Photoaddition of biacetyl and alkenes. Reaction stereochemistry, multiplicity, and photokinetics

Abstract

Quantum yields are reported for the photoaddition of biacetyl, a ketone having a visible absorbing chromophore, and a series of alkenes in benzene solution. Biacetyl phosphorescence quenching and quantum yield data are consistent with a photoaddition mechanism involving biacetyl triplets. Exciplex and biradical intermediates are proposed for photoaddition on the basis of stereochemical results and the dependence of phosphorescence quenching constants on electron donor properties of alkenes. The consequence of utilizing low energy excited states in small ring forming addition reactions is discussed. (Author)