11 Heterocyclic Chemistry By 0. METH-COHN and R. K. SMALLEY The Ramage Laboratories University of Salford Salford M54W 1 Three-memberedRing Compounds 2H-Azirines continue to be used as versatile synthetic reagents. In addition to a full report' on the intramolecular cycloaddition reactions of substituted 2H-azirines noted last year, further preparative uses have been outlined. Photolysis of 3-crotyl-2H-azirine (1)yields the endo-cyclopropanopyrrolesystem (2) which on heating epimerizes to the more stable exo-form. This reaction involves a cycloaddition of the carbenoid mesomer of a nitrile ylide and is apparently the first example of this type involving a 1,3-dipolar specie^.^ (1) (2) But-2-enyl-2H-azirines are thermally decomposed via vinyl nitrenes e.g.(3; R = CO,Me) which undergoes a novel 1,4-hydrogen transfer to give an @-unsaturated imine (4; R =C0,Me). A 1,5-H shift followed by electrocyclic ring-closure and loss of ammonia yields the biphenyl (5)(12%) or by intramolecular Michael addition and loss of methyl acetate 3-methyl-2-phenylpyridine(58%).4 Ph (3) (4) (5) Vacuum pyrolysis of 2-aminoazirines provides a useful sourceof 2-azabutadienes e.g. CH,=C(Me)N=CHNMe, which readily enter into Diels-Alder cycloaddition with suitable dienophiles to give di- and tetra-hydropyridines in practicable yields.' A. Padwa J. Smolanoff and A. Tremper J. Amer. Chem. Soc.,1975,97,4682. Ann. Reports (B),1974,71,319. A. Padwa and P. H. J. Carlsen J. Amer. Chem. Sue. 1975,97,3862. A. Padwa and N. Kamigata J.C.S.Chem. Comm. 1975,789. A. Demoulin,H. Gorissen A.M.Heshin-Frisque and L. Ghosez,J. Amr. am. Soc. 1975,97,4409. 249 0.Meth-Cbhn andR. K.Smalley Pyrazines and dihydropyrazines result from the metal-carbonyl-induced dimeriza- tion of 2H-azirines6 Azirines are useful precursors of nitrile ylides which in turn react via 1,3-dipolar cycloaddition to give a wide variety of five-membered heterocycles. For example azirines on photolysis in the presence of ketones yield A3-~~az~line~?9b whereas with esters or thio-esters the hitherto scarcely known 5-alkoxy-A3-oxazolines are formed.*= Photolysis of p-benzoquinone and 2,3-diphenylazirine in benzene yields the 2H-isoindolo-4,7-dione (6). The quinol precursor of (6) a tautomer of the initially formed quinone-nitrile ylide adduct is isolable in the absence of oxygen.8b 11 Ph R (6) (7) (8) The first example of carbon disulphide addition to an azomethine bond has been recorded during the regioselective cycloaddition of carbon disulphide to 2 H-azirines.' Thiazolo-thiones e.g.(8) are formed by ring-expansion of primary adducts e.g. (7). 2-Chloro-N-acylaziridines available by addition of acyl chlorides to 3,3-dimethyl-2-phenylazirines undergo nucleophilic displacement of halogen in methanol and rearrangement to yield 5-methoxy-A2-oxazolines (9; R' =MeO) whereas with lithium azide in methanol the azido-compound (9; R'=N,) is obtained." In contrast the chloroaziridines undergo only nucleophilic substitution of halogen with silver acetate in acetonitrile to give 2-acetoxy-N-acylaziridines.The preparation of aziridines by the action of Grignard reagents or organolithiums on ketoximes" appears to be of limited synthetic utility and a more reliable versatile variant involves treating ketone dimethylhydrazone methiodides with a Grignard reagent.'* A facile synthesis of 1,2-disubstituted aziridines has been described which employs the lithium aluminium hydride reduction of aa-dichloroanils,e.g. (lo) formed by the action of N-chlorosuccinimide on the appro- priate t-butylidene compound. l3 The trans-2,3-disubstituted 1-t-butylaziridine (1 1) thermally rearranges via an azomethine ylide to 1-t-butyl-3-phenylpyrole some forty times faster than the corresponding cis-isomer. Apparently the thermally required conrotatory ring- opening of the cis-isomer involves unfavourable stereochemical interactions 6 H.Alper and S. Wollowitz J. Amer. chcm. Soc. 1975,97,3541. (a)P. Claus P. Gilgen H. J. Hansen H. Heimgartner B. Jackson and H. Schmid Hefu. aim. Acta 1974,57,2173; (b)A. Orahovats H. Heimgartner H. Schmid and W. Heinzelmann ibid. p. 2626. 8 (a)P. Gilgen H. J. Hansen H. Heimgartner W. Sieber P. Uebelhart H. Schmid P. Schonholzer and W. E. Oberhansli Helu. Chim. Acttr 1975 58 1739; (b) P. Gilgen B. Jackson H. J. Hansen H. Heimgartner and H. Schmid ibid. 1974,57,2634. 9 V. Nair and K. H. Kim J. Org. Chem. 1975,40,1348. A. Hassner S. S. Burke and J. Cheng-fan J. Amer. Chem. Soc. 1975 97,4692. Ann.Reports (B),1974,71,321. It G. Alverhne S. Arsenyiadis R.Chaabouni and A. Laurent Tetrahedron Letters 1975,355. I3 N. De Kimpe R. Verht L. De Buyck and N. Schamp Synrhetic Cornrn. 1975,5,269. Heterocyclic Chemistry 25 1 R2 c1 H. ,Me AN Bu'-N=CH-C-R II PhCO N ini c1 I R1-)-(Me Me Bu' Ph (9) (10) (11) between the 2-and 3-substituents and the bulky t-butyl group a problem absent with the trans-i~omer.'~ In accord with this idea it was found that cis-trans isomerization of (11) proceeds via enolization rather than azomethine ylide participation. Attempts to synthesize diazaspiropentanes (14) by methods analogous to those successfully employed for the preparation of l-azaspiropentanes" have failed. 16a Azides add to methylenoaziridine (12) to give the expected spiroaziridinotriazolines (13) which on thermolysis yield not the hoped-for diazaspiropentanes (14) but a mixture of triazoles (15) and the cyclic amidines (16) (Scheme 1).The latter (15) (16) Scheme 1 compounds (R = Ph p-tosyl or C0,Et) appear to be the first recorded examples of four-membered cyclic amidines.'66 However a 14% yield of the diazaspiropentane (17; R = phthalimido) has been achieved by treating N-phthalimidonitrene with an allene (Scheme 2).l7 Scheme 2 Tetrazolines continue18 to be a convenient source of diaziridines. Photolysis of tetrazolines of type (18;X = 0or NMe) provides a useful synthesis of diaziridinones l4 A. Padwa D. Dean and T. Oine J. Amer. Chem. SOC.,1975,97,2822. Is Ann. Reports (B),1974,71,321. lC (a)J. K. Crandall,L. C.Crawley and J. B. Komin J. Org. Chem. 1975,40,2045;(b)J. K. Crandall and J. B. Kornin J.C.S. Chem. Comm. 1975,436. l7 R. S. Atkinson and J. R. Malpass Tetrahedron Letters 1975 4305. l8 Ann. Reports (B),1974,71,321. 0.Meth -Cbhn and R.K.Smaiiey (19; X=0)and diaziridimines (19; X= NMe). The tetrazoline (18; X = CMe,) however yields not diaziridine (19; X = me,) but rather the isomeric aziridine- imine (20).19 Me ,Me MeN NMe \I MeN-NMe N=N (18) (19) (20) 1,3,5-Triazabicyclo[3,1 ,O]hexane-2,4-dione (21) available in near quantitative yield from the addition of ethoxycarbonylcarbene to the triazolinedione (Scheme 3) represents the first example of carbene addition to an azo linkage.,' h N,CHCO,Et -PhNP, l,y phNk& CH,CI ; 0 "C kNC0,Et 0 0 Scheme 3 3-Acyldiazirines and 1,2,3-oxadiazoles are cyclic valence isomers of a!-diazocarbonyl compounds.Whereas 1,2,3-0xadiazoles are as yet unknown the diazirine isomer has been detected for the first time in the thermally reversible thermochromic system (22) (23).21 N. N=N A newly developed route to oxirans involves highly nucleophiiic selenocarbanion intermediates e.g. (24) (Scheme 4). Originally phenyl selenide (PhSeH) was used,,," but subsequently methyl selenide (MeSeH) has been shown to be a superior reagent.22* A convenient route to trans-trioxa-tris-o-homobenzene(25; X = Y = 0)has been de~cribed,,~" while cis-benzene trioxide (26; X = 0)has been used in a simple total synthesis of ~treptamine,~~ and in the synthesis of (*)-hyo~cyamine.~~" l9 H.Quast and L. Bieber Angew. Chem. Internat. Edn. 1975,14,428. 20 R. A. Izydore and S. McLean J. Amer. Chem. SOC.,1975,97,5611. z1 E. Voight and H. Meier Angew. Gem. Internat. Edn. 1975,14 103. z2 (a) W. Dumont and A. Krief Angew. Chem. Internat. Edn. 1975 14 350; (b) D. Van Ende W. Dumont and A. Krief ibid. p. 700. z3 (a) H. Prinzbach R. Keller and R. Schwesinger,Angew. Chem. Internat. Edn. 1975 14,633; (b)R. Schwesinger and H. Prinzbach ibid. p. 630; (c)H. Prinzbach R. Keller and R. Schwesinger ibid. p. 632. Heterocyclic Chemistry R2 R2 R2 \ I I CO + MeSeH -+ MeSe-C-SeMeB* MeSe-C' I I R'/ R' R' (24) i R3R4C0 ii Me1 I R2 R3 R2 R4 +II Me,Se -C -C -OH R 1 v R4 dl 63 Scheme 4 Thiirans may be synthesized by treating lithium alkylthio-~xazolines~~ (27; X =0) or thia~olines~~ (27; X =S) with ketones at -78 "C.Quantitative stereospecific xQx Y (25) (26) (27) conversion of oxirans into thiirans is possible by treatment with 3-methylbenzothiazole-2-thionein the presence of trifluoroacetic acid.26 Alkenes react with methyl(bismethy1thio)sulphonium hexachloroantimonate (28)at 0 "Cin methylene chloride to give thiiranium salts (29;X= S) in high yield.27 The corre-spondingseleniranium salts (29;X = Se) and selenirenium salts (30)can be similarly prepared by treating alkenes or alkynes respectively with areneselenyl hexa-fluoro-phosphates or -antimonates (ArSe'XF,-; X =P or Sb).** MeS SbC1,-SbFi \x! Y-y+ \S+ I Me Ar MeS/\Me I (28) (29) (30) The electronic structure of thiiren dioxide (31; R =H) has been investigated theoretically and by U.V.photoelectron spectroscopy.29The results indicate that the dioxide is less aromatic than cyclopropenone or tropone. Diphenylthiiren dioxide (31;R =Ph) adds to cyclicenamines to give bicyclicsystems(32; n =6,7 or 8) which can by cyclobutanering scission,yield sulphur-containingheterocycles(33;n =6,7 or 8).30 With acylic enamines thiophen dioxides (33;n = 0)are obtained. 24 A. I. Meyers and M. E. Ford Tetrahedron Letters 1975,2861. *5 C. R. Johnson A. Nakanishi N. Nakanishi and K. Tanaka Tetrahedron Letters,1975,2865. 26 V. Calo L. Lopez L. Marchese and G. Pesce J.CS. Chem. Comm 1975,621. 27 G. Capozzi 0.De Lucchi V.Lucchini and G. Modena Tetrahedron Letters 1975,2603. 28 G. H. &hid and D. G. Garratt Tetrahedron Letters 1975,3991. 29 C. Miilier A. Schweig,and H. Vermeer J. Amer. Chem. Soc.,1975,97,982. 30 M. H. Rosen and G. &net J. Org. Chem. 1974,39,3805. 0.Meth -Cohn and R.K.Smalley Ph R. po +O R The previously unknown cis-benzene trisulphide (26; X =S) has been prepared and shows a pronounced tendency towards polymerization both in the solid state and in a Also act -dioxa-@-thia- and @-oxa-act -dithia- tris-o -homobenzenes (25; X =0,Y =S) and (25; X =S Y =0)have been synthesized from cis-benzene trioxide (26; X =O).31b The monothia-compound reacts with trimethyl phosphite at 20 "Cto give benzene dioxide whereas the dithia-compound under similar condi- tions yields the benzene oxide-oxepin system.2 Four-membered Ring Compounds [3+13 Cycloadditions are comparatively rare events in synthetic heterocyclic chemistry. It is of interest therefore that azetidine-imines e.g. (34) are formed by [3+ 13 cycloaddition of azomethine ylides to various i~ocyanides.~~ Azetidinones (36) are available in good yield (R =Ph 72%) by a new ring-contraction method involving mercuric oxide oxidation of N-aminopyrazolinones (35)and extrusion of nitrogen from the resulting N-nit~ene.~~ COR I (34) Photolysis of (37) the cycloadduct of tetracyclone and the photoisomer of N-methyl-2-pyridone in methanol results in stepwise loss of carbon monoxide and tetraphenylbenzene to give the thermally labile non-isolable N-methylazetinone (38),34 which is converted in methanol into a mixture of methyl cis-and trans-@-methylaminoacrylate by way of its imino-keten valence isomer (39).Ph NMe Ph 31 (a)S. Kagabu and H. Prinzbach Angew. Chem. Internat. Edn. 1975,14 252; (6) H. Prinzbach C. Kaiser and M. Fritz ibid. p. 253. 32 K.Burger F.Maw and A.Braun Synthesis 1975,250. 33 P. Y. Johnson N. R. Schmuff and C. E. Hatch Tetrahedron Letters 1975,4089. 34 G. Kretschmer and R. N. Warrener TetrahedronLetters 1975 1335. Heterocyclic Chemistry Nitrile oxides and 2-phenylbenzazete react to give the highly strained adduct (40) which rearranges uia a non-isolable 2,3,5-oxadiazepine (41) to the more stable isomeric 1,3,5-oxadiazepine (44).35 This remarkable rearrangement is thought to proceed via oxaziridine intermediates (42) and (43) (Scheme 5) since (44) is also obtained on photolysis of the quinazoline N-oxide (45).The reaction is of particular interest since it supports the popular view that oxaziridines are intermediates in the photo-induced rearrangement of many heteroaromatic N-oxides. Ar (40) Ar (45) (44) (43) Scheme 5 2-Alkoxyazirines readily yield new synthetically useful 1,4-dipolar intermediates with acetylenedicarboxylate~~~" With p-tosyl isocyanate the 1:1 and keten~.~~~ adduct (46)is obtained which is claimed as the first stable isolable cross-conjugated 1,4-dipolar species.36c Excess of isocyanate leads to formation of the 2 1adduct (47) in near quantitative yield.Ts OMe MeG,co,fiTS Me Me Me 0 (46) (47) Benzoazetirres (49) are the major products from the photochemical isomerization of 1,2-dihydroquinolines (48) when irradiation is carried out for 5 h in ethan01.~' Further irradiation of the benzoazetines produces the indolines (50). I Ac (48) 3s C. W. Rees R. Somanathan R. C. Storr and A. D. Woolhouse J.C.S. Chem Cornm. 1975,740. 36 D. H. Aue and D. Thomas (a)J. Org. am. 1975,40,2360; (b) ibid. p. 2552; (c) ibid. p. 2356. 37 M. Ikeda S. Matsugashita F. Tabusa H. Ishibashi and Y.Tamura J.C.S. Chem. Comm. 1975,575. 0.Meth-Cohn and R. K. Smalley 1,2-Oxazete N-oxides with one exception are known only as reactive inter- mediates in the thermal and photochemical cleavage of cup-unsaturated nitro- compounds.However a new method involving addition of nitrogen tetroxide at 0 "C to readily accessible 1,l-di-t-butylallenes now permits isolation of the ther- mally labile 4H- 1,2-oxazete N-oxides (51;R =H Br or Cl),which on standing are converted into the more stable crystalline derivatives (52).38a Bu' Bu'77 0-N HH 0-N +\ Bu' NO -0 R (53) (54) I (51) X =CHNO (52) X =COR The parent 4H-l,2-oxazete (54) hitherto known only as a reactive intermediate has been prepared by vacuum pyrolysis (220 "C; Torr) of the remarkably stable nitrosoalkene (53).38bThe oxazete which condenses on a cold-finger trap at -196 "C in 54% yield decomposes on heating to yield di-t-butylketone and hydrogen cyanide which are the sole products if pyrolysis of (53)is carried out at 240 "Cor above.Vacuum pyrolysis (140 "C; 12 Torr) has also proved to be an efficient method of producing 2H- 1,3-thiazetes (56) a new four-membered heterocyclic The 1,3,5-0xathiazine precursors (55) are readily obtained by condensing perfluoroacetone with a thioamide in phosphorus oxychloride-pyridine mixture at -20 "C. The thiazetes exhibit thermal valence isomerism with the acyclic imino- thioamide (57) which can be trapped as a [4 +13cycloadduct with isocyanides or as a [4 +2) cycloadduct with a variety of alkene~.~~' (55) (56) (57) The remarkably stable crystalline 172-oxathietan-2-oxide (59) has been isolated from the reaction of the t-butyl sulphoxide (58) with N-chlorosuccinimide in methylene chloride at room temperature or with thionyl chloride at -70 0C.40At 30 "C (59) extrudes sulphur dioxide to give 2,2-dimethyl-l7l-dipheny1ethylene.0 4 Ph,CCMe,SOBu' PhRMe 1 OH Ph Me (58) (59) 3* K. Wieser and A. Berndt (a) Angew. Chem. Internat. Edn. 1975 14,69; (b) ibid. p. 70. 39 (a)K. Burger J. Albanbauer and M. Eggersdorfer Angew. Chem.Internat. Edn. 1975,14,766; (b)K. Burger J. Albanbauer and W. Foag ibid. p. 767. *T. Durst and B. P. Gimbarzevsky J.C.S. Chem. Comm. 1975,724. 257 Heterocyclic Chemistry 3 Five-memberedRing Compounds 2-Amin0-3-cyano-~~ and 2-amin0-4-cyano-pyrroles~~ have been conveniently sydthesized commencing from malononitrile and succinonitrile respectively and their role as intermediates is exemplified in the synthesis of pyrro10[2,3-b]pyridine.~~ Barltrop has applied his novel permutation-pattern approach to the phototrans- positions of pyrroles.Thus analysis of the products from irradiation of 3- 4-,and 5-methyl-2-cyanopyrrole (in each case a p-cyanopyrrole) is consistent with only one pattern (Scheme 6).43 N-Trimethylsilylpyrrole has been suggested as the pyrrole OCN N H 1.3-walk O H CN PCN CN H H CN Scheme 6 reagent of choice for use in Diels-Alder reactions. The sensitive epi-imino- derivatives are easily isolated by subsequent removal of the protecting group with cold Further examples45 of the use of functionalized dipoles for the synthesis of fused heterocycles (56 656 5566 5666 and 6566 systems) have been reported.46 Base-catalysed rearrangement of bis-propargylamines ethers and sulphides pro- vides an entry into various fused heterocycles (Scheme ,)." Flash vacuum pyrolysis of derivatives of Meldrum's acid has proved a fruitful source of heterocycles by way XxBul (14-5 1%) r"-R Bu' KOBu' L5-R 20°C I R=Ph (12-54:;) Scheme 7 *l H.J. Roth and K. Eger Arch. Pharm. 1975,308 179. 42 A. Brodrick and D. G. Wibberley J.C.S. Perkin I 1975 1910. 43 J. Barltrop A. C. Day P. D. Moxon and R. R. Ward J.C.S. Chem. Comm. 1975,786. 44 P. S. Anderson M. E. Christy G. F. Lundell and G. S. Ponticello Tetrahedron Letters 1975 2553. 45 Ann. Reports (B),1974,71,328. 46 B. E. Landberg and J. W. Low,J.C.S. Perkin I 1975 1326. 47 P. J. Garratt and S. B.Neoh J. Amer. Chem. Soc. 1975 97,3255. 0.Meth-Cohn and R.K.Srnalley of keten intermediates. Thus hydroxy-indoles carbazoles benzothiophens ben- zofurans and dibenzofurans are obtained in 50-90% yield (Scheme 8).48 0 Scheme 8 Another route to indoles lies in the aryne cyclization of a-anions derived from ketone anil~.~' The Fischer indole reaction of the hydrazone (60)gives a rearranged product (61) which has been shown by labelling to involve two consecutive 1,2-shifts of methyl groups rather than a 1,3-shift. Analogous 1,4-shifts have also been ob~erved.~~~*~ hie I Me0,Cy~~ Me02C Me Me (60) (61) The remarkable transmogrifications of substituted indoles with oxygen have been extended by two more examples (Scheme 9).51 0 Me Scheme 9 G.J. Baxter R. F. C. Brown and G. L. McMullen Austral.J. am. 1974,27,2605. 49 L. Lalloz and P. Caub&re,J.C.S. Chem. Cornrn. 1975,745. 50 R. Fusco and F. Sannicolo (a)TefrahedronLetfers,1975,3351; (b)ibid.,p. 465. 51 I. Saito M. Imuta S. Matsugo and T. Matsuura J. Amet. Chem. Sx.,1975,97,7191. Heterocyclic Chemistry 259 A mixture of stable cis-and trans-2,3-diazido-2,3-dihydroindoles results when 1-acylindoles are treated with iodine a~ide.~* Stereospecific hydrogenation of 2,3-disubstituted indoles is observed with sodium in liquid ammonia (cis addition) and borane in THF (trans additi~n).'~ Isatin interacts with potassium cyanide and ammonium carbonate to give the spiro-indolone (62),'4 while related spiro-indolones e.g.(64) may be isolated from the excellent dienophile (63).55 The bornene (64) is readily transformed into 3- phenyl-2-indolone with alkali. The origin of carbazole from 2-azidobiphenyl is still a subject of debate and Sundberg's recent flash photolysis work casts serious doubt on the oft-mooted triplet-nitrene pathway and tends to favour a singlet process.56 H (64) Two simple high-yield routes to imidazoles have been published involving the [4+21 dimerization of the cyanoimine (65) (Scheme 10y7 0- I PhCH=NMe + ~,x CN Ph Y I k-N Ph-CENMe /&-I. Ph PhCONHMe ii. KCN. HCONH,(65) Me Scheme 10 The 2,2-diphenyl-isoimidazoleN-oxides (66) have been described and their nitrone character has been e~ploited.~' Bridged benzimidazoliurn salts (68; X =H n =6-12) benzimidazolones and thiones (68; X =0 and S respectively n =5-12) have been described and their aromaticity studied.The whole series of salts 0-I+ Ph Ph Ph 'NXPh (67) t~ = 3-12 (68) X = H.0-.or S-52 Y. Tamura S. Kwon F. Tabusa and M. Ikeda Tetrahedron Letters 1975 3291. 53 J. G. Berger S. R. Teller C. D. Adams and L. J. Guggenberger Tetrahedron Leners 1975,1807. 54 H. Otomasu K. Natori and H. Takahashi Chem. and Pharm. Bull. (Japan) 1975,23 1431. 55 D. R. Long and C. G. Richards Tetrahedron Letters 1975 1603. 35 R. J. Sundberg D. W. Gillespie and B. A. DeGraff J. Amer. Chem. Soc. 1975,97 6193. 57 N. G. Clark and E. Cawkill Tetrahedron Letters 1975 2717. 58 B. A. J. Clark T. J. Evans and R. G. Simmonds J.C.S.Perkin I 1975 1803. 0.Meth-ahn and R.K. Smalley (X=H) was aromatic but loss of aromaticity was associated with n <7 and n <7-8 in the -one and -thione series re~pectively.~~~~~ Allene carbenes show a remarkable reaction with azobenzene 2-alkenyl- 1-phenylbenzimidazoles e.g. (69) being formed.60 I Ph (69) N-(N-Arylimidoy1)sulphimides are useful photo-sources of the rare imidoylni- trenes giving 2-substituted benzimidazoles in good yield (Scheme 11).61 Various Scheme 11 2-substituted benzimidazoles particularly 2-aryloxy-derivatives trimerize by a radical process on thermolysis giving the tris(benzimidazo1o)triazine (70).622-Methylenebenzimidazolines e.g. (7l),undergo some surprising reactions and the latest example is with carbon tetra~hloride.~~ Remarkably the salts (72) and (73) are isolated! A (72) MeN NMe (73) 59 R.J. Hayward and 0.Meth-Cohn (a)J.C.S. Perkin Z 1975 212; (b) ibid. p. 219. 6o T. Sasaki S. Eguchi and T. Ogawa Heterocycles 1975,3 193. dl T.L. Gilchrist C. J. Moody and C. W. Rees J.C.S. Perkin Z 1975 1964. 62 S. Ishida Y. Fukushima S. Sekiguchi and K. Matsui Bull. Gem. Soc. Japan 1975,48,956. J. Bourson Bull. Soc. chim.France 1975 644. Heterocyclic Chemistry Conjugated diazoalkanes are known to undergo 175-cyclization to give pyrazoles. However the analogues (74) are the first examples to yield both the 1,5- (75) and 1,7-cyclization (76) products as well as the carbene-derived indenes (77).64 80°C+ + + N Me Me H Me (74) The involvement of 1H-azirines in the thermal decomposition of 1,2,3-triazoles has recently been reinforced by '3C-labelling studies6' 1,2,4-Triazoles are con- venient pyrolytic precursors of the useful isoindoles.66 Mono- and di-phenyl deriva- tives were prepared by the same method.1-Aminoalkylbenzotriazole has been shown to be in rapid solvent-dependent equilibrium with its 3-isomer probably by way of the benzotriazolyl anion.67 However 1-methylbenzotriazole 3-oxide is converted irreversibly into its 2-oxide isomer on irradiation.68 Scheme 12 The a-anions of isocyanides have been used as convenient reagents for the synthesisof 2-unsubstituted oxazoles by interaction with acyl halides.69 Oxazolones and various related systems can be conveniently prepared under ambient conditions by the interaction of amino-alcohols (or phenols or thiols) with carbon monoxide in the presence of selenium (Scheme E)." An interesting intramolecular cycloaddition has been described whereby the o-allyloxybenzonitrile oxide (78) yields the fused dihydroisoxazole (79).The corre- sponding propargyloxy-derivative similarly gives the parent is~xazole.~~ The dihy- droxyisoxazoles or disic acids e.g. (80) are amongst the strongest organic acids (78) (79) 64 J. Dingwall and J. T. Sharp J.C.S. Chem. Comm. 1975,128. 65 T. L. Gilchrist C. W. Re& and C. Thomas J.C.S. Perkin I 1975,8. 66 T. L. Gilchrist C. W. Rees and C. Thomas J.C.S. Perkin I 1975 12. 67 J. R. L. Smith and J. S. Sadd J.C.S. Perkin I 1975 1181.68 M. P. Serve W. A. Feid P. G. Seybold and R. N. Steppel J. Heterocyclic Chem. 1975,12 811. 69 R. Schroder U. Schollkopf,E. Blume and I. Hoppe Annafen 1975,533. 'O N. Sonoda G. Yamamoto K. Natsukawa K. Kondo and S. Murai Tetrahedron Leners 1975,1968. R. Fusco L. Garanti and G. Zecchi Chimica e Industria 1975,57,16. 262 0.Meth-Cohn and R.K. Smalley known the example shown having a pK of -0.1.72 o-Dinitrosobenzene is the disputed valence tautomer intermediate believed to account for isomerization of the benzofuroxans. The efficiency of nitrosobenzene as a triplet nitrene trap led Scriven and co-workers to demonstrate the corresponding role of benzofuroxan by isolation of (81).73 Similarly with diphenyldiazomethane benzofuroxan gave the isobenz- imidazole di-N-oxide (82).The usefulness of benzofuroxan in synthesis has been 0-0-OH (81) (82) (83) further extended by its interaction with barbituric acid and with NN’N‘’-trisubstituted hexahydro-syrn-triazinesto give N-hydroxybenzimidazole and 1,3- dihydroxy-2-iminobenzimidazoline(83) The interaction of nitro- compounds with tervalent phosphorus derivatives is still a fertile source of novel heterocycles the ox- and thi-azaphosphoranes (84) being recent example^.^'^^^*^^ Photolysis of the former give moderate yields of carbazole. The oxazaphosphole (85) is a versatile imidazolating agent by way of the nitrile ylide (86).77 oxAr ___* P-OR ox\ ‘NO PhP(OR) ‘ /OR N’ ‘OR Ar (84) X = 0 or S CF3 (85) The regiospecific incorporation of deuterium during the photoisomerkcation of 5-phenylisothiazole to 3-phenylisothiazole has been explained by invoking a dipolar 72 G.Zvilichovsky Tetrahedron 1975,31 1861. 73 A. B. Bulachinski E. F. V. Scriven and H. Suschitzky Tetrahedron Letters 1975,3576. 74 (a)F. Seng and K. Ley Synthesis 1975,703; (b)F. Sung,K. Ley and K. Wagner ibid. p. 703 ’I5 (a)J. I. G.Cadogan B. S. Tait and N. J. Tweddle J.C.S. Chem. Comm. 1975,847; (b)J. I. G. Cadogan and B. S. Tait J.C.S. Perkin I 1975 2396. 76 J. I. G. Cadogan R. 0.Gould and N. J. Tweddle J.C.S. Chem. Cornrn. 1975 773. K. Burger and W.-D. Roth Synthesis 1975,731. Heterocyclic Chemistry intermediate (Scheme 13).78 N-Phenylbenzothiazol-2-oneloses carbon monoxide on pyrolysis giving phenothiazine at 650°C but carbazole at 850°C whereas a mixture of both is formed at 750 "C.The corresponding benzothiazole-2-thione Scheme 13 however shows only N+S migration of the phenyl group yielding 2-phenylthiobenz~thiazole.~~ 1,2,3-Thiadiazoles are versatile synthons of thioketens by flash vacuum pyrolysis. At 30°C the products dimerize to yield the dithietans (87).**The first example of a SH-1,2,3-dithiazole (89) which exists in solution in equilibrium with the thiosulphinylaniline (88) is produced when 2,4,6-tri-t- butylaniiine is treated with sulphur monochloride and triethylamine.'l The first mesoionic selenazole derivative (90) has been reported.82 New synthetic methods are frequently published and fall into two categories those that are more complex difficult to achieve or expensive than the end-products warrant and those that reappear in the literature.Occasionally the intrinsic interest and potential of one of the former methods overcomes other disadvantages. Such an example is Gassman's extension of his indole synthesis to benzofurans (Scheme 14).83 Scheme 14 78 M. Maeda A Kawahara M. Kai and M Kojima Heterocycles 1975,3,389. 79 D. C. K.Lim M. L. Thomson and D. C. de Jongh Canud. J. Chem. 1975,53,2293. 8o G. Seybold and C. Heibl Angew. Chem. Inremat. Edn. 1975,14,248. Y. Inagaki R. Okazaki and N. Inamoto TetrahedronLetters 1975,4575. 82 M. P. Cava and L. E. Saris J.C.S. Chem. Comm. 1975,617. 83 P. G. Gassman and D. R. Arnick Synthetic Comm. 1975,5,325. 264 0.Meth-Cohn and R.K.Smalley Wynberg has previously demonstrated the t-butylation of 2,5-di-t-butylfuran yielding 2,3,5-tri-t-butylfuran. However other di- or tri-alkylfurans undergo t- butylation without ‘reversion-to-type’ (e.g.Scheme 15).84 R = H or R-R = (CH2)2-3 Scheme 15 Tetracyanoethylene oxide is a most unpredictable reagent. Reactions with furan benzofuran thiophens and selenophen give two kinds of product (91)and (92).85*86 NC CN ~. ..II Q 2 *-. c:.. ...,.. NC CN A one-step high-yield synthesis of furan-2-ones has been described by Pad~a.~’ The intermediate may be isolated and separately cyclized if required (Scheme 16). The R2 I CHO CH2Ph PhCH,CO,-+ R1-C-CHO -I C,H,. A I Br R’ R‘ Scheme 16 first general method for furan-2,3-dione synthesis has appeared.The products undergo thermal extrusion of CO (Scheme 17),88and the resulting a-ketoketen may n R2- Scheme 17 dimerize to a pyrandione or be trapped (e.g. with chloral). Brave chemists have explored the chemistry of the highly explosive photo-oxide (93) of 1,3-diphenylisobenzofuran. Amongst interesting results the thermolysis in protic sol- vents yields products (Scheme 18) believed to form from the peroxide (94).89 84 H.Wynberg and U. E. Wiersurn Tetrahedron Letters 1975,3619. 85 S. Gronowitz and B. Uppstrorn Acfa Chem. Scand. (B), 1974,28,981. 86 S. Gronowitz and B. Uppstrom Acfu Chem. Scand. (B),1975,29,441. 8’ A. Padwa and D. Dehm J. Org. Chem. 1975,40,3139. 88 S. Murai K. Hasegawa and N.Sonoda Angew. Chem. Internat. Edn. 1975,14,636. 89 G. Rio and M.-J. Scholl J.C.S. am. Cbmm. 1975,474. Heterocyclic Chemistry 265 + R R= acoph co-Scheme 18 7-Oxanorbornadiene is now readily available in two steps from furan and quantita- tively transforms into 3-oxaquadricyclane (97) on photolysis. This product thermo- lyses to yield an equilibrium of oxepin and benzene oxide (95; R=H) and (96; R = H) and isomerizes with acid to give 5-formylcyclopentadiene.90The well- known photo-conversion of stilbenes into phenanthrenes has been emulated by the transformation of diary1 oxides and sulphides into dibenzofurans and diben- zothiophens in good yield.” The first synthesis of a five-membered mesoionic system containing only oxygen and sulphur as nuclear heteroatoms e.g.(98) has been accomplished by the dehydration of acylthioacetic acids.92 O\ The discovery of thiophen resulted from the formation of the blue dye indophenine obtained by its acid-catalysed reaction with isatin. The polyin- dophenine (99) is useful as a vat dye and p-type emi icon duct or.^^ The versatile Hurtley reaction has recently been ‘rediscovered’ and provides the method of choice 90 H. Prinzbach and H. Babsch Angew. Chern. Internat. Edn. 1975,14,753. 91 K.-P. Zeller and H. Petersen Synthesis 1975,532. 92 K. T.Potts J. Kane E. Carnahan and U. P. Singh J.C.S. Chern. Comrn. 1975,417. 93 G.Kossemehl and G. Manecke Makromol. Chem. 1975,176,333. 0.Meth -Cohn and R. K. Smalley for [c]-fused thiophens as exemplified in Scheme 19.94 It also proceeds satisfactorily with 3-bromothiophen-2-carboxylicacids94 and 2-bromothiophen-3-carboxylic acids.” Interesting but unsuccessful attempts to prepare the bis-thiophen analogues X / CH \ Y ____) Cu NaOEt Bbco2H EtOH x%co2H X,Y = C02Et COR,etc.Z=NHorO Scheme 19 of biphenylene have been de~cribed.~~ The thermal cheletropic extrusion of SO2 from both cis-and trans-isomers of dihydrothiophen 1,l-dioxides (100) and from the corresponding thiepin (101)has been proved to be highly stereospecific in line with orbital symmetry ~~nsiderations.~~~~ 4.. c:i2 \ Me Me (100) (101) A simple method of conversion of 3-methyl- and 3-ethyl-thiophen into the 3-formyl and 3-acetyl derivatives respectively has been reported.” The deep-blue o-thioquinomethides (102) have been made and in the absence of dienophiles yield a coloprless dimer.They behave as interesting dienes in Diels- Alder reactions.99 (102) The 1,6-dioxa-6a-thia- (or -selena-)pentalenes (103)undergo both 0 and C-protonation with acid to give the first examples of oxathiolium and oxaselenolium (104) systems.loo The elusive four-valent sulphurane system (105) has been reported. lo’ 94 D. E. Ames and 0.Ribeiro J.C.S. Perkin I,1975 1390. 95 J. A.Clarke and 0.Meth-Cohn unpublished results. % B. E. Ayres S. W. Longworth and J. F. W. Mdhnie Tetrahedron 1975,31,1755. 97 W.L. Mock (a)J. Amer Chem. Soc.,1975,97,3666;(b) ibid. p. 3673. 98 J. A. Clarke and 0.Meth-Cohn Tetrahedron Letters 1975,4705.99 R.Okazaki and N. Inamoto Chemisfty ktters 1974 1439. loo D.H.Reid and R. G. Webster J.C.S. Perkin I 1975,2097. 101 B.S.Campbell,D. B. Denney D. Z. Denney andLi-Shang Shih J. Amer. Chem. Soc. 1975,97,3850. Heterocyclic Chemistry 267 0-x-0 0-5 0 0 Slo /\ (103) X = S or Se (104) RO OR (105) The chemistry of organic 'metals' continues to develop and conductivity records are regularly broken. The polymer (106)'02 and the complex (107)with a modified ac~eptor"~ are of interest and a simplified synthesis of (log),which is purple in the "kCN s>cs S NCHS CN solid state but pink in so1ution,'04 is noted. However the present good-conductivity prize goes to the annelated diselenadithiafulvene complex (109).'05 A safe preparation of the intermediate (110) has been described.lM The highly effective Diels-Alder diene (1 11) is conveniently availablelo7 and a new highly stereo- and regio-selective hydroboration reagent 1,3,2-benzodioxaborole (1 12) (easily prepared from catechol and borane in THF) has been described."* Thus dec-1-ene and styrene react at the terminal carbon in 98 and 92% yield respec- tively and norbornene reacts ex0 to the extent of 99.5%.lM Y. Ueno Y. Masuyama and M. Okawara Ckmistry Lettern 1975,603. lo3 J. R. Andean C. S. Jacobsen G. Rindorf H. Soling and K. Bechgaard J.C.S. clhem. Comm. 1975 883. lO4 Z. Yoshida T. Kawase and S. Yoneda Tefrahedron Letters 1975,331. lo5 H. K.Spencer,M. V. Lakshmikantham,M. P. Cava and A. F. Garit0,J.C.S.dkm.Comm. 1975,867. lo6 J. R. Anderson and K. Bechgaard J. Org. dhem 1975,40,2016. lo' T. H. Chan and K. T. Nwe Tefruhedron,1975,31,2537. lo8 H. C. Brown and S. K. Gupta J. Amer. Chem Soc. 197597,5249. 0.Meth-Cbhn and R. K. Smalley 4 Six-membered Ring Compounds The reaction of lithiated crotylimines with nitriles (Scheme 20) constitutes a new pyridine synthesis.'og R R R rCNe R +& -6 \ NBu' \ mu' NHBu' Scheme 20 Triaryl-substituted pyridines are available by treating oxazinium salts (113) with 'active' methylene and by the reaction of nitrile ylides with 2,3- diphenylmethylenecyclopropene." ' Diphenylcyclopropenone reacts similarly to yield 4-pyridones. A variation of the Hantzsch synthesis using methyl propiolate (2 moles) an aryl aldehyde (1mole) and ammonium acetate allows the preparation of 1,2,6-~nsubstituted 1,4-dihydropyridines in good yield.'l2 The Diels-Alder adduct (1 14) on treatment with an azide followed by hydrolysis and decarboxylation yields the cyclic hydrazine (1 15). Mercuric oxide oxidation of (115) is accompanied by loss of nitrogen and formation of l-substituted 1,4- dihydropyridines(116) in variable yields (11-90%).' l3 (1 13) (114) (115) (1 16) 1,4-Dialky1-1,4-dihydropyridines are obtainable in excellent yield by Birch reduc- tion of 4-alkylpyridines in the presence of an alkyl halide.'14 In the absence of ethanol superior yields of N"-substituted 4,4'-bipyridyls are claimed. The hitherto almost inaccessible 2-aza-1,4-quinones e.g.(117) are now available by thermal rearrangement of 2-azido-2-cyanocyclopenten-1,3-ones(118) which result from the controlled thermolysis of 2,3-diazid0-1,4-quinones.~~~ K. Takabe H. Fujiwara T. Katagiri and J. Tanaka TetrahedronLetters 1975,4375. 11* I. Shibuya and M. Kurabayashi Bull. Chern. Soc.Japan 1975,48,73. ll1L.Toupet and R. Carrie J.C.S. chem. Comm. 1975,384. 11* T.Cheunat and U. Eisner J.C.S. Perkin I 1975 926. l13 D.M.Stout T. Takaya and A. I. Meyers J. Org. Chem. 1975,40 563. 114 A.J. Birch and E. A. Karakhanov J.C.S. Chem. Cornm. 1975 480. 115 D.S. Pearce M.J. Locke and H. W Moore J. Amer. Oum. SOC.,1975,97,6181. Heterocyclic Chemistry Room-temperature oxidative cyclization of aP,y&unsaturated amides with lithium chloropalladite in acetonitrile solution in the presence of triethylamine provides a new 2-pyridone synthesis.' 160 The parent acids undergo similar cycliza- tions in polar solvents to give 2-pyrones.'16' A general survey of old and new methods for the synthesis of NN'-linked bi(heteroary1s) has been published,' 17a and 1-pyridino-2-pyridones (1 19) members of this class of compounds are of synthetic potential.' '7b For example (119) reacts with sodium sulphinate and with potassium cyanide to give disulphone (120) (64%) and 2-cyanopyridine (87YO),respectively.(1 19) ( 120) Triphenylphosphine in acetonitrile solution has merit as a dealkylating agent for N-alkylpyridinium salts particularly when the alkyl group is benzyL1'' A useful synthesisof 2-aminonicotinaldehydes arises from the acid-promoted ring-opening of the readily available 6,7-disubstituted pyrido[2,3-d]pyrimidines.' l9 Worthyof men-tion is the new oxidant pyridinium chlorochromate (C5H5NHCr0,CI) which is prepared simply and in high yield by adding pyridine to chromium trioxide in 6M-HCl.Under mild conditions it selectively oxidizes alcohols to carbonyl compounds in excellent yield. Further studies'*l on the 'phenylnitrene energy surface' have led to the first synthesis of cyclobuta-[2,3]- and -[3,4]-pyridines. 12* Pyrindanes (121) are obtained in good yield (65%) along with other products from the flash vacuum pyrolysis of p-phenylethylsulphonyl azides at 650 0C.123 The reaction is complex and tempera- ture dependent. At 300"C for example benzothiadiazine dioxide (122) is formed in 12.8% yield.R 3-Oxido-N-phenylpyridiniumbetaine (123) on pbtolysis (A =350 nm) in ethyl acetate yields a mixture of dimer (124) valencebond isomer (125) and the em-and l6 (a)A. Kasahara and T. Saito am. adZnd. 1975,745; (b)T.Izumi and A. Kasahara Bull. Chern.SIC. Japan 1975,48,1673. 117 (a) A. R. Katritzky and J. W. Suwinski Tetrahedron 1975,31 1549; (b) A. R. Katritzky and M. P. Sammes J.C.S. Chem. Comm. 1975,247. 11* J. P.'Kutney and R. Greenhouse Synthetic Comm 1975 119. 119 G. Evens and P. Caluwe J. Org. Chem. 1975,40 1438. IZo E. J. Corey and J. W. Suggs Tetrahedron Letters 1975,2647. lz1 Ann. Reports (B),1974,71 319. lz2 W. D. Crow A. N. Khan and M. N. Paddon-Row Austral. J. Chem. 1975,28,1741.lZ3 R. A. Abramovitch and W. D. Hoicomb J. Arner. Chem. k., 1975,97 676. 0.Meth-Cohn and R. K.Smalley endo-forms of the (3,4)-(2,6) cycloadduct of valence isomer (125) and betaine (123).124 0 (1 23) (124) (125) The variation of reactivity towards cycloaddition with structure of 3-oxidopyridinium and 3-oxidopyrazinium betaines has been rationalized. 4-Oxidoisoquinolinium betaines (127) have been synthesized via the isolable aziridine (126) (Scheme 21).126 ii RN ___ \ \ 0 0 0 -me 21 The chemical versatility of heteroaromatic N-oxides continues to be exploited. Yields in the photo-induced ring-contraction of 4-substituted pyridine N-oxides to 3-substituted pyrrole-2-aldehydes have been found to be dramatically increased if photolysis is carried out in the presence of copper ~ulphate.'~' Pyridine carbamates e.g.(128) are available in practicable yield (50-60%) by the action of cyanogen bromide on pyridine N-oxides. 12* 2-Acylpyridines 2-acylquinolines and 1-acylisoquinolines may be conveniently prepared by treating the appropriate N-oxide with o-benzoylcyanohydrins in hot acetic anhydride.'*' In a variation of a reaction reported last year,130 3,5-dichloropyridine N-oxide will react with ethynes e.g. PhC=CCN to give furo[3,2-b]pyridines e.g. (lD) in one step.'31 lz4 A. R. Katritzky and H. Wilde J.C.S. Chem. Comm. 1975,770. 125 (a)N. Dennis B. Ibrahim and A. R. Katritzky J.C.S. Clrem. Comm. 1975,425; (b)N. Dennis A. R. Katritzky and M. Ramaiah J.CS. Perkin I 1975 1506.126 P. E. Hansen and K. Undheim J.C.S. Perkin I 1975,305. I27 F. Bellamy P. Mertz and 3. Streith;Heterocycles 1975,3 395. '28 M. Hamana and S. Kumadaki J. Pharm. Soc.Japan 1975,95,87. T. Endo S. Saeki and M. Hamana Heterocycles 1975 3 19. Ann. Reports (B) 1974,71 343. 131 R. A. Abramovitch and I. Shinkai J. Amer. Chem. Soc. 1975,97 3227. Heterocyclic Chemistry 271 0 one-pot synthesis of pyrroloindolizines has been announced,*33 which involves treating 2-acetylpyridine with methyl propiolate (2 moles). The reaction can be extended to the preparation of quinolizines if 2-phenacylpyridines are employed in place of the pyridyl ketone. Treatment of acetanilides with HMPA in hot DMF yields 2-dimethylaminoquinolines(40-76%) by way of the amidine intermediates (130).134 Replacement of DMF by acetic acid results in the formation of 2-dimethylaminolepidines but in reduced yields (23-54%).The hitherto inaccessi- ble 2-acyl-3-hydroxyquinolinescan be synthesized by a novel variant of the Smiles rearrangement (Scheme 22). 13’ n Scheme 22 Interest grows in the synthetic applications of intramolecular [4 +21 and 1,3-dipolar cy~loadditions.~~~”” Of the former type mention may be made of the cis stereoselective thermal ring-closure of amides (131;n =2 or 3) to hexahydro-A6- indoles and octahydro-A7-quinolines,respectively.137 In contrast amide (I32) yields mainly the trans-product (133). The quinolyne derived by treating 5-bromoquinoline with potassium amide in liquid ammonia is claimed as the best route (47%) to the otherwise difficultly obtainable 6-aminoquinoline.138 The ring-opening of nitrogen heterocycles with 132 Ann. Repom (B),1974,71,344. 133 R. M.Acheson and J. Woollard J.C.S.Perkin I 1975,740. 134 E. B. Pedersen and S. 0.Lawesson AcfuChem. Scand. (B),1974 28 1045. 135 D. W. Bayne A. J. Niml and G. Tennant J.C.S. Chem. Comm. 1975,782. 136 (a) L. Garanti A. Sala and G. Zecchi J. Org. Chem. 1975,40,2403; (b)R. FUSCO L. Garanti and G. zecchi ibid. p. 1906. 137 W. Oppolzer and W. Frostl Helv. Chim. Acta 1975,58 590. 13* H. Poradowska E. Huakowska and W. Czuba Synthesis 1975,733. 0.Meth-Cohn and R.K. Smalley R' I H (131) (132) (133) thiophosgene reported last year 139has been applied to 4,7-dichloroquinoline and yields the synthetically useful p-(o-thiocyanatopheny1)acrylaldehyde (134).140 With nucleophiles facile cyclization to vinylbenzothiazines (135)is observed.(134) (135) (136) Hydrogenation of quinoline isoquinoline and phenyl-substituted pyridines with platinum oxide in trifluoroacetic acid results in selective reduction of the carbocyclic ring.141a The 5,6,7,8-tetrahydroquinolinesso formed can be further reduced with sodium and ethanol in a high-yield (90%) synthetic route to trans-decahydroq~inoline.'~~~ Ruthenium tetroxide produced in situ by the action of sodium periodate on ruthenium dioxide is advocated as a useful reagent for the rapid high-yield room-temperature catalytic oxidation of quinolines to pyridine- 2,3-dicarboxylic acids.142 N-Methylisoquinolone (136) is available in high yield by Vilsmeier reaction of homophthalic acid at 100 "C,followed by decarb~xylation.~~~ Ozonolysis of 2,3-diarylindoles has been used as a preparative route to o-acylbenzanilides. With potassium amide in liquid ammonia the anilides cyclize to give N-acylacridones via an aryne intermediate.'44 Addition of aromatic diazonium salts to nucleophilic dienes proceeds well in acetonitrile solution in the presence of a Lewis-acid catalyst 14'-arylpyridazinium salts may be obtained. 1and good yields of 3-Azidopyridazine 2-oxides unlike mono- and di-azine N-oxides reported previ~usly,'~~ undergo thermal decomposition to give only acyclic products. For example the azido-N- oxide (137; R =Cl) in boiling toluene loses nitrosyl chloride and gives maleonitrile in 85% yield.I4' Similarly the methoxy-azide (137; R =MeO) and the parent azide (137; R=H) yield methyl p-cyanoacrylate (89Y0) and unstable p-cyanoacry lalde h yde ,respectively.139 Ann. Reports (B),1974,71 343. 140 R. Hull P. J. van den Broek and M. L. Swain J.C.S. Perkin I 1975,922. 141 F.W.Vierhapper and E. L. Eliel (a)J. Org. am. 1975,40,2729;(b)ibid. p. 2734. D. C. Ayres and A. M. M. Hossain J.C.S. Perkin I 1975,707. 143 V. H. Belgaonkar and R. N. Usgaonkar Tetrahedron Lefters 1975,3849. 14* G.4. J. Chen and M. S. Gibson J.C.S. Perkin I 1975 1138. 145 B. A. Carlson W. A. Sheppherd and 0.W. Webster J. Amer. Gem. Soc. 1975,97,5291. 146 Ann. Reports (B) 1973,70,505. R.A. Abramovitch and I.Shinkai J.C.S. Chem. Comm. 1975,703. 14' Heterocyclic Chemistry (137) L (139) The permutation-pattern approach to explain complex photo-induced rearrange- ments of various heterocyclic systems has been applied'48" successfully to the phototransposition of 4-hydroxypyrylium cations.'48b However some aspects of this intriguing approach have been ~hallenged,'~~ that particularly the ~taternent'~~' there is no case in which any connection has been established between Dewar and prismane isomers and the occurrence of phototransposition. It has been pointed out forcibly that Dewar isomers are known in the photorearrangement of perfluoroalkyl-pyridazines to pyra~ines,'~' and examples of prismane intermediates in the photo- isomerization of perfluoroalkylpyridines have recently come to light.149 A startling synthesis of tetrahydropyridazine-metal complexes e.g.(139) has been unearthed during the reaction of dinitrogen tungsten and molybdenum com- plexes (138;M =W or Mo) with alkyl bromides in THF solution in the presence of visible light."l In a unique reaction the complexed nitrogen apparently displaces oxygen from the THFring! The role of the alkyl bromide is as yet unknown but vital since the reaction fails in its absence. Interestingly there is no analogous reaction with tetrahydrothiophen. Fluoromalonodialdehyde FCH(CHO)* is a useful reagent for the synthesis of fluoroheterocycles e.g. 5-fluoro-pyrimidines and -pyrimidone~,'~~ and pyrimidinethiones are available in excellent yield by reaction of vinyl methyl ketones with arylhydrazines in the presence of trimethylsilyl i~othiocyanate.'~~ Access to the hitherto virtually unknown pyrimidine 1,3-dioxides is now possible by manganese dioxide oxidation of the cyclic hydroxamic acid N-oxides (140) (Scheme 23).lS4 R2 RZ R2 (140) Scheme 23 The first example of a thio-Claisen rearrangement in the pyrimidine series has been announced and is worthy of mention as the reaction is a convenient mild synthetic method for 5-alkyl~racils.'~~ A high-yield regioselective alkylation of 148 (a)J.A. Barltrop R. Carder,A. C. Day J. R. Harding and C. Samuel,J.C.S. them. Comm 1975,729; (b) Ann. Reports (B),1973,70,313; (c)J. A.Barltrop and A. C. Day J.C.S. Chern. Comrn,1975,177. 149 R.D.Chambers,R. Middleton and R. P. Corbally J.C.S. Chern. Comrn. 1975,731. 150 R.D.Chambers,J. A.M. McBride J. R. Maslakiewicz and K. C. Srivastava,J.C.S.Perkin I 1975,396. A. A.Diamantis J. Chatt G. A. Heath and G. J. Leigh J.C.S. Uum. Comm. 1975,27. lS2 C.Peichardt and K. Halbritter Annalen 1975,470. R. Neidlein and H. G. Hege Synthesis 1975,50. lS4 A.Ya. Tikhonov and L. B. Volodarsky TetrahedronLetters 1975,2721. lS5 J.-L. Fourrey E. Estrabaud and P. Jouin J.C.S. Chern. Cornrn. 1975,993. 0.Meth-Cohn andR. K.Smalley xanthines and hypoxanthines at N-7 may be achieved by treating the heterocycles as a cobalt complex with an alkyl halide.156 The product from the action of acetic anhydride on o-aminobenzaldoxime long thought to be a benzo-3,1,4-oxadiazepine has now been shown by X-ray analysis to be 2-methylquinazoline 3-0xide.l" Hydroxylamine in aqueous alkali appears to be a useful aminating agent and converts 6-nitroquinoxaline into its 5-amino-derivative under mild condi- tion~.~~* High-temperature (650 "C) pyrolysis of carbamate (141) in a quartz tube provides the first synthesis of 1,3-oxazin-6-one (142) (27%).15'This ring system is of interest as a potential precursor of the as yet unknown azacyclobutadiene.However on photolysis the oxazinone yields only HCN C02,and acetylene possibly by way of the valence isomeric bicyclic system (143). Substituted 1,3-oxazin-6-ones appear as products in the reaction of diphenylketen with a variety of heterocycles,'60 and many of the current results necessitate a re-interpretation of earlier work on this reaction.(141) (142) (143) The C-nitraso-imine (147) a member of a previously unreported class of organic compounds appears to be an intermediate in the lead tetra-acetate oxidation of oxime (144) and in the reaction ofsulphimide (145) with nitrile oxide (146) (Scheme 24).161" The nitroso-imines spontaneously cyclize to 1,2,4-benzoxadiazines e.g. (148),161q6 but in the presence of thebaine an efficient trap for the dienophilic nitroso-group they yield the Diels-Alder [4 + 21 cycloadducts.'"" CO,Et Scheme 24 lS6 L. G. Marzilli L. A. Epps T. Sorrell and T. J. Kistenmacher J. Amer. Chem. Soc. 1975,97,3351. lS7 L.GoliE V. KautiE B. Stanovnik and M. TiSler Tetrahedron Letters 1975,4301. Is8 R.Nasielski-Huikens and M.Benedek-Vamos J.C.S. Perkin I 1975 1229. A. Krantz and B. Hoppe J. Amer. cham. Soc. 1975,97,6590. I6O G.A. Taylor J.C.S. Perkin I 1975 1001. 16* (a)T.L. Gilchrist M. E. Peek and C. W. Rees J.C.S. Chem. Comm. 1975,913;T,L.Gilchrist M. E. Peek and C. W. Rees; (b) ibid. p. 914;(c)T.L.Gilchrist C. J. Harris M. E. Peek and C. W. Rees ibid. p. 962. Heterocyclic Chemistry The 1,2,4-benzoxadiazines undergo a remarkable ring-contraction to benzox- azoles (Scheme 25) itprocess which may well involve a rare but in this instance geometrically favourable intramolecular [,4 +,2,] cycloaddition.16" ANRORC reactions of the type reported 'in some detail last year,'62 have been extended to include triazine and several interesting transformations of pyrylium salts.For example 2,4,6-triphenylpyrylium perchlorate with sodium nitrite in acetonitrile yields the diacylisoxazole (149),la and with guanidine 2-am1no-4,6-diphenylquinazoline,which reacts further with more pyrylium salt to give Scheme 25 the pyridinium perchlorate (150).'65 N-Arylpyridinium salts are also obtained on treating pyrylium salts with pyridinium acylylide~.'~~ In contrast with sulphonium acyl ylides ring-contraction to give furan derivatives e.g. (151) is observed. Ph Ar COAr Ar COON (149) Pyrylium salts e.g. (152; X =0),react with sodium azide to give the 2-azido- derivatives which on warming undergo RORC reactions with loss of nitrogen to yield oxazepine (154; X=O) (90%) via the isolable azirine (153; R=H).16' In contrast the analogous reaction with thiapyrylium salts (152; X =S) generates the thermally unstable thiazepines (154; X =S) which by extrusion of either sulphur or benzonitrile yield pentaphenylpyridine and tetraphenylthiophen respectively.Studies on photolytically induced ring-opening reactions of five- and six- membered oxygen heterocycles have shown that selective excitation of the enol 162 Ann. Reports (B),1974 71 347. A. Rykowski and H. C. van der Plas Rec. Truu. chim. 1975,94,204. 1b4 C. L. Pedersen and 0.Buchardt Am Chem. Scand. (B),1975,29,285. 165 M. P. Zhdanova E. A. Zvezdina and G. N. Dorofeenko Khim. geterotsikl. Soedinenii 1975,277. A. R.Katritzky S. Q. A. Rizvi and J. W. Suwinski Heterocycles 1975,3 379. Ib7 J.-P. Le Roux,J.-C.Cherton and P.-L.Desbene Compt. rend. 1975,280 C 37. 16' 0.Meth-Cohn and R. K.Smalley R Ph &h Ph phfiph Ph X Ph Ph Ph Ph Ph rather than the more usual keto tautomer can occur.'68a The reactions are highly solvent dependent. For example photolysis of chromene (155; R1= OH R2= C0,Me) in acetonitrile yields the dihydrocoumaran (159) via the o-quinonoid intermediate (156) (Scheme 26).168b*c However in benzene solution the valence h I' + q RZ OH I R' C0,Me C0,Me (157) (155) MeY I C0,Me (159) Scheme 26 tautomer (158) of dihydrofuran (157)exists long enough for further light absorption to take place so that loss of carbon monoxide occurs and the o-vinylphenol(l60) is the major product. Selective excitation of an enol tautomer is also observed during photolysis of 3-phenylisocoumaranone.169 and coumarin~~~~ New general syntheses for thiopyran-2-thione~'~~ have appeared the latter method being adaptable for preparing thiocoumarins and 2-quinolones. a-Pyrones are so far unobtainable by [4 +21 cycloaddition of carbon dioxide and dienes. However an equivalent reaction is possible using diethyl ketomalonate and the resulting cycloadduct (161) readily undergoes a bis-Curtius degradation to an a-pyrone.17* 168 (a) A. Padwa and A. Au J.C.S. Chem Gmm 1975 58; (b) A. Padwa A. Au G. A. Lee and W. Owens J. Org. Chem. 1975,40,1142;(c)A. Padwa and A. Au J. Amer. Chem. Soc. 1975,97,242. 169 A. Padwa D. Dehm T. Oine and G. A. Lee J. Amer. Chem. Soc. 1975,97,1837.170 F. Ishii M. Stavaux and N. Lozach Tetrahedron Letters 1975,1473. T. Manimaran T. K. Thiruvengadam and V. T. Ramakrishnan Synthesis 1975,739. 172 R. A. Ruden and R. Bonjouklian J. Amer. Chem. Soc. 1975,97 6892. Heterocyclic Chemistry go-Thiopyrylium-3-olate (162) on basification yields cycloadduct (163) as a mixture of syn and unti forms.173a 2-Benzothiopyrylium-4-olate (164) behaves similarly. 1736 This behaviour is reminiscent of that exhibited by 3-oxidopyridinium betaines (see p. 270). d:Cy-J ( 164) so2 00N3 4% Schmidt reaction on thiochromone SS-dioxide yields besides the expected ring- expanded product (165) the HN,-adduct (166) the first example of a stable a-azido-~ulphone.'~~ The functionalization of As-phosphorins has been reported in some detail.4- F~rrnyl-,'~'" 4-~yano-,'~'" 4-ary1az0-,'~~* and 4-acetamid0-'~'~ derivatives have been prepared and a Claisen rearrangement on the allyloxy-derivative (167; R' = OCH2CH=CH2 R2= Ph) has yielded the phosphacyclohexadiene (168). On further heating (168) undergoes [3 31 sigmatropic shift of the ally1 group and intramolecular [4 + 21 cycloaddition to give the phosphaheterocycle (169). Diphosphorus (170; X = P) and phosphorus-arsenic (170; X = As) heterocycles have been isolated as cis-truns isomers,'76 and the new phosphorus-boron hetero- cycle (17 1)is potentially aromatic. 177 The azaphospha-adamantane (172) undergoes regioselective quaternization at nitrogen with methyl iodide. 178 173 (a)S. Baklien P. Groth and K.Undheim J.C.S. Perkin I 1975,2099;(b)K.Undheim and S. Baklien ibid. p. 1366. 17* I. W. J. Still M. T. Thomas and A. M. Clish Canud. J. Chem. 1975 53,276. '75 (a)H.H. Pohl and K. Dimroth Angew. Chem. Innternat. Edn. 1975,14,11 1; (6)M.Liickhoff and K. Dimroth ibid. p. 112;(c) 0.Schaffer and K. Dimroth ibid. p. 112. 176 G. Markl D. Matthes A. Donaubauer and H. Baier Tetrahedron Letreis 1975 3171. 177 H.0.Berger and H. Noth 2. Narurforsch.,1975,30b 641. 17* D. J. Daigle and A. B. Papperman J. He&mcyclic am. 1975,12,579. 0.Meth-Ghn and R.K.Smalley R2 Ph I I CP3 X I R' NEt (172) (170) (171) 4-Hydroxyarsabenzene has been prepared and unlike 4-pyridone7 appears to exist solely as the hydroxy-form."9 Arsa-anthracenes (174; R =halogen or Me) are conveniently prepared from the readily available arsinic acid (173).lBo R 5 Seven-memberedRing Compoundsand Macrocydes One of the most characteristic and interesting reactions of singlet arylnitrenes is their transformation into their valencetautomeric azirines and thence into azepines in the presence of an amine.However azepine formation is not always observed in the bicyclic series o-diaminoarenes often being preferred. French workers'8' have reported the fist important breakthrough in this area by photolysis of bi- or tri-cyclic azides in strongly basic media. It appears that the intermediate aziridine (175)is very sensitive to acid but stable in basic solution allowing selective conversion into either the azepine or the aminomethoxyarene (Scheme 27).The methoxyazepines are /D~ .:.-..m~3 hr. H 4 dioxan ' '::*. .<.* \ /KOMe-MeOH / Scheme 27 179 G. Mlirkl H. Baier and S. Heinrich Angew. Chem. Internut. Edn. 1975,14 710. 180 R. J. M. Weustink C. Jongsma and F. Bickelhaupt Tetrahedron Letters 1975 199. lS1 J. Ftigaudy C. Igier and J. Barcelo Tetrahedron Letters,1975,3845. Heterocyclic Chemistry easily converted into aminoazepines by amines. All seven chloroacetylaminoethylindoles have been cyclized with loss of HCl by photolysis cyclization occurring preferentially at the ortho or peri position. Positions 3,4 and 6 were highly reactive while position 1was unreactive.'82"b 8 f-J-$co2Et N" H Ph (176) (177) Formation of benzazepines by ring-expansion of quinoline N-oxides (with dimethylsulphoxonium methylide)Ig3 and isoq~inolines'~~ (by art ANRORC mechanism) has been examined the latter offering a useful entry to rhoeadine alkaloid synthesis.The first examples of 3H-1,2-diazepines have been described being derived from ay-dienones and tosylhydrazine. lg5 Unlike their SH-isomers they show no tendency to exist as bicyclic valence tautomers. A simpler approach to difEcultly accessible lH-1,2-benzodiazepines (176) has been as has the preparation of the last remaining unknown benzodiazepinone (177) some derivatives of which show biological (CNS) activity as great as that of ~alium.'~' An efficient synthesis of the potentially degenerate oxepin oxide (178) has been described commencing from oxepin.'88 The small amount of ethanol in commercial chloroform often shows up unexpec- tedly in reactions.Thus the remarkable conversion in Scheme 28 results from the attempt to allylically brominate the thiazepine (179).lg9 The bromobenzothiepinone Scheme 28 (180) undergoes novel rearrangements to give the tricyclic products (181) and (182).190 The first observable silicenium ion (183) is available in solution by the action of trityl perchlorate on the corresponding hydride at -40 to -50°C.'9' Another first is the synthesis of a non-fused borepin (184).'92 la2 (a) Ann.Reports (B) 1974,71,354;(b)S.Naruto ando. Yonemitsu TetrahedronLetters,1975,3399. 183 V. N. Gogte K. M. More and B. D. Tilak Indian J. Chem. 1974,12 1238. la4 M. Shamma and L.Toke Tetrahedron 1975,31,1991. 185 C. D.Anderson J. T. Sharp H. R. Sod and R. S. Strathdee J.C.S. Chem. Comm. 1975,613. la6 L.Garanti A. Scandroglio and G. Zecchi Tetrahedron Letters 1975,3349. la' U.Golik Tetrahedron Letters 1975 1327. la8 W.H.Rastetter J. Amer. Chem. Soc.,1975,97,210. Ia9 I. It0 and T. Ueda Chem. and Pharm. Bull. (Japan),1975,23 1646. 190 P.M.Weintraub and A. D. Sill J.C.S. Chem. Comm. 1975,784. 191 J. Y.Corey J. Amer. Chem. Soc. 1975,97 3237. lg2 J. J. Eisch and J. E. Galle J. Amer. Chem. Soc. 1975,97,4436. 0.Meth -Cohn and R.K. Smalley I Ph NMe (184) (183) Kauff mann has synthesized several cyclopolyheteroaromatics (1 85) by coupling dilithio-biheteroaryls with cuprous chloride lg3 and various related systems e.g.(185) (186) by the same appr0a~h.l~~ The interesting fluxional thiabarbaralene (187) results from an unprecedented 175-cycloaddition of SO2to cyclo-octatetraene in the presence of SbF5 at -70°C. Warming transforms it into the thermodynamically favoured isomer (188; X =S02).lg5A good synthesis of 9-oxabicyclo[4,2,l]nona-2,4,7-triene (188; X = 0)has come to light by the photoinduced interaction of cyclo-octatetraene epoxide with iron pentacarbonyl. 196 N~N (186) 193 T. Kauffmann B. Greving J. Konig A. Mitschker and A. Woltermann Angew. Chem. Internat. Edn. 1975,14,713. 1g4 T. Kauhann B. Muke R. Otter and D. Tigler Angew. Chem. Internat. Edn. 1975,14,714. 195 L.A. Paquette U. Jacobson and M. Oku J.CS. Chem. Comm. 1975 115. 1% R.Aumann and H.Averbeck J. Organometallic Chem. 1975,85,C4. Heterocyclic Chemistry 281 When a bidentate nucleophile reacts with a polynitroaromatic compound the intermediate Meisenheimer-type complex can undergo a second attack leading to novel products. Thus,the benzornorphan (189) is obtainable in 80% yield (Scheme 29).lg7 Ph 'CH-C / 2 PhCH =C R \ NMe N NO2 -0' + '0-NO Scheme 29 Heteroannulenes continue to hold the stage. Thus while the all-cis azoninyl anion (19a)is aromatic its benzo-analogue lacks aromaticity (i.e. is atropic below -35 "C) 190) (191) .andis thermally unstable reverting to the isomer (191) at 0 "C.This isomer in which 19'unfavourable peri-interactions are removed is distinctly diatropic. The para- tropicity (anti-aromatic character judged by n.m.r.) and diatropicity of a series of [12~]- (192; n = 1)and [lLCnJ-annulenes (192; n =2) respectively are reduced in the same order with a series of fused rings attached reflecting the decrease in importance of different participating KekulC structures of the macrocyclic rings.'99~200 The diatropic bridged [14]annulene (193) has been prepared and shows appropriate low-field NH and Me signals in its 'H n.m.r.spectrum.2o1 The first examples of paratropic non-bridged [15 Jannulenes (16~ systems) e.g. (194) have been described.202 19' R. B. Bard and M. J. Straws J. Amer. Chem. Soc.,1975 W,3789. 198 A. G. Anastassiou and E. Reichmanis J.C.S. Gem. Comm. 1975 149. 199 R. H. Wightman and F. Sondheimer TetrahedronLetters 1975,4179.2oo R. R. Jones J. M. Brown and F. Sondheimer Tetrahedron Letters 1975,4183. 201 W. Flitzsch and H. Peeters TetrahedronLetters 1975,1461. 202 R. L. Wife P. J. Beeby and F. Sondheimer J. Amer. Chem. SOC.,1975,97,641. 0.Meth -Cohnand R. K. Smalley (193) R’ = RZ = H or Ac (194) A principal method of approach to cyclophanes lies in the preparation of a dithiacyclophane followed by contractive removal of sulphur. A new method of sulphur removal by action of benzyne has appeared and is the method of choice for [2,2]cyclophane dienes and for paracyclophane~.~’~ The conformational trithiacyclod~decene,~~~ properties of a~a~yclo-~~tane~,~~~ and NN’N”-trimethyltrianthranilide206have been reported. A new route to metacyclophanes in general and [2,6]pyridinophanes in particular involves interaction of a dichloroarene with an am-polymethylene Grignard reagent in the presence of dichloro[ 1,3-bis(diphenylphosphino)propane]nickel(~~).The reaction also has potential for mac- rocyclic pol yether synthe~is.~” Crown ethers and their analogues have become an exciting frontier in research and the year has seen particular drama in the chiral recognition possibilities of ammonium complexes.The development of enzyme-like properties is a fascinating possibility. Thus Cram’s group have developed various chiral crown ethers incor- porating binaphthyl units to enhance chiral barriers,208 and have demonstrated differential complexation of hexafluorophosphate salts of methyl glycinate and ~alinate.~” Chirality has been very conveniently introduced into 18-crown-6 analogues e.g.(195) by use of diols readily prepared from natural carbohydrates such as L-tartaric acid and D-mannitol.210 Having D symmetry the last reagents are homotopic and with enantiomeric guest ammonium salts should lead to preferen- tial diastereoisomeric complexation. This has been demonstrated by n.m.r. spectro- scopy using a-phenylethylammonium hexafluorophosphate.211 New systems 203 T. Otsubo and V. Boekelbeide Tetrahedron Letters 1975 388 1. 204 J. B. Larnbert and S. A. Khan J. Org. Chem. 1975,40,369. 205 W.D. Ollis J. F. Stoddart and M. Nbgridi Angew. Chem. Internat. Edn. 1975 14 168. 2-W. D. Ollis J. A. Price J. S. Stephanatou and J. F. Stoddart Angew.Chem.Internat. Edn. 1975,14 169. 20’ K. Tarnao S. Kodarna T. Nakatsuka Y. Kiso,and M. Kurnada J. Amer. Chem. Soc. 1975,97,4405. 208 F. de Jong M. G. Siegel and D. J. Cram. J.C.S. Chem. Comm. 1975 551. 209 G. W. Gokel J. M. Tirnko and D. J. Cram. J.C.S. Chem. Comm. 1975,444. 210 W. D. Curtis D. A. Laidler J. F. Stoddart and G. H. Jones J.C.S. Chem. Cornm. 1975 833. 211 W. D. Curtis D. A. Laidler J. F. Stoddart and G. H. Jones J.C.S. Chem. Comm. 1975 835. Heterocyclic Chemistry 283 include crown ether-esters with interesting ion-complexing a remark- able caesium-selective 'football' ligand (196)in which the cation is trapped inside the cavity giving the most stable caesium complex known to date,'13 and the non-cyclic polyethers e.g.(197) which are also good complexing agents for alkali-metal and i 0 (196) (197) alkalineearth ions.214 Reinhoudt has proposed the use of Zeise's salts (e.g. KPtCl, C2H,) as a test method for crown ether complexation with cations. The salts are insoluble in chloroform but dissolve on complexation of the cation giving an ethylene signal easily determinable by n.m.r. spectroscopy.21s 6 Reviews The synthesis of heterocycles by cycloaddition to 1-azirines,2'6 by way of ben- zofur~xans,~'~ thioureas,2'8 or cup-unsaturated carbonyl and by ring transformation of isoxazoles220has been surveyed and the chemistry of pyridine221 (final volume of the four-part supplement) non-classical condensed thiophens,222 heterocycles having 8~-electrons,~~~ oxaz~les,~~~ thiiran~,~~~ isatin,226 thio- chr~mones,~~~ various nitrogenous three-membered chromenes,228 benzof~ran,~~~ heterocycle^,^^' heterocycles containing less common heteroatom~,~~~ transition-metal complexes df synthetic macrocyclic ligand~,~,~ and new heterocyclic optical 212 J.S. Bradshaw L. D. Hansen S. F. Nielsen M. D. Thompson R. A. Reeder R. M. Izatt and J. J. Christensen J.C.S. Chem. Comm. 1975,874. z13 E. Graf and J.-M. Lehn J. Amer. Chem. Soc.,1975,97,5022. 214 E. Weber and F. Vogtle Tetrahedron Letters 1975 2415. 215 R. T. Gray and D. N. Reinhoudt Tetrahedron Letters 1975,2108. 216 D. J. Anderson and A. Hassner Synthesis 1975,483. 217 K. Ley and F. Seng Synthesis 1975,415. 218 T. S. Griflin T. S. Woods,and D. L. Klayman Ado. Heterocyclic Chem.1975,18 100. 219 G. Desimoni and G. Tacconi Chem.Rev. 1975,75651. 220 T. Nishiwaki Synthesis 1975,20. Zz1 'Pyridine and its Derivatives' in 'The Chemistry ofHeterocyclic Compounds,' ed R. A. Abramovitch Wiley New York 1975 Vol. 14 Supplement Part 4. 222 M.P. Cava and M. V. Lakshmikantham Accounts Chem. Res. 1975,8,139. 223 R. R. Schmidt Angew. Chem. Internat. Edn. 1975,14,581. 224 A. V. Fokin and A. F. Kolomiets Russ. Chem. Rev. 1975,44 138. 225 I. J. Turchi and M. J. S. Dewar Chem. Rev. 1975,75 389. z26 F. D. Popp Adv. HetermyclicChem 1975,18 1. 227 S. W.Schneller Ado. Heterocyclic Chem. 197518 60. 228 L. Merlini Adv. Heterocyclic Chem. 1975,18 159. 229 P. Cagniant and D. Cagniant Adv. Heterocyclic Chem.,1975,18,338. 230 G.L'Abbt Bull. Soc.chim. France 1975 1127. 231 P. Jutzi Angew. Chem. Internat. Edn. 1975,14232. 232 L. F. Lindoy am. Soc.Rev. 1975,4,421. 284 0.Meth -Cohn and R.K. Smailey brighteners233 has been evaluated. Reviews have appeared on heteroaromatic tautorneri~m~~~ and on the tautomerism and electronic structure of biologically important pyrimidines,235 on the reactions of natural and synthetic P-lactam~,~~~ the 1,3-dipolar cycloaddition reactions of nitrone~,~~~ on the conformation of piperidine and its heterolog~es~~~ and of pentamethylene on diazotization of heterocyclic primary amine~,~~' and on rearrangement of penicillanic acid deriva- tives.241 233 A. Dorlars C.-W. Schellhammer and J. Schroeder Angew. em. Intentat. Edn. 1975,14 665.234 J. Elguero C. Marzin A. R. Katritzky and P. Linda Adu. Heterocyclic Chem. 1976 supplement I. 235 J. S. Kwaitkowski and B. Pullmann Adu. Heterocyclic Chem. 1975,18,200. 236 A. K. Mukerjee and A. K. Singh Synthesis 1975,547. 237 D. St. C. Black R. F. Crozier and V. C. Davis Synthesis 1975 205. 238 I D. Blackburne A. R. Katritzky and Y. Takeuchi Accounts Chem.Res. 1975,8,300. 239 J. B. Lambert and S. I. Featherman Chem. Rev. 1975,75,611 240 R. N. Butler Chem.Rev. 1975,75 241. 241 R. J. Stoodley Tetrahedron 1975,31 2321.