Methanol-Incorporated Photoaddition of N-Methyl-9,10-phenanthrenedicarboximide to Alkenes. Addition at Carbonyl and Phenanthrene-Ring Carbon Atoms

Abstract

Abstract Irradiation of acetonitrile–methanol (2:1 v/v) solutions of N-methyl-9,10-phenanthrenedicarboximide (3) with alkenes 5a–g gave methanol-incorporated adducts (9c–f) at a carbonyl carbon atom in 3, those (10c,f) at a phenanthrene-ring carbon atom, and a methanol-adduct 11g to alkene 5g, together with products 4, 6b,e–g, 7b,e–g, and 8e,f obtained by the photoreactions in benzene. The concentration effect of alkenes 5e,f on yields of products 6e,f, 7e,f, 8e,f, 9e,f, and 10f showed that both 9e,f and 10f arose from a relatively short-lived singlet excited state of 3. The values of the free-energy change associated with an electron transfer (ΔGet) from alkenes 5a–d,g to the singlet excited state of 3 and fluorescence quenching rate constants support a photochemical electron transfer mechanism for the methanol-incorporated addition. Both LiClO4 and BU4NClO4 caused only slight decreases in the relative ratios 10c/9c indicating that both the methanol-incorporated addition at the phenanthrene-ring carbon atom and that at the carbonyl carbon atom might arise from a contact ion pair state. The fact that the methanol-incorporated addition at the arene-ring carbon atom was observed only in the reaction of 3 in a series of N-methylarenedicarboximides, possessing a five-membered imide ring, is interpreted on the basis of the spin density of the radical anions of the imides derived from the photochemical electron transfer.