The [3+2] photocycloaddition reaction between benzenecarbonitriles and alkenes

Abstract

The scope and limitations of the previously reported [3+2] photocycloaddition reactions between dicyanobenzenes and 2,3-dimethyl-2 butene in acetone was investigated. It was found that the reaction is mainly limited to a combination of either benzonitrile, or dicyanobenzene, and alkyl olefins of a relatively low oxidation potential (e.g. 2,3-dimethyl-2-butene or 2-methyl-2-butene). The proposed mechanism for the reaction was substantiated by the isolation of the imine precursors to the indenone products obtained in these reactions. Experimental results seem to point to a charge-transfer (CT) mechanism, although the possibility of a triplet route, involving sensitisation by acetone solvent cannot be ruled out completely.