Studies on Photochemical Reactivities of 2-(Alkylcarbamoyl)quinolines

The photochemistry of three types of 2-(alklylcarbamoyl)quinolines was studied. The illumination of 2-(diethylcarbamoyl)quinolines (1a, 1b, and 1c) afforded 2-(2-ethylaminopropionyl)quinolines (3a, 3b, and 3c) with a small amount of five-membered cyclic products, 1H-pyrrolo[3,4-b]quinolin-3(2H)-ones (4a, 4b, and 4c), both of which were formed via Type-II hydrogen-atom abstraction from the T1 state. 2-(Ethylcarbamoyl)quinoline (1d) did not undertake any photochemical change. The photochemical inactivity of 1d could be attributed to the unfavorable orientation of its carbamoyl substituent for intramolecular hydrogen-atom abstraction by a ring nitrogen. The illumination of 2-(alkylcarbamoyl)-3-methyl quinolines (2a and 2b) afforded 2-(N-acetyl-N-alkylcarbamoyl)-3-methyl quinolines (5a and 5b), which were suggested to be formed by the atmospheric oxidation of an unstable photoproduct formed via the S1 state.