Role of the electron-donating methoxy group on the photo-induced cyclization of 2-azadienes: a mechanistic study

A combined experimental and computational investigation has shown that the photocyclization of 2-azadienes to isoquinolines is consistent with a unimolecular process in the triplet state and that the (n,π*) transition is involved. The presence of a methoxy group favours the photoreaction. According to calculations, the reaction should proceed by a conformational equilibrium in the ground state followed by excitation and subsequent cyclization. The presence of an equilibrated triplet-state intermediate along the reaction path is consistent with a measurable luminescence.