Addition of Ketene Silyl Acetals to 10-Methylacridone via Photoinduced Electron Transfer

Photoaddition of β,β-dimethyl-substituted ketene silyl acetals to 10-methylacridone occurs efficiently under irradiation of the visible light in benzene as well as acetonitrile to yield the siloxy adduct. The carbon-oxygen bond of the adduct is readily cleaved by an acid to yield the corresponding 9-alkylated 10-methylacridinium ion. The comparison of the observed rate constants determined from the dependence of the quantum yields on the concentrations of ketene silyl acetals as well as the fluorescence quenching by ketene silyl acetals with those predicted for the electron transfer processes indicates that the photoaddition proceeds via the photoinduced electron transfer from β,β-dimethyl-substituted ketene silyl acetals to the singlet and triplet excited states. No photoaddition of nonsubstituted ketene silyl acetal to 10-methylacridone occurs, since the electron donor ability is too weak to transfer an electron to the excited states of 10-methylacridone as expected from the higher oxidation potential compared with the β,β-dimethyl-substituted analogues.