Furan (1, X=O) and some pyrrole (1, X=NCOOR) derivatives of o-divinylbenzenes give upon irradiation in diluted solutions furo- and pyrrolo-fused bicyclo[3.2.1]hexene derivatives 4. Contrary to these results the irradiations of stilbenylsydnones (2) give bicyclo[3.3.0]diaza-heptadiene structure (5). The determination of these bicyclic structures by 1H NMR using different techniques will be discussed.

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