10 Aromatic Compounds By H. HEANEY Department of Chemistry The University of Technology Loughborough Leicestershire LE11 3TU General.-Predictions that the nuclear polarisation found in cage recombination products from radical pairs will depend upon the multiplicity of the electronic state have been verified for the reaction system benzoyl peroxide in carbon tetrachloride. A warning has been given concerning the interpretation of CIDNP effects as involving major pathways in all cases2 In spite of this these effects are taken as good evidence for the intervention of caged radical species3 The first reported observation of a I9F n.m.r. CIDNP effect was noted in the reaction of p-fluorobenzyl chloride with n-b~tyl-lithium.~’ The detection of hindered rotation and inversion by n.m.r.spectroscopy has been re~iewed.~ Barriers to rotation and nitrogen inversion have been studied for example in the case of tetraben~ylhydrazine.~ Relatively slow inversion at nitrogen has been observed by variable-temperature n.m.r. studies on (1;X = C1 or F).6 The major invertomer is the one shown; this effect may result from Me ON A x N x& X\ X\ X A intramolecular charge-transfer from the lone pair to the halogenated-arene residue. The Report last year’ mentioned the barrier to rotation in p-nitroso- NN-dimethylaniline. Further results have been presented which show that the barrier is markedly dependent on the nature of the para-substituent and a Hammett correlation gives AGS (at 133 K) = 5.1 (k1.0) kcal mol- for rotation ’ R.Kaptein J. A. den Hollander D. Antheunis and L. J. Oosterhoff Chem. Comm. 1970 1687. J. Jacobus Chem. Comm. 1970 709. (a) R. W. Jemison S. Mageswaran W. D. Ollis S. E. Potter A. J. Pretty I. 0. Sutherland and Y. Thebtaranonth Chem. Comm. 1970 1201; (b) J. W. Rakshys ihid. p. 578; (c)G. Ostermann and U. Schollkopf Annalen 1970,737 170. H. Kessler Angew. Chem. Internat. Edn. 1970 9 219. M. J. S. Dewar and W. B. Jennings Tetrahedron Letters 1970 339. ‘ G. W. Gribble N. R. Easton and J. T. Eaton Tetrahedron Letters 1970 1075. ’ Ann. Reports (B) 1969 66 324. 328 H. Heaney in NN-dimethylaniline.8 Good agreement with racemisation data has been observed for the activation parameters for rotation of the phenyl groups in 2,4,2',4-tetra-t-butyl-6,6'-dimethyldiphenylaceticacid by n.m.r.spectros~opy.~ The mechanism of enantiomer and diastereomer interconversion in triaryl- methyl cations has been studied using a m-difluoromethyl group as a diastereo- topic probe. The results obtained support the view that the trityl propeller conformation interconverts via a two-ring flip transition state.' The full paper describing the conformational changes in trisalicylides has appeared.' ' A number of other studies' report the results of variable-temperature n.m.r. studies and these include'2f interconversions between various folded and twisted conformations in bisfluorenylidenes (2). The remarkably low energy barrier to rotation about the formal C=C double bond may well be encouraged by ground-state strain and a transition state of high stability.Large positive nuclear Overhauser effects have been observed between 'H and 19F in a number of fluoro-aromatic compounds for example l-fluoro- naphthalene. l3 Whereas the methyl resonance in 1-fluoro-8-methylbiphenylene is a singlet the methyl resonance in 1-fluoro-8-methylfluorene (3) is a doublet I6JHF)= 8.3 Hz.14 This together with other values has been quoted as further evidence in favour of a through-space mechanism for the transmission of certain spin-spin interactions. Homoaromaticity. The extraction of the hydrocarbon (4) into a superacid medium at ca. -128 "C gave the 1,4-bishomotropylium ion (5).15 The n.m.r. spectrum remained unchanged up to +20 "C,and when the solution was quenched with * R.K. Mackenzie and D. D. MacNicol Chem. Comm. 1970 1299. 0.S. Akkerman Rec. Trau. chim. 1970 89 673. lo J. W. Rakshys S. V. McKinley and H. H. Freedman J. Amer. Chem. SOC. 1970 92 3518. A. P. Downing W. D. Ollis and 1. 0.Sutherland J. Chem. SOC.(B) 1970,24. l2 (a)C. H. Bushweller M. Sharpe and S. J. Weininger Tetrahedron Letters 1970 453; (b)G. Montando S. Caccamese P. Finocchiaro and F. Bottino ibid. p. 877; (c) R. E. Carter and J. Mhrton Actu Chem. Scund. 1970 24 195; (6)H. 0. House. W. J. Campbell and M. Gall J. Org. Chem. 1970 35 1815; (e) M. Nbgradi W. D. Ollis and I. 0. Sutherland Chem. Comm. 1970 158; cf) I. R. Gault W. D. Ollis and I. 0.Sutherland ibid. p. 269. l3 R. A. Bell and J. K. Saunders Chem.Comm. 1970 1078. l4 G. W. Gribble and J. R. Douglas J. Amer. Chem. SOC.,1970,92 5765. Is G. Schroder U. Prange N. S. Bowman and J. F. M. Oth Tetrahedron Letters 1970 3251; M. Roberts H. Hamberger and S. Winstein J. Amer. Chem. SOC. 1970 92 6346. Aromatic Compounds 329 sodium methoxide in methanol the compound (6) was isolated. The n.m.r. spectrum of the monohomotropylium ion (7) determined at 251 MHz has been interpreted in terms of a model in which the planar C(3)-C(4)<(5) segment is 8 (4) (5) (6) (7) slightly tilted (in the direction towards C(*Jwith respect to the plane formed by C(1)-C(2)-H(2).16 An improvement in the synthesis of 2,3-homotropone1' derivatives has been achieved by the reaction of tropone with sulphonium ylides.I8 Thus the ylide (8) affords (9)in 75% yield.The n.m.r. spectrum of (9) in deuterio- sulphuric acid shows the expected chemical shift differences associated with the ion (10). The isolation of homotropylium metal carbonyl salts (12; M = Cr Mo or W) has been reported. 19 The new synthesis involves the abstraction of hydride ion by the triphenylmethyl cation from cyclo-octatriene complexes (1 1 ;M = Cr Mo or W). The existence of a bishomoindenyl anion (14)has been suggested in order to account for the kinetics of deprotonation of (13)." Apparently the fused benzene ring provides about 0-8 times the assistance of a double bond in the carbanion series compared with a value of about 0.5 in the cation series. The protonation of the non-classical anion (15) can be achieved stereoselectively.2 Dimethyl l6 P.Warner D. L. Harris C. H. Bradley and S. Winstein Tetrahedron Letters 1970 4013. Ann. Reports 1963 60,351. l8 Y.Sugimura and N. Soma Tetrahedron Letters 1970 1721. '' R. Aumann and S. Winstein Tetrahedron Letters 1970 903. J. W. Rosenthal and S. Winstein Tetrahedron Letters 1970 2683. I' J. M. Brown and E. N. Cain J. Amer. Chem. SOC.,1970,92 3821. 330 H. Heaney sulphoxide approaches almost exclusively from the exo-face whereas when using methanol approach is from the endo-face. Benzene and Derivatives.-The following topics have been reviewed syntheses of aromatic compounds,22 the methods of synthesis and reactions of benzo-cy~lobutene,~~ n-complexes as intermediates in reaction^,,^ and the distortions of the Ir-electron system in substituted benzene^.,^ The use of the phenacyl group for protecting phenols and acids has been reported.26 Phenacylsulphonylation provides a new method for the protection of amine~.~~ Both of these protecting groups may be removed easily with zinc and acetic acid at room temperature.In the case of the reaction with primary amines the products can be alkylated efficiently and hence this also affords a new approach to the preparation of secondary amines. The cleavage of the aryl-tin bond in aryltrimethylstannanes by nitrosyl chloride provides a new route to aryl-nitroso-compounds.28NN-Dideuterioanilines and 0-deuteriophenols with a high isotopic purity have been prepared by the cleavage of the appropriate trimethylsilyl derivatives with O-deuteri~methanol.~~ Electrophiles attack benzoquinuclidine (16) at position 7to afford for example (17; Y = NO or S02Cl).30 The difference from the normal reactions of NN-dialkylanilines results from the lone pair of electrons on nitrogen in (16) being orthogonal to the n-electron system.Hydrogen bromide acts as a catalyst in the isomerisation and disproportionation of p-bromophenol~.~ No rn-bromo-phenols were detected but the resultant mixtures contained large proportions of o-bromophenols. The analogous chloro-compounds do not undergo this type of reaction under similar conditions. The mechanism of this reaction probably involves slow debromination and concurrent rapid rebromination. The reaction represents a useful method of preparing certain o-bromophenols.The displace- ment of a t-butyl group by an attacking electrophile has been noted on many occasions. However in the reaction of 1,3,5-tri-t-butylbenzenewith phosphorus 22 J. W. Barton in ‘Modern Reactions in Organic Synthesis’ ed. C. J. Timmons Van Nostrand Reinhold London 1970 p. 240. 23 I. L. Klundt Chern. Rev. 1970,70,471. 24 D. V. Banthorpe Chem. Rev. 1970,70,295. 25 A. R. Katritzky and R. D. Topsom Angew. Chem. Internat. Edn. 1970,9 87. 26 J. B. Hendrickson and C. Kandall Tetrahedron Letters 1970 343. 2’ J. B. Hendrickson and R. Bergeron Tetrahedron Letters 1970 345. 28 E. H.Bartlett C. Eaborn and D. R. M. Walton J. Chem. SOC.(C),1970 1717. 29 A. R. Bassindale C. Eaborn and D. R. M.Walton J. Chem. SOC.(C),1970 1577. 30 R. P. Duke R. A. Y. Jones A. R. Katritzky E. E. Mikhlina A. D. Yanina L. M. Alekseeva K. F. Turchin Yu. N. Sheinker and L. N. Yakhontov Tetrahedron Letters 1970 1809. 3’ E. J. O’Bara R. B. Balsley and I. Starer J. Org. Chem. 1970,35 16. Aromatic Compounds 331 trichloride in the presence of aluminium chloride the displaced group is trapped intramolecularly with the formation after hydrolysis of (18).32 The boron- trifluoride-catalysed ethylation of benzene has been studied using [2-'4C]ethyl fluoride.33 The electrophile involved is an ethyl carbonium ion in a non-polar (18) solvent or an unionised complex in a basic organic solvent. The trichloro- methylation of 2-substituted-l,3,5-trimethylbenzenesby carbon tetrachloride in the presence of aluminium chloride followed by methanolysis affords sub- stituted methyl benzoates in high yield.Rearrangement products were obtained in addition to the expected products when the 2-substituent was hal~gen.~" The rearrangement was accounted for in terms of electrophilic attack at the 5-position by the trichloromethyl carbonium ion (or its equivalent) followed by a 1,2-methyl shift. Thus for example (19)gave (20)and (21) in 70 "/ and 30% yield respectively. Evidence has been presented which supports the view that aluminium-chloride-catalysed Diels-Alder reactions proceed via zwitterionic intermediates. Thus the compound (22) gives rise to a mixture of cis-and trans-isomers of both (23) and (24).35 The isolation of stable adducts in the acetoxylation of aromatic hydrocarbons by nitric acid in acetic anhydride36 lends support to the view3' that an addition- (24) (25) (26) 32 M.Yoshifuji I. Fujishirna R. Okazaki and N. Inamoto Chem. andInd. 1970 625. 33 A. Natsubori and R. Nakane J. Org. Chem. 1970 35 3372. '' H. Hart and J. F. Janssen J. Qrg. Chem. 1970 35 3637. 35 H. W. Thompson and D. G. Melillo J. Amer. Chem. SOC.,1970,92 3218. 36 D. J. Blackstock A Fischer K. E. Richards J. Vaughan and G. J. Wright Chem. Comm. 1970 641; D. J. Blackstock J. R. Cretney A. Fischer M. P. Hartshorn K. E. Richards J. Vaughan and G.J. Wright Tetrahedron Letters 1970 2793. 37 P. B. D. de la Mare and R. Koenigsberger J. Chem. Soc. 1964 5327. 332 H. Heaney elimination mechanism operates.p-Xylene affords a pair of cis-(25) and trans-(26)isomers both ofwhich give aryl acetates on decomposition even in propionic acid. This suggests that the breakdown involves an intramolecular 1,2-shift. Some aspects of the use of thallium and its salts in organic synthesis have been reviewed.38 The control over ortho-substitution previously reported in the thallation of benzoic acid by thallium(rI1) trifluoroacetate also operates with methyl benzoate benzyl alcohol and benzyl methyl ether.39 These results indicate the intermediacy of an electrophile-substrate complex. A number of aldehydes have been prepared by the reaction of an olefin with thallium(II1) nitrate in a nucleophilic solvent.40 P-Methylstyrene for example gave phenylace- tone in 81 "/ yield.The oxidation of 4-methoxychalcone (27) with methanolic thallium(m) acetate gives 3,3-dimet hox y-2-p-met hoxyphenyl- 1 -phenylpropan- 1 -one (28).41 I4C-Labelling experiments have shown that the reaction involves a 1,2-aryl migration in contrast to the 1,Zaroyl migration which occurs with chalcone ep~xides.~~ The oxidation of chalcones with thallium(I1r) nitrate in an aqueous acid-glyme system results in the formation of benzil~.~~ Trans-thallation reactions have been studied using phenylthallium(I1r) bis(trifluor0- acetate) and an excess of substituted arene.44 Me Me Ph,Cr 3THF (29) Me (32) The reaction of triphenyltris(tetrahydrofuran)chromium(m) with but-2-yne yields inter alia 1,2,3,4tetramethylnaphthalene.Labelling and kinetic isotope experiments exclude certain mechanisms and suggested the mechanism shown 38 E. C. Taylor and A. McKillop Accounts Chem. Res. 1970,3,338. 39 E. C. Taylor F. Kienzle R. L. Robey and A. McKillop J. Amer. Chem. SOC.,1970 92 2175. 40 A. McKillop J. D. Hunt E. C. Taylor and F. Kienzle Tetrahedron Letters 1970 5275. " W. D. Ollis K. L. Ormand and I. 0.Sutherland J. Chem. SOC.(C),1970 119. 42 Ann. Reports 1956 53 144. 43 A. McKillop B. P. Swann and E. C. Taylor Tetrahedron Letters 1970 5281. 44 A. V. Huygens J. Wolters and E. C. Kooyman Tetrahedron Letters 1970 3341. Aromatic Compounds [(29) +(32)].45 Positional isomers (33) and (34) have been isolated from the product of the irradiation of 3,a-dimethylstyrene in the presence of penta- ~arbonyliron.~~ Intramolecular aromatic substitution in transition-metal com- plexes has been reviewed.47 Me WCO) (co)3Fewe Me (CQ FeDMe (33) (34) Fe(CO) Interest in the reactions of aryl-lithium reagents continues.o-Nitrophenyl-lithium is unstable at temperatures above ca. -100"C and forms an unstable dimer possibly (39 which on oxidation with methyl chloroformate yields 2,2'-dinitr0biphenyl.~' The reaction of pentachlorophenyl-lithium with aromatic nitriles has been shown to be re~ersible.~' Thus the ketimine (36)when converted into its lithio-derivative was shown to give rise to p-tolunitrile and pentachloro- phenyl-lithium. Me (35) a~c1 CI (36) The system ethylene-palladium chloride-silver nitrate has been shown to be very efficient in promoting the oxidative coupling of aromatic compounds to biaryl~.~' The autoxidation of 4-alkyl-2,6-di-t-butylphenols is catalysed by the cobalt complex (37) and results in the formation of cyclohexadienones (38) in (37) (38) 45 G.M. Whitesides and W. J. Ehmann J. Amer. Chem. Soc. 1970,92 5625. 46 R. Victor R. Ben-Shoshan and S. Sarel Chem. Comm. 1970 1680. 47 G. W. Parshall Accounts Chem. Res. 1970 3 139. 48 P. Buck R. Gleiter and G. Kobrich Chem. Ber. 1970 103 1431. 49 D. J. Berry and B. J. Wakefield J. Organometallic Chem. 1970 23 1. Y. Fujiwara I. Moritani K. Ikegami R. Tanaka and S. Teranishi Bull. Chem. Soc. Japan 1970,43 863. 334 H. Heaney high yield via the corresponding hydroperoxides.’ On the other hand the oxidation of 2,4-di-t-butylphenol by the system oxygenxuprous chloride- morpholine gave (39).52 k % 0 0 I‘ 0 0 -N.-Y n 1 U HH‘ u nHH 11 --(40) (41) (42) Reduction of the quinone epoxide (40) with sodium borohydride leads to the naturally occurring dihydroquinone epoxide ( & )-terremutin (41) and its C-4 epimer (42).53 N.m.r. data for both compounds show that the original assign- ment of stereochemistry was incorrect. 2,5-Diazido-3,6-di-t-butyl-1,4-benzo-quinone (43) undergoes very ready thermal cleavage to give the surprisingly stable yet very reactive keten (45),presumably by way of (44).54 Evidence for the intermediacy of p-quinone methides in the oxidation of phenols has involved trapping the reactive species.’ ’ Thus when 2,6-di-t-butyl-p-cresol was oxidised c”’o $c=o N2 -N + N 2-NyJfqvP NC (451 0 CH(0Me) 0 (46) (43) (44) with manganese dioxide in methanol the acetal(46) was is~lated.~’’ The possi- bility that differing acid-catalysed rearrangements of cyclohexa-2,4-dienones proceed through either n-or z-protonated ketones has been suggested in order to account for the large number of reaction types found.56 The dienone (47) rearranges slowly in the presence of acid solely to (48) possibly via the z-pro- tonated species while (49) rearranges more rapidly to (50),possibly uia the n-pro- tonated species.Deuterium-labelling experiments show that the rate-deter- mining step in the dienone-phenol rearrangement of 4,4-dimethylcyclohexa-dienone involves the methyl migration to (51) and not the subsequent deproto- nation.”” The acidity dependence of the activity coefficient ratio fss+/ft 51 T.Matsuura K. Watanabe and A. Nishinaga Chem. Comm. 1970 163. 5z D. G. Hewitt Chem. Comm. 1970,227. 53 G. Read and V. M. Ruiz J. Chem. SOC.(C) 1970 1945. ” H. W. Moore and W. Weyler J. Amer. Chem. SOC.,1970,92,4132. 55 (a)J. W. A. Findlay and A. B. Turner Chem. and Znd. 1970 158; (b) C. M. Orlando J. Org. Chem. 1970 35 3714. ’’ B. Miller J. Amer. Chem. Sac. 1970 92 432 6246 6252. ’’ (a)V. P. Vitullo and N. Grossman Tetrahedron Letters 1970 1559; (b)V. P. Vitullo Chem. Comm. 1970 688. Aromatic Compounds in the rate-determining step suggests that the transition state is less solvated than the ground state by one water molecule.576 N-Alkyl-N-chloroanilines have been shown to be methoxylated in the para-position via silver-ion-assisted ionisation in methanol.58a Evidence for the intermediacy of anilenium ions has now been obtained using N-chloro-4-t-butylaminobiphenyl,which affords the cyclohexadienone (52) in good yield.'*' The dehydration of the dienol (53) results in the formation of the biphenyl derivative (54).59 That the reaction pro- ceeds through the triene (55) was established by trapping the intermediate with tetracyanoethylene which resulted in the formation of (56).6 Me CHCl Me CHCI (CN12 I l lO 1M e 6'.;.HCl2 p h e CH3 Me0 Ph HO Ph Ph CHCI (57) (58) (59) The trans-hexa-2,4-dienyl phenyl ether (57) rearranges in an excess of NN-di-ethylaniline at 186 "Cto the phenols (58) and (59).The latter is the first example of a [5~,5s]sigmatropic rearrangement which has been shown to proceed via a ten-membered transition state.60 [1,7a]Sigmatropic hydrogen shifts are involved in the isomerisation of cis,cis-to cis,trans-o-dipropenylbenzeneand vice versa ; the trans,trans-isomer rearranges at 225 "Cto (60) and this involves a disrotatory cyclisation followed by a [1,5]hydrogen shift.61 The mesitylallene (61) rearranges firstly via an aromatic [1,5s]sigmatropic hydrogen shift to an o-quinodimethane which then gives the dihydronaphthalene (62) or me~itylbuta-1,3-diene.~~ (a) P. G. Gassman G. Campbell and R. Frederick J. Amer. Chem. Soc. 1968 90 7377. (b) P.G. Gassman and G. A. Campbell Chem. Comm. 1970,427. 59 M. S. Newman and W. X. Bajzer J. Org. Chem. 1970. 35,270. 'O Gy. Frater and H. Schmid Hefv. Chim. Acra 1970 53 269. 61 H. Heimgartner H.-J. Hansen and H. Schmid Hefv. Chim. Acta 1970 53,173. " H. Heimgartner J. Zsindely H.-J. Hansen and H. Schmid Heh. Chim. Acta 1970 53. 1212. 336 H. Heaney The thermal rearrangements of the pentenylphenol(63) have been reported.63 A quantitative conversion into the two isomers (65) and (67) was observed which possibly involves the intermediates (64) and (66) respectively MewMe Me Thio-Claisen and thiopropynyl rearrangements of prop-2-ynyl and allenyl phenyl sulphides have been The data are best rationalised as involving a thiopropynylic rearrangement which establishes an equilibrium (68) (69).The compound (68) then leads to (70) and (69) to (71) by thio-Claisen rearrange- ments. p-Tolyl phenyl sulphide undergoes partial disproportionation to diphenyl and di-p-tolyl sulphides when treated with aluminium chloride. 14C-Labelling has shown that the disproportionation occurs by the migration of an arylthio- The reaction of diphenyl disulphide with for example triethyloxonium fluoroborate gives (72) (73) and products derived from (73). That the reactions proceed by an intermolecular mechanism was shown by deuteriation studies and 63 C1. Moreau F. Rouessac and J. M. Conia Tetrahedron Letters 1970,3527. 64 H. Kwart and T. J. George Chem. Comm.. 1970,433. 65 T. Fujisawa N. Ohtsuka and G.Tsuchihashi Bull. Chem. SOC.Jupan 1970,43 1189; S. Oae M. Nakai and N. Furukawa Chem. and Ind. 1970 1438. 337 Aromatic Compounds (78) (79) by the isolation of (74) when the reaction was carried out in anisole.66 2-Nitro- benzenesulphenanilides for example (79 undergo unusual thermal rearrange- ments in the presence of an excess of the corresponding amir~e.~' The compounds (76)--(78) were isolated and include a product of intramolecular transfer of oxygen from the nitro-group to sulphur. Reactions of 2-(alkoxyamino)diaryl sulphones such as (79)with sodium methoxide in methanol result in the loss of the H (801 alkoxy-group and the formation of the diphenylamine (80) and the quinone di-imine (81).68 The evidence available indicates that the products do not arise uia nitrenes.Recent aspects of the chemistry of sulphonyl nitrenes have been re~iewed.~' Thermally generated electrophilic aryl nitrenes have been shown to undergo intermolecular substitution reactions with aromatic substrate^.^' The pyrolysis of oxindole at 850 "Cgave benzonitrile together with a number of other products. I3C- and ''C-Labelling experiments have shown that the nitrile carbon is formed almost exclusively from the benzene ring of the oxindole and that the C-3 of " B. Miller and C.-H. Han Chem. Comm. 1970 623. '' F. A. Davis R. B. Wetzel T. J. Devon and J. F. Stackhouse Chem. Comm. 1970 678. 68 M. F. Grundon R. H. Hall R. McD. Hunter and D. J. Maitland Chem. Comrn. 1970 1280. 69 R. A. Abramovitch and R.G. Sutherland Fortschr. Chem. Forsch. 1970 16(1) 1. '* R. A. Abramovitch and E. F. V. Scriven Chem. Comm. 1970 787. 338 H. Heaney oxindole is incorporated into the ring of ben~onitrile.~ ' o-Tolylnitrene is a likely intermediate. Contrary to the general belief aromatic nitro-compounds are reduced to some extent by sodium borohydride in aqueous or aqueous alcoholic alkali to their radical anions.72 The decomposition of arenediazonium ions in acidic methanol proceeds either by a radical mechanism forming the arene or by an ionic mechanism forming the meth~xyarene.~~ The rates of the two reactions are sufficiently similar to suggest that both proceed via a common intermediate. The formation of spirocyclohexadienyl dimer~'~ from the diazonium salts by reaction with sodium iodide in acetone supports a radical mechanism for the interaction of iodide ions with diazonium salts.The free-radical phenylation of hexafluorobenzene results in the formation of 2,3,4,5,6-pentafluorobiphenyl. The relative yields of the product and residue depend on the temperature used for the distillation of the biaryl from the reaction mixture. It was suggested that this supports the view that the biaryl is formed partly by the defluorination of dimers such as (82) during the isolation.76 FF FF c6c15 a0 c6c15 Fm: Ph FF FF CI c1 (82) (83) The preparations of the remarkably stable perchlorotriphenylmethyl-car-banion7' and -carbonium ions7* have been reported. The perchlorotriphenyl- carbonium hexachloroantimonate may be kept under water for several days without significant decomposition.However when it is dissolved in wet methy- lene chloride it is hydrolysed rapidly to (83). The reactions of 2,4-dinitro-1 -naphthyl ethyl ether with n-butyl- and t-butyl- amine have been studied by the stopped-flow method in dimethyl ~ulphoxide.~~ The kinetics show that the first stage involving the formation of for example the intermediate (84) is not base-catalysed and that (84) is rapidly converted EtO. ,&H,Bu' (84) '' R. F. C. Brown and M. Butcher Tetrahedron Letters 1970 3151. l2 M. G. Swanwick and W. A. Waters Chem. Comm. 1970,63. 73 T. J. Broxton J. F. Bunnett and C. H. Paik Chem. Comm. 1970 1363. 74 Ann. Reports (B) 1969 66 356.75 D. H. Hey G. H. Jones and M. J. Perkins Chem. Comm. 1970 1438. 76 P. H. Oldham G. H. Williams and B. A. Wilson J. Chem. SOC.(B),1970 1346. 77 M. Ballester and G. de la Fuente Tetrahedron Letters 1970 4509. '' M. Ballester J. Riera-Figueras and A. Rodriguez-Siurana Tetrahedron Letters 1970 3615. 79 J. A. Orvik and J. F. Bunnett J. Amer. Chem. SOC.,1970 92 2417. Aromatic Compounds 339 into the relatively stable deprotonated ion. The preparation of Meisenheimer complexes involving the addition of an alkyl anion has been reported." Thus 1,3,5-trinitrobenzene reacts for example with tetramethylammonium tetra-n- butylboride and results in the formation of the complex (85). Similarly the complex (86) was obtained in high yield by the reaction with tetramethylammo- nium borohydride.81 Other Meisenheimer complexes have been studied.82 The formation of bicyclic anions for example (87) which was originally thought only to occur with 1,3,5-trinitrobenzene and certain specific ketones has now been found to be much more general.The reaction occurs between a variety of structurally different ketones and keto-esters and various electron-deficient benzenes.' 0-Benzylvanillin(88) has been found to react with sodamide in liquid ammonia to form (90) in 35 % yield.84 It is probable that the intermediate (89) with the negative charge delocalised by the carbonyl group is involved. In view of the difficulties involved in making amino-arylaldehydes this method is promising. A comparison of the rates of methoxydechlorination of 4-chloro-3,4-dinitro- and 4-chloro-3,3'-dinitro-diphenylmethanessuggests the importance of homo- conjugation involving structures such as (91) in stabilising the intermediate PhCH20 - PhCH,O OCHO OMe OMe (88) (89) (90) R.P. Taylor J. Org. Chem. 1970 35 3578. 81 R. P. Taylor Chem. Comm. 1970 1463. E. J. Fendler J. H. Fendler C. E. Griffin and J. W. Larsen J. Org. Chem. 1970 35 287; M. J. Strauss Chem. Comm. 1970,76; E. Bergman N. R. McFarlane and J. J. K. Boulton ibid. p. 51 1. 83 M. J. Strauss T. C. Jensen H. Schram and K. O'Conner J. Org. Chem. 1970,35,383. 84 D. C. Ayres and R. B. Chater Tetrahedron Letters 1970 171 1. 340 H. Heaney in~olved.~’ Nucleophilic substitution reactions in which a formal expulsion of hydride ion occurs have been reported using phenylacetonitrile derivatives and nitrobenzene.86 Compounds of the type (92) and reduction products were obtained.Benzene Isomers. Hexamethyl-‘Dewar’-benzenereacts with cyanogen azide in a time- and temperature-dependent manner and results in the formation of three distinct products [probably (93)-(95)] of skeletal rearrangement.87 The H NC N (93) (94) (95) product formed when t-butylacetylene reacts8’ in the presence of bis(benzoni-tri1e)palladium chloride has been shown not to be a tri-t-butyl ‘Dewar’ benzene- palladium chloride c~mplex.~’ o-Xylylene has never been isolated but its transient existence has been established by Diels-Alder reactions. The ‘Dewar’ analogue (97) has been prepared at ambient temperatures and isolated at low temperatures by the reaction of potassium t-butoxide with the di-toluene-p- sulphonate (96).” Benzynes.1-(2-Carboxyphenyl)-3,3-dimethyltriazine(98) is a new relatively stable non-explosive precursor for benzyne. When a solution of the triazine was heated under reflux in chlorobenzene in the presence of tetraphenylcyclo-pentadienone 1,2,3,44etraphenylnaphthalene was isolated in 80 % yield.’ N-Nitroso-N-acylanilines isomerise in carbon tetrachloride to form aryldiazo- nium carboxylates several of which have been isolated.” These salts may well serve as benzyne precursors. For example a 46 % yield of 1,2,3,4-tetraphenyl- naphthalene was isolated when benzenediazonium p-chlorobenzoate was heated in carbon tetrachloride in the presence of tetracyclone.Similarly the portion- wise addition of crystalline benzenediazonium fluoroborate to tetracyclone 85 S. Clementi V. Mancini and G. Marino Chem. Comm. 1970 1457. 86 M. Makosza and M. Jawdosiuk Chem. Comm. 1970 648. *’ A. G. Anastassiou and S. W. Eachus Chem. Comm. 1970 429 88 Ann. Reports (B) 1969 66 337. 89 K. L. Kaiser and P. M. Maitlis Chem. Comm. 1970 942. yo F. R. Farr and N. L. Bauld J. Amer. Chem. Soc. 1970,92,6695. 91 J. Nakayama 0. Simamura. and M. Yoshida Chem. Comm. 1970 1222. y2 C. Riichardt and C. C. Tan Chem. Ber. 1970 103 1774. Aromatic Compounds 341 potassium acetate and acetic acid in benzene heated under reflux gave the tetraphenylnaphthalene in very good yield.’j Furthermore competition data for reactions of benzyne with mixtures of a number of dienes gave values which were identical with those obtained in reactions involving N-nitro~oacetanilide.’~ On the other hand the failure to isolate a benzyne adduct from the decomposi- tion of N-nitrosoacetanilide in the presence of furan must place the intermediacy of benzyne in doubt in this case.94 However decomposition of N-nitrosoacetanilides is complex,’ and it has been suggested that the decomposition of the aryldiazonium acetates to aryl radicals competes successfully with the decomposition to an aryne in the presence of an excess of N-nitro~oacetanilide.~~ In accord with this view the isolated yield of 1,2,3,4-tetraphenylnaphthalene became 88 % when a cold solution of N-nitrosoacetanilide was added slowly to a solution of tetracyclone in benzene containing potassium acetate at 60 “C.The reactions of t-butyl-substituted benzynes have been reported in which the aryldiazonium ion was the prec~rsor.’~ The thermal decompositions of 3-carboxy- and 4-carboxy-benzenediazonium chlorides have been studied and products were obtained which were rationalised as involving the 1,3- and 1,4-deh~drobenzenes.’~ 7-QuinoIinyne and a-naphtha- lyne show a much reduced selectivity in reactions with bases when compared with 5-quinolinyne and ben~yne.~* The low-yield dimerisation of p-naphthalyne has been reported,” and the anticipated adducts of both a-and P-naphthalyne with benzene have been prepared’” in order to study the di-n-methane rearrange- ments of these compounds.2-Iodophenylazotriphenylmethanehas been shown to decompose to 2-iodophenyl radicals but not to benzyne. lo’ The unimolecular radical elimination of iodine from 2-iodophenyl radicals must therefore be questioned. The photolysis of 1,2-di-iodotetrafluorobenzenein benzene gives rise to products derived both from the 2-iodotetrafluorophenyl radical’02 and from tetrafluorobenzyne.’02b The aryne product is identical to that produced from other precursors involving non-photochemical methods and thus also suggests that the aryne does not arise by the loss of an iodine atom from the 2-iodotetrafluorophenyl radical. The reaction of benzyne with 1,2-dideuteriocyclohexenewas found to give only the product expected from the concerted ene-rea~ti0n.I’~ This result ” C.Riichardt and C. C. Tan Angew. Chem. Internat. Edn. 1970,9 522. 94 J. I. G. Cadogan J. Cook M. J. P. Harger and J. T. Sharp Chem. Comm. 1970 299. 95 G. R. Chalfont and M. J. Perkins J. Amer. Chem. SOC.,1967,89 3054. 9b R. W. Frank and E. G. Leser J. Org. Chem. 1970,35,3932; and references cited therein. 9’ H. E. Bertorello R. A. Rossi and R. H. de Rossi J. Org. Chem. 1970 35 3332; R. H. de Rossi H. E. Bertorello and R. A. Rossi ibid. p. 3328. y8 T. Kauffmann H. Fischer R. Niirnberg and R. Wirthwein Annalen 1970 731 23. 99 C. F. Wilcox and S. S. Talwar J. Chem. SOC.(0,1970 2162. loo H. E. Zimmerman and C. 0.Bender J. Amer. Chem. SOC.,1970,92,4366. lo‘ G. W. Clark and J. A. Kampmeier Chem.Comm. 1970 996. (a)J. M. Birchall R. N. Haszeldine and J. G. Speight J. Chem. SOC.(0,1970 2187; (b) J. P. N. Brewer I. F. Eckhard H. Heaney M. G. Johnson B. A. Marples and T. J. Ward ibid. p. 2569. lo’ G. Ahlgren and B. Akermark Tetrahedron Letters 1970 3047. 342 H. Heaney should be contrasted with that found using triplet excited maleate.'04 The reaction of benzyne with cyclohepttfg]acenaphthene (99) does not result in the (99) 100) formation of a cycloadduct. Dehydrogenation to cycloheptLfg]acenaphthylene (100) occurs possibly by an orbital-symmetry-allowed electrocyclic dehydro- genation. lo5 The previous suggestion lo6 that benzocyclobutene derivatives arise via an allene in the reaction of benzyne with ethoxypropyne receives support from studies of the reactions of benzyne with a number of allenes.lo7 As well as (2 + 2) cycloaddition products ene-type reactions lead to 1,3-dienes or acety- lenes.Some aspects of the chemistry of highly halogenated arynes have been re- viewed.lo* Reactions of arynes with cinnamaldehyde yield flavenes for example benzyne forms (101) while with benzaldehyde tetrachlorobenzyne affords the 2,4-diphenyl-1,3-benzodioxan (102).'09 The cycloaddition reactions of 3,17p-dimethoxyoestra-l(l0),2,4-triene with tetrafluorobenzyne afford enol ethers which are rapidly hydrolysed to ketones,' lo while reaction between 1,3,5- trimethoxybenzene and tetrafluorobenzyne yields after hydrolysis the phenolic CI Ph (103) ( 104) (105) lo4 G.Ahlgren and B. Akermark Tetrahedron Letters 1970 1885. P. Flowerday M. J. Perkins and A. R. J. Arthur J. Chem. Soc. (0,1970 290. lo6 Ann. Reports (B) 1968 65 356. lo' H. H. Wasserman and L. S. Keller Chem. Comm. 1970 1483. 'OM H. Heaney Fortschr. Chem. Forsch. 1970 16(1) 35. lo9 H. Heaney and C. T. McCarty Chem. Comm.. 1970 123. lo I. F. Eckhard H. Heaney and B. A. Marples J. Chem. Soc. (C) 1970,2493. Aromatic Compounds acid (103).' '' Although benzyne has been found not to form cycloadducts with biphenylene low yields of the expected adducts were isolated from reactions with the tetrahalogenobenzynes (104; X = F or C1).'I2 The addition of benzyne to 5,5-dimethoxytetrachlorocyclopentadienegives the acetal (105) in good yield which on hydrolysis decarbonylates spontaneously to form 1,2,3,4-tetrachloro- naphthalene.'I3 The silver-ion effect on the reaction of benzyne with benzene has been noted previously.Similarly the product ratio in the reaction of ben- zyne with cyclo-octatetraene is dramatically affected by trace amounts of silver ions.'14 In the absence of silver (106)is the major product while in its presence (108) is the major product and probably arises uia (107). (107) (108) The full paper on the generation and reactions of benzynequinone has appeared.' ' The suggestion that tropolonyne intermediates may be involved in certain reactions has been verified.'16 Thus the intermediacy of (109) was implicated by the reaction of 3-bromotropolone with potassium t-butoxide in dimethyl sulphoxide in the presence of 1,3-diphenylisobenzofuran.The adduct (1 10) was isolated in good yield. 8-Cyanoheptafulvene reacts with ben- zyne to form the .8 + .2 cycloadduct (1 11) exclusively.' l7 Deuterium-labelling experiments have been used to demonstrate that the cycloadditions of benzyne (109) (1 10) (111) to cyclopentadienyl- and indenyl-magnesium bromide involve the anions. The absence of possible intermediates from two-step ionic mechanisms has been sug-gested as evidence in favour of a concerted .4 + R2s mechanism. ' Interest in the reactions of aryl-lithium compounds with sulphur compounds' ' continues. The reaction of tri-p-tolylsulphonium bromide with p-tolyl-lithium ' ' B. Hankinson and H. Heaney Tetrahedron Letters 1970 1335.'I2 H. Heaney K. G. Mason and J. M. Sketchley Tetrahedron Letters 1970 485. 'I3 J. W. Wilt and A. Vasilianskas J. Org. Chem. 1970 35 2410. 'I4 E. Vedejs and R. A. Shepherd Tetrahedron Letters 1970 1863. 'I5 C. W. Rees and D. E. West J. Chem. SOC.(C),1970 583. 'I6 T. Yamatani M. Yasunami and K. Takase Tetrahedron Letters 1970 1725. M. Oda and Y. Kitahara Bull. Chem. SOC.Japan 1970,43 1920. 'I8 W. T. Ford R. Radue and J. A. Walker Chem. Comm. 1970,966. 'I9 Ann. Reports (B) 1969 66 329. 344 H. Heaney gave 4,4'-dimethylbiphenyl (71.5%) and 3,4'-dimethylbiphenyl (5.1 %). On the other hand the reaction of p-tolyl-lithium with di-p-tolyl sulphoxide gave 3,4'-dimethylbiphenyl (25.6%) and 4,4'-dimethylbiphenyl (31.4 %).I2* These results were interpreted as involving 4-methylbenzyne in the major pathway of the reaction of the sulphoxide.The decomposition of pentafluorophenylmagnesium bromide in dioxan in the presence of a number of transition-metal complexes has led to the isolation of two complexes which may involve aryne-metal bonds. '21 Benzyne reacts with diaryl diselenides and with diaryl ditellurides to cause metalloid-metalloid bond ~1eavage.I~~ The reactions of arynes with triarylphosphines produce betaines which are stabilised by protonation using for example fluorene or by alkylation using for example methyl iodide.'23 Good yields of tetra-aryl- phosphonium salts may be obtained by this method. Non-benzene Systems.-Three- and Four-membered Rings. The reaction of trichlorocyclopropenium tetrachloroaluminate with phenols or anisole at 30-80 "C yields symmetrical para-substituted triarylcyclopropenium chlor-ide~.'~~ At 0-10 "Cdiarylcyclopropenium ions are formed which give diaryl- cyclopropenones after hydrolysis.Monoarylcyclopropenium salts may also be isolated and hence a route to unsymmetrical diarylcyclopropenones or triaryl- cyclopropenium salts is available. The triarylcycloprapenium ion (112) on treatment with triethylamine in chloroform gave the diarylquinocyclopropene (113).'25 The reversible oxidation of bis(p-hydroxyary1)quinocyclopropenes affords radialenes such as (114). The treatment of tetrachlorocyclopropene with phyph :+ I 8 OH tri-n-butyltin hydride effects successive removal of the chlorine atoms.'26 Hydrolysis of the appropriate dichlorocyclopropenes leads to cycloprope-Th e electrolysis of the triphenylcyclopropenium cation results lZo K.K. Andersen S. A. Yeager and N. B. Peynircioglu Tetrahedron Letters 1970 2485. Iz1 D. M. Roe and A. G. Massey J. Organometallic Chem. 1970 23 547. Iz2 N. Petragnani and V. G. Toscano Chem. Ber. 1970 103 1652. lz3 G. Wittig and H. Matzura Annalen 1970 732 97. lz4 R. West D. C. Zecher and G. Goyert J. Amer. Chem. SOC.,1970,92 149. lZ5 R. West and D. C. Zecher J. Amer. Chem. Soc. 1970,92 155 161. Iz6 R. Breslow G. Ryan and J. T. Groves J. Amer. Chem. Soc. 1970,92,988. lz7 R. Breslow and G. Ryan J. Amer. Chern. SOC.,1967,89 3073. Aromatic Compounds in one-electron reduction to the radical which dimerises to give (115) in good yield.The formation of 1,2,4,5tetraphenylbenzene when the diphenyl-cyclopropenyl cation is reduced by the addition of sodium borohydride was mentioned last year.' 29 Inverse addition results in the formation of diphenyl-cyclopropene in high yield. I3O The previously reported hypothesis for the formation of the benzene derivative has been confirmed and diphenylcyclo- propene forms the adduct (116) with 1,4-diphenylisobenzofuran. The reduction of diphenylcyclopropenone by dissolving metals yields tetraphenylresorcinol as the major product. l3' Since diphenylcyclopropenone is completely protonated in sulphuric acid nitration results in rneta-sub~titution.'~~ The reaction of Me Ph diphenylcyclopropenone with 1,3-diphenylisobenzofuran gives the benzo-tropone derivative (117).'33 This reaction may be regarded as being of the type involving a 1,3-dipolar species with a carbonyl ylide.Reactions of enamines and ynamines with diphenylcyclopropenone result in cleavage of the C(2)-C(3) bond. By contrast the reaction of trans-pyrrolidinepropene with diphenyl- cyclopropenethione results in the cleavage of the C(1)-C(3) bond and the forma- tion of (118).' 34 Michael addition of triphenylphosphine to diphenylcyclopro- penone results in the formation of the ketenphosphorane (119).13' Subsequent addition of 2,6-dimethylphenyl isonitrile gave the iminocyclobutenone (120). The conversion of bromocyclo-octatetraene to P-bromostyrene' 36 has been studied and its mechanism established.13' Valence-tautomerism to (121) is 12' T. Shono T. Toda and R. Oda Tetrahedron Letters 1970 369. 129 Ann. Reports (B) 1969 66 344. I3O D. T. Longone and D. M. Stehouwer Tetrahedron Letters 1970 1017. 13' E. A. Harrison Chem. Comm. 1970 982. '32 C. W. Bird and A.F. Harmer Org. Prep. and Proced. 1970 2 79. 33 J. W. Lown T. W. Maloney and G. Dallas Canad. J. Chem. 1970,48 584. 34 J. W. Lown and T. W. Maloney Chem. and Ind. 1970 870. 135 N. Obata and T. Takizawa Tetrahedron Letters 1970 2231. 13' Ann. Reports 1952 49 176. 13' R. Huisgen and W. E. Konz J. Amer. Chem. Soc. 1970 92 4102; W. E. Konz W. Hechtl and R. Huisgen ibid. p. 4104; R. Huisgen W. E. Konz and G. E. Gream ibid. p. 4105. 346 H. Heaney followed by ionisation to the homocyclopropenium salt (122).Ion recombination then leads to the cyclobutene derivative (123) which on conrotatory ring-opening leads to trans-P-bromostyrene. The naphthoquinone-diphenylacetylenephotoadduct (124) can be converted into the dienolate with sodium hydride but on quenching with water the hydroquinone (125) slowly dime rise^.'^^ A polarographic investigation of (125) shows not only that it is difficult to oxidise the compound to the quinone (126) but also that the quinone is even less stable than (125). Strain and substituent effects are thought to be minimal and it is thought that the major difficulty is associated with the antiaromaticity of the cyclobutadiene ring. The o-quinonoid allene (128) has been generated by pyrolysis of the spirobisulphone (127).13’ A number of products were isolated from the pyrolysate including the 1,l’-spirobi- (benzocyclobutene) (129).The anion (130),which should be antiaromatic has been prepared and an approximate pK for (131) obtained. 14* This latter reveals a strong destabilisation in (130). ‘” R. Breslow R. Grubbs and S.-I. Murahashi J. Amer. Chem. Soc. 1970 92 4139. 139 M. P. Cava and J. A. Kuczkowski J. Amer. Chem. Soc. 1970,92,5800. lQo R. Breslow and W. Washburn J. Amer. Chem. SOC.,1970,92 427. Aromatic Compounds Five- Seven- and Nine-membered Rings. Aspects of the chemistry of conjugated cyclic chlorocarbons have been re~iewed.'~' In spite of a high degree of sym- metry a number of fully chlorinated aromatic compounds for example hexa- chlorofulvene have significant dipole moments when measured in benzene solution.These results indicate further the ability of these chlorocarbons to form charge-transfer complexes with the s01vent.l~~ The pyrolysis of bicyclo[2,2,l]hepta-2,5-diene-2,3-dicarboxylicanhydride at 700"Cmainly gives benzocyclobutenone while at 900"C the pyrolysate consists mainly of the fulveneallene (132).143 Cyclopentadienylsodium reacts with a wide variety of S-methyl isothiuronium iodides (133) to form 6,6-diaminofulvenes (1 34) in good yield. 144 6-Aminofulvene-2-aldimines,for example (135),exhibit very fast (132) (1 33) classical aromaticity due to delocalisation of electrons through the hydrogen bond does not exist.'45 The 1 1-adduct (136)of 6,6-dimethylfulvene and dichloroketen is solvolysed to an unexpected tropolone derivative possibly as shown (136)+(1 39).146 Similarly the adduct formed between dichloro- [2-14C]keten and cyclopentadiene is solvolysed to tropolone in which all of the 14C activity was located at positions 3 and 7 (140).147This result supports the above mechanism. (136) (137) (138) (139) A number of oxazole derivatives for example (141),are quantitatively con- verted into acetamidobenzotropones for example (142),with one mole of selenium dioxide. Hydrolysis then affords the corresponding benzotropolones. 14* 14' R. West Accounts Chem. Res. 1970 3 130. 14' I. Agranat H. Weiler-Feilchenfeld and R. M. J. Loewenstein Chem. Comm. 1970 1153. 143 0. A. Marner F. P. Lossing E.Hedaya and M. E. Kent Canad. J. Chem. 1970 48 3606. 144 K. Hartke and G. Salamon Chem. Ber. 1970,103 133. U. Miiller-Westerhoff J. Amer. Chem. Soc. 1970 92 4849. 146 T. Asao T. Machiguchi T. Kitamura and Y. Kitahara Chem. Comm. 1970 89. 147 T. Asao T. Machiguchi and Y. Kitahara Bull. Chem. SOC.Japan. 1970,43,2662. 14' E. Galantay and W. R. J. Simpson Chem. Comm. 1970 754. 348 H. Heaney Electron transfer from cycloheptatriene and bitropyl to tris-(p-bromopheny1)- amminium salts is a convenient synthetic high yield route to tropylium The reaction of 4-phenyl- 1,2,4-triazoline-3,5-dione with tropone affords the normal .4 + 2,cycloadduct whereas with tropolone the compound (143) was ~btained.''~ The reaction of diphenylnitrile imine (144) with tropone leads to the formation of two adducts.The compound (145) is that predicted for the concerted .4 + .6 1,3-dipolar cy~loaddition.'~' The Claisen re-arrangement of tropolone allyl ethers has been little studied. A comparison with the reactions of mesityl ethers may be drawn from the results obtained with 3,5,7-trimethyltropoloneallyl ether (146). The major (75%) product has been shown to be (147) while two minor products were also ~btaged.''~ P-Chloro- glutaryl dichloride reacts with an excess of diazomethane to form the bis-a- diazoketone. This compound decomposes in the presence of copper acetylace- tonate at high dilution in benzene to afford 6-chlorocyclohept-2-ene-1,4-dione. 0 (146) (1 47) Dehydrochlorination then leads to 4-hydroxytropone in good yield.l5 The reaction of 7-hydroxymethylcycloheptatrienewith di-iron nonacarbonyl gave 149 P.Beresford and A. Ledwith Chem. Comm. 1970 15 so T. Sasaki K. Kanematsu and K. Hayakawa Chem. Comm. 1970,82. K. N. Houk and C. R. Watts Tetrahedron Letters 1970 4025. IS2 M. M. A1 Holly and J. D. Hobson Tetrahedron Letters 1970 3423. Is' J. Font F. Serratosa and J. Valls Chem. Comm. 1970 721. Aromatic Compounds heptafulveneiron tricarbonyl (148). The heptafulvene complex reacted with dimethyl acetylenedicarboxylate and gave after dehydrogenation the azulene (149).lS4 The abstraction of a proton from (150) using sodium hydrogen car- bonate yields (15 l).’ ’’ The reaction of bicyclo[5,4,l]dodecapentaenylium COZ Me NC $J (150) fluoroborate with dimethyl malonate in the presence of triethylamine gave a mixture of (152) and (153).Dehydrogenation with chloranil gave the hende- cafulvenes for example (154).’ 56 (152) Me0,CAC02Me (154) (153) Dibenzo(3,4 :5,6)-cyclononatetraene (155) has been prepared by the reaction of 2,2‘-biphenyldicarboxaldehydewith the 1,3-bis-ylide from 1,3-bis-(triphenyl- phosphonio)propane dibromide. 57 Treatment of (155) with n-butyl-lithium generates a non-planar anion which changes slowly at room temperature to the planar aromatic anion (156).ls7“ When a solution of (156) was quenched with water the phenanthrene derivative (1 57) was ~btained.”~“ The potentially aromatic thionin ring system (158) has been ~repared.”~ However the spectral evidence indicates that the thionin ring is non-planar and hence is non-aromatic.D. J. Ehntholt and R. C. Kerber Chem. Comm. 1970 1451. ls5 K. Takahashi N. Hirata and K. Takase Tetrahedron Letters 1970 1285. 156 L. Knothe D. Forster H. Achenbach H. Friebolin and H. Prinzbach Tetrahedron Letters 1970 3075. 15’ (a) P. J. Garratt and K. A. Knapp Chem. Comm. 1970 1215; (b) M. Rabinovitz A. Gazit and E. D. Bergmann ibid. p. 1430. ls8 P. J. Garratt A. B. Holmes F. Sondheimer and K. P. C. Vollhardt J. Amer. Chern. SOC.,1970 92 4492. 350 H. Heaney Cyclophanes and A~ulenes.-A combination of n.m.r. and optical rotation studies have been used to establish the activation parameters for the barriers to ring rotation in the chiral [2,2]metaparacyclophanes (159; R = C0,H or CHO).15' The optical stability of (159; R = C0,H) indicates that only one of the two rings is flipping and an examination of molecular models suggests that the steric barrier to passing the meta- past the para-ring should be consider- ably less than the alternative process.The full account of the preparation of the multilayered [2,2]paracyclophane (1 60) has appeared. 6o The compound is a mixture of symmetric and dissymmetric isomers. (160) Unusual meta-bridged biphenyls have been isolated from a natural source and shown to have the structures (161; X = H,OH or O).I6' Paracyclopha-diynes for example (162) have been prepared and their electronic spectra show the expected transannular interaction between the benzene ring and the con- jugated diyne unit.162 A number of cyclophanes have been prepared by the extrusion of sulphur di0~ide.I~~ These include the conversion of (163) to ls9 D.T. Hefelfinger and D. J. Cram J.Amer. Chem. SOC.,1970,92 1073. 160 D. T. Longone and H. S. Chow J. Amer. Chem. SOC.,1970,92.994. 16' R. V. M. Campbell L. Crombie B. Tuck and D. A. Whiting Chem. Comm. 1970 1206. 16' T. Matsuoka Y. Sakata and S. Misumi Tetrahedron Letters 1970 2549. Ib3 Ann. Reports (B) 1969 66 337. Ih4M. Haenel and H. A. Staab Tetrahedron Letters 1970 3585. Aromatic Compounds 351 The synthesis of hexahydro[2,2,2]phenanthrenophane and hence [2,2,2]phenan- threnophane has been des~ribed.'~~ A number of reports of the synthesis of aza- oxa- and thia-cyclophanes have appeared.166 HO (163) (164) The chemistry of dihydropyrenes has been re~iewed.'~' A new synthesis of trans-15,16-dimethyldihydropyrenehas been reported starting with the anti-dithia[3,3]metacyclophane (165).Conversion into the bis-sulphonium salt and (165) (166) (167) (168) Stevens rearrangement gave a mixture of the [2,2]metacyclophanes (166) which on re-methylation followed by Hofmann elimination gave the metacyclophane (167) isolated as its valence tautomer (168).' 68 It is ofinterest that conformational inversion does not occur during the sequence. A new route to the dithia[3,3]meta- cyclophanes required in the above synthesis involves the desulphuration of for example (169) with tri~(diethy1amino)phosphine.'~~ The first example of a cis-15,16-dihydropyrene has been reported.''O The synthesis uses the principles outlined above and results in the formation of (170). Molecular models suggest 16' R. Paioni and W. Jenny Hefv. Chim. Acta 1970 53 141. 166 F. Vogtle and P. Neumann Tetrahedron Letters 1970 115; Chem. Comm. 1970 1464; F. Vogtle Annafen 1970 735 193. 167 V. Boekelheide Proc. Welch Foundation 1968 XII 83. R. H. Mitchell and V. Boekelheide Tetrahedron Letters 1970 1197. 169 V. Boekelheide and J. L. Mondt Terrahedron Letters 1970 1203. I7O R. H. Mitchell and V. Boekelheide Chem. Comm. 1970 1555. 352 H. Heaney that the ring portion of the molecule has a shallow saucer-shaped geometry and n.m.r. measurements support this view. Further examples of the new synthesis include (171)171 and (172) the first tris-bridged cyclophane in which only two linking atoms are present.17* S S I I S S The photocyclisation of cis-stilbenes such as (173) results in the formation of tetrahydropyrenes for example (174) which are dehydrogenated by D.D.Q.to the trans-l5,16-dihydr0pyrenes.'~~ The syntheses of a series of trans-15,16-dihydr~pyrene'~~" and trans-15,16-dialkyldihydropyrenes174b have been des- cribed. The n.m.r. spectra of the series methyl ethyl and n-propyl are interesting because they provide a map of the magnetic effects due to the ring current.174b Me L I (173) Me (175) The synthesis of the bridged [16]annulene (175) has been re~0rted.l~~ The n.m.r. data on the mixture of derived dianions indicate that although as expected (175) shows the presence of a paramagnetic ring-current it is nonetheless not a satisfactory model for a neutral rigid [4n]annulene having a planar perimeter.V. Boekelheide and P. H. Anderson Tetrahedron Letters 1970 1207. V. Boekelheide and R. A. Hollins J. Amer. Chem. SOC., 1970 92 3512. H. Blaschke C. E. Ramey I. Calder and V. Boekelheide J. Amer. Chem. Soc. 1970 92 3675. l'' (a) R. H. Mitchell and V. Boekelheide J. Amer. Chem. SOC. 1970 92 3510; (b) V. Boekelheide and T. A. Hylton ibid. p. 3669. R. H. Mitchell and V. Boekelheide Chem. Comm. 1970 1557. Aromatic Compounds The chemistry of bridged annulenes has been reviewed. ’ A particularly interesting series of papers from the group at Koln describe the syntheses and some of the chemistry of new bridged annulenes.The bridged 1071-electron analogue of tropone (177) has been ~ynthesised.”~ The key intermediate (176) was dehydrogenated by DDQ. N.m.r. and chemical data support the polyenone structure. However the n.m.r. spectrum of (177) in deuteriotrifluoroacetic acid indicates that the protonated form (178) is aromatic. Bicyclo[5,4,l]dodeca- pentaenylium fluoroborate (179) has been prepared by the reaction of a bis-ylide derived from 1,3-dibromopropane with cycloheptatriene-1,6-dialdehyde. The abstraction of hydride ion then gave (1 80). 78 0 The synthesis of the aromatic 1,6 :8,13-propandiylidene[l4]annulene (184) the n.m.r. spectrum for which was reported last year,’79 has now appeared.I8* The key intermediates in the synthesis are (181)-(183).The next higher homo- logue (185) has been prepared and its n.m.r. spectrum is very similar to that for E. Vogel Proc. Welch Foundation 1968 XII. 215. W. Grimrne J. Reisdorf W. Tunemann and E. Vogel J. Amer. Chem. SOC.,1970 92 6335. ‘78 E. Vogel R. Feldmann and H. Diiwel Tetrahedron Letters 1970 1941. ’79 Ann. Reports (B) 1969 66 351. E. Vogel A. Vogel H.-K. Kubbeler and W. Sturm Angew. Chem. Internat. Edn. 1970 9 5 14. 354 H. Heaney (184).l8 Hence one concludes that the bridge experiences steric deformation rather than the annulene ring. The synthesis of syn-1,6-methano-8,13-oxido[ 141- annulene (188) has been reported.'82 Surprisingly the tetrabromides derived from (186) and from its anti-isomer both gave (187) on dehydrohalogenation.Dehydrogenation with DDQ then gave (188). The n.m.r. spectrum and reactions for example Friedel-Crafts acylation indicate that (1 88) is aromatic. On the other hand the anti-1,6 :8,13-bismethano[l4]annulene(189) deviates so far from planarity that the delocalisation energy is insufficient to equalise the C-C bond lengths.'83 The hydrocarbon (190) reacts with triamminetricarbonyl- chromium to form a complex which on the basis of n.m.r. evidence was formu- lated as the homoaromatic species (191).'84 Similarly the n8s+ .2 cycloadduct formed by the reaction of tetracyanoethylene with the tetraene (192) exists in the open cycloheptatriene form and not as the norcaradiene form.'85 The hydrocarbon (193) reacts with alkali metals to give eventually the dianion (194) the first analogue of a biphenylene in which one of the o-phenylene rings has been replaced by a l0n-electron system.The dianion is however non- aromatic and is probably associated with a barrier to ring-flattening arising from the antiaromaticity of the cyclobutadienyl ring.'86 The photolysis of (195)- (197) at -100°C results in the formation of the very labile [12]annulene (198) and variable-temperature n.m.r. spectroscopy at temperatures between -170 and + 120 "C shows that a mobile equilibrium exists.'87 Perturbation theory predicts that dibenzo[cd,gh]pentalene should be a particularly good model of a 181 E. Vogel W. Sturm and H.-D. Cremer Angew.Chem. Internat. Edn. 1970 9 516. 182 E. Vogel U. Haberland and J. Ick Angew. Chem. Internat. Ed. 1970 9 517. 183 E. Vogel U. Haberland and H. Giinther Angew. Chem. Internat. Ed. 1970,9 513. 184 W.-E. Bleck W. Grimme H. Gunther and E. Vogel Angew. Chem. Internat. Edn. 1970 9 303. ins G. C. Farrant and R. Feldman Tetrahedron Letters 1970 4979. 186 C. S. Baxter P. J. Garratt and K. P. C. Vollhardt J. Amer. Chem. SOC. 1969 91 7783. 187 J. F. M. Oth H. Rottele and G. Schroder Tetrahedron Letters 1970 61 ;J. F. M. Oth J.-M. Gilles and G. Schroder ibid. p. 67. Aromatic Compounds 355 periphery [12]annulene. The first example to be described is the dianion (199) and the n.m.r. spectrum is in accord with this view.' 88 A number of other papers refer to annulene syntheses,' 89 including a slightly improved synthesis of [181annulene.l90 Electrophilic substitutions have been studied further using [181annulene.l Monodehydro[22]annulene has been synthesised and is aromatic 19* as also is the dianion of an octadehydr0[24]annulene.'~~ b a*-(199) Polycyclic Compounds.-The cycloaddition reactions of dimethyl acetylene- dicarboxylate with 1-methoxy- and 1-(NN-dimethylamino)-indeneresult in the formation of cyclobutene derivatives.'94 The dimethylamino-compound under- goes a particularly ready ring-opening to (200). The thermal reorganisation of (201) to (202) has been studied.'95 Deuterium from the seven-membered ring was scrambled in the benzo-ring in re-isolated (201) and a series of 1,Shydrogen (200) shifts were suggested as possibly accounting for the observed results.The thermolysis of (203)takes an interesting course to give (204).'96 Tertiary amines catalyse the tautomeric conversion of (205; R = H) to (206). The methyl and acetyl derivatives (205; R = Me or Ac) are isomerised to the enol ether (207) "' B. M. Trost and P. L. Kinson J. Amer. Chem. SOC.,1970,92 2591. A. B. Holmes and F. Sondheimer J. Amer. Chem. SOC.,1970 92 5284; K. Endo Y. Sakata and S. Misumi Tetrahedron Letters 1970 2557. 190 H. P. Figeys and M. Gelbcke Tetrahedron Letters 1970 5139. lY1 E. P. Woo and F. Sondheimer Tetrahedron 1970 26 3933. 19' R. M. McQuilkin and F. Sondheimer J. Amer. Chem. SOC.,1970,92 6341. 193 R. M. McQuilkin P. J. Garratt and F.Sondheimer J. Amer. Chem. Suc. 1970 92 6682. IY4 T. W. Doyle Canad. J. Chem. 1970,48 1629; 1633. 195 G. W. Gruber and M. Pomerantz Tetrahedron Letrers 1970 3755. 196 R. Criegee and B. Bastani Chem. Ber. 1970 103 3942; J. Ipaktschi ibid. p. 3944. 356 H. Heaney and the nitronic anhydride (208)re~pectively.'~' The isoindene acetal(210) has been generated from the dibromo-compound (209).lg8 Spiroconjugation with the acetal function was suggested in order to account for the long-wavelength OMe Ph Ph X Ph Ph absorption (A,, 537 nm) and for the instability of (210). In the absence of suit-able trapping agents the dimer (21 1) was isolated. The thermal rearrangements of a number of 2,2-diphenyl-methylenecylopropanes,for example (212) have been re~0rted.l~~ The conversion to (214) almost certainly involves the inter- mediacy of (213).In accord with the conservation of orbital symmetry trans-2- benzylidene- 1 -(diphenylmethylene)indane(2 15) undergoes a thermal disrotatory ring-closure followed by a suprafacial [1,5]-hydrogen shift to give (216).200 The w e @Me Ph \' Ph Me \ Ph (212) (214) 197 J. Skramstad Tetrahedron Letters 1970 955. 198 J. M. Holland and D. W. Jones Chem. Comm. 1970 122. I99 M. Jones M. E. Hendrick J. C. Gilbert and J. R. Butler Tetrahedron Letters 1970 845. 20c H. G. Heller and K. Salisbury J. Chem. SOC.(0,1970 399. Aromatic Compounds 3-methyl derivative only gives one product and this indicates that a steric effect determines which of the two possible disrotatory processes occurs.Ph 'Ph (215) (214) The reaction of 2-bromomethyl-2'-iodobiphenylwith methyl-lithium results in the formation of fluorene,201 Evidence was presented which suggests that the cyclisation involves the lithio-compound (217). Persulphate oxidation of o-phenylphenoxyacetic acids (218 ;R = H or Me) generates o-phenylphenoxy- methyl radicals which cyclise onto the neighbouring benzene ring.202 Li CH,.Br 0-CR2.C02H (217) (218) Thermal rearrangements of dimethylvinylidene benzobicyclo[n,l,O]alkenes (n= 3 or 4) have been studied.203 Thus the indene derivative (219; R = H) gave the naphthalene (220; R = H) while (219; R = Me) gave (221) in refluxing benzene but (221) and (222) at 450 "C.On the other hand (223) gave the acetylene (224) at 450 "C. The reactions appear to proceed via concerted processes involving a %-R \ (222) (223) 'c (224) I Y-hydrogen migration from a carbon atom a-to the cyclopropane ring to one of the carbon atoms in the allene residue. The self oxidation-reduction of 1,2- dihydronaphthalenes in 90 %sulphuric acid has been shown to involve carbonium ion rearrangement^.^'^ Thus the compound (225) gives the corresponding normal tetralin and naphthalene derivatives together with about 25-30 % of the products 201 L. J. Altman and T. R. Erdman J. Org. Chem. 1970,353237. 'OL P. S. Dewar A. R. Forrester and R. H. Thomson Chem. Comm. 1970,850. '03 I. H. Sadler and J. A. G. Stewart Chem. Comm. 1970 1588. *04 H.Tournier R. Longeray and J. Dreux Tetrahedron Letters 1970 21. 358 H. Heaney (225) (226) in which methyl groups have been transposed. A low yield of the tetralin (226) derived from one of the suggested carbonium ions was also isolated. The hydrocarbons (227 ;X = C1 Br I or H) isomerise stereospecifically when heated Me Me Me Me Me Me Me (227) (228) (229) at 150 "C and form the vinylnaphthalenes (228; X = Cl Br I or H).205The reactions probably proceed via a series of valence isomerisations and an allylic rearrangement of (229). Certain 2-substituted or-naphthols for example 2-n-propyl- 1-naphthol have been shown to react with diazomethane to give as the major product the azo- compound derived from the coupling of the naphtholate anion with the methane- diazonium ion for example (230).206 Ph OMe Attempts have again been made to prepare a simple derivative of 2,3-naphtho- q~inone.~~' The oxidation of 2,3-dihydroxy-l,4diphenyInaphthalenewith silver oxide or lead tetra-acetate results in the formation of a trimer.When the oxidation was carried out in butadiene at -40°C the adduct (231) was isolated in good yield. A blue pigment obtained from the wood of Diospyros buxifolia has been shown to have the structure (232),208 while a tetrameric naphthoquinone probably '05 R. Criegee C. Schweickhardt and H. Knoche Chem. Ber. 1970 103 960. '06 J. St. Pyrek and 0.Achmatowicz Tetrahedron Letters 1970 2651. '07 D. W. Jones and R. L. Wife Chem. Comm. 1970 1086. 0.C.Musgrave and D. Skoyles Chem. Comm. 1970 1461. Aromatic Compounds (233) was isolated from D. Dehydrogenation of the hydroxyanthrone (234) by DDQ leads to the unstable quinone (235).2'0 A number of papers have reported the elaboration of quinones using cycloaddition reactions of acetylenes with rhodium complexes.2 The complex (236) reacts for example with diphenylacetylene to form the quinone (237). 0 2-Thianorbiphenylene (238) has been prepared and its n.m.r. chemical shift data show the paramagnetic ring-current shielding effect of the [4n]cyclobuta- dienyl ring."' The primary processes in the ion beams of mass spectrometry and in plasmas are apparently similar and this feature has been used prepara- tively in the decarbonylation of fluorenone to bi~henylene.~'~ The reaction of methylmagnesium iodide with the photodimers of 1,4-naphthoquinone affords tetra-ols the dehydration of which gave a fair conversion to 5,6,11,12-tetramethyl- dibenzo[b,h] bip hen ylene (239).Nucleophilic substitution in polynuclear aro- matic fluorocarbons using the anion [(x-C,H,)Fe(CO),] -occurs in accord with 209 K. Yoshihira M. Tezuka and S. Natori Tetrahedron Letters 1970 7. 'lo P. Boldt and A. Topp Angew. Chem. Internat. Edn. 1970 9 164. 2" E. Miiiier and E. Langer Tetrahedron Letters 1970 989 993; E. Miiller E. Langer H. Jakle and H. Muhm ibid.,p. 5271. 212 P. J. Garratt and K. P. C. Vollhardt Chem. Comm. 1970 109. 2'3 H. Suhr and R.I. Weiss Angew. Chem. Internat. Edn. 1970,9 312. 214 N. P. du Preez P.J. van Vuuren and J. Dekker J. Org. Chem. 1970,35 523. 360 H. Heaney previously established tendencies. The reactivity of octafluorobiphenylene is particularly high in this reactiom2 '' Me Me (239) A number of naturally occurring anthraquinones have been synthesised by making use of the cyclisation of the carbanion (240).2'6 A new method of protecting alcoholic functions consists of the conversion to the 9-anthroxy- derivative via the tosylate. Removal of the protecting group can be achieved by singlet oxygen oxidation to the anthracenyl peroxide (241) followed by yNrOMe OR Me0 0 OMe (240) catalytic hydrogenolysis.2 '' The initial reduction product is presumably the hemi-acetal which decomposes spontaneously to the alcohol and 9-hydroxyan- throne.The n.m.r. spectra of a series ofp-quinodimethanes have been reported.21 * The signal disappearance time was used as a measure of their stabilities and as expected 9,lO-anthraquinodimethaneis more stable than 1,4-naphthoquinodi- methane which is more stable than p-quinodimethane. Nuclear Overhauser enhancements have been used to show that the preferred orientation of 9-alkyl groups is pseudo-axial in a series of 9-alkyl-9,lO-dihydroanthra~enes.~ ' Phenanthrene and its 9-alkyl and 9,lO-dialkyl derivatives are efficiently reduced to the 9,1O-dihydro-compounds by lithium in ammonia in the presence of colloidal iron. The disubstituted compounds undergo stereospecific cis-reduc- tion.220 The reduction of pyrene with lithium in liquid ammonia affords 1,9- dihydropyrene (242) one of five predicted theoretically equivalent structures.22 ' M.I. Bruce J. Organometallic Chem. 1970,21 415. '16 C. H. Hassall and B. A. Morgan Chem. Comm. 1970 1345. W. E. Barnett and L. L. Needham Chem. Comm. 1970 1383. 'I8 D. J. Williams J. M. Pearson and M. Levy J. Amer. Chem. Soc. 1970,92 1436. 219 A. W. Brinckmann M. Gordon R. G. Harvey P. W. Rabideau J. B. Stothers and A. L. Ternay J. Amer. Chem. Soc. 1970,92 5912. 220 P. W. Rabideau and R. G. Harvey J. Org. Chem. 1970,35,25. 221 R. G. Harvey and P. W. Rabideau Tetrahedron Letters 1970,3695. Aromatic Compounds 36 1 The reductive methylation of naphthalene is remarkably dependent on the metal used. Thus lithium in liquid ammonia followed by an excess of methyl bromide gave 1 -methyl- 1,4-dihydronaphthalene in high yield while when using sodium cis-1,4-dimethyl-l,4-dihydronaphthalene was the major product.222 The decomposition of dibenzosemibullvalene-l-carboxaldehydetoluene-p-sulphonyl hydrazone (243) with several bases has been investigated.223 The major product in each case was benzo[c]fluorene (244) together with the allene (245).The unique geometry of the semibullvalene nucleus results in the rearrange- ment of the derived carbene principally by a pathway involving a 1,3-aryl shift CH =N.NH.O.SO,.C,H,.Me-p CH2 II 4 qm \ -(243) (244) (245) to what is formally a trans-disposed carbon atom. The reaction between acenaph- thylene and cyclopentadiene under kinetically controlled conditions gives the endo-and exo-Diels-Alder adducts in the ratio 3 :l.224Despite a number of unsuccessful attempts to prepare 1,2-epoxyacenaphthene this compound can be prepared from acenaphthylene using m-chloroperbenzoic acid.22J The protonation of the stereoisomeric spirocyclopropaneanthrones (246) and (247) in 96% deuteriosulphuric acid leads to stable carbonium ions which retain their stereochemistry upon deprotonation.226 The n.m.r.spectra are consistent with the formation of static bridged ions for example (248). The acetolysis of trans-9,1O-bis(hydroxymethyl)-9,1O-dihydrophenanthrenebisto-luene-p-sulphonate gives the rearranged trans-diol (249) under kinetic control. The stereospecificity was attributed to the involvement of the phenonium ion (250).227 The preparation of homotriptycene has been described via the ring lz2 P.W. Rabideau and R. G. Harvey Tetrahedron Letters 1970,4139. 223 L. A. Paquette and G. V. Meehan J. Amer. Chem. SOC.,1970,92 3039. 224 R. Baker and T. J. Baker J. Chem. SOC.(0,1970 596. 225 T. H. Kinstle and P. J. Ihrig J. Org. Chem. 1970 35 257. 226 J. W. Pavlik and N. Filipescu Chem. Comm. 1970 765. 12’ E. Cioranescu M. Banciu M. Elian A. Bacur and C. D. Nenitzescu Annafen 1970 739 121. 362 H. Heaney expansion of the triptycylcarbinyl cation.228 The reaction of l-aminomethyl- triptycene (251) with nitrous acid gave rise to a mixture (252 ;R = OH or OAc). The degeneracy of the ion (253) was established by deuterium labelling. One of the Diels-Alder adducts obtained from an enol-acetate of isophorone and p-benzoquinone (254) undergoes slow acid hydrolysis to give after acetylation a mixture including (256) which undoubtedly arises by a Grob-fragmentation of (255).229 l-(NN-Dimethy1amino)benzobarrelenederivatives rearrange to 4-(NN-dimethy1amino)biaryls on being heated in protic media.230 Thus (257 ; R = H) gives (258) while (257 ; R = Me) gives the cyclohexadienone (259).F (257) (258) (259) The benzo-(CH), hydrocarbon (260) has been prepared and its thermal isomerisation studied.23 The major product is (261). The precise mechanistic 228 S. J. Cristol and D. K. Pennelle J. Org. Chem. 1970 35 2357. lZy J. Wolinsky and R. B. Login J. Org. Chem. 1970,354 1986. 130 H. Heaney and S. V. Ley Chem.Comm. 1970 1184. 23' L. A. Paquette and J. C. Stowell Tetrahedron Letters 1970 2259; E. Vedejs ibid. 1970 4963. Aromatic Compounds details are in doubt. The acidity of the vinylic protons in dibenzobarrelenes has been utilised in the metallation of for example (262).232The lithio-compound is stable at -70 "C but at higher temperatures dimeric and trimeric products were isolated. The trimer is a tri-triptycene. (260) (261) (262) The acid-catalysed hydrogen-exchange of phenalenone occurs at position 2 to afford (263).23 The reaction of ethoxyphenalenium fluoroborate with lithium 1,3-di-t-butylcyclopentadienideresults in the formation of (265)in Me low yield.234 This could have arisen by the intramolecular nucleophilic attack involving the expected compound (264).Protonation of 3,5,8,10-tetramethylace-heptylene in trifluoroacetic acid at -15°C leads by kinetic control to the &!!: (269) 232 C.F. Huebner R. T. Puckett M. Brzechffa and S. L. Swartz Tetrahedron Letters 1970 359. 233 A. A. El-Anani C. C. Greig and C. D. Johnson Chem. Comm. 1970 1024. 23J I. Murata T. Nakazawa and M. Okazaki Tetrahedron Letters 1970 3269. 364 H. Heaney conjugate acid (266) which is dark At room temperature the thermo- dynamically more stable conjugate acid (267) or (268) which is red is formed. Like acenaphthylene the isomeric compound cyclopent[cd]azulene (269) undergoes 1,2-cycloaddition reactions at the double bond in the five-membered ring with for example dimethyl acetylenedicarboxylate.The stable azulenes (270) and (271) are formed.236 The compound (269) also undergoes cycloaddition reactions with carbenes for example with ethoxy~arbonylcarbene.~~~ Valence isomerisation leads directly to the 2H-benzazulene (272). E. Haselbach Tetrahedron Letters 1970 1543. 23b K. Hafner and R. Fleischer Angew. Chem. Internat. Edn. 1970 9 247. 237 K. Hafner and W. Rieper Angew. Chem. Internat. Edn. 1970 9,248.