Methanol-incorporated photoaddition of N-methyl-1,2-naphthalenedicarboximide with alkenes and dienes.

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Irradiation of acetonitrile-methanol solutions of N-methyl-1,2-naphthalenedicarboximide (1b) with 1,1-diphenylethylene gave a methanol-incorporated adduct at a carbonyl carbon atom in 1b together with 2,2-diphenylethyl methyl ether as a typical electron-transfer photosensitized product. The photoreaction of 1b with α-methylstyrene, styrene (2c), or 2-methyl-2-butene in the same solvent system gave a regio-isomeric pair of a mixture of two diastereomers of methanol-incorporated adducts at carbonyl carbon atoms. The irradiation of 1b with 2,3-dimethyl-2-butene and ethyl vinyl ether (2h) in benzene–methanol afforded methanol-incorporated adducts, although no reaction was observed for irradiation in acetonitrile–methanol. The irradiation of 1b with 2,5-dimethyl-2,4-hexadiene in acetonitrile–methanol also resulted in the formation of methanol-incorporated adducts. The values of the free-energy change associated with an electron-transfer (ΔGet) from the alkenes to the singlet excited state of 1b and fluorescence quenching rate constants support the photochemical single-electron-transfer mechanism for the addition. A preferential addition at the carbonyl carbon atom in 1b as well as that at the more sterically hindered carbonyl carbon atom in the reaction of 1b with 2c and 2h is explainable on the basis of the spin densities of the radical anion of 1b derived by a photochemical single-electron-transfer.
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