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

alpha -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 (O-2(.-)), the former of which oxidizes 1, while O-2(.-) reacts with the resulting 1(.+) to give the major oxidation products. (C) 2001 Elsevier Science Ltd. All rights reserved.