Sydnones nitrilimines from

Photochemical cycloaddition reactions214-218 between sydnones (1) and 1,3-dipolarophiles take place to give products which are different from, but isomeric with, the thermal 1,3-dipolar cycloaddition products.3 These results are directly interpreted in terms of reactions between the 1,3-dipolarophiles and die nitrilimine (316). The photochemical reactions between sydnones and the following 1,3-dipolarophiles have been reported dicyclopentadiene,214 dimethyl acetylene dicarboxylate,213-218 dimethyl maleate,213 dimethyl fumarate,213 indene,21 carbon dioxide,213 and carbon disulfide.217... 

Two further papers in a series on the generation of nitrilimines (RC=NNR ) by irradiation of sydnones suggest that the reactive excited state is a (n, n ) triplet state,and demonstrate again the use of the reactive nitrilimines in the synthesis of heterocyclic compounds. In continuing studies on the formation of thiirens from 1,2,3-thiadiazoles (23), the parent thiiren has been characterized in a low-temperature matrix after photolysis of (23 R = R = H). Product analysis in experiments with C-substituted substrates suggests that thiiren is formed to a considerable extent thermally but to a lesser extent photochemically from (23 R = H, Ri = Ph). 

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