Photochemical reactions of pyrazin-2(1H)-ones

Abstract

Irradiation of 1-alkyl-5,6-diarylpyrazin-2(1H)-ones (1a–c) in alcohol under oxygen gave N-alkyl-acetamide derivatives (2a–e) in 21–69% yield. The formation of acetamide derivatives (2) arises via the endoperoxide intermediates (3), initially produced by the reaction of the pyrazin-2(1H)-ones (1), which act as their own sensitizer, with singlet oxygen followed by O–O bond fission, alcohol addition, and rearrangement accompanied by the elimination of the corresponding nitrile derivative. The pyrazin-2(1 H)-ones (1a–d) rapidly reacted with singlet oxygen to afford the stable endoperoxides (3a–d). On the other hand, the pyrazin-2(1H)-ones (1a–d) were inert to the photolysis in benzene or methanol under argon.