10 Aromatic Compounds By R. BOLTON Department of Chemistry Bedford College London NW14NS 1 General and Theoretical Considerations Calculations by ab initio methods are the basis of a discussion' of the stabilities of the isomeric CloHlo annulene systems. Similarly ab initio modelling of substituent effects in the Hammett LFER correlation is the basis of an important contribution from Streitwieser's school.' An equally useful contribution extending the relation- ship is the hyperbolic modification suggested by Lewis Shen and More O'Ferrall in a paper that deserves study.3 In this context the introduction of a new substituent constant uc+, is relevant. Derived by Brown by methods that parallel those used to obtain the most successful u+fun~tion,~" it applies to 13Cn.m.r.spectroscopic chemical shifts in carbocations and is based upon the a,a-dimethylbenzyl ('t-cumyl') system The parameters fit well with the result of measurements in the 2-butyl- 2-phenyl and 4-heptyl-4-phenyl carbocationic and also have been applied with similar success to the 3-aryl-3-pentyl and 2-aryl-2-adamantyl analogues.4c The significance of these new parameters and the breadth of their application are still to be determined. The M function has been reconsidered and improved by Marziano and his colleagues5 and awaits an exhaustive study of its potentialities. MIND0/3 calculations of the structure fragmentation and scrambling of phenyl carbocations have been reported6 and so have studies of the protonation of ethylene and of benzene.These calculations7" follow an earlier assessment of the relative importances of u-and 1.r-complexes in the protonation of benzene7' and suggest that while the heat of reaction is reduced by proton solvation the desolvation of the proton is not complete until well after the transition state; considering the very high solvation energy of H' in comparison with activation energies of processes that readily occur at ordinary temperatures this conclusion might have been expected from thermodynamic considerations alone. Twist in 2,4,6-trialkyl-L. Farnell J. Kao L. Radom and H. F. Schaefer tert. J. Am. Chem. SOC.,1981,103,2147. E.R. Vorpagel A. Streitwieser jun. and S. D. Alexandratos J. Am. Chem. SOC.,1981 103 3777. E.S. Lewis C. C. Shen and R. A. More O'Ferrall J.Chem. Soc. Perkin Trans. 2 1981 1084. '(a)H. C. Brown and Y. Okamoto J.Am. Chem. SOC.,1958,80,4979;(b)H.C.Brown M. Periasamy and K.-T. Liu J. Org. Chem. 1981 46 1646; (c) D.P. Kelly M. J. Jenkins and R. A. Mantello J. Org. Chem. 1981,46 1650. N. C.Marziano A. Tomasin and P. G. Traverso J. Chem. SOC.,Perkin Trans. 2 1981 1070. M. Tasaka M. Ogata and H. Ichikawa J. Am. Chem. SOC.,1981,103 1885. '(a)T. Sordo M. Arumi and J. Bertran J. Chem. SOC.,Perkin Trans. 2 1981 708; (b)T.Sordo J. Bertran and E. Canadell J. Chem. SOC.,Perkin Trans. 2 1979 1486. 205 206 R. Bolton biphenyls8 and in 2,4,6-trisubstituted benzophenones' has been studied by dynamic n.m.r. spectroscopic methods; the rotation about the central bond in 9,9'-bifluorenyl has similarly been investigated." Two interesting systems have come under study recently.The first is the iodonium derivative (l),"' the synthesis of which had been claimed by both the present authorslla and by Beringer and his group.llb The instability of the system both towards decomposition and towards the collapse of ion pairs to covalently bonded isomers complicated its identification; however salts with BPh,- and with SbC16- counter-ions were isolated"' despite the formal similarity with the cyclopentadienyl carbocation. Part of this stability may well depend upon the phenyl substituents. The second structure of interest is that of arsabenzene (2). Although the details of the mechanisms of reaction have not been conclusively demonstrated the system undergoes hydrogen exchange with trifluoroacetic acid in dichloromethane as well as Friedel-Crafts acetylation by acetyl chloride-aluminium chloride (CH2C12 -78 "C)and nitration (HN03-A~20).'2 Both the mild reaction conditions and the orientation of attack (ortho and para to the hetero-atom) contrast sharply with those of pyridine and further studies of (2) will be of interest.2 Benzene Derivatives Electrophilic Substitution.-The recent p~blication'~ of studies in the gas phase of the interaction between Me+ NO' NO2+ and 02NCH2+ with benzene fluoro- or chloro-benzene anisole toluene or benzotrifluoride shows that here no Wheland- type intermediates predominate but that charge transfer is the main process. The obvious differences between these processes and a number of classical electrophilic reactions show clearly the role of the solvent in determining the course of the reaction so that theoretical calculations of electrophilic substitution reactions must take account of solvation to be valid.Each of the main schools has contributed to aspects of nitration. Ridd and his colleagues14 have confirmed and extended their earlier report of the course of the nitration of derivatives of "aimethylaniline by nitric acid in 70% sulphuric acid. The formation of (3)requires nitrous acid and the previously proposed mechanism * G. Hafelinger and M. Beyer Chem. Ber. 1981,114,109. Y. Ito Y. Umehara K. Nakamura Y. Yamada T. Matsuura and F. Imashiro J. Org. Chem. 1981 46,4359. lo G.A. Olah L. D. Field M. I. Watkins and R. Malhotra J. Org. Chem. 1981,46 1761. (a) G. R. Buske and V. R. Sandel Abstr. 6th Great Lakes Regional Meeting Am. Chem. SOC. Houghton MI U.S.A. June 22-23 1972; (6)F.M.Beringer P. Ganis G. Avitabile and H. Jaffe J. Org. Chem. 1972,37,879;(c)V.R. Sandel G. R. Buske S. G. Maroldo D. K. Bates D. Whitman and G. Sypniewski J. Org. Chem. 1981,46,4069. l2 A. J. Ashe tert. W.-T. Chan T. W. Smith and K. M. Taba J. Org. Chem. 1981,46 881. l3 J. D.Morrison K. Stanney and J. Tedder J. Chem. SOC.,Perkin Trans. 2 1981,838,967. l4 F. Al-Omran K. Fujiwara J. C. Giffney J. H. Ridd and S. R. Robinson J. Chem. SOC.,Perkin Trans. 2,1981 518. Aromatic Compounds LJ R was strengthened by the identification of the cation radical (4) [reaction (l)].Rearrangement of (3)gives the o-nitroaniline derivative (5); the m-isomer is thought to arise by direct electrophilic attack. These conclusions were justified by a study of the enhancement of the ”N n.m.r. signal in the course of the nitration of NNdimethylaniline by H1’NO3 in 85-90’/0 sulphuric acid. p-Nitro-NN-dimethyl- aniline but not the m-isomer nor the nitric acid reagent showed an enhanced emission signal that subsequently reverted to a weaker absorption signal. l5 The enhancement and the change of phase were consistent with the formation of a radical pair such as (6) arising not from electron transfer within a caged system but from the random association of NO,’ and ArHt and so suggested a mechanism for the formation of the p-nitro product different from that of the m-isomer (formation of which showed no radical component).The formation and isolation of (3; R = Me) had already been reported,16 but it was significant that enhancement of the ‘’N n.m.r. signal (‘CIDNP’) was again observed during the exchange of the nitro group between isotopically different (3) and nitric acid; in both cases the signal from the (3) present was enhanced whether it was the reagent or the product but here both signals were absorption and not emission phenomena.” Draper and Ridd have also studied the nitration of some quaternary anilinium derivatives in 63.7-100% nitric acid at 25 “Cand have coupled this with a study of the nitration of a number of activated aromatic compounds (usually phenolic ethers) in which a first-order contribution competed with a zeroth-order component in the kinetic form.18 The latter process reflected the formation of nitronium ions as a kinetically limiting step and demonstrated the rate-determining formation of an encounter pair.In 83-98% H3P04 phenol and anisole may show a zeroth-order kinetic form in their nitration by a deficiency of nitric acid. The reaction rate may also under certain conditions show a first-order dependence upon the concen- tration of the arene but be independent of its nature. Such behaviour was consistent with an encounter-controlled nitration.” The nitration of durene l5 J. H. Ridd and J. P. B. Sandall J. Chem. SOC.,Chem. Commun. 19111,402. l6 P. Helsby J. H. Ridd and J.P. B. Sandall J. Chem. SOC.,Chem. Commun. 1981 825. ’’ P. Helsby and J. H. Ridd J. Chem. SOC.,Chem. Commun. 1980 926. l8 M.Draper and J. H. Ridd J. Chem. SOC.,Perkin Trans. 2 1981 94. l9 H. W. Gibbs L. Main R. B. Moodie and K. Schofield J. Chem. SOC.,Perkin Trans. 2 1981 848. 208 R. Bolton (1,2,4,5 -tetramethylbenzene) in aqueous sulphuric acid occurs under encounter- controlled conditions whereas that of 3-nitrodurene proceeds at one-twentieth of the rate; the corresponding reactions of prehnitene (1,2,3,4-tetramethylbenzene) occur at 41 times the rate of the nitro-derivative and there is an impressive parallel between such results and those found using a theoretical mixing-reaction model with NO2+PF6- in nitromethane attacking nitromethylbenzenes.20 A more complicated situation was found in the nitration of styrene derivatives (PhCH=CHX) in sulphuric acid; electron-withdrawing groups are necessary to prevent or minimize the competing electrophilic addition to the olefinic bond but even in cases where this has been successful the interpretation of the results in terms of classical electronic effects is difficult.The comparison between the behaviour of such systems and the corresponding PhX structure seems to be a valuable test of the various mechanisms proposed to explain the orientation of electrophilic attack; the difficulties of interpretation perhaps explain the general lack of work in this field.21 Suzuki and his colleagues have demonstrated that the nitration of monoacyl- and 1,3-diacyl-polymethylbenzenesto give side-chain nitration products occurs preferentially at the most crowded carbon atom in the latter case at the site between the two acyl groups.22 They have also extended their studies of anomalous nitration to the thiophen systems and showed that 2,s-dimethylthiophen undergoes nitration with copper nitrate and acetic anhydride to give some benzyl nitrate analogues and that 3,4-dibromo-2,5-dimethylthiophen shows similar behaviour on treatment with nitric acid in di~hloromethane.~~ Fischer and his group have continued their studies of the ips0 adducts with a report of the stereochemistry of the 1,4-dimethyl-4- nitrocyclohexa-2,5-dienolsand their acetates and methyl and a report of the complex behaviour of the diastereoisomers resulting from the addition of nitronium acetate to p-ethyltoluene.Aluminium hydride cleaves these species stereospecifically to give diols which may undergo methylation. Re-aromatization of these reduction products depended on its direction upon the substituent (NO2 OH OMe OAc) attached to the cyclohexadiene carb~cation.~’ The nitration of more fully substituted aromatic systems provides readily isolable adducts; thus 2,4-dibromo-3,6-dimethylphenolgives (7a)26 and 2,4,5-tribromo-3,6-dimethyl-phenol gives the analogous compound (7b). Compound (7b) undergoes ring- contraction on treatment with aqueous sodium carbonate (Scheme 1)to give (8) which is the major product obtained under aqueous nitration condition^.^^ Olah has reportedz8 the use of silver nitrate-boron trifluoride as a nitration agent in acetonitrile including a study of the mechanism of the reaction; he has also ” A.K. Manglik R. B. Moodie K. Schofield E. Dedeoglu A. Dutly and P. Rys J. Chem. SOC.,Perkin Trans. 2 1981 1358. R. B.Moodie K. Schofield P. G. Taylor and P. G. Baillie J. Chem. Soc. Perkin Trans. 2 1981,842. 22 H. Suzuki M. Hashihama and T. Mishina Buff. Chem. SOC.Jpn. 1981,54 1186. 23 H.Suzuki I. Hidaka A. Iwasa and T. Mishina Bull. Chem. SOC.Jpn. 1981 54,771. 24 A.Fischer G. N. Henderson T. A. Smyth F. W. B. Einstein and R. E. Cobbledick Can. J. Chem. 1981,59 584. ’’ A. Fischer and G. N. Henderson Can. J. Chem. 1981,59,2314. 26 M. P. Hartshorn H. T. Ing K. E. Richards and W. T. Robinson J. Chem. Soc. Chem. Commun. 1981,225. *’ P.A. Bates E. J. Ditzel M. P. Hartshorn H. T. Ing,K. E. Richards and W. T. Robinson Terrahedron Lett. 1981,22,2325. 28 G. A. Olah A. P. Fung S. C. Narang and J. A. Olah J. Org. Chem. 1981,46,3533. Aromatic compounds 209 Br I Me (7) 111 a; X=H b; X = Br Reagents i HN0,-HOAc; ii Na,CO (aq); iii HN0,-HOAc-H,O Note Reactions (ii) and (iii) occur only with X = Br Scheme 1 extended the range of N-nitro heterocyclic compounds able to behave as sources of nitronium ion to include N-nitropyrazole which in the presence of Lewis or Bronsted acids acts as a rather unselective nitrating agent. Like the corresponding reagents reported previously this N-nitro derivative shows little relationship between substrate and positional reactivity in its attack upon alkylben~enes.~~ In view of the variety of mechanisms of aromatic nitration which have recently been discovered a study of the displacement of 3-substituents in indole to give 3-nitroindole might have offered valuable support to the more unusual proposals.However this ips0 displacement although it took place with either nitrous or nitric acid in acetic acid does not allow an assured interpretation because of the somewhat forcing conditions employed. The authors consider NO’ or NO2+to be the respon- sible reagents but the formation of dinitrogen tetraoxide (a necessary consequence of oxidation when nitrous acid is used) allows a number of alternative Halogenation studies have concentrated upon the addition products.de la Mare’s school have continued their careful identification and characterization of addition compounds formed during the attack upon aromatic systems with reports of the tetrachlorotetrahydro-2-methyl naphthalene^^' and an analysis of the 13C n.m.r. spectra of these and the corresponding derivatives of na~hthalene.~~ They have also investigated the properties of the bromination products of the isomeric cresols including dienone structures and their thermal and photochemical reactions. The action of hydriodic acid (55% HI) upon polybromophenols offers a route to 3,5-disubstituted phenols that are otherwise not easily prepared; thus 5-bromo-3- methylphenol 3-bromo- and 3,5-dibromo-4-methylphenol, and 3-bromo- 5-bromo- and 3,5-dibromo-2-methylphenolmay all be obtained from the corres- ponding cresols through their polybrominated derivative^.^^ The difficulties of distinguishing the contribution of r-complexes to the course of electrophilic substi- tution reactions have been referred and the argument may be given new 29 G.A. Olah S. C. Narang and A. P. Fung J. Org. Chem. 1981,46,2706. 30 M. Colonna L. Greci and M. Poloni J. Chem. SOC. Perkin Trans. 2 1981 628. ” P. B. D. de la Mare and B. C. J. McKellar J. Chem. SOC. Perkin Trans. 2 1981,42. 32 G. A. Bowmaker D. Calvert P. B. D. de la Mare and B. C. J. McKellar J. Chem. SOC. Perkin Trans. 2 1981 1015. 33 J. M. Brittain P. B. D. de la Mare and P. Newman J. Chem. SOC. Perkin Trans. 2 1981 32. 34 R. Bolton Annu. Rep. Prog. Chem. Sect. B 1979 186.210 R. Bolton impetus by Fukuzumi and Kochi’s report,35 in which they claim the first systematic and general study of charge-transfer complexes between arenes and chlorine bromine or mercury(I1) trifluoroacetate. Me0 \ Me0 The bromination of 6,7-dimethoxy-l-phenyl-1,2,3,4-tetrahydronaphthalene (9) in acetic acid with pyridine showed concomitant acetoxylation at C-8; the corres- ponding reaction of 3,4-dimethoxy-di- or -tri-phenylmethanes (10)showed acetoxy- lation at C-2 but l-(3’,4‘-dimethoxyphenyl)-1,2,3,4-tetrahydronaphthalene (11) gave no such The authors interpret their observations in terms of a ‘doubly benzylic’ carbocation though it is unclear to the Reporter why an addition- elimination mechanism was rejected. Friedel-Crafts alkylation processes were involved in the catalysed (A12Br6-HBr) rearrangement of [l-’3C]toluene in which the methyl group was shown to undergo 1,2-shifts about the ring.The formation of doubly labelled diethylbenzene from ethylbenzene occurred at the same rate as 13Cappeared at the para position so that transalkylation-dealkylationwas found to proceed intermolecularly under these c~nditions.~~ It has been observed that treatment of benzene with aluminium chloride alone gives alkylbenzenes and biphenyl38” and that the presence of carbon monoxide and hydrogen is not necessary nor are the isotopes incorporated in these arenes when 13C0 or 2H2is present. From these findings the earlier of the influence of transition-metal carbonyls upon these reactions must be viewed with reserve.A study of the variation of the isomer distribution in the acetylation of naph- thalene in 1,2-dichloroethane at 20 “Cinterprets the results in terms of a separate third-order process by which the a-isomer is formed and a second-order process that produces the The mathematical analysis for the successful separ- ation of these two contributions is necessarily complicated and is applicable only with some assumptions that limit the range of results for which the treatment is valid. Although good agreement was found between the experimental results and the parameters derived from them the absolute values of these parameters are conditioned by the limits of the mathematical analysis one requirement of which is that both the time of reaction and the extent of formation of the &isomer are small; in some cases it is not certain that the second condition is met adequately ’’ S.Fukuzumi and J. K. Kochi J. Org. Chem. 1981,46,4116. 36 W. M. Bandaranayake and N. V. Riggs Aust. J. Chem. 1981,34,115. ’’ R. M. Roberts and S. Roengsumran J. Org. Chem. 1981,46 3689. ’* (a) L. S. Benner Y.-H. Lai and K. P. C. Vollhardt J. Am. Chem. SOC.,1981 103 3609; (6) G. Henrici-Olive and S. Olive Angew. Chem. Int. Ed. Engl. 1979 18 77. 39 A. D. Andreou R. V. Bulbulian P. H. Gore F. S. Kamounah A. Y. Miri and D. N. Waters J. Chem. Soc. Perkin Trans.2 1981 376. Aromatic Cornpo u nds 211 and an iterative computer simulation method might provide numerical values somewhat different from the rate constants.It has also been shown4' that the acetyl-group exchange which occurs on treatment of acetomesitylene (2,4,6- trimethylacetophenone) or acetodurene (2,3,5,6-tetramethylacetophenone)with [14C]acetyl chloride-aluminium chloride involves ips0 attack at C-1 for there was no detectable displacement of deuterium when 3,5-dideuterioacetomesitylenewas used. The reaction must not therefore involve diacylation as a necessary precursor to exchange and the reaction is not therefore reversible in the classical sense (Scheme 2). MeOC COMe COMe M e 8 M e o.,._- e MeoMe Me Me Me COMe Me Reagents i Me'"C0CI; ii -MeCOCI Scheme 2 Nucleophilic Substitution.-Comparatively little new material has been reported during the last year the literature containing mainly extensions or confirmations of known reactions.Thus a further report of the nucleophilic displacement reactions of halogenobenzene complexes to metal-carbonyl systems consolidates earlier reported The rate of reaction of chloro-2,4-dinitrobenzeneis reported with a number of derivatives of 4-aminothiane (12) in 80% aqueous di~xan;~' here the interest lies not with the mechanism of the displacement but rather with the properties of the primary amines. Bamkole Hirst and 0nyid0~~ have reported a study of the reaction of fluoro-or chloro-2,4-dinitrobenzene with 2,2,2-trifluoroethylamine. No base catalysis is found here; it occurs in the corresponding displacement reaction of 1,3,5-trinitrobenzene but only in acetonitrile and not in dimethyl sulphoxide.The reaction of aniline with 1,3,5-trinitrobenzene shows base catalysis by DABCO (diazabicyclo-octane) in both solvents. Such a capricious catalysis admits a number of explanations but the ready formation of Meisenheimer 40 A. D. Andreou R. V. Bulbulian P. H. Gore D. F. C. Morris and E. L. Short J. Chem. SOC.,Perkin Trans. 2 1981 98. "'A. C. Knipe S. J. McGuinness and W. E. Watts J. Chem. SOC.,Perkin Trans. 2 1981 193. 42 P. L. Subramanian K. Ramalingam N. Satyamurthy and K. D. Berlin J. Org. Chem. 1981,46,4384. 43 T. 0.Bamkole J. Hirst and I. Onyido J. Chem. SOC.,Perkin Trans. 2 1981 1201. 212 R. Bolton complexes from this trinitrobenzene under very similar conditions suggests a poss- ible mechanism. Among a number of contributions to more detailed knowledge of such complexes Crampton and Gibson44 have reported that in the reaction of 1,3,5-trinitrobenzene with n-butylamine benzylamine isopropylamine or piperidine in dimethyl sulphoxide proton transfer becomes kinetically significant.The possible contribution which the stability of the Meisenheimer complex may make to the observed kinetics is shown in a study of the nucleophilic attack by tetramethylammonium hydroxide in aqueous t-butanol upon some polynitroben- zene derivatives. 1,3,5-Trinitrobenzene gives the cr-adduct ;chloro-2,4-dinitroben-zene gives 2,4-dinitrophenol. The rates of these two processes fall when the amount of water in the solvent is increased. In contrast picryl chloride gives picric acid at a rate which increases with increasing concentration of water in the solvent mixture and this behaviour is ascribed to the necessary formation of the 3-hydroxy add~ct.~~ The number of a-complexes possible increases considerably when more than one reaction centre is available as shown by the behaviour of 2,4,6-trinitrobenzyl chloride and of 2,4,6-trinitrotoluene with the latter compound continues to provide a rich source of Meisenheimer adducts.The SNAr mechanism has been associated with some of the more successful applications of the Hammett equation. This year the Nigerian workers have reported the effect of substituents at the 2- and 2,5-positions of aniline upon the rate of displacement of chlorine from picryl chloride in acetonitrile. Additivity was found only to a limited extent.47 In the 2-bromo-3-nitro-5-X-thiophen system (X = Br CONHz COMe SO,Me CN or NOz) an inconsistency was found with the expectations of the structure-reactivity relati~nship.~~ The authors might take comfort from a recent review49 of the limitations of predictions based upon this relationship.Aminodemethoxylation of 5-acetyl-2-methoxy-3-nitrothiophenand of 5-carbomethoxy-2-methoxy-3-nitrothiophenby piperidine shows catalysis by both piperidine and methoxide ion; loss of the methoxy group is also reported to show general acid catalysis.50 Nucleophilic attack of 2,4- and 2,6-dinitroanisole by piperidine or N-methylpiperidine shows the duality of reaction which a number of such systems undergo. Thus methylation competes with dinitroarylation.The authors seem surpri~ed,~' but Miller and Moran5' recently reported a similar reaction and indeed allied processes have been long known.53 The synthesis of l,3,5-trifluoro-2,4,6-trinitrobenzenes4" has led to a study of some of its nucleophilic displacement reactions. The combination of electron-withdrawing groups promotes 44 M. R. Crampton and B. Gibson J. Chem. SOC., Perkin Trans. 2 1981 533. 45 A. D. A. AlAruri and M. R. Crampton J. Chem. SOC., Perkin Trans. 2 1981 807. 46 D. N. Brooke M. R. Crampton G. C. Corfield P. Golding and G. F. Hayes J. Chem. SOC., Perkin Trans. 2 1981 526. 47 T. A. Emokpae J. M. Nwaedozie and J. Hirst J. Chem. SOC., Perkin Trans. 2 1981 883. 48 G. Consiglio C. Arnone D. Spinelli R.Noto and V. Frenna J. Chem. Soc. Perkin Trans. 2 1981 388. 49 C. D. Brown Tetrahedron 1980 36 3641. G. Consiglio C. Arnone D. Spinelli and R. Noto J. Chem. SOC.,Perkin Trans. 2 1981,642. N. S. Nudelman and D. Palleros J. Chem. Soc. Perkin Trans. 2 1981,995. 52 J. Miller and P. J. S. Moran J. Chem. Res. 1980 (S) 62 (M)0501. 53 M. Kohn and F. Grauer Monatsh. Chem. 1913,34 1751. 54 (a)W. M. Koppes M. E. Sitzmann and H. G. Adolph U.S.P. 4 173 591 (Chem. Absrr. 1979 91 39 112); (6) W. M. Koppes G. W. Lawrence M. E. Sitzmann and H. G. Adolph J. Chem. Soc. Perkin Trans. 1 1981 1815. Aromatic Compounds 213 some remarkably easy reactions such as the displacement of fluorine by bromide ion in acetonitrile at room temperature and the hydroxydefluorination of 5-fluoro-2,4,6-trinitro-1,3-diaminobenzeneby 15 h boiling in 96% aqueous acetic The acid-catalysed hydrolysis of 2-fluoropyridine and of a number of analogously substituted derivatives of methylpyridine quinoline and pyrimidine occurs in aqueous hydrochloric acid at a rate which follows ho at low acidities but then shows maxima at higher acid concentrations.The application of various functions such as w w” and the Bunnett-Olsen equation led to the conclusion that the hydrolysis of the pyrimidine derivatives involved the slow attack by water upon the cation and that the slower substrates showed additional contributions by proton transfer to water Perchloroindane has been showns6 to react with ethoxide ion to give first the 5-ethoxy derivative and then the 1,1,5-triethoxy analogue.Errors in the literature were corrected and a number of interesting reactions are described. The ring-opening of pyrylium ions by primary amines is reported to be fast with strong bases and base-catalysed with the weaker amines. The subsequent ring- closure to form the pyridine system is acid-catalysed and apparently suffers from steric hindrance and concomitant electronic effects while the effect of solvents as might be predicted from such a multi-stage reaction is ~ornplex.~’ Katritzky and his colleagues have reported the kinetics of decomposition of N-benzyl-2,4,6- triphenylpyridinium ions,58a the effect of pyridine substituents in the decomposition of N-benzylpyridinium ions (in which the rate variations are most simply tied to the steric effects of the leaving group),586 and a study of the result of introducing substituents into the phenyl system of N-benzyl-2,4,6-triphenylpyridiniumion when the different degrees of contribution of SNl and sN2 processes were associated with the nucleophiles involved.The rates of displacement were dependent upon the ionic strength of the medium when anionic nucleophiles were used but not surprisingly with neutral The mechanism continues to attract attention and a report of some further reactions of 2-chloropyrimidine 4-chloro- 2,6-dimethoxypyrimidine,3-chloro-6-methoxypyridazine,and 2-chloropyrazine with enolates in liquid ammonia extended the range of the process.59 An elegant and much needed demonstration of a chain process similar to this SRNl mechanism was made by Eberson and Jonnson60 who reasoned that as bis(pentafluorobenzoy1) peroxide attacked chlorobenzene at the ips0 position,61 p-fluoroanisole should undergo attack by benzoyl peroxide to lose fluorine.The logic was not flaw- less for fluorobenzene undergoes much less selective attack by bis(pentafluor0- benzoyl) peroxide than does either chloro- or bromo-benzene and much less ester ” H. R. Clark L. D. Beth R. M. Burton D. L. Garret A. L. Miller and 0. J. Muscio jun. J. Org. Chem. 1981,46,4363. 56 M. Ballester J. Riera L. Julia J. Castaner and F. Ros J. Chem. Soc. Perkin Trans. 1 1981 1690. s7 A. R. Katritzky and R. H. Manzo J. Chem. SOC.,Perkin Trans.2 1981 571. (a) A. R. Katritzky G. Musumarra K. Sakizadeh and M.Misic-Vukovic J. Org. Chem. 1981 46 3820;(6)A.R.Katritzky A. M. El-Mowafy G. Musumarra K. Sakizadeh C. Sana-Ullah S. M. M. El-Shafie and S. S. Thind J. Org. Chem. 1981 46 3823; (c) A.R.Katritzky G. Musummara and K. Sakizadeh J. Org. Chem. 1981,46,3831. 59 D. R. Carver A. P. Komin J. S. Hubbard and J. F. Wolfe J. Org. Chem. 1981,46,294. 6o L.Eberson and L. Jonsson J. Chem. SOC.,Chem. Commun. 1981,133. P. H. Oldham and G. H. Williams J. Chem. SOC.(C),1970 1260. 214 R.Bolton is produced;62" nor is benzoyloxydehalogenation common in the reaction of benzoyl peroxide with polyfluorobenzenes.62b Nevertheless in solutions of potassium acetate in acetic acid a chain reaction was set up in which fluorine in p-fluoroanisole was displaced mainly by acetate ion the ratio of acetate to benzoate attack being between 2.6 and 7.3 to 1and demonstrating thereby the chain process.Diazonium ion studies have been limited to a detailed study of the association of crown ethers with these ions in which the earlier was confirmed,63b and to an attempt to show the two-stage nature of the Sandmeyer reaction. The Ko~hi~~ mechanism allowed two essential roles to the copper catalyst and it was intended to replace copper in the second process by adding another metal salt (Scheme 3). Of the additives chosen only iron(II1) showed a little catalytic efficacy PhN2+ + X-+ Cu' + Ph*+ N2 + X-+ Cu2+ Ph*+ CuX2 + PhX + CuX (X = Bror C1) Scheme 3 in the absence of copper(1) chloride but in its presence iron(@ salts ferrocene and tin@) chloride all showed the ability to promote the Sandmeyer reaction although the best yields with these additives were only marginally better (68%) than without (63°h).65Sandmeyer's discovery was as he reported,66 a happy accident but Hodgson6' has made a thorough study of the effect of a number of metal salts upon promoting this decomposition of diazonium salts in hydrochloric acid media; he also found iron(II1) chloride to be as weakly efficient as the present author finds it and this aspect of the work is confirmed well by the earlier study.It seems however that the demonstration of a two-stage mechanism by this latest method65 relies upon the assumption that where copper(1) has been oxidized to copper(I1) in the first step it cannot be subsequently reformed by iron(II) ferrocene or tin(I1).Oxidation potentials appear to allow such a process although it may be too slow to occur under the reaction conditions; until this point has been demon- strated the two-stage mechanism cannot be regarded as proved by these particular experiments. The arguments against an earlier mechanism and based upon the expected reactions of [ArI]' might also be criticized. Homolytic Aromatic Substitution.-The use of 'CIDNP' in demonstrating free- radical processes has been extended to the decomposition of azosulphones (ArN=NS02Ar') whose homolysis has been shown68 to be associated with anomalies in the 'H and 13Cn.m.r. spectra. The photolysis of p-toluoyl peroxide of p-tolyl sulphide sulphoxide or sulphone or of p-iodotoluene in mixtures of pyridine and pentadeuteriopyridine shows only slight isotope eff e~ts.~~ This con- trasted with the considerable isotope effects that have been found specifically in 62 (a)M.W. Coleman Ph.D. Thesis University of London 1972; (b) R. Bolton J. P. B. Sandall and G. H. Williams J. Fluorine Chem. 1978 11,591. (a) R. A. Bartsch and P. N. Juri J. Org. Chem. 1980 45 1011; (b)H. Nakazumi I. Szele and H. Zollinger Tetrahedron Lett. 1981 22 3053. 64 J. K. Kochi J. Am. Chem. SOC.,1957 79 2942; Tetrahedron 1962,483. " C. Galli J. Chem. SOC., Perkin Trans. 2 1981 1459. 66 T. Sandmeyer Ber. 1884 17 1633. 67 H. H. Hodgson S. Birtwell and J. Walker J. Chem. SOC.,1942 720; jbid. 1944 18. 68 M. Yoshida N. Furuta and M.Kobayashi Bull. Chem. SOC.Jpn. 1981,54,2354. 69 T. Nakabayashi T. Horii S. Kawamura and Y. Abe Bull. Chem. SOC. Jpn. 1981,54 2535. Aromatic Compounds 215 phenylation of 4-methylpyridine at the 2-position (kH/kD,3.7)by the thermolysis of benzoyl per~xide.~’ The discrepancy may reflect differences in the source and energy of the attacking radicals but raises some doubts about mechanistic interpreta- tions which the generalization from the earlier work allows. A confirmation of earlier work was found in a careful study of the phenylation of some simple arenes by the thermolysis of benzoyl peroxide at 80 “C. Earlier measurements of substituent effects and isomer distributions had relied upon the measurement of yields of biaryls that were often far short of those calculated; the assumption was often made that isomer ratios and even relative yields of competition products between arenes were not changed in consequence.The use of oxidation catalysts improved the biaryl yields to much nearer those expected from the stoicheiometry of reaction (2):71 ArH + RCOOOCOR = ArR + RC02H + COz (2) Measurements of the rates of thermolysis of dibenzylmercury derivatives in octane were used as a basis of substituent constants that are appropriate to homolytic processes (a’).” However the relatively small effects of substituents in homolytic processes mean a correspondingly large sensitivity to polar contributions whether derived from solvent interactions or reagent-substrate interactions. These are not constant and are not properties of the substituent alone; they must vitiate the general applicability of such a’values.3 Synthetic Aspects Mercuration of 1,2,4-trichlorobenzene by mercury(@ trifluoroacetate at the boiling point gives bis(2,3,6-trichlorophenyl)mercury (13).73 The corresponding 2,4,5- trichlorophenyl derivative is obtained using trifluoroacetic acid as solvent; at higher temperatures the 2,4,5-isomer rearranges so that the formation of these two organomercurials apparently reflects the imposition of thermodynamic or of kinetic control. The general difficulties of preparing 1,2,3,4-tetrasubstituted benzenes makes this synthesis important. r CI i Xenon(I1) fluoride in dichloromethane has been reported to give monofluorinated arenes with aromatic hydro~arbons;~~ thus 1-fluoro- and 2-fluoro-9,lO-dihydroan-thracene are obtained in the ratio 2 :3 from 9,lO-dihydroanthracene.In the presence of boron trifluoride xenon(I1) fluoride adds fluorine to pentafluorobenzene deriva- tives (C6F,X; X = H c1,Br or C6F5) to give l-X-heptafluorocyclohexa-1,4-dienes 70 S. Vidal J. Court and J. M. Bonnier J. Chem. SOC.,Perkin Trans. 2 1976,497. ’*R. Bolton B. N. Dailly K. Hirakubo K. H. Lee and G. H. Williams J. Chem. Soc. Perkin Trans. 2 1981 1109. 72 S. Dincturk R. A. Jackson M. Townson H. Agirbas N. C. Billingham and G. March J. Chem. Soc. Perkin Trans. 2 1981 112 1. ” G. B. Deacon and B. S. F. Taylor Aust. J. Chem. 1981 34,301. 74 B. Sket and M. Zupan Bull. Chem. SOC.Jpn. 1981,54,279. 216 R.Bolton (14) (14),75in a manner similar to that of KC OF,.^^ Ethers such as PriOC6Fs give a slightly more complex reaction to provide hexafluorocyclohexa-2,4-and -2,5-dienones [reactions (3)and (4)].Fluorine can also be introduced into phenol anisole toluene and biphenyl by the fluoroxysulphate ion (FSO,-) in acetonitrile. The mechanism of the substitution is uncertain but fluorine is found attached to sites ortho and guru to the substituent. On the other hand toluene also gives benzyl fluoride which suggests a radical component to the reaction that might otherwise seem to have electrophilic chara~ter.~~ Naphthalene is also attacked by this reagent.78 A particular application of such reactions might be the preparation of radio-labelled fluorocarbons containing 18F.Two further reports of syntheses of such materials have appeared this year. The first relies upon the cleavage of C-Sn bonds by molecular fluorine at -78°C [reaction (S)].Even at this temperature molecular fluorine is used as a 1% mixture in neon; radiochemical yields of 8% (R = Ph) and 37% (R = Bu; theoretical maximum 50%) are rep~rted.~' -78 "C,CFCI PhSnR3 + [18F]F2 Ph18F Alternatively fluorine may be introduced into the aromatic system through conventional diazonium ion chemistry. Although the Balz-Schiemann reaction is usually used to prepare such aryl fluorides it is wasteful of radio-label since three-quarters of the inorganic fluorine is lost as boron trifluoride. Ng Katzenellen- bogen and Kilbourn" successfully used the original Wallach" process in which a triazene (15)is decomposed by hydrogen fluoride.A second process in which the decomposition of an aryl azide (16)gives p-fluoroaniline was found to be less useful since the reaction required about three times the half-life of the radioisotope." Photocyanation of naphthalene or biphenyl occurs with potassium cyanide in aqueous acetonitrile or with sodium cyanide in methanol though in yields only in the range 12-27% .82 Aryl nitriles were found to act as necessary electron acceptors '' S. Stauber and M. Zupan J. Org. Chem. 1981,46 300. 76 I. W. Parsons J. Fluorine Chem. 1972-3 2 63. 77 D. P. Ip G. D. Arthur R. E. Winans and E. H. Appleman J. Am. Chem. Soc. 1981,103,1964. 70 S. Stauber and M. Zupan J. Chem. Soc.Chem. Commun. 1981,148. 79 M. J. Adam B. D. Pate T. J. Ruth J. M. Berry and L. D. Hall J. Chem. SOC.,Chem. Commun. 1981,733. 80 J. S. Ng J. A. Katzenellenbogen and M. R. Kilbourn J. Org. Chem. 1981 46 2520. 0. Wallach Liebigs Ann. Chem. 1886 235 255; 0.Wallach and F. Heusler Liebigs Ann. Chem. 1888,243,219. N. J. Bunce J. P. Bergsma and J. L. Schmidt J. Chem. SOC.,Perkin Trans. 2 1981,713. Aromatic Compounds +-Ar-N=N-N 3 Ar-N=N=N (15) (16) so that sodium cyanide in aqueous acetonitrile photocyanated phenanthrene naph- thalene methoxynaphthalene or rn-dimethoxybenzene usually in 50-70% yield but with only 30-50% conversi~n.~~ Lapin and KurzS4 report the photochemical cyanomethylation of electron-rich aromatic systems over 22 h irradiation; yields are poor (16% for pdimethoxybenzene) although the conversion is somewhat higher.Nitromethylation of arenes has already been reported.85a A mechanistic study of the hydrogen isotope effect showed k,/k 4.0-4.2 for deuterionitromethane (D,CNO,) but 1.05 for hexadeuteriobenzene compared with C6H6.It followed that the Mn"' acetate used was involved kinetically with the formation of the reagent and that hydrogen loss from the intermediate in the aromatic substitution is not rate-limiting.85b Cerium(1v) as cerium ammonium nitrate is effective also but concomitant nitration occurs. The orientation of attack (55% ortho attack of toluene) is considered consistent with a homolytic aromatic substitution mechanism and is similar to that shown by phenyl radicals.85c Electrolytic (anodic) nuclear acetoxylation of alkylarenes is brought about by a non-divided cell containing palladized The purpose of the catalyst is to promote hydrogenolysis at the cathode of the side-chain acetoxylation products thus allowing the phenol esters to accumulate.The attack of carboethoxycarbene upon arenes which gives cycloheptatrienecar- boxylate esters in which the polyene system is not conjugated with the ester function is catalysed by rhodium(r1) salts such as the trifluoroacetate [strictly tetrakis(perfluoroalkylcarboxylato)dirhodium(~~)].Even hexafluorobenzene is attacked in a reaction with considerable synthetic potential." March and Engenito" have attempted to improve the yield of amidation products by the process given in reaction (6) ArH + MeCONH(0H) ArNHCOMe (6) but could not realize more than ca.50% yields with aromatic ethers which seem to have been the only substrates studied. Potassium metal in a mixture of polyglycol methyl ethers causes ethylene to alkylate aromatic hydrocarbons of the general formula ArR." Attack takes place at the benzylic positions and at sites ortho and meta (but not para) to the alkyl 83 M. Yasuda C. Pac and H. Sakurai J. Chem. Soc. Perkin Trans. 1 1981 746. 84 S. Lapin and M. E. Kurz J. Chem. Soc. Chem. Commun.. 1981,817. 85 (a) M. E. Kurz and T. Y. R. Chen J. Org. Chem. 1978 43 239; (b)M. E. Kurz P. Ngoviwatchai and T. Tantrarant J. Org. Chem. 1981,46,4668; (c)M. E. Kurz and P. Ngoviwatchai J. Org. Chem. 1981,46.4612.86 L. Eberson and E. Oberrauch Acta Chem. Scand. Ser. B 1981,35,193. 87 A. J. Anciaux A Demonceau A. F. Noels A. J. Hubert R. Warin and P. Teyssie J. Org. Chem. 1981,46,873. nn J. March and J. S. Engenito jun. J. Org. Chem. 1981,46,4304. 89 W. E. Russey and M. W. Haenel Tetrahedron Lett. 1981,22,4065. 218 R. Bolton I+ethylated reduction products Scheme 4 group; the reaction products are themselves unstable towards further hydrogenation under these conditions (Scheme 4). In the absence of ethylene these products if they are formed at all arise in lower yields and in different ratios -presumably through cleavage of the solvent. A kinetic study of the hydroxylation of benzene or of toluene by potassium peroxydiphosphate in aqueous acid (0.05-1 .OM) in the presence of copper(I1) showed the general similarity between this reagent and the peroxydis~lphate.~~" This latter reagent gives phenol biphenyl and 0-and p-nitrophenols in its reaction with a mixture of benzene and nitrobenzene (water 80°C).90b In the absence of benzene or when it is replaced by toluene or by anisole no nitrophenols are formed.Since the anisole radical cation is said to add water and toluene preferen- tially gives material derived from the benzyl radical the mechanism (Scheme 5) is H/'OH proposed in which the benzene radical cation (17) undergoes hydrolysis to give (18) from which hydroxyl radicals may be generated. The application of this suggestion to synthetic uses will be interesting.Phenols also arise from the photolysis of a-azohydroperoxides in mixtures of arenes and acetonitrile. The isomer distribu- tion changes when oxygen and not argon is present and this was held to show a change of mechanism away from the formation of aryl radicals and so a distinction from Fenton's reagent or radiolytic sources of hydroxyl radical." In this context it may be appropriate to report that Mishra and Symons9* demonstrated the inter- mediacy of u* radicals (in which the electron is localized to the C-halogen CT* orbital rather than the usual expectation of a v* orbital) in the irradiation of halogenobenzenes (y 6oCosource ca. 1Mrad 77 K). Electrophilic attack of alkylbenzenes by hydrogen peroxide with HF-BF occurs at -60 to -78 "C. Further attack is presumably minimized by the low temperatures 90 (a) K.Tomizawa and Y. Ogata J. Org. Chem. 1981,46 2107; (b)M. K. Eberhardt J. Am. Chem. SOC.,1981,103,3876. 91 T. Tezuka N. Narita W. Ando and S. Oae J. Am. Chem. SOC.,1981,103 3045. 92 S. P. Mishra and M. C. R. Symons J. Chem. SOC.,Perkin Trans. 2 1981 185. Aromatic Compounds 219 and highly acidic condition^.'^ Under circumstances where oxidation may occur quinones may arise from attempts to nitrate phenols by nitrate salts in trifluoroacetic anh~dride,’~ and a variety of interesting products may be obtained under special conditions Thus oxidation of 2-bromo-4,6-di-t-butylphenol (19a) with potassium hexacyanoferrate(II1) in benzene gives 1,4-dihydro-4-bromo-2,4,6,8-tetra-t-butyl-1-0xodibenzofuran (20a) which with methanol or ethanol gives the 4-alkoxy analogues (20b) but with isopropanol provides the fully aromatic derivative (2 1) (Scheme 6) presumably through the 4-isopropoxy species (20c).On the other hand 2-chloro-4,6-di-t-butylphenol (19b) gives 6,6’-bis(2,4-di-t-butyl-6-chloro-cyclohexa-2,5-dienone) (22) and 2,4-di-t-butyl-4-chloro-6-(2,4-di-t-butyl-6-chlorophenoxy)cyclohexa-2,5-dienone(23) the fluorine analogue of which is the sole product of oxidation of 2-fluoro-4,6-di-t-butylphenol by hexacyanofer- rate(111).~’ Benzene seleninic anhydride [(PhSe=O),O] oxidizes phenols specifically giving the o-quinone. Both naphthols afford 1,2-naphthoquinone 2,4- di-t-butylphenol provides 4,6-di-t-butyl-o-benzoquinone, and carvacrol and thymol both give 3-methyl-6-isopropyl-o-benzoquinone.96 The limits of the method are still to be assessed but some substrates such as 2,4-dimethylphenol and o-nitro- phenol do not undergo the reaction.Oxidative cleavage by 30% hydrogen per- oxide of p-cycloalkenyl groups provides hydroquinones from such para-substituted phenols in high (60-90%) yields and may be an appropriate synthetic method.97 Methods to obtain a-naphthols have also been reported. The condensation of diphenylacetaldehyde with diethyl malonate or with P-keto-esters provides the expected a$-unsaturated ester. However the presence of molecular sieves encouraged cyclization to give derivatives of 4-phenyl-1-naphthol [reaction (7); X = C02Et COMe or COPh]:98 Ph2CHCHO + CH,XCO,Et + Ph,CHCH=C(X)CO,Et +@Jx / (7) Ph 1-Aryl-2-benzoylcyclopropanes(24) cyclize under the influence of Lewis acids to give 4-aryltetralones but apparently only under conditions in which the aryl group and usually the benzoyl fragment as well has hydroxyl or alkoxyl sub- ~tituents.’~A method which appears to have more general synthetic potential involves the Michael addition of lithium phthalide to a variety of olefins.The 4-hydroxytetralones which are formed readily undergo acid-catalysed dehydration to form a-naphthols.”’ In the presence of both aluminium chloride and boron ArvcoPh (24) 93 G. A. Olah A. P. Fung and T. Keumi J. Org. Chem. 1981,46,4305. 94 J. V. Crivello J. Org. Chem. 1981 46 3056. 95 M. Tashiro H. Yoshiya and G. Fukata J. Org.Chem. 1981 46 3784. 96 D. H. R. Barton A. G. Brewster S. V. Ley C. M. Read and M. N. Rosenfeld J. Chem. SOC.,Perkin Trans. 1 1981 1473. 9’ D. V. Rao and F. A. Stuber Tetrahedron Lett. 1981 22 2337. G. A. Taylor J. Chem. SOC.,Perkin Trans. 1 1981 3132. 99 W. S. Murphy and S. Wattanasin J. Chem. SOC.,Perkin Trans. 1 1981 2920. loo N. J. P. Broom and P. G. Sammes J. Chem. SOC.,Perkin Trans. 1 1981,465. 220 R. Bolton trifluoride chloromethyl cyanide (chloracetonitrile) attacks phenols to give o-chloroacetylphenols exclusively.'o' The authors make the point that although the reaction conditions seem very similar to those of the Houben-Hoesch reaction under the latter conditions only the p-hydroxyketone is found. It is perhaps worth recalling that the orientation of the Houben-Hoesch reaction like that of the Fries rearrangement may be altered by changing the temperature at which the reaction occurs so that the contribution useful though it is might be most useful in the preparation of thermally unstable hydroxyacetophenones.(19) a; X == Br (20) a; X = Br b; X == C1 b; X = MeOor EtO c X = OPr' (19b) A + Reagent i K,Fe(CN),-C,H Scheme 6 Mixed acid anhydrides are obtained by the decomposition of diazonium borofluorides in acetonitrile in the presence of carbon monoxide sodium carboxy- late and a palladium(0) catalyst [reaction (S)] lo* ArN2+ + CO + RC02-+ ArCOOCOR + N2 (8) Palladium(I1) acetate is important in the synthesis of ortho-substituted aniline derivatives. Acetanilide and rn-and p-substituted analogues form derivatives of (25) which undergo reactions at multiple bonds that involve cleavage of the C-Pd bond and formation of a new carbon-carbon bond (Scheme 7).'03 2-Bromoacetanilide can also provide anthranilic acid derivatives through palladium complexation and subsequent attack by carbon monoxide; yields range between 70% and 90%.104 lo' T.Toyoda K. Sasakura and T. Sugasawa J. Org. Chem. 1981 46 189. lo' K. Kikukawa K. Kono K. Nagira F. Wada and T. Matsuda J. Org. Chem. 1981 46 4413. lo3 H. Horino and N. Inoue J. Org. Chem. 1981,46,4416. D. Valentine jun. J. W. Tilley and R. A. Le Mahieu J. Org. Chem. 1981,46,4614. Aromatic Compounds 221 ~NHCOR CH=CHCOMe Scheme 7 Potassium amide gives o-hydroxyphenylamidines upon reaction with either o-or m-halogenobenzamides and these products on heating give benzoxazoles.The ring-closure occurs as a second stage in this synthetically useful reaction because of the instability of the benzoxazole system to amide ion.'O5 o-Bromo- or o-iodo- styrene oxide with n-butyl-lithium at -78 "Cprovides a preparation of l-hydroxy- benzocyclobutene.106 A new synthesis of benzo( 1,2;4,5)dicyclobutene by reaction of n-butyl-lithium with 2,2',2',5-tetrabromo-p-diethylbenzene(26)has been repor- ted"' and the useful intermediate 1-bromobenzocyclobutene (27) is obtained in 2045% yield from the interaction of bromoform potassium carbonate and cycloheptatriene in the presence of 18-crown-6 ether.lo8 CH,CH ,Br BrQ Br m-,Br CH ,CH ,Br (26) (27) Oxidation of a side-chain as in p-ethylanisole by copper(I1) sulphate and sodium peroxydisulphate in aqueous acetonitrile seems to be a promising route to aldehydes and ketones; in certain systems such as &methoxytetralin aromatization is also Benzhydrol derivatives may be made from benzaldehydes with -I substituents through their reaction with aryltrimethylsilanes in dimethylformamide in the presence of potassium t-butoxide.Labile ethers such as Ar,CHOSiMe are first formed and they cleave to give the alcohol [reaction (9)]:"' KOBut in HCONMe2 ArAr'CHOSiMe3 + ArCHOHAr' ArCHO + Ar'SiMe3 lo' M. I. El-Shiekh A. Marks and E. R. Biehl J. Org. Chem. 1981 46 3256. E. Akgun M. B. Glinski K. L. Dhawan and T. Durst J. Org.Chem. 1981,46,2730. lo' C. K. Bradsher and D. A. Hunt J. Org. Chem. 1981,46,4608. lo* M.R.de Camp and L. A. Viscogliosi J. Org. Chem. 1981,46 3918. lo9 M.V. Bhatt and P. T. Perumal Tetrahedron Lett. 1981,22,2605. 'lo F.Effenberger and W. Spiegler Angew. Chem.,Znt. Ed. Engl. 1981 20,265. 222 R. Bolton The preparation of 2,4-dinitrobenzenesulphonic acid from chloro-2,4-dinitrobenzene and potassium metabisulphite has been studied; the abstract however confuses the product with 2,4-dinitrobenzoic acid.' l1 A condensation between two three-carbon fragments affords a new synthesis of 2,6-disubstituted aniline derivatives. Yields are usually low (30%) but may reach 50% in special instances.l12 The preparation of 1,2,3,4-tetra-t-butylbenzene,and of 2,3,4,5-tetra-t-butyl- biphenyl as well as the analogously substituted furan and pyridine systems has been achieved through the Diels-Alder reaction of (28) with triple-bond systems such as RC=CCO2Me (R = H or Ph) and Me02CCN which provides a Dewar- benzene structure (or Dewar-pyridine structure) from which these compounds may be ~btained."~ (28) Oxidative coupling of arenes to obtain symmetrically substituted biaryls has remained popular since the first commercial synthesis of biphenyl by the thermal dehydrogenation of benzene.Thallium(II1) trifluoroacetate with 10% palladium(@ acetate is reported to be more effective in combination than either reagent is alone; the yields claimed114 certainly make this method of preparing some biaryls very attractive.A peculiar but preparatively useful reaction involves the rearrangement of arylhydrazines of derivatives of benzophenone by polyphosphoric acid. The process seems to have resemblances to the Benzidine Rearrangement so that (29) provides (30) (reaction (lo)].' Benzophenones and acetophenones having a p-hydroxyl function correspondingly give biaryl ethers. *lS6 PPA_ (30) The synthesis of some hydroxy-9,lO-dihydrophenanthrenesrecently reported' l6 relies upon the nucleophilic properties of the carbanions formed during the Birch reduction. Thus the dianion from the reduction of 2,5dimethoxybenzoic acid is alkylated by 2-(3',5'-dimethoxypheny1)ethyl iodide to give 1,4-dihydro-2,5-dimethoxy-l-(3',5'-dimethoxyphenyl)benzoicacid which affords a mixture of "' M.Gisler and H. Zollinger Angew. Chem. Int. Ed. Engl. 1981,20 203. '" P.Camps C. Jaime and J. Molas Tetrahedron Lett. 1981 22 2487. '13 A.Krebs E. Franken and S. Muller Tetrahedron Lett. 1981 22 1675. 'I4 A.D.Ryabov S. A. Deiko A. K. Yatsimirsky and I. V. Berezin Tetrahedron Lett. 1981 22 3793. 'I5 (a)R. Fusco and F. Sannicolo J. Org. Chem. 1981,46,83;(6)ibid. p. 90. K.-D. Krautwurst and W. Tochtermann Chem. Ber. 1981,114,214. Aroma tic Compounds hexahydro-5,7-dimethoxy-2-phenanthrones(31) [reaction (1l)]. Aromatization of (31) to give derivatives of 9,1O-dihydrophenanthr-2-01is achieved with pyridinium perbromide followed by treatment with n-butyl-lithium (Scheme 8). Allyltrimethylsilyl-lithium reacts with keto-acetals to give species from which by treatment with titanium(1v) chloride new benzene rings may be obtained.This promises to be a good general route to derivatives of biphenyl and of 9,lO- dihydrophenanthrene.' l7 CH2CH21 I M&OMe C02H -M&o ' MeOoOMe Me0 / Me0 (31) Reagents i D;o2-;ii Py+W; Me0 Scheme 8 4 Polybenzenoid and Non-benzenoid Systems Polybenzenoid Systems.-The ready loss of iodine and subsequent dimerization by some derivatives of naphthalene such as (32)are solid-state phenomena said1'* to arise from charge-transfer interaction between adjacent molecules in the crystal layers so that the ease of reaction reflects the packing efficiency; substituent effects are the result of influences upon this close packing rather than being electronic in character.The formation of 1,2,3,4-tetrahydrophenanthrenemay occur in the cyclization (BF3-Et20) of either isomer of 4-(naphthy1)butanol. The high susceptibility of the a-position to attack is reflected by a second mechanism unique to 4-(1'-naph-thyl)butanol in which ips0 attack followed by rearrangement is a minor (16%) contributor. 'I9 11' M. A. Tius TetrahedronLett. 1981 22 3335. D. W. Cameron G. I. Feutrell L. J. H. Pannan C. L. Raston B. W. Skelton and A. H. White J. Chem. SOC.,Perkin Trans. 2 1981 610. A. H. Jackson P. V. R. Shannon and P. W. Taylor J. Chem. SOC.,Perkin Trans. 2 1981,286. 224 R. Bolton Reagents i CHGCLi; ii reduction; iii HI or POCI Scheme 9 The unstable 2,3-naphthoquinone has been trapped by cyclopentadiene during its formation from 2,3-dihydro~ynaphthalene.’~’ The synthesis of anthraquinones by the use of isobenzofulvalene (33) analogous to the behaviour of isobenzofuran is described,121 and oquinones (e.g.phenanthraquinone) afford a good general annelation reaction through the formation of the diacetylene diol (34) and ring- closure of the derived diallyl diol (35) (Scheme 9).12* Amongst new and interesting systems Paquette and his colleague^^^^^ have reported the preparation of three derivatives of 114sopropylidenedibenzonorbor-nadiene in which the two benzene rings are dissimilarly substituted. The syntheses themselves are interesting and the influence of the two different aromatic systems upon the orientation of electrophilic attack (epoxidation) of the olefinic bond may have considerable significance in understanding mechanisms of electrophilic addi- tion and considering recent observations in free-radical chemistry (36) (37) ‘Iptycene’ is the suggested generic name of systems such as triptycene p-pentipty- cene {5,7,12,14-tetrahydro- 5,14[ 1’,2‘] 7,12[ 1”,2”]-dibenzopentacene (36)} the o-analogue and the tris-derivative (37).They may be made by methods that exactly parallel the synthesis of triptycene from o-dihalogenobenzenes n-butyl-lithium and anthracene but use ‘diaryne intermediates’ from 1,2,3,4- and 1,2,4,5-tetra- bromobenzene or 2,3,6,7-tetrabromonaphthalenederivative^.'^^ ‘’O V. Horak F. V. Foster R. de Levie J. W. Jones and P. Svoronos TetrahedronLett. 1981 22 3577. R.A. Russell E. G. Vikingur and R. N. Warrener Aust. J. Chem. 1981 34 131. K. B. Sukumaran and R. G. Harvey J. Org. Chem. 1981,46,2740. (a) L. A. Paquette F. Kilnger and L. W. Hertel J. Ore. Chem. 1981 46 4403; (b) R. Bolton J. P. B. Saridall and G. H. Williams J. Fluorine Chem. 1978 11 591; J. Chem. Res. 1977 (S) 24 (M)0373. H. Hart S. Shamouilian and Y. Takehira J. Org. Chem. 1981,46 4427. Aromatic Compounds The addition of tetranitroethylene to anthracene gives 11,11,12,12-tetranitro- 9,1O-dihydro-9,10-ethanoanthracene(38). Hexanitroethane loses dinitrogen tetraoxide readily to form the reagent; (38)analogously gives 11,12-dinitro-9,10- dihydro-9,10-ethenoanthracene, whose chemistry is interesting and will repay fur- ther study.Addition expectedly occurs with cyclopentadiene but nucleophilic displacement by benzylamine gives a zwitterionic product with loss of one nitro group.12' (38) Halogenated derivatives of diphenyl ether have been found among the com- ponents of some Western Australian sea sponges.'26 Although this is not a unique occurrence the incidence of tetrabromo compounds (39) allied to the teratogen (40)suggests a possible natural source of such materials or perhaps the accumula- tion of particular pollutants by the organism. A study of the i.r. spectra of some derivatives of pyrene has led the authors to conclude that some of the more common substitution patterns may be easily recognized by this method.'27 Such a clear distinction is not available by 220MHz n.m.r.studies although 1,6- and 1,8- disubstituted systems could be recognized with difficulty'28" and older methods relied upon empirical and poorly based rules-of-thumb.'286 (39) (40) The synthesis of a klavinone (41 )129a--cand of an allied has been accomplished. The studies of electrophilic substitution of 4H-cyclo- penta[d,e,f]phenanthrene now include sulph~nation,'~~ which was predictably more complicated than bromination or Friedel-Crafts acylation and a study of protiodetritiation which deserves praise because of the small scale of the detailed studie~.'~' The deductions from this second report were somewhat less satisfactory '" K. Baum and T. S. Griffin J. Org. Chem. 1981,46,4811. R. Capon E. L. Ghisalberti P. R. Jefferies B.W. Skelton and A. H. White J. Chem. SOC.,Perkin Trans. 1 1981 2464. '" P. E. Hansen and A. Berg Acta Chem. Scand. Ser. B 1981 35 131. 12* (a)J. Grimshaw and J. Trocha-Grimshaw J. Chem. SOC.,Perkin Trans. 1 1972,1622; (6)H. Vollmann H. Becker M. Corell and H. Streeck Liebigs Ann. Chem. 1937 531 11 ('Da .. . alle 3,8-Derivative hoher schmelzen als die entsprechenden 3,lO-Derivative . ..'). (a) A. S. Kende and J. P. Rizzi J. Am. Chem. SOC.,1981 103 4247; (6) B. A. Pearlman J. M. McNamara I. Hasan S. Hatakeyama H. Sekizaki and Y. Kishi J. Am. Chem. Soc. 1981 103,4248; (c) P. N. Confalone and G. Pizzolato J. Am. Chem. SOC.,1981,103 4251; (d)Z. Ahmed and M. P. Cava Tetrahedron Lett. 1981 22 5239. 130 M. Yoshida M. Kobayashi M. Minabe and K. Suzuki Bull. Chem.SOC.Jpn. 1981 54. 1186. 13' W. J. Archer and R. Taylor J. Chem. SOC.,Perkin Trans. 2 1981,.1153. 226 R. Bolton (41) for there was a clear agreement between the isomer distribution predicted by calculation and those found in hydrogen exchange and in attack by nitric acid in acetic anhydride (where the incidence of addition oxidation and nitrous acid catalysis made the mechanism less certain) but not acylation and bromination which are generally found to be more representative electrophilic processes. Non-benzenoid Systems.-The synthesis of the [101annulene derivative (42) from the previously reported bis-aldeh~de'~~" has been achieved;'32b and trans-15,16-dimethyl-1,4:8,1 l-ethanediylidene[l4]annulene(43) has been prepared and under- goes nitration with copper nitrate and acetic anhydride at the 6-po~ition.l~~ (42) (43) Conventional syntheses of tetrakisdehydro[ 16]annuleno[ 18]ann~lene'~~~ and of the [18][20]'346 and [14][20]134c analogues are reported.Dicyclobuta[a,c]anthracene was obtained by a cyclization between the dianion of dimethylcyclohexene-4,5-dicarboxylic acid and the appropriate derivative of 1,2-bis (bromome t h yl) benzene ; the reaction is presumably general and therefore a useful annelation reaction. 135 Photochemical dimerization of methyl naphthalene-2-carboxylategives (44) from which by removal of the carbomethoxy groups and rearrangement of the (44) X = C02Me Br or H 13' (a)T. L. Gilchrist C. W. Rees D. Tuddenham and D. J. Williams J. Chem. SOC., Chem.Commun. 1980 691; (6)T. L.Gilchrist D. Tuddenham R. McCague C. J. Moody and C. W. Rees J. Chem. SOC., Chem. Commun. 1981,657. 133 W. Huber J. Lex T. Meul and K. Mullen Angew. Chem. Int. Ed. Engl. 1981,20 391. 134 (a) K. Sakano T. Makagawa M. Iyoda and M. Nakagawa Tetrahedron Lett. 1981 22 2655; (6) Y. Yoshikawa M. Iyoda and M. Nakagawa Tetrahedron Lett. 1981,22,2659;(c)Y. Yoshikawa M. Iyoda and M. Nakagawa Tetrahedron Lett. 1981 22 1989. 13' C. W. Doecke and P. J. Garratt J. Chem. SOC.,Chem. Commun. 1981,873. Aromatic Compou nds carbon skeleton through formation of the rhodium complex p,p’dinaphthalene [5,6,11,12-tetrahydro-5,12:6,11-diethenodibenzo[~,e]cyc1o-octene (45)] is obtained after removal of rhodium by tripheny1pho~phine.l~~ At room temperature (45) in turn provides 1,2:7,8-dibenzo-4a,4b,8a,8b-tetrahydrobiphenylene.(45) The synthesis of naphtho[l,8-a,b:4,5-a’,b’]diazulene from [2,2](1,3)-azulenophane was brought about by iodine followed by chloranil. The electronic spectrum shows considerable absorption (E ca. lo2)past 1400 nm further into the red than either the dihydro intermediate or the starting material. The authors concluded from this that the newly formed central bond must contribute to the delocalization although in their argument they seem to come close to confusing resonance structures and tautomer~.~~’ 1,4-Dihydro-l,4-ethenobenzotropylium ion (46) has been obtained through the oxidation of 1-amino-1H-cycloheptatriazol-6-one in the presence of the oxepin (47); the adduct (48) then provides (46) by conventional methods (Scheme N 1 + -* u- 0 (47) Reagent i Pb(OAc) Scheme 10 Carcinogenic Hydrocarbons.-Mechanisms of carcinogenesis by polybenzenoid aromatic hydrocarbons now focus attention upon the arene oxides the dihydro- diols and the epoxides derived from these.Thus the aromatization of 1-(trimethyl- sily1)benzene 1,2-oxide provides phenol and 0-(trimethylsily1)phenol at a rate which is linked to the pH of the system. The subtleties of the process are evident when deuterium labelling is The aromatization of toluene 1,2-oxide and 2,3- oxide are also re~0rted.l~~’ The mechanism of formation of these intermediates seems to have received less attention; the detailed study of the parallel process in Y.Tobe F. Hirata K. Nishida H. Fujita K. Kimura and Y. Odaira J. Chem. SOC.,Chem. Commun. 1981,786. 13’ Y. Fukazawa M. Aoyagi and S. Ho Tetrahedron Lett. 1981 22 3879. ”* T. Nakazawa K. Kubo and I. Murata Angew. Chem. Znt. Ed. Engl. 1981 20 189. (a) J. E. Van Epp jun. D. R. Boyd and G. A. Berchtold J. Org. Chem. 1981 46 1817; (b) H. J. Org. Chem. 1981,46 1948. S.-I. Chao G. A. Berchtold D. R. Boyd J. N. Dynak J. E. Tomaszewski H. Yagi and D. M. Jerina 228 R.Bolton a cyclophane system and the catalysis which cobalt mesotetraphenylporphyrin brings may well be significant. Benz[a]anthracene oxides have now been made optically pure. Thus the (-)-enantiomer of the 8,9-oxide a major initial metabolite was shown to be [8S,9R] by correlation with (+)-trans-9S-bromo-8S(menthyloxyacetoxy)-8,9,10,11-tetrahydr~benz[a]anthracene.'~' The (+)-enantiomer of the 10,11-oxide was found to be (lOS,llR) and that of the 5,6-oxide was (5S,6R).'42The synthesis of the dihydrodiols of benzo-[b]- -[j]- and -[k]-fluoranthenes was achieved by a stereo- specific route from the appropriate tetrahydroketones through reduction dehydra- tion the Prevost reaction allylic bromination dehydrobromination and finally hydrolysis; the route was intended to provide solely trans-diol~.'~~ In contrast Lee and who have used epoxidation of the bay region dihydrodiols of dibenz[a,h]anthracene and of 7-methylbenz[a]anthracene to give syn-diol epoxides were perturbed by the unexpected cis-directing effect of the benzylic hydroxy groups.Both cis-and trans-3,4-dihydroxy-1,2,3,4-tetrahydrophenan-threne have been obtained optically pure the trans-isomer having the (-)-(3R,4R) configuration and the cis-enantiomer being (+)-(3S,4R).'45 Halogenated biphenyl oxides show increased stability towards both acids and bases upon increased extent of halogen sub~titution.'~~ Arene 1,4-oxides which arise from cycloadditions involv- ing furan or benzo[~]furan,'~~~ may be deoxygenated by low-valent forms of iron tungsten or titanium formed from the reaction of the metallic halide with n-butyl- lithium at -78 "C.The single-step process usually gives good yields; 1,4,5,8,9,10- hexamethylanthracene has been prepared by this method.'476 A detailed study of the bonding between polybenzenoid hydrocarbons and DNA that occurs on irradiation (regardless of the intermediates that seem likely to be involved) has taken the pragmatic approach of measuring the uptake of radiolabelled aromatic The application of Longuet-Higgins' calculations'49a to measure the reactivity of various sites in the bay regions of polybenzenoid car- cinogens towards addition has been used to rationalize the orientation of attack and the subsequent reactions of these Those factors which make epoxidation preferred by allowing delocalization of charge also encourage the formation of benzylic carbocations in the subsequent ring-cleavage.The anodic fluorination of benz[a]anthracene involves attack mainly at C-7 with a little of the 12-fluoro isomer and some 7,12-difl~oro-arene.~~~ 3-Methylcholanthrene has been I.Erden P. Golitz R. Nader and A. de Meijere Angew. Chem. Int. Ed. Engl. 1981 20 583. 14' D. R. Boyd K. A. Dawson G. S. Gadaginamath J. G. Hamilton J. F. Malone and N. D. Sharma J. Chem. SOC. Perkin Trans. 1 1981 94. D. R. Boyd G. S. Gadaginamath N. D. Sharma A. F. Drake S. F. Mason and D. M. Jerina J. Chem. SOC. Perkin Trans. 1 1981 2233. 143 S. Amin V. Bedenko E. LaVoie S. S. Hecht and D. Hoffman J. Org. Chem. 1981,46,2573. H. Lee and R. G. Harvey Tetrahedron Left.,1981,22 1657. D. R. Boyd R. M. E. Greene J. D. Neill M. E. Stubbs H. Yagi and D. M. Jerina J. Chem. SOC. Perkin Trans. 1 1981 1477. I. L. Reich and H. J. Reich J. Org. Chem. 1981,46 3721. (a)W. Friedrichsen Adv. Heterocyclic Chem.1980 26 142 182; (6) H. Hart and G. Nwokogu J. Org. Chem. 1981,46,1251. G. M. Blackburn A. J. Flavell L. Orgee J. P. Will and G. M. Williams J. Chem. SOC.,Perkin Trans. 1 1981,3196. (a) H. Longuet-Higgins J. Chem. Phys. 1950 18 265 et seq.; (6) J. P. Lowe and B. D. Silverman J. Am. Chem. SOC. 1981,103,2852. R. F. O'Malley H. A. Mariani D. R. Buhier and D. M. Jerina J. Org. Chem. 1981,46 2816. 14' Aromatic Compounds obtained from the Elbs reaction of l-naphthyl-7-methylindan-4-ylketone; the intermediate 7-methylindane-4-carboxylic acid was prepared from the Diels-Alder adduct of sorbonitrile and cyclopentanone pyrrolidine enarnine by aromatization. 15’ 5 Cyclophanes The recent publications in this field have included some elegant synthetic work.Cyclophane systems are now being extended through their heterocyclic analogues to include macrocyclic ethers and amines which are more properly akin to the crown ethers and whose properties are more correctly discussed in this light. A second direction of expansion is towards metallocene systems. For example ruthenocenophane and ruthenocenoferrocenophane derivatives have been repor- ted. Examples are [3,3](l,l’)ruthenocenophane-2,14-dien-l,l6-dione(49) and [5,5](l,l’)ruthenocenophane-2,14,17,29-tetraen-l, 16-dione (50) which arise from the simple Claisen-Schmidt condensation of ketones (acetone or other methyl ketones) and the metallocene-1,l’-dialdehyde[reactions (12) and (13)]:15* OCHO 2 Ru + 2MeCOMe + Ru Ru (13) oCH0 oCH=CH-co-cH= cHJJ (50) [2.2.2]Paracyclophane [‘T-prismand’ (5 l)]was prepared from p-xylylene chlor- ide in a Wurst-type synthesis.Its major interest at present is the size of the cavity which complexes silver ions very well (K = ca. 200; cf. K = ca. 2 for simple arene~).’~~ Gas-phase pyrolysis has led to the synthesis of 4,16- and 4,13-diaza- [2.2.2.2](1,2,4,5)cyclophane (52) and (53) re~pectively,’~~ and this process was used .by Boekelheide and Sekine successfully in the preparation of c2.2.2.2.2.21-(1,2,3,4,5,6)cyclophane [‘superphane’ (54)]. 155 Staab and Appel have also reported the synthesis and properties of some 4,7-diaza(2,2)para~yclophanes,’~~ and Bock- mann and Vogtle’57 have investigated the synlanti interactions that may be seen in the proton n.m.r.spectra of some dithia[3,3]metacyclophanes.Such temperature 15* P. W. Tang and C. A. Maggiulli J. Org. Chem. 1981,46 3429. 152 S. Kamiyama A. Kasahara T. Izumi I. Shimizu and H. Watanabe Bull. Chem. SOC.Jpn. 1981,54 2079. lS3 J.-L. Pierre P. Baret P. Chautemps and M. Armand J. Am. Chem. SOC.,1981 103,2986. lS4 H.C.Kang and V. Boekelheide Angew. Chem. Int. Ed. Engl. 1981,20 571. 155 Y.Sekine and V. Boekelheide J. Am. Chem. SOC.,1981 103 1777. lS6 H.A. Staab and W. K. Appel Liebigs Ann. Chem. 1981 1065. K. Bockmann and F. Vogtle Chem. Ber. 1981 114 1065. 230 R. Bolton @ / (51) (52) (53) (54) dependence of the ‘H n.m.r. spectrum also occurs with 8,16,24,32-tetraphenyl[2,2,2,2]metacyclophane (55).158 (55) In general the conformation changes occurring with change of temperature and seen in the altered n.m.r.spectrum are the main reason for preparing cyclophanes once the synthetic challenge has been met; however Th~lin”~ has made three new [2,]-p- [4,-,]cyclophane systems and studied their cyclic voltammetric behaviour. The radical anion derived from [2.2.2.2](1,2,4,5)cyclophane has also been investi- gated by Gerson Lopez and Boekelheide,16’ who showed two species to be present. These differed in their extent of association with the gegen-ion (IC), the distinction arising from the different degrees of symmetry of the two systems and the consequent differences in spectroscopic behaviour. (56) Among the more remarkable systems that have been synthesized are the paddle- wheel system (56),[2,2]-4,4’-tran~-stilbenophane (57) and the series of compounds K.Bockmann and F. Vogtle Chem. Ber. 1981 114 1048. B. Thulin J. Chem. SOC.,Perkin Trans. 1 1981,664. 160 F. Gerson J. Lopez and V. Boekelheide J. Chem. SOC.,Perkin Trans. 2 1981 1298. Aromatic Compounds 231 (57) based upon p-terphenyl and exemplified by (58). The photodimerization of (E,E,E)-1,3,5 -tristyrylbenzene produces (56),whose structure was determined by n.m.r. and confirmed by X-ray crystallography. Iodine blocks the course of the dimeriz- ation and gives instead the dicyclobutapyrene derivative (59).16' Conventional syntheses from bibenzyl-4,4'-dialdehyde produced (57) which isomerized to the cis,cis product presumably through a cis,trans isomer.'62 The synthesis of deriva- tives such as [58] allowed interesting changes of the 'H n.m.r.spectrum to be observed with changes of temperature since the substituents in the bridge systems are in an unusually anisotropic en~ir0nment.l~~ Similar n.m.r. studies have been made of [2.2.2.2]cyclophanes with ethylene bridges,'64 of their [2.2.2.2.2.21cyclophane analogues 165 and of [5.S]paracyclophanetetraenessuch as (60).166 [3.3]-Other workers have investigated [3.31(2,6)naphthalenophane~,'~~ (1,5)(2,6)naphthalenophane~,'~~ and [3.2](1,4)naphthalen0phane.'~~Somewhat Ph Ph (59) J. Juriew T. Skorochodowa J. Merkuschew W. Winter and H. Meier Angew. Chem. Int. Ed. Engl. 1981 20 269. D. Tanner and 0.Wennerstrom Tetrahedron Lett.1981 22 2313. K. Bockmann and F. V6gtle. Liebigs Ann. Chem. 1981 467. 164 T. Olsson D. Tanner B.Thulin 0.Wennerstrom and T. Liliefors Tetrahedron 1981 37 3473. 16' T. Olsson D. Tanner B. Thulin and 0.Wennerstrom Tetrahedron 1981 37 3485. T. Olsson,D. Tanner B. Thulin and 0.Wennerstrom Tetrahedron 1981 37 3491. N. E. Blank and M. W. Haenel Chem. Ber. 1981,114,1520. 16' N. E. Blank and M. W. Haenel Chem. Ber. 1981,114,1531. 232 R. Bolton less imaginative synthetic routes led to 1,8,19,26-tetraoxo[8.8](2,6)-naphthalenophane-3,5,2 1,23 -tet~aynel~~ and to 6,21-dioxo-5,22-diaza[ 10.101- para~yclophane,'~' although the interest in the former heterocycle was based upon the unusually large (6.5 A) cavity. Calixarenes continue to be st~died,'~' but the reported properties are disappointing considering their apparent potential.(61) A new system (61) has been obtained by conventional though arduous methods; few resonance interactions are found,17* although this comes as no surprise. Allied to this last system are the triangulenes for which n.m.r. studies suggested a pyramidal structure (62; n = 0 or 1)until sufficiently flexible to form a mobile helical system (62; n = 2).173 OMe and (64) In a section dealing with perseverance in the face of synthetic difficulties one must record studies of the 13C n.m.r. spectra of pre~atenanes,'~~ the synthesis of the [2]prerotaxane (63),17' and the recognition of the distinguishible isomeric [3]catenanes which may be represented by (64).176 169 B.J. Whitlock E. T. Jarvi and H. W. Whitlock J. Org. Chem. 1981.46 1832. 170 H. Okamoto J. Kikuchi and J. Sunamoto J. Chem. Soc. Perkin Trans. I 1981 3125. 17' C. D. Gutsche B. Dhawan K. H. No and R. Muthukrishnan J. Am. Chem. SOC.,1981 103 3782. M. Nakazaki K. Yamamoto andT. Toya J. Org. Chem. 1981,46 1611. 173 D. Hellwinkel A. Gerhard and M. Melan Chem. Ber. 1981 114 86. 174 E. bgemann K. Rissler G. Schill and H. Fritz Chem. Eer. 1981,114,2245. 17' G. Schill and H. Ortlieb Chem. Ber. 1981,114,877. G. Schill K. Rissler H. Fritz and W. Vetter Angew. Chem. hr. Ed. Engl. 1981 20 187.