Photodehydrocyclization of azaderivatives of 2-styrylnaphthalene

Abstract

Photocyclization of aza-derivatives of 2-styrylnaphthalene has been studied. 6-Styrylquinoxaline and 7-methyl-6-styrylquinoxaline gave the dehydrophotocyclized products in good yields. Sensitization and quenching studies indicate the photocyclization to proceed from the lowest excited singlet $^1(\pi,\pi^{\ast}$ state. Conformational equilibrium of cis 6-styrylquinoxaline in the ground state is expected and the barrier is estimated to be 4.6 kcal/mole. Only one conformer undergoes photodehydrocyclization reaction. This was explained by relative electron density difference in the excited state calculated by PM 3 method.