Photochemical behaviour of α-diketones on a silica gel surface: a novel photoreaction by intramolecular trapping of an excited ketone carbonyl oxygen by an aryl group

Abstract

Irradiation of the benzils 1a,b having the lowest n,π* excited state on dry silica gel with a high-pressure mercury lamp gives the benzoic acids 3a,b and bibenzofuranones 4a,b, whereas irradiation of 1-phenylpropane-1,2-dione 1c and biacetyl 1d gives acetaldehyde and/or benzoic acid; under these conditions, 4,4′-dimethoxybenzil 1e, the lowest excited state of which is possibly the π,π* state, fails to react.