Reduction of 10-methylacridinium ion by alkenes via photoinduced electron transfer

The photoaddition reactions of various alkenes with 10-methylacridinium ion occur efficiently in methanol to yield the adducts in which the methoxy group from methanol is generally introduced in the less substituted sp² carbon under irradiation of the visible light. In the case of photochemical reaction of cyclohexene with AcrH⁺, however, cyclohexene adduct with no incorporation of methoxy group from methanol was obtained as well as the methoxy-incorporated adduct. When a sterically hindered alkene, 2,3-dimethylbut-2-ene is employed, no methoxy group is incorporated in the adduct. On the other hand, the photoaddition of but-2-ene affords two regioisomers, the ratio of which varies slightly depending on the cis- and trans-isomers as well as reaction temperature. The reaction mechanism involving photoinduced electron transfer from alkenes to the singlet excited state of 10-methylacridinium ion provides a comprehensive and confirmative basis for understanding the product distributions, the fluorescence quenching by alkenes, and the dependence of quantum yields on the alkene concentrations.