Photochemical behavior of some α, β-unsaturated lactams. Dependence of reaction path on multiplicity

Abstract

Whereas direct irradiation (2537 Å) of 5,6-dihydro-4,6,6-trimethyl-2(1H)-pyridone 1 (1a) produced almost exclusively the cleavage products 2 and 3, the acetophenone sensitized reaction (3500 Å) gave a single cyclobutane dimer. In contrast, direct (2537 Å) or sensitized (acetophenone, 3500 Å) irradiation of the homo derivative 7 of compound 1 gave approximately the same mixture of two cyclobutane dimers. It was thus demonstrated that dimer formation proceeded by way of a triplet excited state and that the cleavage reaction most probably occurred via an excited singlet state.A structure for each cyclobutane dimer in the seven-membered series was proposed on the basis of its spectral properties.