Photoinduced electron transfer oxidation of α-methylstyrene with molecular oxygen sensitized by dimethoxybenzenes: a non-singlet-oxygen mechanism

α-Methylstyrene (1) was photooxidized with oxygen in the presence of a series of alkylated dimethoxybenzenes as a sensitizer in acetonitrile, affording the cleaved ketone (2), epoxide (3) as well as a small amount of the ene product (4) in ca. 1:1:0.04 ratio. A non-singlet-oxygen mechanism is proposed, in which an excited sensitizer is quenched by oxygen to produce a sensitizer radical cation and a superoxide ion (O2−), the former of which oxidizes 1, while O2− reacts with the resulting 1+ to give the major oxidation products.