates of cleavage of the reported mesityl ketones suggest that analogous cleavage of the acid might not occur too slowly to be significant.Acylation by CH3CO+ has been studied in the gas phase and has important differences from the corresponding liquid-phase pro~ess.~’ The extended study of the acylation of hydrocarbons by Gore and his workers now includes studies upon triphenylene and chrysene in which the semi-quantitative work of earlier chemists has been refined to quite remarkable limits;58 as with the earlier work upon the acylation of naphthalene and 1-chloronaphthalene the identification of quite small amounts of isomers in admixture is reported. Competition studies have been applied to the reaction of dimethylketen with arenes in the presence of aluminium(II1) chloride.’’ Quite different values for the Hammett slope (p’) were proposed depending upon whether the substituents were more ( pf = -0.92) or less (p+ = -6.6) electron-donating than hydrogen.Similar behaviour was reported to occur with diphenylketen; however the conclusions are open to the criticisms that all competition reactions are prone to as well as to the specific reservation of the paucity of the number of points comprising the first part of the plot. Mercuriation by mercury(I1) trifluoroacetate in trifluoroacetic acid has also received careful and systematic study. The results were interpreted in terms of a rapidly formed T-complex (showing only a slight hydrogen-isotope effect in its formation) followed by a slow substitution process that is characterized by a substan- tial kinetic hydrogen-isotope effect.The complexity of the reaction however operates against a full understanding of the system even under such conditions.60 In studies of exchange of hydrogen isotopes Taylor and his workers have made two significant contributions. The first involves the effect of the orientation of the substrate upon reactivity and deals with measures of hydrogen isotope exchange in polyphenylene systems where either crown or helical orientation can be found and where the interconversion of the systems is not a complication under the reaction conditions.61 The second dealt with the effect of the cyclopropyl substituent on rates of aromatic detritiation; a series of careful measurements have quantified the effect of the group and set it in the context of the behaviour of the more conventional alkyl systems.The possibility of slight hydrogen-bonding behaviour 56 J. A. Farooqi P. H. Gore E. F. Sadd D. N. Waters and G. F. Moxon J. Chem. SOC.,Perkin Trans. 2 1980 835. 57 M. Speranza and C. Sparapani J. Am. Chem. Soc. 1980,102,3120. ’* P. H. Gore F. S. Kamounah and A. Y. Miri J. Chem. Res. 1980 (S) 40 (M) 0530. 59 K. R. Fountain P. Heinze D. Maddex G. Gerhardt and P. John Can. J. Chem. 1980,58,1939. ‘’C. W. Fung M. Khorramdel-Vahed R. J. Ranson and R. M. G. Roberts J. Chem. Soc. Perkin Trans. 2 1980 267. 61 M. M. Hirschler and R. Taylor I. Chem. SOC.,Chem. Commun. 1980,967. Aromatic Compounds 163 of the three-membered ring was deduced.62 Ridd and his c011eagues~~ have made a study of N-H hydrogen isotope exchange in protonated NN-dimethylaniline systems.An interesting contrast is found in the modes of reaction of the N-deuterio- NN-dimethylanilinium ion (9)and of N-deuterio-NN-dimethyl-3,5-xylidinium ion (10). The first compound undergoes hydrogen exchange at a rate which decreases regularly as the acidity of the solvent increases; the second shows the same behaviour to levels of about 84% sulphuric acid but then shows an acceleration in the rate of exchange. This was understood to show a change of mechanism in which exchange was now occurring between the solvent and hydrogen atoms attached to sites ortho- and para- to the nitrogen atom. Substituent effects were the same suggesting a common step in which these aromatic sites undergo proton attack; the resulting Wheland intermediate may lose hydrogen however either from carbon or from nitrogen.The catalysis of this exchange of hydrogen isotopes by nitrosonium ions which depends upon the concentration of NO' and whose rate is inversely propor- tional to the acidity of the medium (H!) was explained in terms of a loose complex between NO' and the anilinium ion with consequent loss of a proton from nitrogen. DkMe DAMe, I I (9) (10) Nitration continues to show new and unexpected facets. Helsby and Ridd64 have shown that the adducts arising from ipso-attack during the nitration of aromatic amines such as N,Nf,2,4,6-pentamethylaniline may be isolated with care as the hexafluorophosphate.Fischer and his colleagues6' have studied particularly the products of ipso-nitration of some para-substituted toluenes while the rearrange- ment of some such adducts has been shown not to involve only acid catalysis;66 light also causes the formation of aromatic products (Scheme 3).67 A new mechanism of reaction could be indicated by the observation6' that the nitration of phenols is catalysed by lower oxides of nitrogen although the diastereoisomeric ethyl ethers Mfiy (70 :30 ratio) Ac hvy hv CsH, p-xylene Y Me NO Scheme 3 62 P. Fischer and R. Taylor J. Chem. SOC.,Perkin Trans. 2 1980 781. 63 (a)J. R. Blackborow D. P. Clifford I. M. Hollinshead T. A. Modro J. H. Ridd and M. C. Worley J. Chem. Soc. Perkin Trans.2 1980,632;(6) D.J. Mills and J. H. Ridd ibid.,p. 637. 64 P.Helsby and J. H. Ridd J. Chem. SOC.,Chem. Commun. 1980 926. " A.Fischer D. L. Fyles and G. N. Henderson J. Chem. SOC., Chem. Commun. 1980,513. 66 A.Fischer and J. N. Ramsey Can. J. Chem. 1974,52 3960. 67 H. Shosenji K. Esaki and K. Yamada. Tetrahedron Lett. 1980 21 91. 68 D.S.Ross G. P. Hum and W. G. Blucher J. Chem. Soc. Chem. Commun. 1980 532. 164 R. Bolton observation itself is still consistent with the classical concept of nitration through prior nitrosation. Olah6’ has demonstrated the formation and properties of two new species i.e. N-nitropyridinium ion and N-nitroquinolinium ion from the reaction of nitronium salts with the appropriate heterocyclic base. These salts then behave as sources of modified nitronium ion giving both the orientation and as a generalization the rates of attack expected from such species.Differences in the rates of reaction arising from substitution in the pyridinium system have been ascribed among other factors to changes in the N-N resonance interaction and consequent alterations in the strength of the bond being broken during reaction. Measurements of ‘thermodynamic nitration rates’ have been rep~rted.~’ The first paper deals with the nitration of benzene and some derivatives in aqueous sulphuric or perchloric acids and interprets the results in terms of a function M, whose parallel with some of the terms in the Hammett acidity function and allied param- eters reflects its origins.The intention is to derive appropriate rate constants after allowance has been made for activity-coefficient effects; the need for this new function is not in the Reporter’s opinion conclusive. The various attempts to reflect the influence of proton-donors upon the observed rates of acid-catalysed reactions have had only limited success (e.g. see ref. 71) possibly because of the need to link equilibrium positions for protonation with kinetic properties of reacting systems and the most successful of these may owe its efficacy to its emphasis upon the comparison of the effects of acids upon two reacting systems under kinetic condition^.^^ The formation of 3-bromo-4-methylpheno1 by the bromination of p-cresol in HF-SbF mixtures73 may be consistent with deactivation of the hydroxyl function in such media but n.m.r.evidence substantiates the arg~ment’~ that ipso-attack occurs and that the orientation which is observed arises from an acid-catalysed rearrangement of an intermediate dienone. Considerable interactions across large distances seem to occur in the bromination of 9-substituted hexahydro-1,4- methanobiphenylenes (ll) where the change to a 9-methoxyl substituent increases the rate by a factor of 3 x lo5 over that found for the 9-keto-cornpo~nd.~~ 9 4 Nucleophilic Aromatic Substitution Meisenheimer Complexes.-The formation of such complexes has been reported in the 1:1 interaction of sodium methoxide with picramide a number of N-substituted picramides and NN-dimethylpicramide in methanol,76 of potassium 69 G.A. Olah S. C. Narang J. A. Olah R. L. Pearson and C. A. Cupas J. Am. Chem. SOC.,1980 102,3507. 70 N. C. Marziano P. G. Traverso and G. G. Cimino J. Chem. Soc. Perkin Trans. 1 1980 574. 71 M. A. Paul and F. A. Long Chem. Rev. 1957,57 1,935. 72 J. F. Bunnett and F. Olsen J. Chem. SOC., Chem. Commun. 1965,601; Can,J. Chem. 1966,441897. 73 J. P. Jacquesy M.-P. Jouannetoud and S. Makani J. Chem. SOC., Chem. Commun. 1980 110. 74 J. M. Brittain P. B. D. de la Mare and P. A. Newman Tetrahedron Lett. 1980,21,4111. 75 M. N. Paddon-Row B. V. Lap H. K. Patney and R. N. Warrener Aust. J. Chem. 1980 33 1493. 76 M. R. Crampton and B. Gibson J. Chem. Soc. Perkin Trans. 2 1980,752. Aromatic Compounds t-butoxide with 2,4,6-trinitrotoluene in t-butyl and of methoxide ion with NN-dimethylpicramide in mixtures of dimethyl sulphoxide and methanol7' and with N-methylpicramide in the same mixture when loss of protons competes with the formation of u-complexe~.~~ When cyanide ion or isopropoxide ion attack 4-nitrobenzofuroxan (12) attack first takes place at C-7 to give (13);" however concurrent attack at both C-5 and C-7is detected with methoxide ion in methanol and the kinetics of formation of these two complexes have been determined.'l Formation of spiro-complexes might be expected with suitably substituted picryl derivatives and thus NN'-dimethyl-N'-picrylethylenediamine(14) gives the system (15) with triethylamine in aprotic solvents such as dimethylformamide or dimethyl sulphoxide; rearrangement then occurs with the displacement of a nitro-group.82 O2N MeN J 0 H (14) Even the dianion of 3-carboxy-4-nitrobenzenesulphenicacid is reported to form a stable Meisenheimer complex in 15.3M-potassium hydroxide solution.83 The reduction of halogeno-nitro- and -polynitro-benzenes with sodium boro- hydride in dimethyl sulphoxide leads in some cases to the formation of hydride Meisenheimer complexes which although unstable may be observed by 'H n.m.r.rneasurement~.~~ The rate of decomposition of a number of complexes between 1,3,5-trinitrobenzene and aliphatic monoketones in the presence of triethylamine when brought about by acid (pH 1 to 6) shows no simple dependence upon the structure of the ketone.85 It seems that under the experimental conditions the Janowski reaction does not take place.A remarkably stable Meisenheimer complex has been reported from the reaction of 2-phenylbenzopyrylium ions (flavylium ions) and hydrogen sulphite anion.86 In contrast all attempts to obtain a Meisenheimer complex from the interaction of triethylamine or diethylamine with 1,5-dimethyl-2,4,8-trinitronaphthalenein dimethyl sulphoxide-methanol mixtures failed because of the preferential formation of the benzyl ~arbanion,'~ a complication which attended the corresponding process with methoxide ion." After a detailed study of the possible contributions of elec- tron transfer and proton transfer in determining the products of reaction of 77 A. R. Norris Can.J. Chem. 1980 58 2178. E. Buncel M. Hamaguchi and A. R. Norris Can. J. Chem. 1980 58 1609. 79 E. Buncel M. Hamaguchi and A. R. Norris Can. J. Chem. 1980,58,1615. M. E. Moir and A. R. Norris Can. J. Chem. 1980 58 1691. F. Terrier H. A. Sorkhabi F. Millot J. C. Halle and R. Schaal Can. J. Chem. 1980 58 1155. E. Buncel M. Hamaguchi and A. R. Norris J. Chem. SOC., Perkin Trans. 2 1980 2205. 83 R. L. Blakeley and B. Zerner J. Am. Chem. SOC., 1980,102,6586. 84 V. Gold A. Y. Miri and S. R. Robinson J. Chem. SOC.,Perkin Trans. 2 1980,243. R. A. Renfrow M. J. Strauss and F. Terrier J. Org. Chem. 1980,45,471. 86 R. Brouillard and J.-M. el H. Chahine J. Am. Chem. SOC.,1980 102 5375. 87 E. Buckley J. E. Everard and C. H. J. Wells J. Chem. SOC.,Perkin Trans.2 1980 132. 88 S. R. Robinson B. C. Webb and C. H. J. Wells J. Chem. SOC., Perkin Trans. 2 1976 273. 166 R. Bolton p-nitrotoluene with bases the intervention of three anionic species i.e. p-nitrotoluene anion p-nitrotoluene radical anion and the p,p'-dinitrobibenzyl radical anion was deduced. The relative proportions of each depended upon the reaction conditions; mechanisms were produced to explain these SNArand SRNlProcesses.-In the latest of a series of studies seeking to test the applicability of the additivity principle to substituent effects upon the rate of reaction of picryl chloride with aniline good agreement was found with groups meta to the ieaction sitego whereas para-substituted anilines showed much poorer agreement." Miller and Morang2 have reported rates of methanolysis of both picryl chloride and of picryl methyl ether; the product in both cases is picric acid since the ether is unstable to the reaction conditions.Among other reports involving similar systems the formation of products of displacement by nucleophiles from 1,5-dichloroan- thraquinone deserves mention,93 as does the unexpected loss of a nitro-group when p-cresol is caused to react with N-methyl-4-nitrophthalimide (Scheme 4).94 A xo NMe+ 6 ooa:~e i hydrolysis I + / + products O2N / / Me / 0 Me 0 Reagents i K,CO, Me2S0 at 142"C Scheme 4 side-reaction of 3,5-dichloro-2-nitroanisolewith aniline provides both preferential displacement of chlorine that is ortho to the nitro-group (presumably from hydro- gen-bonding as with the orientation of attack of pentafluoronitrobenzene by amines) and hydrolysis of the methoxyl function although in only 6.5% yield (Scheme 5).95 Me0 0N02 xPhNH2 PhNH29at18O0C+ c:o:()2 for 3 h / NHPh C1 / NHPh CI 0n02 Scheme 5 Zoratti and Bunr~ett~~ have identified two mechanisms by which the hydroxy- dehalogenation of p-iodo p -bromo- or p-chloro-toluene may occur in aqueous hydroxide at temperatures as high as 333 "C.In the absence of catalytic quantities of metal ions the same mixture of rn-and p-cresol results from all three substrates suggesting that there are benzyne intermediates whose selectivity towards nucleophiles is the subject of a second paper.97 In the presence of copper ions but not of iron nickel manganese or cadmium a non-aryne type of displacement 89 E.Buncel and B. C. Menon J. Am. Chem. SOC.,1980,102,3499. 90 T.A.Ernokpae 0.Eguavoen and J. Hirst J. Chem. SOC.,Perkin Trans. 2 1980 829. 91 T.A. Emokpae 0.Eguavoen K.-U.-Rahman and J. Hirst J. Chem. SOC.,Perkin Trans. 2 1980,832. 92 J. Miller and P. J. S. Moran J. Chem. Res. 1980,(S)62,(M) 0501. 93 E. H.Ruediger M. L. Kaldas S. S. Gandhi C. Fedryna and M. S. Gibson J. Org. Chem. 1980 45 1974. 94 H. M.Relles D. S. Johnson and B. A. Dellacoletta J. Org. Chem. 1980,45,1374. 95 W.Ried and G. Sell Chem. Ber. 1980,113,2311. 96 M. Zoratti and J. F. Bunnett J. Org. Chem 1980,45 1769. 97 M. Zoratti and J. F. Bunnett J. Org. Chem. 1980 45 1776. Aromatic Compounds 167 occurred in which hydroxydehalogenation gave isomerically pure p -cresol.The function of the copper is still open to discussion; organometallic derivatives were considered though the metal might be acting as a specific solvent of incipient halide ions. The mechanism has presented yet another unusual aspect. Following the observation of unusual kinetic form,98 Bunnett and his school have detected a major effect that has been ascribed to the leaving group and which operates after it has left. The origin of such an effect is the free-radical character of the reaction and the reaction conditions. In a system where electrons are derived by the solution of potassium metal in liquid ammonia an electron gradient can be imagined to be set up between the surface of the metal and the molecules of the attacking aryl halide.Under normal mixing conditions this gradient may well vary in slope owing to changes in the local concentrations of the reacting species. Like a number of free-radical processes the implications are of a diff usion-controlled process in which not only the nature of the aryl halide but also its situation vis-a-vis other possible reagents is supremely important in determining its fate.99"00 The SRNl mechanism has also been used preparatively"' to provide a route to benzofurans. 5 Diazonium Ions The effect of complexation upon the rates of decomposition of aryldiazonium ions has been measured in 1,2-dichloroethane where the greatest stabilization was found with a 2 1-membered macrocyclic polyether system.lo2 A similar technique was used to measure the extent of ion-pairing between ArN2' and its gegen40n.l'~ The degree of association between various diazonium ions and 18-crown-6 has been measured by the calorimetric titration method;lo4 a comparison between results obtained using the two techniques would be a valuable extension.The 4-morpholinobenzenediazonium ion has undergone X-ray crystallographic analy- sis; the distortion of the ring that was found was explained in terms of non-quinonoidal perturbations and it was correlated with SCF cal~ulations.'~~ The reactions of anti-arylazo methyl ethers in methanol which involve ionization are catalysed by acids; the rates of a number of such reactions have been reported and they provide evidence of general acid catalysis.'06 Carbonylation occurs when aryldiazonium tetrafluoroborates are treated with carbon monoxide under slight pressure and in the presence of a palladium(0) catalyst as well as sodium acetate.Mixed anhydrides presumably formed by trapping the acylium ion by acetate anion are thought to be intermediates; the uptake of carbon monoxide has formal equivalence with the exchange of nitrogen with the aryl cation.'" 98 R. G. Scamehorn and J. F. Bunnett J. Org. Chem. 1979,44,2604. 99 R. R. Bard J. F. Bunnett X.Creary and M. J. Tremelling J. Am. Chem. Soc. 1980 102 2652. loo M. J. Tremelling and J. F. Bunnett J. Am. Chem. SOC.,1980 102 7375. 101 R. Beugelmans and H. Ginsburg J. Chem. SOC.,Chem. Commun. 1980 508. lo' R.A. Bartsch and P. N. Juri J. Org. Chem. 1980,45 1011. lo3 P. N. Juri and R. A. Bartsch J. Org. Chem. 1980 45 2028. R. M. Izatt J. D. Lamb C. S. Swain J. J. Christensen and B. L. Haymore J. Am. Chem. SOC.,1980 102,3032. lo' N. W. Alcock T. J. Greenhough D. M. Hirst T. J. Kemp and D. R. Payne J. Chem. SOC.,Perkin Trans.2 1980 8. lo6 T. H. Broxton and A. C. Stray J. Org. Chem. 1980 45 2409. lo' K. Nagira K. Kikukawa F. Wada andT. Matsuda J. Org. Chem. 1980 45 2365. 168 R.Bolton 6 Preparative Aspects Benzene Derivatives.-Elemental fluorination using dilute solutions of the halogen in nitrogen at -78 "C provides monosubstitution products by a process which seems to be electrophilic in character.'08 The preparative fluorination of benzene (61% yield) and of nitrobenzene benzonitrile benzoic acid and acetophenone can be brought about by using silver@) fluoride in n-hexane.The major initial product from benzene is 3,6-difluorocyclohexa-1,4-diene(16),arising from cis-addition across the ring the substitution product presumably arises by thermal decomposi- tion of (16).'09 Little selectivity is observed and all positions are attacked with similar ease in the cases cited. (16) (17) The synthesis of a number of alkyl and benzyl fluorides has been brought about by an application of the susceptibility of pyrylium ions to nucleophilic attack. N-Substituted 2,4,6-triphenylpyridiniumfluorides (17) arising from the reaction of the appropriate primary amine with 2,4,6-triphenylpyrylium fluoride undergo thermal decomposition to provide the appropriate aliphatic fluoride.The quaternary ammonium salt could be obtained in 72-86% yield and in all but one case the yield of benzyl fluoride was in the region of 65% .'lo Direct cyanation of arenes has been reported previously,"' but a recent communi- cation lists conditions in which the substitution is brought about in a plasma that arises from the discharge of a r.f. generator operating at 13.56 MHz. Benzene was found to give benzonitrile in 94%yield (64% based on cyanogen; 45% conversion) with small quantities of the dicyanobenzenes being formed. The process seemed to be only slightly selective; all sites in some monosubstituted benzenes including the ipso-position were attacked with similar facility.In this the process appears to be even less selective in orientation than conventional free-radical substitu- tions. l2 Photoreduction of chlorobenzene chloro-naphthalenes and chloro-biphenyls may be brought about in alkanes. The mechanism is thought to involve homolysis in the triplet state when the energy of this excited state is comparable with that of the C-C1 bond attacked. 113~1 l4 Trifluoromethanesulphonic acid ('triflic acid') has been reported to be an efficient catalyst in the Houben-Hoesch reaction bringing about the ready formation of acylation products from the reaction of nitriles with phenols or phenolic In contrast much of the reactivity of methyl and ethyl triflates under Friedel-Crafts conditions appears to depend upon this acid; the pure esters are rather weak alkylating agents.'16 lo* F.Cacace P. Giacomello and A. R. Wolf J. Am. Chem. Soc. 1980,102,3511. Io9 A. Zweig R. G. Fischer and J. E. Lancaster J. Org. Chem. 1980 45 3597. A. R. Katritzky A. Chermprapai and R. C. Patel J. Chem. Soc. Perkin Trans. 1 1980 2901. 'I1 E. Havinga and J. Cornelius Chem. Reu. 1975,75 353. Y.-H. So and L. L. Miller J. Am. Chem. Soc. 1980,102,7119. N. J. Bunce J. P. Bergsma W. De Graaf Y. Kumar and L. Ravanal J. Org. Chem. 1980,102,3798. K. H. Eichin H.-D. Beckhaus and C. Ruchardt Tetrahedron Lett. 1980,21 269. B. L. Booth and G. F. M. Noori J. Chem. SOC.,Perkin Trans. 1 1980,2894. B. L. Booth R. N. Haszeldine and K. Laali J. Chem. Soc. Perkin Trans. 1 1980 2887. Aromatic Compounds Studies of the alkylation of phenols have been extended through consideration of the conditions needed for cyclization of species such as (18)'17 and by a report of the use of magnesium derivatives to promote high specificity of attack to sites that are ortho to the phenolic group during such cyclizations."* The mechanisms deduced from the experimental evidence are not uniquely demanded by these facts and the complexity of behaviour of a@ -unsaturated ketones during addition reactions may be found to be operating in this instance as well.Metal complexes may also act in a recently reported preparation of salicylaldehydes by the attack of formaldehyde upon phenols in the presence of tin(1v) chloride and a tertiary amine such as tri-n-octylamine. '19 The yields (under favourable conditions) recom- mend this process over most alternatives.(18) (19) A much wider use of metallation is found in the reaction of an excess of n-butyl-lithium with benzyl alcohols in the presence of NNN'N'-tetramethylethyl-enediamine in pentane. The resulting lithium (0-lithio-ary1)methoxides(19) may react with electrophiles including alkylating agents and carbonyl compounds to provide a wide range of ortho-substituted benzyl alcohols.120 The 'anomalous' reactions of benzyl Grignard reagents as exemplified in reaction (3) (which represents the earliest evidence121) have been re-investigated under conditions in which an intermediate (20) can be obtained. This species decomposes to give both the hydrocarbon (21) and the product (22) (Scheme 6).lZ1 PhCH2MgX + HCHO + o-MeC6H4CH20H (3) The preparation of ortho- substituted benzoic acids has been reported using diphenyliodonium-2-carboxylate (23) and specifically copper(I1) as a necessary CH Reagents i HCHO; ii MgCl (22) Scheme 6 '17 W.S. Murphy and S. Wattanasin J. Chem. Soc. Perkin Trans. 1 1980 1555. "IW. S. Murphy and S. Wattanasin J. Chem. Soc. Perkin Trans. I 1980 1567. G. Casiraghi G. Casnati G. Puglia G. Sartori and G. Terenghi J. Chem. SOC.,Perkin Trans. 1 1980,1862. N. Meyer and D. Seebach Chem. Ber. 1980,113,1304. "' C. Bernardon and A. Deberly J. Chem. SOC.,Perkin Trans. 1 1980 2631; cf. M. Tiffeneau and R. Delange C. R. Hebd. Seances Acad. Sci. 1903,137 573 (J. Chem. SOC., 1904 A.i.48). 170 R. Bolton catalyst.The mechanism of the reaction is thought to differ from that found with copper(1) catalysts with a greater specificity in the displacement. Although such a reaction is limited to the insertion of groups through nucleophilic attack it offers a route to a number of anthranilic acid derivatives and hence to the wealth of chemistry that these provide.'22 (23) The preparation of o -alkyl-nitrobenzenes (0-RC6H,N02)through the interaction of nitrobenzene and an excess of Grignard reagent continues to arouse interest. The reaction itself is old but the preparative use of the process relies upon the reali~ation'~~ that oxidation of the reaction mixture with potassium permanganate is necessary if one is to maximize the yield of nitro-arene. Similarly the details have been published of short optimized syntheses by which derivatives of p-resorcylic acid may be prepared by conventional classical A novel synthesis of benzyl ethers and one which may prove to have mechanistic interest involves the sequential treatment of an alcohol with chloro(phenylmethy1- ene)dimethylammonium chloride and sodium hydrogen telluride.The process was applied to the synthesis of 3p-benzyloxycholest-5-ene,but the authors point out that the mild and non-basic conditions (within the limits imposed by HTe-) allow the method to be applied to carbohydrate hemi is try.'^^ Derivatives of 2-aminobenzhydrol may be obtained readily in good yield (70%) and under mild conditions by the attack of benzaldehyde derivatives upon sub- stituted anilines in the presence of phenyldichloroborane and triethylamine as shown in reaction (4).126 Two variants on the classical bromodediazoniation reaction [reaction (5)] have been proposed.In the first,12' the use of tin(I1) or ascorbic acid to reduce copper(I1) in situ has been claimed to improve the yield of aryl bromides that are formed by the Sandmeyer reaction. In the second,'28 two methods for introducing bromine into an aromatic system are combined. Copper(I1) bromide and chloride have been to introduce the appropriate halogen into highly activated systems such as anthracene and the combination of molecular bromine and copper(I1) bromide ''' R. A. Scherrer and H. R. Beatty J. Org. Chem. 1980 45 2127. 123 G. Bartoli M. Bosco and G.Baccolini J. Org. Chem. 1980,45 522. A. G. M. Barrett T. M. Morris and D. H. R. Barton J. Chem. SOC.,Perkin Trans. I 1980 2272. lZ5 A. G. M. Barrett R. W. Read and D. H. R. Barton J. Chem. SOC.,Perkin Trans. 1 1980 2184. 126 T. Toyoda K. Sasakura and T. Sugasawa Tetrahedron Lett. 1980,21 173. lZ7 C. Galli Tetrahedron Lett. 1980,21 4515. M. P. Doyle M. A. van Lente R. Mowat and W. F. Fobare J. Org. Chem. 1980 45 2570. lZ9 W. C. Alcorn F. M. Cromarty J. Flood J. M. Mancilla A. D. Mosnaim D. C. Nonhebel and I. Scullion J. Chem. Res. (S) 1980 102. Aromatic Compounds brings about multiple bromination of aromatic amines at sites that are ortho and para to the nitrogen atom. If this reaction is carried out in a solvent such as carbon tetrachloride then the subsequent addition of t-butyl nitrite to a solution that contains hydrogen bromide allows the amino-group to be replaced by bromine in a formal bromodeamination step.Oxidative bromination and partial demethylation occur when NN-dimethylaniline is subjected to these reaction conditions; when the alkyl nitrite is added nitration products are formed perhaps through a free- radical process. HONO CuBr,HBr ArNH2 +ArNiBr-ArBr (5) Two uses of peroxy-acids are important. The reaction of alkyl-benzenes with trifluoroperoxyacetic acid is reported to give only aliphatic carboxylic acids by ring-opening; no aromatic carboxylic acids arising from oxidation of the side-chain are found.130 The degradation of 'susceptible' aromatic rings such as those contain- ing hydroxyl functions has been long used to prepare such ring-fission products as in the synthesis of benzene derivatives by the oxidation of 2-naphthol but the apparently specific breakdown of an aromatic ring that is without such vulnerable sites is new.The second application of peroxy-acids is in the formation of aromatic nitro-groups by oxidation of amino-systems. Again the method is not new; for example the synthesis of 2,6-dichloronitrobenzeneinvolves such a process.'31 The novelty arises from the use of Caro's acid as a solution of hydrogen peroxide in concentrated sulphuric acid or of the equally powerful peroxytrifluoromethanesul-phonic acid. With such reagents the oxidation of polynitro-aniline derivatives has been achieved in some cases for the first time.I3* p-Diacyl-benzenes are also not readily available.However they may be prepared by the oxidation of their dihydro-derivatives which are formed by the displacement of trimethylsilyl groups from the addition products that are formed in the reaction of trimethylsilyl chloride with either benzene or p-xylene (Scheme 7).133 H. 'SiMe H COR' COR2 Reagents i Me,SiCl; ii R'COCI; iii 0 Scheme 7 Arene-metal complexes have recently featured in a number of synthetic pro- cesses. Thus the treatment of 3-[(2-bromoaryl)amino]cyclohex-2-en-1-ones (24) with a catalytic quantity of a Pd" species brings about intramolecular cyclization to give 1,2-dihydrocarbazol-4(3H)-onesvia aryl-palladium complexe~,'~~ as shown R. Liotta and W. S. Hoff J.Org. Chem. 1980,45 2887. 13' A. S. Pagano and W. D. Emmons Org. Synth. Coll. Vol V (1973) 367 (Wiley New York). 132 A. T. Nielsen R. L. Atkins W. P. Norris C. L. Coon and M. E. Sitzmann J. Org. Chem. 1980,45 2341. M. Laguerre J. Dunogues and R. Calas Tetrahedron Lett. 1980 21 831. 134 H. Iida Y. Yuasa and C. Kibayashi J. Org. Chem. 1980 45 2400. 172 R. Bolton 0 0 N AR1Q-bR' R' / N R' X R2 X R2 (24) Reagents i [Pd(OAc),(PPh,),] NaHCO, DMF Scheme 8 in Scheme 8. Arene-metal complexes are also highly activated towards nucleophilic attack whether at the ring or at a suitable site in the side-chain and the ease with which the carbon-metal bond may subsequently be broken allows groups such as -Cr(C0)3 to act as removable activating groups bringing about processes which would otherwise be difficult.Thus a synthesis of acorenone and of acorenone B has as its first stage the attack of a cyanhydrin acetal anion upon o-methylanisole that is complexed to chromium; the effect is the nucleophilic displacement of hydrogen by ultimately an acyl group (Scheme 9).13' Similarly activation of CN i/ iii-vi f--Meq 0 I CN Reagents i [Cr(CO),l; ii Li OAOA ;iii LiNR,; iv CF,SO,H; v NH3 H,O; vi H' H,O Scheme 9 styrene-like double-bonds may be achieved. 136 A preparation of 3-methoxyphthalic anhydride which is required in the synthesis of hydroxy-polyannular systems for work on carcinogenicity has been rep~rted.'~' It relies upon a Diels-Alder process [reaction (6)] with the advantage of an improved yield and minimal losses of the sort that occur in a more conventional route because of the appreciable solubility of the acid and its precursors in water.M. F. Semmelhack and A. Yamashita J. Am. Chem. SOC.,1980,102 5924. 136 M. F. Semmelhack W. Seufert and L. Keller J. Am. Chem. SOC.,1980 102,6584. 13' M. S. Newman and K.Kanakarajan J. Org Chem. 1980,45 3523. Aromatic Compounds OMe OMe qo2Et+ 0 Oc0."' 173 15O-20O0C+ [-C,H,;86%1 /C0,Et C02Et Polybenzenoid Systems.-Oxidative coupling of benzene derivatives that contain electron-withdrawing groups or those which only slightly withdraw electrons (but not -NO2 or -COX) is brought about by thallium(II1) trifluoroacetate in trifluoroacetic acid or in carbon tetrachloride or in acetonitrile that contains boron trifluoride etherate.The process seems to involve aryl cations from heterolysis of the thalliation product; these attack a second molecule of arene to give an intermedi- ate whose oxidation is achieved by Tl"'.'38 Unsymmetrical biaryls are formed when species such as (P-RC~H~)P~(OAC)~ decompose in arenes in the presence of trifluoroacetic acid.139 The reaction is speeded by aluminium(II1) salts but no rearrangement occurs even when alkyl groups are present. The substitution appears to have electrophilic requirements but does not involve the free carbo-cation p-RC,H,'; it has been suggested14' that the slow stage of the reaction involves the formation of a .rr-complex between the reagent and the arene without the fission of the C-Pb bond.Derivatives of naphthalene and of biphenyl can be obtained by the reaction of NN-dimethylformamide dimethyl acetal with 1-aryl-3-alkyl- or -aryl-propan-2- ones. Thus 1,3-diphenylpropanone gives NN-dimethyl-3-phenylnaphthalene-l-carboxamide (25) (Scheme 10) on heating with the acetal in an autoclave. Similarly CONMe Me,NCH(OMek za Z\ / /Ph (25) a; Z = H b; Z = CF3 c;z = c1 Scheme 10 1-(m-trifluoromethylphenyl)-3-phenylpropanonegives only (25b) but 1-(m -chlorophenyl)-3-phenylpropanone gives not only (2%) and the 5-chloro-isomer but also NN-dimethyl-3-(m-chlorophenyl)naphthalene-l-carboxamide. The pro- posed mechanism was justified by experiments using 13C labelling.'41*'42 A key step in the synthesis of 3,4-dihydro-2( 1H)-fluorenones and hence of the gibberellin ~keleton,'~~ rests upon the Birch reduction (using Li and NH3) of 2,5-dimethoxyben- zoic acid and the subsequent alkylation of the dianion by benzyl halide in situ.Fluorenone-1 -carboxylic acid (26) has been found to bring about transamination of amino-acids (as o-formylbenzoic acid but it has the two advantages 13' A. McKillop A. G. Turrell D. W. Young and E. C. Taylor J. Am. Chem. Soc. 1980 102,6504. 139 H. C.Bell J. R. Kalman J. T. Pinhey and S. Sternhell Tetrahedron Lett. 1974 857. H. C.Bell J. R. Kalrnan G. L. May J. T. Pinhey and S. Sternhell Aust. J. Chem. 1979 32 1531. 14' R.F.Abdulla T. L. Ernrnick and H. M. Taylor Synth. Commun. 1977,7 305;R.F.Abdulla K. H. Fuhr and H.M. Taylor ibid. 1977,7 313. 14' R.F. Abdulla K. H. Fuhr R. P. Gajewski R. G. Suhr H. M. Taylor and P. L. Unger J. Org. Chem. 1980,45,1724. 143 J. M. Hook and L. N. Mander J. Org. Chem. 1980,45 1722. 144 C.A. Panetta and A. L. Miller J. Org. Chem. 1978.43 2113. 174 R. Bolton (i) that its synthesis is easy and and (ii) that primary aliphatic amines also undergo transamination with the new reagent. The mechanism of the process however probably differs fundamentally from that achieved under enzyme con- ditions. 146 Anthracene precursors have been made by Diels-Alder addition of benzyne to diene systems such as furans and carbazoles. Initially14' the bis-aryne which is the formal intermediate was generated by the decomposition of organometallic com- pounds in which fluorine was adjacent to the metal and was expelled with it; conditions have now been reported where the much more readily obtained tetra- bromides (27b) are used su~cessfully.'~~ The greater availability of these starting materials now makes this synthetic route more attractive.Me (27) a;Z = F b;Z = Br Carcinogenic Hydrocarbons.-The mechanism of carcinogenic action of hydrocar- bons has attracted interest; the reactivity towards chemicals is compared to that as a mutagen. Access to the great collection of Professor E. Clar has allowed a wide range of hydrocarbons to be studied in an attempt to parallel the reactivity towards maleic anhydride with either theoretical measures of reactivity or with carcinogenic activity.149 Another set of investigation^,'^^ also dedicated towards comparison between theory and experiment took the hydrogenation of such poly- benzenoid systems as their type reaction.In both cases acceptable parallels were found. The application of partial hydrogenation of multi-ring aromatic systems has already been reported as a potent means of directing orientation of attack towards unusual sites; the synthesis of derivatives of dibenz[a,h]anthracene which were held to be the ultimate metabolites (for a review see ref. 151)of this hydrocarbon was achieved by first preparing 1,4,7,8,11,14-hexahydrodibenz[a,h]anthraceneby reduction with lithium in liquid amm~nia."~ Specifically labelled systems show the course of metabolism of such hydrocarbons.The synthesis of deuterium-labelled derivatives of 7,12-dimethylbenz[a]anthracene(28) has been brought about by the 14' 14' Me (28) 145 L. F. Fieser and A. M. Seligman J. Am. Chem. SOC., 1935 57,2174. 146 C. A.Panetta and A. S. Dixit J. Org. Chem. 1980,45,4503. G. Wittig and H. Harle Liebigs Ann. Chem. 1959 623 17. H. Hart C. Lai G. Nwokogu S. Shamouilian A. Teuerstein and C. Zlotogorski J. Am. Chem. SOC. 1980,102,6649. 149 D. Bierman and W. Schmidt J. Am. Chem. Suc. 1980,102,3163. P. P.Fu H. M. Lee and R. G. Harvey J. Org. Chem. 1980 45 2797. 15' D. E.Hathway and G. Kolar Chem. SOC.Reu. 1980 9,241. Is* H.M.Lee and R. G. Harvey J. Org. Chem. 1980,45,588. Aromatic Compounds hydrogenolysis of the appropriate bromo-arene.However although complete incor- poration of deuterium could be brought about by lithium aluminium deuteride when halogen in the side-chain was displaced the corresponding displacement of bromine from ring positions did not give 100°/~ labelling with deuterium unless both the reagent and the water that was used to quench the reaction were fully labelled.” The synthesis of 8-and of 1l-methoxy-7,12-dimethylbenz[a]anthracenesled to the preparation of the corresponding hydroxy-derivatives; the starting materials however were obtained by the reduction of the diols that were formed by organometallic attack upon the corresponding 7,12-dione. In this process it was noticed that the reducing agent seemed to be an organotin species when tin(I1) and hydrochloric acid were used and not a free carbo-cati~n.’~~ The reductive methyl- ation of polycyclic quinones a process that is used extensively in the synthetic chemistry of Fieser (e.g.see ref. 155) and of Newrnanls4 has been re-introduced as a route to obtaining polymethyl-polybenzenoidsystems. Organolithium com- pounds have replaced the Grignard reagents with an attendant increase in the observed yields and a diminished sensitivity to steric effects.ls6 The preparation of 8- and of l0-fluoro-3-methylcholanthrenesby the Elbs reaction has been repor- ted,lS7 together with the observation that the process fails to provide the 11-and 12-fluoro-analogues. The somewhat uneven success which has attended the use of this reaction to prepare the corresponding methoxy-derivatives suggests that its application is limited; no reasons are immediately available.The one-pot synthesis of polycyclic aromatic quinones reported by Manning in 1977 has been improved by using photochemical and not thermal conditions for the addition of quinones to the 1,l-diaryl-ethylenes. A range of polybenzenoid systems are therefore avail- able in principle and the subsequent use of photochemical annelation with iodine present to oxidize the initially formed dihydro-arene generates even larger systems. Thus 5-(2-naphthyl)benzo[b]chrysene-9,14-dione(29) itself generated by the reaction of 2-bromo-3-methoxy-l,4-naphthoquinoneand 1-(l-naphthyl)-l-(2-naphthyl)ethylene provides the quinone (30) which on reduction gives dinaphtho[l,2-c :2,3-e]pyrene (Scheme 11).lS8Kaupp and his co-workers have undertaken further studies into the diene-addition reactions of anthra~ene’~~”~~ and 9-phenylanthra~ene’~~ and of dibenz[a,c]- and dibenz[~,h]-anthracene,’~~ which are processes of some synthetic importance.The chemistry of 1,g-diphenylanthracene including an improved synthesis of the parent hydrocarbon has been described.16* Considerable differences in the steric environments of the 9-and 10-positions are reflected in the considerable differences in their chemistry. Thus reduction of 1,8-diphenylanthraquinonegives 153 S. R. Adapa Y. M. Sheikh R. W. Hart and D. T. Witiak J. Org. Chem. 1980 45 3343. M. S. Newman and K. Kanakarajan J. Org. Chem. 1980,45,2301. ”’ R. B. Sandin and L.F. Fieser J. Am. Chem. SOC.,1940,62 3098. lS6 M.Konieczny and R. G. Harvey J. Org. Chem. 1980,45 1308. lS7 M.S.Newman and V. K. Khanna J. Org. Chem. 1980,454507. 15’ K.Maruyama T. Otsuki and K. Mitsui J. Org. Chem. 1980,45,1424;W. B. Manning J. E. Tornaszewski G. M. Mushik and R. I. Sato ibid. 1977 42 3465. lS9 G. Kaupp and H.-W. Griiter Chem. Ber. 1980,113 1458. G. Kaupp and E. Teufel Chem. Ber. 1980 113 3669. G.Kaupp and H.-W. Gruter Chem. Ber. 1980,113 1626. H.0.House N. I. Ghali J. L. Haack and D. Van Derveer J. Org. Chem. 1980,45 1807. 176 R. Bolton I + + mBr \ ' 0 'OMe ZCH2 0 / Reagents i hv;ii I, hv; iii LiAlH Scheme 11 only the 9-anthrone in which the carbonyl group is flanked by the two aryl systems and only some organometallic reagents were able to react with this shielded ketone function.An addition reaction between 10-diazoanthrone or 4-diazonaphthalene- 1(4H)-one and benzyne or 1,2-naphthyne gives indazole derivatives which upon thermo- lysis provide hydroxy-derivatives of considerably complex systems such as fluoran- thene benz[a]aceanthrylene and naphth[2,1 -~]aceanthrylene.~~~ The synthesis and determination of the absolute stereochemistries of (+)-and (-)-benzo[a]pyrene 7,8-oxides have been achieved starting from the separated diastereoisomers of frans-8-bromo-7-(menthyloxy)acetoxy-7,8,9,lO-tetrahydro-benz[a]pyrene; the (+)-isomer of this bromo-ester was shown by X-ray analysis to have the absolute stereochemistry (7S,8S) and this in turn correlates the stereochemistry of a number of mammalian metab01ites.l~~ Quinones have been used as routes to a number of systems.Thus hydroquinone monomethyl ethers or substituted benzofurans may be formed in a Michael reaction involving either diethyl malonate or ethyl a~etoacetate;'~~ allylation of quinones by allyltin species in the presence of Lewis acids such as BF3 is a synthetically useful (72-'78O/0 yield) route to various vitamin and coenzyme struc- tures.166 K. Hirakawa T. Toki K. Yamazaki and S. Nakazawa J. Chem. SOC.,Perkin Trans. 1 1980 1944. 164 D.R.Boyd G. S. Gadaginamath A. Kher J. F. Malone H. Yagi and D. M. Jerina J. Chem. SOC. Perkin Trans. 1 1980 2112. 165 K.A. Parker and S.-K.Kang J. Org. Chem. 1980,45 1218. 166 Y. Naruta J. Am.Chem. SOC.,1980,102,3774. Aroma tic Compounds The electrophilic substitution reactions of 4H-cyclopenta[deflphenanthrenehave been studied further ;167 more modern analytical techniques have shown acylation to be a more complex process than the earlier reports suggested.168 The correspond- ing 8,g-dione (31) has also been studied; many of its reactions are predictable by analogy with fluorene on the one hand or with phenanthraquinone on the The possible ring-contraction reaction to give the dibenzopentalene structures does not seem to have been attempted. (31) The ozonolysis of 1,2-dichloroacenaphthylenegives two stable ozone adducts whose chemistry has not yet been fully studied. These results when the identity of the adducts are fully known may be important to the mechanism of ozoniz- ation.17' Photochemical Processes.-Photochemical reactions of benzene with furanl'l and with 1,2- 1,3- and 1,4-dienes have been reported,17* and a review of photochemical rearrangements has appeared.173 The photo-induced decomposition of peroxyacetic acid in xylenes has demonstrated an orientational preference in the attack by hydroxyl radicals which show the electrophilic properties previously found (e.g.see ref. 46) but the orientation of attack of xylenes by methyl radicals appears to be determined by the wavelength of the light that causes photolysis of the peroxy- As light of higher energy causes a preference for rnetu-alkylation the facts are reminiscent of the competition between thermodynamic and kinetic control in the heterolytic alkylation mechanism and may admit of a similar explanation.The photochemical reactions of pyridine and of 2-fluoropyridine with aliphatic amines include nucleophilic displacement in the case of the fluoropyridine but unusual compounds are formed with triethylamine including not only the dealkyla- tion product but also a second species whose identity has been discussed in terms of previously proposed mechanisms. 17' Photoresponsive crown ethers have been studied using the cis-trans isomerization of azobenzene as the test process.176 Sensitized fluorescence of 9,lO-dibromoanthracene has been the subject of some kinetic M. Yoshida K. Hishida M. Minabe and K. Suzuki J. Org. Chem. 1980,45,1783. 16' W. E. Bachman and J.C. Sheehan J. Am. Chem. SOC.,1941,63,2598. 169 M. Yoshida A. Kadokura M. Minabe and K. Suzuki Bull. Chem. SOC.Jpn. 1980,53 1179. 170 H. Seltzer S. Gab and F. Korte Angew. Chem. Int. Ed. Engl. 1980.19,474. 171 J. C. Berridge A. Gilbert and G. N. Taylor J. Chem. SOC.,Perkin Trans. 1 1980 2174. 172 J. C.Berridge J. Forrester B. E. Foulger and A. Gilbert J. Chem. SOC.,Perkin Trans. 1 1980 2425. 173 G. Kaupp Angew. Chem. Int. Ed. Engl. 1980,19,243. 174 Y. Ogata and K. Tomizawa J. Org. Chem. 1980,45,785. '" A.Gilbert and S. Krestonosich J. Chem. SOC.,Perkin Trans. 1 1980 2531. 176 S.Shinkai T. Nakaji Y. Nishida T. Ogawa and 0.Manabe J. Am. Chem. SOC.,1980,102,5860. 177 T.Wilson and A. M. Halpern J. Am. Chem. SOC.,1980,102,7272,7279. 178 R.Bolton Polyhalogeno-aromatic Chemistry.-The cycloaddition reactions of polyfluoro- derivatives of Dewarthiophen and pyrroles have been re~0rted.I~~ Decafluoro-fluoranthene is reported to be formed along with the more expected of its nucleo- philic reactions;179 a similar study has been made of the reactions of heptafluoro- 2-naphthyl-lithi~m.'~' Kinetic measurements of the nucleophilic attack of polyfluoro-arenes have been continued,181 and they have somewhat extended the previous reports of the series. Some of the most impressive chemistry of the octafluorofluorene system is attributable to the effect of the fluorine substituents which stabilize the fluorene anion and its analogues considerably.'** Polychloro-aromatic chemistry is represented by some carefully described work on the coupling reactions by which copper brings about the formation of biar~1s.I~~ Y.Kobayashi A. Ando K. Kawada A. Ohsawa and I. Kumadaki J. Org. Chem. 1980 45 2962; Y. Kobayashi A. Ando K. Kawada and I. Kumadaki ibid. pp. 2966,2968. J. Burdon H. S. Gill I. W. Parsons and J. C. Tatlow J. Chem. Soc. Perkin Trans. 1 1980 1726. J. Burdon H. S. Gill and I. W. Parsons J. Chem. Soc. Perkin Trans. 1 1980 2494. R. D. Chambers D. Close and D. L. H. Williams J. Chem. Soc. Perkin Trans.2 1980,778. R. Filler A. E. Fiebig and M. Y. Pelister J. Org. Chem. 1980,45 1290. A. G. Mack H. Suschitzky and B. J. Wakefield J. Chem. SOC.,Perkin Trans. 1 1980 1682.