11 Heterocyclic Chemistry By A. J. BOULTON School of Chemical Sciences University of East Anglia Norwich NR4 7TJ 1 Heterocycles in Functional Group Transformations Mukaiyama has continued to exploit quaternary salts containing reactive halogen atoms as a means of converting stable organic functions into good leaving groups. The conversions of trialkylammonium dithiocarbamates into isothiocyanates,' of thioureas into carbodi-imides2 (using reagent l) of alcohols into chloride^,^ formamides into is~cyanides,~ and epoxides into 1,2-dichlorides (using Z),5 are briefly reported. More preliminary notes describe the further work of Katritzky's group on the reaction of pyrylium salts (3) with primary amino-functions to give (3) x=o (4) X=NCH*R Me I ' T.Shibanuma M. Shiono and T. Mukaiyama Chem. Letters 1977,573. * T. Shibanuma M. Shiono and T. Mukaiyama Chem. Letters 1977,575. T. Mukaiyama S. Shoda and Y. Watanabe Chem. Letters 1977,383. Y. Echigo Y. Watanabe and T. Mukaiyama Chem. tetters 1977,697. ' Y. Echigo Y. Watanabe and T. Mukaiyama Chem. Lencrs 1977,1013. 25 1 252 A. J. Boulton pyridinium salts (4) which then lead to iodides6 (using 3 A = I) and esters’ (using 3 A = BF4) from primary amines RCH2NH2 and by rearrangement carbodi-imides ArN :C :NAr’ from amidrazones ArNHCAr’ :NNHzs (using 3 A = ClO,). ‘Sac-charin chloride’ the benzisothiazole (5) is suggested as a useful reagent for the production of p -1actams from acids and imines.’ Another condensing technique uses 2-chlorobenzothiazole which activates a primary alcohol as outlined in Scheme 1.The quaternary salt (6) may alkylate another nucleophile (the method works with a wide variety of these) possibly with the pseudobase (7) as an inter- mediate.” 2 General Heterocyclic Synthesis The salt (8)is a versatile reagent for the synthesis of many heterocycles (with five- six- and seven-membered rings) with the structural element (A);” the isomeric arrangement (B) had earlier been shown to be derived similarly from (9).12 Both starting-materials are made from dimethyl phosgenimmonium chloride (Scheme 2). N-Ethoxycarbonylthioamides (10) provide smaller pieces for building into hetero- cycles three-atom and one-atom units are incorporated on reaction (a) with 1,2- and 1,3-binucleophiles and (b) with 1,4- and larger binucleophiles re~pective1y.l~ +-R RN=CCl-NR-CCI=NMe2Cl + -/ RNyyMe2 RN=C=NR (8) + (A) Me2N=CC12 C1 Scheme 2 3 Three-membered Rings Attempts to prepare oxirene by heating epoxy-barrelenes have been unsuccessful.At 300-400 “C cycloheptatriene aldehyde derivatives were obtained from (11) N. F. Eweiss A. R. Katritzky P.L. Nie and C. A. Ramsden Synthesis 1977 634. ’ U. Gruntz A. R. Katritzky D. H. Kenny M. C. Rezende and H. Sheikh J.C.S. Chem. Comm. 1977 701. ’A. R. Katritzky P.L. Nie A. Dondoni and D. Tassi Synthetic Comm. 1977,7 387. M. S. Manhas H. P. S. Chawla S. G. Amin and A. K. Bose Synthesis 1977,407. lo F. A. Souto-Bachiller and S. Masamune Tetrahedron Letters 1977 1881.’‘ A. Elgavi and H. G. Viehe Angew. Chem. Internat. Edn. 1977,16 181. l2 Z. Janousek and H. G. Viehe Angew. Chem. Internat. Edn. 1973 12,74. l3 B. George and E. P. Papadopoulos J. Org. Chem. 1976,41 3233; ibid. 1977,42,441 2530. Heterocy c Zic Chemistry (acidic alumina brought about the same transformation) but at 600-800°C flash thermolysis did produce some ketene the expected rearrangement product of ~xirene.'~ The bridged anthracenes (12; R=H and Me) rearranged on heating rather than eliminating the bridge." Developments in the study of the Wolff rearrangement and the involvement of oxirenes and their interconversion with a-ketocarbenes are treated in Chapter 5 of this Volume. (11) (1 2) (13) Thiirene seems to be slightly less elusive than oxirene its marrix-isolation has been reported along with an i.r.study and data were also obtained on mono- and di-deuterio- and methyl derivatives and on selenirene.16 Benzothiirene appears to be an intermediate in the pyrolytic formation of two isomeric thianthrenes from a monosubstituted 1,2,3-ben~othiadiazole,'~ although this view is challenged by another group." Thiirenium salts appear to be more stable and one of these (13)has been studied by X-ray crystallography. The ring C-S bonds are unusually long (1.82 A; cf. 1.80 8 for the S-Me bond)." Thiirenium salts are prepared by methods analogous to those used for the thiiranium seleniraniurn and selenirenium salts reported earlier.** Oxidation of thioketen monomers e.g.(14) with a pyrroline-l-oxide forms thiiran-2-ones (thiol-a -lactones) e.g (15) the structures of which were established by i.r. CQ. 1800cm-') and the X-ray crystallography of (15).22 0 (14) (15) (16) (17) -Flash photolysis of the cis and trans isomers of a-cyanostilbene oxide (16) forms carbonyl ylids (PhCH=b-CPhCN) which are highly coloured and the rates of their reactions and their interconversion could be studied. Upper and lower limits are suggested for the depths of the energy troughs in which the ylids lie.23Irradia-tion of naphthoquinone oxides in the presence of norbornene and other dipolaro- philes forms bridged benzoxepin cycloadducts derived from the valence tautomer (17).24 l4 E. Lewars and G. Morrison Tetrahedron Letters 1977 501.Is H. Hart J. B. C. Jiang and M. Sasaoka J. Org. Chem. 1977,42 3840. l6 A. Krantz and J. Laureni J. Amer. Chem. Soc. 1977,99,4842. l7 T. Wooldridge and T. D. Roberts Tetrahedron Letters 1977 2643. L. Benati P. C. Montevecchi and G. Zanardi J. Org. Chem. 1977,42 575. l9 R. Destro T. Pilati and M. Simonetta J.C.S. Chem. Comm. 1977 576. 2o G. Capozzi V. Lucchini G. Modena and P. Scrimin Tetrahedron Letters 1977 91 1. cf. Ann. Reports (B),1975,72 253. '* E. Schaumann and U. Behrens Angew. Chem. Internat. Edn. 1977,16 722. 23 R. Huisgen V. Markowski and H. Hermann Heterocycles 1977,7,61. 24 S. Arakawa J. Org. Chem. 1977,42 3800. 254 A. J. Boulton cis-2-Vinyl-3-ethynyloxirane(18) has been shown to rearrange cleanly via two Cope rearrangements to the cyclopropane (19).With the corresponding N-t- butylaziridine (20) however the presumed intermediate (21; X = NBu') is side-tracked by an intramolecular proton shift and the product is 1-t-b~tylazepine.~' (18) x=o (20) X=NBu-t (22) R = H C1 or Me R \ CR=CCI (24) (23) Viehe et ai.26have discovered an interesting analogy to the rearrangement of singlet oxygen-diene adducts (A2-1,4-peroxides) to bis-epoxides the nitroso- olefins (22) with cyclopentadiene form the diene mono-oxide-mono-imines (23) via (4 +2) cycloadducts (24) which are detectable intermediates at -60 "C. The addition of nitronic esters (25) to acetylenes (26) does not form the expected N-alkoxyisoxazolines (27); these are probable intermediates but they immediately rearrange to 2-acyl- 1-alkoxyaziridines.The stereochemistry of this reaction has been studied and it was found that the products (28 29) are formed stereo- specifically only with respect to the relative configurations of the substituents on H YCO H"' R2 + yco-1 N OMe OMe OMe R' =CN or C02Me R2=H or vice verso Y = COPh COMe or C02Me *' N. Ma,nisse and J. Chuche J. Amer. Chern. SOC.,1977,99 1272. 26 H. G. Viehe R. Merenyi E. Francotte M. Van Meerssche G. Germain J. P. Declerq and J. Bodart-Gilmont J. Amer. Chem. Soc. 1977 99 2340. 27 R. Grei and R. Carrii J. Amer. Chem. SOC.,1977,99,6667;J.C.S. Chem. Comm. 1975 112. Heterocyclic Chemistry 255 The automerization rates of perfluorotetramethyl Dewar thiophene (30) and its S-oxide have been compared.28 The former exchanges slowly (AG' 93.8* 0.5 kJ mol-' at 157"C) the latter extremely rapidly (AGS 28*0.5 kJ mol-' at -136 "C),but the authors suggest that the mechanism is probably similar.Me (31) R = subst. phenyl (32) R=NMe2 Dh (33) (34) + H2C=O S S '0- ~i 'Me NMe 0 Me -Me H2C' '6 (35) (36) (39) 1977 saw the publication of a number of papers from the Zurich group on the chemistry of 2H-azirines. The U.V. spectra and also the regiospecificity of cyclo-addition to various dipolarophiles of the benzonitrile isopropylides formed by photochemical ring-opening of the azirines (3l) are in~estigated.~' 3-Dimethyl- amin0-2~2-dirnethylazirine (32) is a fertile source of interesting reactions. With a munchnone (1,3-oxazolium-5-olate) it appears to add to the acylamidoketen valence tautomer (r.t. in MeCN); subsequent rearrangement and recyclization leads to the amino-oxazoline (33).30Azirine (32) forms eight-membered hetero- cycles (34; X = CO SO*)by insertion into the heterocyclic rings of phthalimide and ~accharin.~'The adduct with CS exists as the betaine (35) in the solid phase but mainly as the open-chain structure (36) in non-polar Isothiocyanates form adducts of structure similar to (35) amongst other things.33 With substituents other than methyl at C-2 other types of product are sometimes formed.34 2E C. H. Bushweller J. A. Ross,and D. M. Lemal J. Amer. Gem. Soc. 1977,99,629. 29 U. Gerber H. Heimgartner H. Schrnid and W. Heinzelrnann Helv. Chim.Acta 1977,60,687. 30 J. LukAE J. H. Bieri and H. Heimgartner Helu. Chim. Am 1977,60 1657. 31 S. Chaloupka P. Vittorelli H. Heimgartner H. Schrnid H. Link K. Bernauer and W. E. Oberhansli Helu. Chim. Acta 1977,60 2476. 32 S. Chaloupka H. Heimgartner H. Schmid H. Link P. Schonholzer and K. Bernauer Helv. Chim. Acta 1976 59 2566. 33 E. Schaumann E. Kausch and W. Valter Chem. Ber. 1977,110,820. 34 E. Schaumann S. Grabley K. D. Seidel and E. Kausch Tetrahedron Letters 1977 1351. 256 A. J. Boulton The detection of dioxirane (37) by mass35 and microwave36 spectrometry as a transient intermediate in the gas-phase ozonolysis of ethylene has been claimed. Calculations3’ had earlier suggested that it should compare favourably in stability with the zwitterionic (38) and diradical (39)open-chain forms and that its de- composition might proceed by 0-0 cleavage; some kinetic evidence appears to support this view.38 L’abbk et aL3’ have described the preparation of alkylidenediaziridines (40).They do not isomerize to aziridinimines on heating but rather form methacrylic amidines (41). With phenyl isocyanate the adduct (42)is obtained. The thermal rearrangement of aziridinimines (e.g. 43S 44) has been studied kinetically. UnfortunateIy they also decompose very easily and these reactions compete with the rearrange men^^' T Me Me2C=C=NAr PhCH2NdMe L+ PhCH2NC +MeS02N3 NBu‘ +Me2C=NBut +t -BuNH~ -PhCH2N=CMe2 +t-BuNC (44) Quast’s group have made further contributions to this general theme (‘hetero- trimethylenemethanes’).Phenyl isocyanate adds to a diaziridinimine (45; R1= R2= R3=Pr’) to form a 1,2,4-triazolidinonimine (46); deuterium-labelling [(CD3),CH] demonstrated (a) that the diaziridinimine did not scramble the label between the N atoms and (b),that addition occurred across the exocyclic and one of the ring N atoms as expected.41 The addition of (45) to dimethyl acetyl- enedicarboxylate eventually yields a 1:3 adduct of spiro-construction (47).42 The possibility of thiaziridinimine-diaziridinethione involvement in some reactions of 35 R. I. Martinez R. E. Huie and J. T. Herron Chem. Phys. Letters 1977 51 457. 36 F. J. Lovas and R. D. Suenrarn Chem. Phys. Letters 1977 51,453. 37 W. R. Wadt and W. A. Goddard J. Amer. Chem.SOC.,1975,97 3004. 38 J. T. Herron and R. E. Huie J. Amer. Chem. SOC.,1977,99 5430. 39 G. L’abbC C. C. Yu and S. Toppet Angew. Chem. Internat. Edn. 1977,16,475. 40 H. Quast and P. Schafer Tetrahedron Letters 1977 1057. 41 H. Quast and E. Spiegel Angew. Chem. Internat. Edn. 1977 16 109. 42 H. Quast K. H. Ross,E. Spiegel K. Peters and H. G. von Schnering Angew. Chem. Internat. Edn. 1977,16 177. Hete roc y c1ic Chemistry thiatriazoles and tetrazolinethiones has been raised by L'abbk,43*44 but this seems to be speculative at present. (451 (46) (47) E=C02Me (48)R1= Me,R2= R3= H (49) R' = H,R2R3= C4H4 (50) (51) PhC=C-SiMe2-SiMe3 hl; PhVSiMe Si (52) Me2 (53) The irradiation of 3-oxidopyridazinium betanes (48) and the corresponding phthalazines (49) in acetonitrile forms bicyclic valence isomers (50).These compounds show little or no amide resonance ca. 1750 cm-') and in protic solvents the five-membered ring is opened; recyclization and aromatization pro- duces the rearranged pyridazinones (5l).45 A further development on the silirene front46 is the reported photochemical conversion of the acetylenic disilane (52) into the cyclic isomer (53). In several reactions of (53) which were investigated external groups were inserted into the Si-C(Ph) bond.47 4 Four-membered Rings By a careful choice of temperature wavelength of illumination (270nm) and matrix material it has proved possible to convert the oxazinone (54; R' = R2= H) into its bicyclic valence isomer (55). Shorter wavelengths (254 nm) produced the keten (56); both valence isomerizations were reversed thermally.Substituted oxazinones behaved similarly. Prolonged irradiation of the lactone (55; R'= Me R2=Buf) gave the dimer(s) of the azete (57),when conducted at -70°C in 2-methyltetrahydrofuran but at 7K (Ar matrix) fission products (CO, acetylenes and cyanides) were formed which were consistent with the formation of (57) rather than with cleavage of (55)to a nitrile and ~xetone.~~ (Scheme 3) '' G. L'abbk G. Verhelst and S. Toppet J. Org. Chem. 1977,42 1159. 44 G. L'abbC G. Verhelst and G. Vermeulen Angew. Chem. Internat. Edn. 1977,16 403. 45 Y. Maki M. Kawamura H. Okamoto M. Suzuki and K. Kaji Chem. Letters 1977 1005. O6 Ann. Reports (B) 1976 73 243. 47 H.Sakurai Y. Kamiyama and Y. Nakadaira J. Amer. Chem. SOC.,1977 99 3879. G. Maier and U. Schafer Tetrahedron Letters 1977 1053. cf. also A. Krantz and B. Hoppe J. Amer. Chem. Soc. 1975,97,6590. 258 A. J. Boulton 0 Me AN QR OMe Ph Me O q O M e -PhqOMe "'@TLR PhOMe Me (59) (58) (60) (61) R =Tosyl or C02Me Further examples49 of azetines have been reported. The hl-azetin-3-one acetal (58) is formed by thermal decomposition of the photoadduct (59) of 6-methyl-2-phenyl- 1,3-0xazin-4-one and l,l-dimeth~xyethene,~~ while photolysis of the tetracyclic compounds (60) gave the A2-azetine derivatives (6 l)? Adam et al. have given details for their synthesis of 1,2-dioxetanones (62) by carbodi-imide cyclization of a-hydroperoxy-carboxylic for which a con- venient preparation has been rep~rted.~" An optically active 172-dioxetane has been prepared54 and its crystal structure was determined;55 it was found to emit circularly polarized chemiluminescence when it dec~rnposed.~~ Singlet oxygen adds to the dihydrodioxin (63) at -78 "C to form the (4+2) cycloadduct which rearranges to the dioxetane (64) (silica gel r.t.in xylene); the luminescent de- composition of (64) occurs at 80 0C.57 Benzothiet (65) has been prepared by flash vacuum pyrolysis of benzo[b]thio- phene 1,l-dio~ide.~~ Thiete dioxides (66) on heating form vinyl sulphenes which undergo (4+2) cycloaddition to olefins. Yields are poor however unless conditions are favourable (as for instance when the olefin is ~trained).~~ The remarkable diphosphete (67) is reported by Appel et a1.60as a stable white solid.49 cf.Ann. Reports (B),1975 72 254; ibid. 1976,73 243. so T. H. Koch R. H. Higgins and H. F. Schuster Tetrahedron Letters 1977,431. s1 R. N. Warrener G. Kretschmer and M. N. Paddon-Row J.C.S. Chem. Comm. 1977 806. 52 W. Adam A. Alzerreca J. C.Liu and F. Yany J. Amer. Chem. Soc. 1977 99 5768. " W. Adam and 0.Cueto J. Org. Chem. 1977,42 38. '4 H. Wynberg and H. Numan J. Amer. Chem. SOC.,1977,99,603. s5 H. Numan J. H. Wieringa H. Wynberg J. Hess and A. Vos J.C.S. Chem. Cornm. 1977 591. 56 H. Wynberg H. Numan and H. P. J. M. Dekkers J. Amer. Chem. SOC.,1977,99 3870. 57 A. P. Schaap P. A. Burns and K. A. Zaklika J. Amer. Chem. SOC.,1977,99 1270. W. J. M. van Tilborg and R.Plomp J.C.S. Chem. Comm. 1977 130. s9 D. C. Dittmer J. E. McCaskie J. E. Babiarz and M. V. Ruggeri J. Org. Chem. 1977 42 1910. 6o R. Appel F. Knoll and H. D. Wihler Angew. Chem. Internat. Edn. 1977 16 402. Heterocyclic Chemistry + Ph,P -PPh2 rJ+2c1-Ph,P PPh 5 Five-membered Rings Simple furans can be elaborated into a variety of useful ‘synthons’ according to several research groups. The acid-catalysed rearrangement of 2-furylcarbinols(68) to 5-hydroxycyclopenten-3-oneshas been used in prostaglandin-intermediate synthesis.61 Rather than undergo simple acyloin reduction furoic esters form the OCHR RQC0,Et -B SiMe3 RCOCH2CHI I OH OH I C=CSiMe3 (68) (69) 0 RCH2I C + R‘/ \() \CH I HC \“Me2 (71) dLi 0 I c NMe I Scheme 4 G.Piancatelli A. Scettri and S. Barbadoro Tetrahedron Letters 1976 3555; G. Piancatelli and A. Scettri ibid. 1977 1131. 260 A. J. Boutton acetylenic derivatives (69) by ring cleavage with sodium and trimethylsilyl chloride in tetrahydrofuran followed by acid workup.62 Further synthetic possibilities of this product are explored.63 2,5-Dilithiated furan thiophene and pyrroles have been in~estigated,~~ and the lithiated bromofuran (70) has provided another route to 'rose f~ran'.~~ Glyoxal monohydrazones (e.g. 71) provide a route to 2,3-disubstituted pyrroles and their 1-amino-substituted derivatives as outlined in Scheme 4.66 A convenient synthesis of azulenes is claimed from the (6+4) cycloaddition of B-dialkylamino-fulvenes to thiophene dio~ide.~~,~~ Indoles (72) are formed by intramolecular cyclization of a-lithiated o-tolyl isocyanides (a favourable '5-Endo-Dig' process in Baldwin's scheme6').The lithio derivatives (73; R = H) can be alkylated at -70 "C and the product again metal- lated (PriNLi) to (73; R = alkyl); cyclization occurs on heating to room tempera- ture." HR L -1 H (73) (74) I . R' Et Me J (77) (76) i Et shift and cyclization ii Chloranil(-4H) x-Y c R' (75) Mschanisms of alkyl group migration in the Fischer indolization reaction of the hydrazone (74) have been e~amined.~' The major product (75) is suggested to be e 62 I. Kuwajima K. Atsumi and I. Azegami J.C.S. Chem. Comm. 1977 76. " K. Atsumi and I.Kuwajima Tetrahedron Letters 1977 2001. 64 D. J. Chadwick and C. Willbe J.C.S. Perkin I 1977 887. " N. D. Ly and M. Schlosser Helv. Chim. Acta 1977,60 2085. "T. Severin and H. Poehlmann Chem. Ber. 1977,110,491. 67 D. Copland D. Leaver and W. B. Menzies Tetrahedron Letters 1977 639. S. E. Reiter L. C. Dunn and K. N. Houk J. Amer. Chem. SOC.,1977,99,4199. 69 J. E. Baldwin J.C.S. Chem. Comm. 1976 734. 70 Y. Ito K. Kobayashi and T. Saegusa J. Amer. Chem. SOC. 1977,99,3532. B. Miller and E. R. Matjeka Tetrahedron Letters 1977 131. Heterocyclic Chemistry 261 formed via (76) which arises from two 1,2-alkyl shifts (or a 1,5-shift?) from the primary rearrangement ions (77; R=Me R’=Et and vice versa). In the final migration step the ethyl group moves in preference to the methyl.Minor products are produced by 1,2-alkyl shifts in (77) leading to 1,4-dialky1-5,6,7,8-tetrahydro-carbazoles. Peri-bridged naphthalene systems (78) continue to receive attention. The reac- tions of methyl-lithium followed by methyl iodide on the three congeners (78; X = Y = S Se and Te) contrast in that the dithio-compound forms 1,8-bis(methyl- thio)naphthalene (79; R = R’= SMe) the diseleno- gives a 4:1 mixture of the bis(methylse1eno)naphthalene and the mono-C-alkylated compound (79; R = SeMe R’ =Me) while the ditelluride loses the tellurium altogether giving 1,8-dimeth~lnaphthalene.~~ The synthesis of analogues with mixed group six elements (78; X=S Y=Se and Te and X=Se Y=Te) has been rep~rted.’~ The dithiole 1,l-dioxide (78; X = S,Y = SO,) forms a mixture with the monoxide and trioxide (78; X= SO Y = S and SO2 respectively) when treated with NaOH followed by HC1.74,75 An extensive series of interesting papers describes the work of J.C. Martin’s group on the heterocyclic sulphuranes. The optically active chlorosulphurane (80) was found to racemize slowly,76 and the two isomers of the spiro-compound (81) interconverted also slowly (AG* ca. 125 kJ m~l-l).~~ The mechanism of these reactions is uncertain. The X-ray crystal structure of the asymmetric compound (82) shows that the S-0 bond lengths are significantly different (a 1.955 A b 1.713 A),78a state of affairs reminiscent of that obtaining with the S-S distances found in unsymmetrically substituted thiathiophthenes.R2 Me Me /\ Ph C1 (80) Me (83) (81) R’= Me R2 = Et (82) R’= R2= CF3 Et Et Et R2 R2 eFe [:o EtfiMe c <,o~MeB,l=l ,BMe +m+ * / 1.-, .._. BIN,-,NR’ S B Et Et (84) (86) R/\X (85) (87) 72 J. Meinwald D. Dauplaise F. Wudl and J. J. Hauser J. Amer. Chem. SOC. 1977 99 255. 73 J. Meinwald D. Dauplaise and J. Clardy J. Amer. Chem. Sm. 1977.99 7743. 74 B. I. Stepanov V. Ya. Rodionov M. A. Andreeva V. P. Perevalov and S. E. Voinova Zhur. nbshchei Khim. 1977,47 234. These authors claim the trioxide as a new compound; see however ref. 75. 75 J. L. Kice and H. Margolis J. Org. Chem. 1975,40 3623; M. M. Chau and J. L. Kice J. Org. Chem. 1977,42,3265. 76 J. C. Martin and T. M. Balthazor J. Amer. Chem. SOC.,1977,99 152.77 L. J. Adzirna and J. C. Martin J. Org. Chem. 1977 42 4006. ’‘ L. J. Adzima E. N. Duesler and J. C. Martin J. Org. Chem. 1977 42 4001. 262 A. J. Bouiton Phenylene orthosulphite (83) has been reported as showing an AA'BB' 220 MHz 'H n.m.r. spectrum indicating a four-fold (D2d)symmetry at least when time- averaged. It is very unstable to moist~re.~' The reaction between ethylene and ozone has been studied by i.r. in CO and CC14 matrices at temperatures down to 65 K. The secondary ozonide (1,2,4- trioxolan) was the major product observed but a less volatile minor compound remained after that along with ethylene ozone and COz had been pumped off at -120 "C and this was assumed to be the primary ozonide 1,2,3-trioxolan (84).80 For the gas-phase ozonolysis of ethylene see Section 3.A number of appetizing sandwich compounds containing boron heterocycles including some of the triple-decker type were reported during 1977. Both sides of the 1,3-diborole ring are complexed in (85)," and both sides of a 1,2,5-thiadi- borolene (86) accept cobalt" and manganeseg3 tricarbonyl bonding units. 1,3,2-Diazabarolenium salts (87) are formed by the reaction of a-di-imines with dihalo- borane~.~~ which They can be reduced to the very unstable 1,3,2-dia~aborolenes,~~ may be stabilized in the form of Cr(C0)3 comple~es.~~ Some water-stable iron tricarbonyl compounds of boroles have been prepared.86 4-Oxazolin-2-ones (88; R = H or Ph X = NH or NAc) with dienes form Diels- Alder adducts which can be hydrolysed to provide a synthesis of p-amino-alco-hols in the same way that 1,2-diols can be made using vinylene carbonate (88; R=H X=O).87 Another illustration of the synthetic use of oxazoles is in the heating of 3-sulphoximino-2-oxazolidinones(89); these decompose as indicated to leave an olefin and they have been used in attempts to prepare the (2) (successfully) and (E)isomers of bicyclo[3,3 llnon- 1-ene.88 Potts has extended his work on the mesoionic heterocycles of general structure (90; X Y = 0 S Se or NR').These compounds are conveniently prepared by reaction of a 1,2-bielectrophile RCHBrCOCl (R=Ph or C02Et) with a wide variety of 1,3-bin~cleophiles.~~ 79 G. E. Wilson and B. A. Belkind J. Org. Chem. 1977,42,765. 'O B. Nelander and L.Nord Tetrahedron Letters 1977 2821. " W. Siebert and M. Bochmann Angew. Chem. Internat. Edn. 1977,16 857. 82 W. Siebert and W. Rothermel Angew. Chem. Internat. Edn. 1977 16 373. 83 W. Siebert and K. Kinberger Angew. Chem. Internat. Edn. 1976,15,434. 84 G. Schmid and J. Schulze Chem. Ber. 1977,110 2744. " G. Schmid and J. Schulze Angew. Chem. Infernat. Edn. 1977 16 249. 86 G. E. Herberich J. Hengesbach 0.Kotle and W. Oschmann Angew. Chem. Infernat. Edn. 1977,16 42. J. A. Deyrup and H. L. Gingrich Tetrahedron Letters 1977 31 15. ''M. G. Kim and J. D. White J. Amer. Chem. SOC.,1977,99 1172; cf. Ann. Reports (B),1975,72,312. 89 K. T. Potts S. J. Chen J. Kane and J. L. Marshall J. Org. Chem. 1977,42 1633; K. T. Potts and S. J. Chen ibid. p. 1639; K. T.Potts F. Huang and R. K. Khattak ibid. p. 1644. Heterocyclic Chemistry (91) (92) The structures of Reissert salts have been reformulated as fused 5-amino- oxazolium systems (9 1) rather than the 4H-imino-structures previously assigned." The fused oxazolo[5,4-b]pyridine (92) is formed as a 3 1 addition product of benzoyl isocyanide and dimethyl acetylenedi~arboxylate.~~ The thermal rearrangement of 5-hydrazinoisoxazoles has been studied in some detail.92 The products are 1-and 4-aminopyrazolin-5-ones, and tetrahydro- 1,2,4- triazin-6-ones in varying proportions depending on the solvent and substituents. Another interesting rearrangement product was observed when the photochemistry of a variety of N-alkyl-2,1-benzisoxazoliurnsalts was in~estigated.~~ In protic solvents N-substituted o-amino-phenyl ketones are formed with further substitu- tion in the benzene ring (e.g.93-94); this is perhaps unexceptional but in acetonitrile the 1-adamantyl-3-phenyl compound gives a red salt for which the structure of the cation is suggested to be (95) or (96). The former is supported by Ph I - PhCNO HN-0 (97) PhCN + HNOz Ph (98) 'NOH yo M.J. Cook,A. R. Katritzky and A. D. Page J. Amer. Chern. Soc.,1977,99,165. 91 G. Hofle and B. Lange Angew. Chern. Internat. Edn. 1977,16,262. 92 G. Adembri A. Camparini F. Ponticelli and P. Tedeschi J.C.S. Perkin I 1977 971. 93 N. F. Haley J. Org. Chem. 1977,42 3929. 264 A. J. BouIton 13 C n.m.r. the latter by its i.r. spectrum.Another interesting observation in the isoxazole series is the curious insertion of the PhC element of benzonitrile oxide into some isoxazolin-5-ones (97; substituents unspecified) which forms 1,3-0xazin- 6-ones (98); the route suggested is Benzothiazoles with a nitro-group in the benzene ring react with alkylmagnesium bromides followed by addition of boron trifluoride etherate to the complex to produce alkyl-nitroso-benzothiazoles(e.g. 99+100) in fair to good yields.95796 It remains to be seen what role if any the thiazole ring plays in this rather unexpec- ted reaction. The full paper has appeared from Meth-Cohn’s group on the preparation of benzimidazole- 1,3-dioxides (101) from benzofuroxan and secondary nitroparaffins and of 1-hydroxybenzimidazole-3-oxidessimilarly from primary nitroparaffins.The products undergo some curious and fascinating reactions with a variety of reagents [(NC)2C=C(CN)2 MeO2CC=CCO2Me malononitrile] ; with the acetyl- enic ester the structure (102) is formed.97 2H-Benzimidazoles (e.g. 103) suffer nucleophilic attack by amines and sulphides; the products are oxidized by the starting compounds to the correspondingly substituted derivatives (104).98 (99) 0-(103) X=H (104) X=Nu E (1 02) E = C02Me COR I + ,COR‘ “HN) NN rJ-I I COR COR R (105) (106) (107) 1-Alkyl and 1-arylimidazoles react with acyl chlorides in the presence of tri- ethylamine in polar solvents (e.g. MeCN) to form the 2-acyl derivatives. Possibly the zwitterion (105) is involved in this reaction.99 Imidazole itself gives the dimeric 94 G.Lo Vecchio F. Foti G. Grassi and F. Risitano Tetrahedron Letters 1977 21 19. 95 G. Bartoli and G. Rosini Synthesis 1976 270. % G. Bartoli R. Leardini M. Lelli and G. Rosini J.C.S. Perkin I 1977 884 ’’ D. W. S. Latharn 0.Meth-Cohn H. Suschitzky and J. A. L. Herbert J.C.S. Perkin I 1977 470. 98 A. M. Jefferson and H. Suschitzky J.C.S. Chem. Comm. 1977,189. 99 E. Regel and K. H. Buchel Annulen 1977 145. Heterocyclic Chemistry compound (106),'0° under the same conditions while with isocyanates in hot solution 2-carboxamides are formed."' Benzimidazole suffers a three-pronged attack by 2,2'-dichlorocarbonyldiphenylamine;the structure of the product (107) has been confirmed by X-ray crystallography.lo* Prolonged irradiation of the pyridoindazole (1 08)in tetrahydrofuran forms S -carboline (109) and a spiro-intermediate is proposed (110) being one of many canonical forms by which it can be repre~ented."~ However the thermal rear- rangement of the 3-imidazolyl and 3-pyrazolylanthranils (1 11) and (1 12) leads to a variety of products which are reasonably suggested to arise by rearrangement of spiro-intermediates (113).'04 The Authors argue that in the case of the re-arrangement of the 3-(2-pyridyl)anthranil which cleanly forms pyrido[ 1,241- cinnolin-11-one (1 14),'05 a spiro-2-pyridine intermediate of type (113) is improbable. r=Y Me (1 13) (114) (115) (111) X=N,Y=CH (112) X=CH,Y=N The structure (1 15) of the product of reaction of 2-phenacylisoquinolinium bromide and ammonium acetatelo6 has been confirmed by X-ray crystallo- graphy.lo' Two pyrazole syntheses from azines were noted in the year under review.a'-0x0-aP-unsaturated azines (1 16) for which a variety of synthetic methods are available give pyrazolyl ketones and esters (1 17; R' = alkyl aryl or alkoxy) on heating.'" This is an extension of a reaction reported some ten years ago,'O9 and appears to be efficient and versatile. The other synthesis involves cyclization of simple ketazines with lithium di-isopropylamide in hexamethylphosphoramide and lea E. Regel Annulen 1977 159. lo' E. P. Papadopoulos J. Org. Chem. 1977,42 3925. lo' A. Banerji J. C. Cass and A. R. Katritzky J.C.S. Perkin I 1977 1162. Ifl3J.H. Boyer and C. C. Lai J.C.S. Perkin I 1977 74. lf14R. Y. Ning J. F. Blount P. B. Madan and R. I. Fryer J. Org. Chem. 1977,42 1791. lo' R. Y. Ning W. Y. Chen and L. H. Sternbach J. Heterocyclic Chem. 1974,11 125. If16R. F. Cookson D. P. Nowotnik R. T. Parfitt J. E. Airey and A. S. Kande J.C.S.Perkin I 1976. 201. lo7 H. J. Lindner and B. Kitschke Tetrahedron Letters 1977 2091. lo' T. A. Albright S. Evans C. S. Kim C. S. Labaw A. B. Russiello and E. E. Schweizer. J. Org. Chem. 1977,42,3691. lo' R. L. Stern and J. G. Krause J. Org. Chem. 1968 33 213; J Heterocyclic Chem. 1968 5 263. 266 A. J. Boulton is exemplified by pinacolone azine (118). The product (119) contains an extra carbon atom; this is evidently C-5 of the ring and is derived from the solvent."' The propensity for azines to undergo 'criss-cross' electrocyclic reactions is also illustrated in some work of Burger on what he terms 'dipole metathesis'.The azomethineimine (120) adds to electrophilic olefins and with acetylenes it under- goes a series of somersaulting additions to provide a variety of 1'5-and 1'7-dipolar systems."' Other work from Delaware"* is relevant to this area. R4 R3 RJ R3 rn R5CH ,N -%R5PN N N/ II I I R'C-COR CHR~-COR' MeC-Bu' MeCHBu' (120) (121) R =H or Me (122) 1,4-Dinitropyrazoles (12 1) with secondary amines undergo interesting cine-substitution with departure of the leaving group from the nitrogen. With the isomeric 1,3-dinitro compound (122) the amine simply removes the l-nitro- group.'13 A potentially useful synthesis of 1-substituted pyrazole-2-oxides (123) is the reaction of nitrile oxides with imidoyl-substituted oxosulphonium ylids (124).'14 Freeman's group has published further results in the 4H-series.The chlorination of pyrazoles 1-hydroxypyrazoles and their 2-oxides forms 4-chloro-derivatives;' 15*116 these with methoxide introduce a methoxy substituent into a + OMe Me-SO I R 0-OH (124) (123) (125) (126) methyl group either in the 4- or 3-position probably via diazafulvene derivatives e.g. (125)+(126). Silver acetate converts 4-chloro-4H-pyrazole-1,2-dioxides into the 4-acetoxy-dioxides but the 4-chloromonoxides (127) give 3-acetoxy 'lo Y. Tamaru T. Harada and Z. Yoshida Tetrahedron Letters 1977 4323. 'I' K. Burger H.Schickaneder and C. Zettl Angew. Chem. Internat. Edn. 1977,16 54 55. 'I2 S. Evans R. C. Gearhart L. J. Guggenberger and E. E. Schweizer J. Org. Chem. 1977,42,452. C. L. Habraken and E. K. Poels J. Org. Chem. 1977,42,2893. R. Faragher and T. L. Gilchrist J.C.S. Perkin I 1977 1196. 'I5 J. P. Freeman and E. R. Janiga J. Org. Chem. 1974 39 2663. J. P. Freeman and J. F. Lorenc J. Org. Chem. 1977 42 177. Heterocyclic Chemistry derivatives (128). With silver nitrate the monoxides (127) decompose to acetyl- enes probably through the 3-hydroxy-3H compounds (129) but 3-acetoxy compounds in part revert to 4-hydroxy derivatives besides decomposing to acetyl- enes (not invariably the expected ones carrying the 4-and 5-~ubstituents).'~' 0-0-(127) (128) R = Ac (129) R=H 3H-Pyrazoles readily lose nitrogen on irradiation The sufphur-containing derivatives (130; n = 0 1 and 2) form carbenes (131) which can be intercepted with olefins and cyclopropenes (132) which can be trapped by 1,3-dipolar cyclo- addition of dimethyldiazomethane and in the case of the sulphone (132; n = 2) by (135) X = S 0,CO 1 RZ R2 (136) (137) Diels-Alder addition to furan.The question whether or not an equilibrium exists between the carbenes (131) and the cyclopropenes (l32) was not settled but products of the carbene mode of addition are produced even after the irradiation has ceased.'l8 An account of a careful study of the photodecomposition of spiro- pyrazoles (1 33) using monochromatic radiation has been given.' '' The benzo- cyclopropenes (1 34) which are the first identifiable products undergo further J.P. Freeman E. R. Janiga and J. F. Lorenc J. Org. Chem. 1977,42 3721. M. Franck-Neumann and J. J. Lohmann Angew. Chem. Internat. Edn. 1977,16 323. E.Luddecke. H.Rau H. Durr and H. Schrnitz Terrahedron 1977,33,2677. 268 A. J. Boulton photoreactions which depend on the nature of the substituents and the illumina- tion. Spiropyrazoles (135) on irradiation form spirocyclopropenes (136) and in some cases fused indenes (e.g. 137). It is not yet clear whether (137) is formed via (136).'*' Pyrolysis of 172,3-thiadiazole cleanly forms thioketene which was characterized by its photoelectron spectrum.'*' For the pyrolysis of 172,3-benzo- thiadiazoles see Section 3.The rearrangement of the oxadiazolinethiones (1 38) to thiadiazolinones has been studied for a wide range of alkyl and aryl substituents. The reaction proceeds well photochemically and also thermally when catalysed by copper; without the copper only the 3-aryl compounds give thiadiazolinones. These results are in striking contrast to the very ready thermal rearrangement of open-chain oxime -thiono- carbamates.12* An extension of an old-fashioned rearrangement forms 1,2,4-thiadiazoles (139; X Y = N CH CMe or CPh) from 3-amino-1,2-oxazoles (140). The intermediate thioamides can sometimes be is01ated.l~~ The reaction of an aroyl chloride in pyridine with 5-amino-1,2,3,4-thiatriazole(141) eventually provides the diox- athiadiazapentalene system (142) with loss of Imidoyl chlorides behave similarly to give thiatetra-azapentalenes (143),44 but with acetyl chloride a more profound reorganization produces the thiadiazole (144).124 Further examples (145; X = 0 or S) of the 'extended thiathiophthene' system have been ~repared.'~' NHPh X Y/' VN\NHPh U (1 39) N AcHN(/ ]NHAc S-N (ACCI HzNTN~y ArCXCI S-N N Arf/ x-s-x NyAr (144) (141) (142) X=O (143) X=NAr' R' I2O H. Durr S. Frohlich B. Schley and H. Weisgerber J.C.S. Chem. Comm. 1977 843. H. Bock B. Solonki G. Best and P. Rosmus J. Amer. Chem. SOC.,1977,99 1663. 122 A. Pelter and D. Sumengen Tetrahedron Letters 1977 1945. 123 N. Vivona G. Cusmano and G. Macaluso J.C.S. Perkin I 1977 1616. R. J. S. Beer and I. Hart J.C.S.Chem. Comm.1977. 143. 12' E. G. Frandsen J.C.S. Chem Comm. 1977 851. Heterocyclic Chemistry 269 The addition of a sulphene to the dithiazolinimines (146) is reported to form the rearranged system (147). 126 Addition of benzonitrile oxide to sulphines generally produces 1,4,2-oxathiazole-4-oxides(1 48) but in the case of fluorenethione-S- oxide the isomeric 1,5,2-oxathiazole-5-oxideis also f0~med.l~' A very interesting reaction occurs between 2,5-dimethylfuran and nitrosocar- bonylbenzene PhCONO. The 1,3,4-dioxazole (149) is formed possibly by rear- rangement of the primary Diels-Alder adduct as indicated and it is reversible! The product (149) on heating regenerates the two original Diels-Alder participants.l** Me Ph 11 J 0-0 1,2,4-Dioxazoles (150) are produced by the reaction of singlet oxygen with oxa~oles.~*~ Their decomposition gives a variety of products including diacyl- amines.I3O The reaction of 1,3,4-thiadiazoliurn pseudobases (15 1) with diethyl acetyl- enedicarboxylate in boiling benzene involves an ylid intermediate and an unusual p-nitrophenyl group migration. The products (152) undergo further addition of an a1k~narnine.l~~ (Scheme 5). /C,H,N02 + /C,H,N02 + /C6H,NO, N-N N-N -N-N L -Ark YH OR -Ark. ,!-s S (151) \;102CCGCCO*Et 41.52) Scheme 5 '26 H.W.Linden and J. Goerdeler Tetrahedron Letters 1977 1729. 127 B. F. Bonini G. Maccagnani G. Mazzanti L. Thijs P. M. M. Ambrosius and B. Zwanenburg J.C.S. Perkin I 1977 1468. 12' C. J. B. Dobbin D.Mackay M. R. Penney and L. H. Dao J.C.S. Chem. Comm. 1977,703. '29 M. L. Graziano M. R. Iesce A. Carotenuto and R. Scarpati J. Heterocyclic Chem. 1977 14 261; Synthesis 1977 572. I3O M. L. Graziano A. Carotenuto M. R. Iesce and R. Scarpati Tetrahedron Letters 1977,447. 13' G. Scherowsky K.Dunnbier and G. Hofle Tetrahedron Letters 1977,2095. 270 A. J. Boulton Dehydrodithizone (1 53) and its oxygen analogue (154) both ‘Type B mesoionic compounds’ in the classification of Ollis and Ram~den,’~~ are thermally rearranged to the isomeric ‘Type A’ heterocycles (155).’33 Dehydrodithizone reacts with tetracyclone to give an interesting product (1 56)containing an open-chain azimine grouping rather than the isomeric fused dihydrotetrazole which seems to be an elusive The structure of (156) was proved by X-ray crystallography and the same technique was applied to solve the structure of the reaction product (157) of glyoxal and the bis-azo compound (1~9.l~~ Ph I Ph Ph XYN+ I Ph yh N+ Phn >N’ *NPh N-N .N-N \ \ Ph Ph 0 Ph N (153) X=S (155) (156 (154) X=O Q The 1,2,3,5-dithiadiazolium system (159; R=Bu’ CCI3 or Ph) has been pre- pared by the reaction of the nitriles RCN with trithiazyl chloride S3N3C13.’36 The reactions of this and other thiazyl chlorides with a variety of olefinic substrates have been studied by Barton and B~bb;’~’ isothiazoles and thiadiazoles are among the products observed.(159) An interesting study of thioamide base-pairing through hydrogen bonds has been reported.13* In CCl the tetrahydropyrimidine-2-thione(160) (weakly associated ‘32 D.W. Ollis and C. A. Ramsden Ado. Heterocyclic Chem. 1976,19,1. 133 P. N. Preston and K. Turnbull J.C.S. Perkin Z 1977 1229. 134 G. V. Boyd T. Norris and P. F. Lindley J.C.S. Perkin Z 1976 1673; ibid. 1977 965. 13’ P. Skrabal and M. Hohl-Blumer Helv. Chim. Acta 1976 59 2906; P. Luger J. Malkowski and P. Skrabal ibid. 1977 60 1545. 136 G. G. Alange A. .I.Banister B. Bell and P. W. Millen Znorg. Nuclear Chem. Letters 1977 13 143. 13’ D. H. R. Barton and W. A. Bubb J.C.S. Perkin Z 1977,916. 13* E. Gentric J. Lauransan C. Roussel and J. Metzger Tetrahedron Letters 1977 251. Heterocyclic Chemistry by itself because of the weak hydrogen bonding tendency on the part of its NH group) when mixed with an equal proportion of the benzothiazolinethione (161) (which is fairly strongly dimerized on account of the very acidic NH group and in spite of its weakly basic thione S-atom) forms a hydrogen-bonded dimer pair as shown with an association constant almost twice the value of that for the homo- associated pair (161)*.1.r. spectroscopy was used to determine the equilibrium constants and the results agreed well with the predictions based on calculation. The structures (162; R = alkyl X = S or Se) are assigned on the basis of 13C n.m.r. evidence to the products of alkylation followed by demethylation of 1-aryl-5-methylthio- and -methylseleno-tetrazoles. The same technique is used to distinguish between tautomeric thiol and thione structures and the corresponding selenol-selenones in a series of az01es.l~~ An interesting case of tautomerism arises with the bicyclic phosphorus compound (163).The exchange is sufficiently rapid at room temperature that the n.m.r. spectra indicate overall two-fold symmetry of the molecule; the signals separate at low temperature (-60 "C; 13Cn.m.r. at 22.63 MHz). Compound (163) arises by disproportionation of the diazaphospholane (164) as shown. 140 Several 1977 papers illustrate the propensity for PI1*to expand its valency to P" particularly when the atom is contained in a five-membered ring. Equilibria have been studied for a variety of systems of the type (165)+ (166) (X= 0 or NR) and the results were rationalized using Pearson's HSAB treatment.I4l The P-Hphos-phoranes (166; X = 0)react with aldehydes and ketones to form products (167),'42 which have been studied by i.r.and n.m.r. spectroscopy. 143 Bicyclic phosphoranes 139 J. R. Bartels-Keith M. T. Burgess and J. M. Stevenson J. Org. Chem. 1977,42 3725. Id* H. Sliwa and J. P. Picavet Tetrahedron Letters 1977 1583 and personal communication. 14' A. Munoz Bull. SOC. chim. France 1977 728. 14' H. Gerrna and R. Burgada Buil. SOC. chim. France 1975,2607. 143 H. Germa M. Bon and F. Mathis Bull. SOC. chim. France 1977 508. 272 A. J. Boulton containing nitrogen (e.g. 168) are reversibly formed from the PIrrcompounds (169).144 6 Six-membered Rings The relationship between odd alternant hydrocarbon anions and six-membered mesomeric betaines has been used by Ram~den'~~ to formulate general rules for predicting whether 1,3-dipolar reactivity can be expected.The statement is made that 'neutral heterosystems isoelectronic with irreducible odd alternant hydro- carbon anions cannot be represented by non-polar structures if the lone-pair originates at an unstarred position.' This arises from simple parity arguments. The treatment places for example the pyrazinium derivative (170) into the class of fully conjugated mesomeric betaines entirely distinct from the pyrimidine (17 l) which is a cross-conjugated dipole. In fact the former behaves as a 1,3-dipole the latter as a 1,4-dipole. Sammes's group exploited the 1,4-dipolar reactivity of compounds of type (171) earlier,146 and they have now presented further examples (172+173) in which intramolecular cyclization of olefinic acetylenic or cyano substituents to pyrimidine rings -not necessarily dipolar -leads to useful syntheses of annulated pyridines and pyrimidine^.'^^ I R (172) X = CH or N (171) R = OH Meor Ph Considerable interest is still shown in conformational analysis and several papers have illustrated the great value of the information provided by '3Cn.m.r.Some years ago 1-chloropiperidine was studied by 'H n.m.r. and a barrier to ring inversion of 56.5 kJ mol-' was found.14' This technique gave no information on the N-inversion process except that it had to be faster. The I3C n.m.r. has now shown that at -32 "C the C1-axial form is ca. 4% abundant (AGO ca.6 kJ mol-') with AG* 43 kJ mol-I for the N-inversion process.'49 For such heavily-biased equilibria the dynamic 13Cn.m.r. method is particularly useful as illustrated in the case of the perhydro- 1,2,4-triazines and -1,3,4-thiadiazine~.'~~ The conformations of 1-methylpiperidinium salts in water provided evidence for solvation of the NH' group as a factor in influencing equilibria.''' 144 D. Houlla F. H. Osman M. Sanchez and R. Wolf Tetrahedron Letters 1977 3041. 14' C. A. Ramsden J.C.S. Chem. Comm. 1977 109. Ann. Reports (B),1975 72 312. 147 L. B. Davies P. G. Sammes and R. A. Watt J.C.S. Chem. Comm. 1977,663. 14* J. B. Lambert W. L. Olivers and B. S. Packard J. Amer. Chem. SOC.,1971,93 933. 149 F. A. L. Anet and I. Yavari Tetrahedron Letters 1977 3207.lS0 A. R. Katritzky R. C. Patel and D. M. Read Tetrahedron Letters 1977 3803. E. L. Eliel C. Y. Yen and G. Zuniga Juaristi Tetrahedron Letters 1977 2931. Heterocyclic Chemistry Further use of ion cyclotron resonance to determine gas-phase basicities and hence to obtain estimates of tautomeric equilibrium constants has been made.'52 1H-2- and 4-Pyridinethione structures strongly favoured in polar solvents are of minor importance in the gas phase. 3-Acetyl-2-ethoxy-3,4,5,6-tetrahydropyridine (174a) exists practically completely as such in CDC13 but the similarly constructed furopyridine (175) strongly prefers the NH form (b). It is suggested that a destabil- izing interaction exists between the lone pairs of the heteroatoms in (175a); this is avoided in (174a) by rotation of the ethoxy group.153 CoMe = N N OEt Q;;=0 momo H(1 74b) (175a) H(175b) (1 74a) A number of papers featured the thermal and photochemical destruction of heteroaromatic six-membered rings.The irradiation of [ 1,4-15N2]-1,2,4,5-tetra-zine under a variety of conditions (exciting both singlet and triplet states) produced N2 and HCN but no C2Hz or doubly-labelled N2,suggesting that 1,4-bonding plays no significant role in the photodecomposition of tetra~ine.'~~ The fused 1,2,3- triazine (176) loses nitrogen to form the nitrile (177).15' Py?idine-1-oxide when irradiated at 10 K in an argon mattix forms an unstable isocyanide the anion (178) of which is much more stable being formed if the irradiation is carried out at room temperature in aqueous base.'56 Pyridazine- 1,2-dioxide (179) has been found (after a false start1") to be isomerized to the dihydroisoxazoloisoxazole(180).15* It is tempting to ascribe this to cleavage of (179) to 1,4-dinitrosobutadiene which then undergoes serpentine bicyclization in a manner for which several precedents C.B. Theissling N. M. M. Nibbering M. J. Cook S. El-Abbady and A. R. Katritzky Tetrahedron Letfers 1977 1777. See also M. J. Cook A. R. Katritzky M. Taagepera T. D. Singh and R. W. Taft J. Amer Chem. SOC. 1976,98,6048. H. Sliwa and L. Delaunay Tetrahedron Letters 1977,2793. D. S. King C. T. Denny R. M. Hochstrasser and A. B. Smith J. Amer. Chem. Soc. 1977,99,271. I. Ito N. Oda S. I. Nagai and Y. Kudo Heterocycles 1977,8 319.0.Buchardt J. J. Christensen C. Lohse J. J. Turner and I. R. Dunkin J.C.S. Chem. Comm. 1977 837. H. Arai A. Ohsawa K. Saiki and H. Igeta J.C.S. Chem. Comm. 1977 133. H. Arai A. Ohsawa K. Saiki H. Igeta A. Tsuji T. Akimoto and Y. Iitaka J.C.S. Chem. Comm. 1977,856. 274 A. J. Boulton exist.159 Vacuum pyrolysis of benzo[c]cinnoline derivatives has provided further examples of aza-biphenylenes. 160 An attempted halogen-lithium exchange in the acetal (181) led after hydrolytic work-up to the pyridone (182). The proposed explanation which was consistent with deuterium-labelling experiments involved metallation at the pyridine 3-position indicated followed by cleavage to the nitrile (183) and recyclization. In the reaction of the pyridinium salt (184) with a secondary amine it is the pyridine 2-position which is deprotonated; the ylid cyclizes to the ester group and the pyridine ring is then opened leaving a 4-isoxazolinone (185).16' R2NH; -R,N-(CH=CH), 3 N-0 0 0,CMe,CO,Et (185) (184) The pyrolysis of aryl propargyl ethers provides a goldmine of interesting chem- istry.The two isomeric cyclobutapyridines (186) and (187) (ratio 2 :1 50% overall yield) are formed in a curious reaction (the mechanism of which requires fuller investigation) from 4-propargyloxypyridine at 550 0C.163 Abramovitch et aZ.'64 have reported the preparation and some reactions of 1-aryloxypyridinium salts and 1-aryloxy-2-pyridones. The salts prepared from the N-oxides and diaryliodonium fluoborates are unstable and rearrange usually under the influence of bases.With phosphorus oxychloride the pyridones form pyrido[ 2,3 -b 3benzofurans. see e.g. G. Maier and M. Wiessler Tetrahedron Letters 1969 4987. A recent dihydro-pyrrolopyrrole (R. M. Carr. R. 0.C. Norman and J. M. Vernon J.C.S. Chem. Comm. 1977 854) also conforms to the same structure type and may be formed analogously. 160 S. Kanoktanaporn and J. A. H. MacBride Tetrahedron Letters 1977 1817. G. R. Newkome J. D. Sauer and S. K. Stakes J. Org. Chem. 1977,42 3524. 16* H. Sliwa and A. Tartar Tetrahedron Letters 1977 311. 163 J. M. Riemann and W. S. Trahanovsky Tetrahedron Letters 1977 1867. 164 R. A. Abramovitch and M. N. Inbasekaran Tetrahedron Letters 1977 1109; R. A. Abramovitch G.Alvernhe and M. N. Inbasekaran ibid. p. 1113. Heterocyclic Chemistry 275 The full pape? has appeared on the preparation and reactions of 1,l'-bi-pyridinium salts which have been mentioned in these Reports earlier.'66 The pyridine-N-imine derivatives (188) undergo a variety of thermal and photochemical cyclization reactions an outline of which is presented in Scheme &I6' and/or I-0- N Scheme 6 [1,2,4]-Triazino[ 1,6,5-ji]quinolines (189) can be prepared by N-amination followed by cyclization of 8-acylaminoquinolines (1 90). The red products behave as 1,3-(or 1,ll-) dipoles (189; R =H) giving the cyclazine derivative (191) with dime t hyl acetylene dicarboxylate. RCONH R R R R + p-II NH NH \/ \/ (192) The diazenium salt (192) can be obtained by electrochemical oxidation of 1-amino-1,2,3,4-tetrahydroquinoline.In acid it adds to olefins; in base it forms a 2-tetra~ene.l~~ Cycloaddition reactions also trap the azomethine ylid (193) generated by acetic anhydride-triethylamine dehydration of the N-oxide (194)."' 165 M.P. Sammes H. K. Wah and A. R. Katritzky J.C.S. Perkin I 1977 327. Ann. Reports (B),1975,72,269; ibid. 1976,73,429. A. Kakehi S. Ito K. Uchikama Y. Konno and K. Kondo J. Org. Chem. 1977,42,443. 168 Y. Tamura Y. Miki H. Hayashi Y. Sumida. and M. Ikeda Heterocycles 1977.6 281. 169 G. Cauquis B. Chabaud and Y. Gohee Tetrahedron Letters 1977 2583. 17* M. Ikeda Y. Miki S. Kaita Y. Nishikawa and Y. Tamura J.C.S.Perkin I 1977,44. 276 A. J.Boulton The preparati~n'~' and stability'72 of N-ethoxycarbonyl-1-pyrindine(195) is discussed by Anastassiou et al.They claim that the ethoxycarbonyl grouping robs the heterocyclic system of none of its aromaticity in contrast to what is observed with 1-e thoxycarbonylazonine. Dihydropyridines are featured in a number of noteworthy papers. 1-Carbo-methoxy-1,2-dihydropyridinewas the starting-point for a synthesis of the dihydro- azabarrelene (196) which is a remarkably unstable compound decomposing to benzene in a few hours. 173 Surprisingly organomagnesium and organocadmium reagents attack 1-acylpyridinium salts at the 2-position so quickly that competition from attack at the carbonyl group is not serious. The acid chloride can even be added to a mixture of the organometallic reagent and the pyridine competition from the acid chloride under these conditions is also negligible.174 1,2-Dihy- dropyridines have been used in syntheses of di- and tetra-hydroazocines and-of pyrr~lizidines.'~~ A new technique for preparing Reissert compounds using tri- methylsilyl cyanide and aluminium chloride allows their formation in water-free solvents and so permits use of acid chlorides which are sensitive to hydr01ysis.l~~ Spiro-l,4-dihydropyridines(197) are formed by addition of dimethyl acetyl- enedicarboxylate to a wide variety of heterocyclic imines.177 I C02Et (195) (197) so; X =S or NMe E =C02Me Me (199) Me Chau and Kice have found that the dibenzodithiin trioxide (198) with sulphite ion produces the Bunte salt S-oxide (199) an unusual and unstable type of 171 A.G. Anastassiou S. J. Girgenti R. C. Griffith and E. Reichmanis J. Org. Chem. 1977,42 2651. 172 A. G. Anastassiou and E. Reichmanis J. Amer. Chem. SOC. 1977 99 7392. 173 H. Sliwa and Y. le Bot Tetrahedron Letters 1977,4129. 174 R. E. Lyle J. L. Marshall and D. L. Comins Tetrahedron Letters 1977 1015. 175 P. S. Mariano M. E. Osborn D. Dunaway-Mariano B. C. Gunn and R. C. Pettersen J. Org. Chern. 1977,42,2903. 176 S. Ruchiwarat N. Phadungkul M. Chuankamnerdkarn and C. Thebtaranonth Heterocycles 1977,6 43. 177 H. Quast and E. Spiegel Tetrahedron Letters 1977 2705. Heterocyclic Chemistry ~tructure."~ Interesting sulphur-containing six-membered rings that were noted were the 2,1,3-benzothiadiazinium system (200),17' and the 1,2,4-oxathiazine (201),'80 the latter arising by bromine oxidation of the thiourea (202).The synthetic utility of 2-chloro-1,3-dithian has been investigated.'" The rearrangement of optically active 10-thia-anthracenes (203) occurs with predominant racemization but some retention of optical activity in the product (204).18* H Ar I Ar (203) 0Li+ phnoH As X I I Ar Me (207) (208) R=Ac (210) (211) X = P As Sb (209) R=H (212) X=CMe Research on six-membered rings with more unusual heteroatoms has been the subject of much activity and here too several rearrangements have been dis- covered. The benzyl group migrates on heating from the arsenic atom to the 4-substituent in (205); this has been known for some time in the phosphorin series.'83 Aryl groups undergo 1-2 migration with acid catalysis in (206)Ig4 and (207);18' hydrolysis of the acetoxy-derivative (208) forms the hydroxy-compound (209) which appears to exist as although alkylation of 4-hydroxyarsenin "'M.M. Chau and J. L. Kice J. Org. Chem. 1977,42 3103 3265. 179 W. Kosbahn and H. Schafer Angew. Chem. Internat. Edn. 1977,16 780. lSo S. Solyom P. Sohar L. Toldy A. Kalman and L. Parkanyi Tetrahedron Letters 1977 4245. C. Kruse N. Broekhof A. Wijsrnan and A. van der Gen Tetrahedron Letrers 1977,885; E. C. Taylor and J. L. LaMattina ibid. 1977 2077. '" C. A. Maryanoff. K. S. Hayes and K. Mislow J. Amer. Chem. Soc. 1977,!39 4412. G. Markl and J. B. Rampal Tetrahedron Letters 1977 2569.G. Markl and R. Liebl Angew. Chem. Internat. Edn. 1977,16,637. G. Markl and J. B. Rampal Tetrahedron Letters 1977 3449. 278 A. J. Boulton gives the l-alkyl-4-0ne.'~~ The 'phosphaphenol' (210) too appears to be prefer- red over a ketonic tautomer.'86 Diels-Alder addition and retro-addition of dimethyl acetylenedicarboxylate and methyl propiolate to arsabenzene and its 2-methyl derivative have been studied. Some dimethyl phthalate is produced indicating that 1-arsabarrelene derivatives are not exclusively formed but that also some of the 2-arsa compounds arise; these can lose HC-As to produce the ~htha1ate.l~' Methyl-lithium adds the alkyl group to the heteroatoms of phospha- arsa- and stiba-benzene in contrast to pyridine to give the anions (211).The chemical shifts of the protons on the pentadienyl fragments are very similar to those in (212) suggesting that little or no stabilizing interaction is derived from the presence of the heteroatom in (211).'88 (214) (213) (217) (2 18) (219) X =0,CR2 Irradiation of the 1,4-diphosphorin (213) is reported to form the diphos- phabenzvalene (214) a remarkably stable while with carbon tetra- chloride it reacts in an odd way giving the 1,4-bridged compound (215) and the unstable dichloro-derivative (216) which was not Representatives of &N3P (217)191 and CN2P3 (218)'92 ring systems were noted. With group IV elements the stannins (219) with sp2-hybridization of all the ring carbon atoms were prepared,'93 and a report on the generation of a silabenzene appeared this is mentioned in Chapter 6.7 Seven-membered and Larger Rings Like the thiirenes mentioned earlier so 1-benzothiepins are stabilized appreciably by quaternization at sulphur. The benzothiepinium salt (220) has a half-life of 69 hours at 80"C (CD,N02) while (22 1) is nearly half gone in three hours (80OC CCl,). The sulphoxide (222) is much less stable than either the sulphone (223) much more.'94 G. Markl G. Adolin F. Kees and G. Zander Tetrahedron Letters 1977 3445. "'A. J. Ashe and H. S. Friedman Tetrahedron Letters 1977 1283. A. J. Ashe and T. W. Smith Tetrahedron Letters 1977 407. Y. Kobayashi S. Fujino H. Hamana I. Kumadaki and Y.Hanzawa I. Amer. Chem. Soc. 1977.99 8511. '90 Y. Kobayashi I.Kumadaki H.Hamana and S. Fujino Tetrahedron Letters 1977 3057. 191 P. P. Kornuta N. V. Kolotilo and L. N. Markovskii Zhur. obshch. Khim. 1977,47,342. 19' R. T. Oakley and N. L. Paddock Canad. J. Chem. 1977,55,3651. 193 G. Markl and J. B. Rampal Tetrahedron Letters 1977 2325. H. Hofmann and A. Molnar Tetrahedron Letters 1977 1985. 19' 279 Heterocyclic Chemistry (220) X=iMe (224) (a) R=H (225) (221) x=s (b) R = C02Me (222) x = so (223) X=SOz The equilibrium between 1-tosylazepines (224) and the corresponding benzene N-tosylimines (225) has been investigated by "C and 'H n.m.r. spectroscopy. Although the signals from the imine (225a) were not directly observed line- broadening phenomena of the azepine bands revealed its presence (ca.l0/o) and gave AG' ca. 46 kJ mol-' for the activation barrier. The imine (225b) was more abundant at equilibrium (ca. 10% at -70 "C,in [2H6]-acetone).195 A full paper has appeared on Becker and Gustafsson's work on the action of amines on the 'spiro-benzoxete' oxidation dimers of 2,4-di-t-alkylphenol~.'9~The azepinone product (226) is rapidly oxidized (NaBi03) to the tricyclic compound (227); this forms a tetracyclic photo-isomer which can be oxidized to the spiro-benzofuranone (228).19' Some further work has been reported on the interesting rearrangement of 3,4-diazanorcaradienes to 6H-1,4-diazepines which was mentioned in these Reports last year,I9* and some ambiguities in the details of the various steps have been ~1arified.l~~ Details of the preparation of 1H-and 3H-1,2- benzodiazepines have been published.200 & Me But/ \ \ OH / -B u ' I Bu' o I -6 But IBu' --+ B ~ Bu' ' ~ L 00 ~ Bu' (226) (227) (228) / (230) R=Li (234) (231) R=H (233) R =Me Ph (232) R=Me 19' H.Prinzbach H. Babsch H. Fritz and P. Hug Tetrahedron Letters 1977 1355. '% cf Ann. Reports (B) 1976,73,271. The dimers have recently been shown to possess oxepino[2,3-6]-benzofuran structures H. Meier H. P. Schneider A. Ricker and P. B. Hitchcock Angew. Chem. Internat. Edn. 1978,17 121. o~ 19' 19' H. D. Becker and K. Gustafsson J. Org. Chem. 1977,42,2966. Ann. Reports (B).1976,73 271. 199 G. Reissenweber and J. Sauer Tetrahedron Letters 1977 4389; H. D. Fuhlhuber and J. Sauer ibid. 1977,4393.2oo T. Tsuchiya J. Kurita and V. Snieckus,J. Org. Chem. 1977,42 1856; cfi Ann. Reports (B),1974,71 354. 280 A. J.Boulton A neat procedure for preparing the dizenzo[ f,h][ 1,5]diazonine system is repor- ted,201 in the base-promoted cleavage of a transannular bond in the dihydro- pyrazole derivative (229). The lithium salt (230) can be protonated and alkylated to give the neutral species (23 1) and (232). 1,8-DiIithionaphthalene on reaction with dichlorostannanes gave the peri-naphtho-fused distannocins (233). X-ray crystallography showed the central ring to be strongly distorted from planarity but the molecule (233; R = Me) was con- formationally mobile down to -100 “C the methyl protons appeared as a singlet in the n.m.r. spectrum. The oxadistannepin (234) was also prepared.202 The dimerization of 3-( 1-imidazolyl and 1-benzimidazolyl)quinolines,by e.g.metalation (PriNLi) followed by oxidation yields e.g. interesting fused diazocines (235).203 Other ring assemblies of note include the circulenes and helicenes pro- duced by oligomerization by acid of quinones which have been studied by X-ray crystallography. The ‘closed tetramer’ (236) was found to be planar.2o4 The pre- paration of the ‘phenanthrolinophane’ (237)205 parallels that of the corresponding hexa-aza compound (238) reported earlier.206 (237) X=CH (238) X=N A method for the repetitive ring-expansion of cyclic allylsulphonium allylides is described from two laborat~ries.~~’*~~~ For example (Scheme 7) 2-vinyltetra- s? P+ Scheme 7 201 D.G. Farnum and K. Rasheed J. Org. Chem. 1977 42 573. The ring system (230) is incorrectly named and numbered in this paper. ’02 J. Meinwald S. Knapp. and T. Tatsuoka Tetrahedron Letters 1977 2247. 203 T. Kaufmann D. Tigler and A. Woltermann Tetrahedron Lett& 1977 741. 204 J. E. Bug H. Erdtman H. E. Hogberg B. Karlsson A. M. Pilotti and A. C. Soderholm Tetrahedron Letters 1977 1831. 205 S. Ogawa J.C.S. Perkin I 1977 214. 206 S. Ogawa T. Yamaguchi and N. Gotoh J.C.S.Perkin I 1974,976. *07 R. Schmid and H. Schmid Helv. Chim. Acta 1977,60 1361. 208 E. Vedejs M. J. Mullins J. M. Renga and S. P. Singer Tetrahedron Letters 1978 519. Heterocyclic Chemistry hydrothiophen can be converted into a 2-vinylthiocin (239)’and the process could be repeated to produce 11- 14- and 17-membered monothia-cycloalkenes.Although 1,4-diazabicyclo[ 2,2,2]octane is a well-known compound its homolo- gues with bridges of other lengths are difficult to obtain. Alder et aL209have now described a procedure starting from bridged hydrazines which promises to be quite versatile. The formation of 1,4-diazabicyclo[3,3,3]undecane(240) is shown in Scheme 8. (240) Scheme 8 Polydentate ligands containing oxygen nitrogen and sulphur are an active area of research and the preliminary notes of previous years are being followed by detailed papers. Cram’s series of six2l0 are particularly noteworthy as are Stod- dart’s reports on chiral crown ethers211 and on macro-bicyclic polyethers with bridgehead carbon atoms,212 in which the question of ‘in-out’ isomerism is dis- cussed.An ‘in-out -out-in’ isomerization process has been observed in this type of compound the chiral ‘cryptand’ (241) shows two bridgehead carbon signals at -70 “C,but only one at +112 OC and the achiral homologue (242) also isomerized apparently much more rapidly.’13 (241) n=l (242) n= 2 Ari octa-aza cage compound (243) (for which the trivial name ‘sepulchrate’ was coined in keeping with the somewhat morbid nomenclature for this type of compound) has been assembled by reaction of the tris(ethylenediamine)cobalt(IIi) ion with formaldehyde and ammonia.214 The nitrogen atoms in the bridges preserve their (chiral) octahedral arrangement about the metal atom disinterment of which was not accomplished.’09 R. W. Alder R. B. Sessions J. M. Mellor and M. F. Rawlins J.C.S. Chem. Comm. 1977 747. Part 6 R. C. Helgeson T. L. Tarnowski J. M. Timko,and D. J. Cram J. Amer. Chem. Soc. 1977,99 6411. 211 I. J. Burden A. C. Coxon J. F. Stoddart and C. M. Wheatley J.C.S. Perkin I 1977,220;W.D.Curtis D. A. Laidler J. F. Stoddart and G. H. Jones ibid. p. 1756. ’12 A. C. Coxon and J. F. Stoddart J.C.S. Perkin I 1977 767. ’13 B. H. Gregory A. H. Haines and P. Karntiang J.C.S. Chem. Comm. 1977 918. I. 1. Creaser J. M. Harrowfield A. J. Herlt A. M. Sargeson J. Springborg R. J. Geue and M. R. Snow,J. Amer. Chem. SOC.,1977,99,3181. 282 A. J. Boulton 8 Reviews A two-volume monograph on heterocyclic stereochemistry has been p~blished.~~’ Other aspects of general heterocyclic chemistry which have been reviewed include (2+ 2)-cycloaddition and cycloreversion reactions,216 reactions involving cyclo- elimination of nitr~gen,~” the thermochemistry of the alkylation of tautomeric the gas-phase thermal and photochemical decomposition of heterocycles containing 0 N or S,219 and the rearrangements of N-oxides.220 Macrocycles containing ‘sub heterocyclic rings’ -he terocyclophanes for the most part -have been Among reviews of specific ring systems or groups of systems are two of particular interest to phosphorus chemists ‘Compounds of Two-co-ordinated Phosphorus’222 include the A 3-phosphorins and the diaza- and triaza-phospholes and ‘Polycyclic Carbon-Phosphorus encompass a wide variety of structural types.Other topics reviewed are pyrrolodiazines with bridgehead nitrogen,224 6,8-dioxabicyclo[3,2 llo~tanes,~~~ boraheterocycle~,~~~ the heterocyclic analogues of prostaglandin^,^^^ thiiranium and thiirenium ions,228 tetrazole~,~~~ tellurophenes 230 thieno~yridines,~~~ isoxa~olidines,~~~ and oxazolone~,~~~ 1,2-and dioxetan~,~~~the mesomeric betaine derivatives of heteropentalene~.~~’ Reviews on the electrocyclic ring-opening reactions of ethylene the action of hydroxylamines and hydrazines on y-pyrone derivatives,237 and the photochemistry of 2H-azirine~~~~ deal with special aspects of specific heterocyclic rings. A monograph devoted to pyrroles has appeared.239 Chemical Society pub- lications of particular heterocyclic interest include the regular specialist reports on ’15 W.L. F. Armarego ‘Stereochemistry of Heterocyclic Compounds’ Parts I and XI Wiley-Interscience New York 1977. ’I6 D. N. Reinhoudt Ado. Heterocyclic Chem. 1977 21 253. ’17 H. Meier and K. P. Zeller Angew. Chem. Internat. Edn. 1977 16 835. ’18 P. Beak Accounts Chem. Research 1977,10 186. 219 S. Braslavsky and J. Heicklen Chem. Rev. 1977 77 473. 220 S. Oae and K. Ogino Heterocycles 1977,6 583. ’” G. R. Newkome J. D. Sauer J. M. Roper and D. C. Hager Chem. Rev. 1977,77,513. 222 N. I. Shvetsov-Shilovskii R. G. Bobkova N. P. Ignatova and N. N. Mel’nikov Uspekhi Khim. 1977 46 967; Russ. Chem. Rev. 1977,46 514. 223 S. D. Venkataramu G. D. MacDonell W. R. Purdum M.El-Deek and K.D. Berlin Chem. Rev. 1977,77 121.224 D. E. Kuhla and J. G. Lombardino Adv. Heterocyclic Chem. 1977,21 1. 225 H. C. Brown and E. Negishi Tetrahedron,1977 33 2331. 226 P. P. Mundy K. B. Lipkowitz and G. W. Dirks Heterocycles,1977,6 51. 227 E. I. Levkoeva and L. N. Yakhontov Uspekhi Khirn. 1977,46 1074; Russ. Chem. Rev. 1977,46 565. 228 G. H. Schmid in ‘Topics in Sulfur Chemistry’ ed. A. Senning and P.S. Magee Thieme Stuttgart 1977 vol. 3. 229 R. N. Butler Adv. Heterocyclic Chem. 1977 21 223. 230 F. Fringuelli G. Marino and A. Taticchi Adv. Heterocyclic Chem. 1977 21 119. 231 J. M. Barker Adv. Heterocyclic Chem. 1977 21 65. 232 R. Filler and Y. S. Rao Adv. Heterocyclic Chern. 1977 21 175. 233 Y. Takeuchi and F. Furusaki Adv. Heterocyclic Chem. 1977,21,207. 234 W. Adam Adv.Heterocyclic Chem. 1977 21,437. 235 C. A. Ramsden Tetrahedron,1977,33 3203. 236 R. Huisgen Angew. Chem. Internat. Edn. 1977 16 572. 237 C. Morin and R. Beugelmans Tetrahedron,1977,33,3183. 238 P. Gilgen H. Heimgartner H. Schmid and H. J. Hansen Heterocycles,1977 6 143. 239 R. A. Jones and G. P.Bean ‘The Chemistry of Pyrroles’ (Organic Chemistry monographs) Academic Press Inc. London 1977 vol. 34. Heterocyclic Chemistry 283 aromatic and Group VI and a volume on the 0-lactam which should prove extremely valuable to the many active research workers in this field. ‘The Alkaloids’ ed. M. F. Grundon (Specialist Periodical Reports)The Chemical Society London 1977 vol. 7. 241 6 Aromatic and Heteroaromatic Chemistry’ ed. C. W. Bird and G.W. H. Cheeseman (Specialist Periodical Reports) The Chemical Society London 1977,vol. 5. 242 ‘Organic Compounds of Sulphur Selenium and Tellurium’ ed. D. R. Hogg. (Specialist Periodical Reports) The Chemical Society London 1977,vol. 4. 243 ‘Recent Advances in the Chemistry of 0-Lactam Antibiotics’ ed. J. Elks (Special Publication no. 28) The Chemical Society London 1977.