Alkenyl-substituted diaryl-nitrile-iminesgenerated by photolysis or thermolysis of alkenyl-substituted 2,5-diaryl-tetrazolesundergo a regioselective intramolecular [2 + 31 cycloaddition to yield new heterocyclic compounds, e.g. fused 2-pyrazolines. With alkinyl derivatives, the corresponding pyrazoles have been formed. UV evidence is given for the intermediate nitrile-imine at -190'. The latter can be trapped using an excess of carboxylic acid (UV evidence for a new intermediate at -120"). In this case, the corresponding rearranged addition product N'-acyl-N'-aryl-benzohydrazide is isolated in good yield. Synthesealkenylsubstituierter 2,5-Diaryltetrazole. -Die in Schema 2 aufgefiihrten Tetrazole 6a-g wurden in Analogie zu [33] hergestellt. Dazu wurden die entsprechenden Arylaldehyde 4a [34], 4b [35], 4c [36], 4d [37], 4e [38] sowie der in Analogie zu [38]Schema 2 ' PhN +CI-e 2 * P' Ph Pyridln/-15" N=N 4a-c x = o 6 a -c a n = l , R = H 5 a -c X = N -N H -T~S b n = l , R=CH, c n = 2 , R = H 4 d X = O 5 d X=N-NH-TOS 6d 4e,f X = O 5e9f X=N-NH-Tos

Intramolecular 1,3-Dipolar Cycloaddition Reactions of Alkenyl-substituted 3,4-DiarylsydnonesThe 3,4-diarylsydnones 1 and 12a-with an ally1 or alkcnyloxy substituent on the N(3)-phenyl group have been synthesized by classical methods starting from 2-allylaniline and the corresponding alkenyloxyanilines, respectively (Schemes 2 and 3 ) . Whereas the allyl-substituted sydnone 1 undergoes an intramolecular 1,3-dipolar cyclodddition at rooin temperature in solution to yield 13 (Scheme 4), the alkenyloxy-substituted sydnones 12a-e are thermally stable. On irradiation of 1 and 1 2 a 4 , formation of the fused dihydropyrazoles 2 and 14a-d (Schemes I and 5 ) is observed. In the case of 12d, the yield of 14d is very low, and the symmetric 1,2,3-triazole 15a has been isolated as the main product. A very likely reaction mechanism for the formation of the photoproducts involves decdrboxylation of the sydnones to give a nitrile-imine which undergoes an intramolecular 1,3-dipolar cycloaddition onto the C=C bond.

On the Photochemistry of Sydnones and 1,3,4-0xadiazolin-2-ones SummaryThe photochemical behaviour of several 3,bdisubstituted sydnones (cf: Scheme 5) in dioxane solution was investigated. The pure sydnones give, as was already reported

Thermal and photochemically induced intramolecular 1,3-dipolar cycloaddition reactions of 4-phenyl-3-(2-allylphenyl)-sydnone SummaryThe title compound 9 was synthesised in the usual way, starting from 2-allylaniline and ethyl 2-bromo-2-phenylacetate, via the nitrosaminacid 8 (Scheme 2). 9 reacts at room temperature with its potential azomethinimine-function in an intramolecular 3)Teil der geplanten Dissertation.Eine ausfuhrliche Mitteilung sol1 in dieser Zeitschrift erscheinen.