Photocyclization of 2-(dialkylamino)ethyl acetoacetates: Remote proton transfer and stern-volmer quenching kinetics in the system involving two reactive excited states

Article abstract of DOI:10.1002/(SICI)1099-1395(199604)9:4<221::AID-POC773>3.0.CO;2-I

Upon irradiation, 2-(dibenzylamino)ethyl and 2-(N-benzyl-N-methylamino)ethyl acetoacetate (1a and 1b) undergo photocyclization via remote proton transfer from the benzyl group to the acetyl carbonyl oxygen to give eight-membered azalactones. Irradiation of the corresponding (diisopropylamino)- and (dimethylamino)ethyl esters gave no azalactones. Introduction of the methyl group on C-2 of 1a brought about a complicated photoreaction, probably due to competition of α-cleavage. The Stern-Volmer plots for the photoreaction of 1a did not show the linear relationship indicating that the photoreaction proceeds from two reactive excited states. The Stern-Volmer quenching equation for the system was obtained by applying the steady-state approximation and was used for the analysis of the photoreaction of 1a. The triplet lifetime was determined to be 1.6 × 10^-8 s.