Photocyclization Reaction of Aza-derivatives of 2-Styrylnaphthalene

Abstract

Photocyclization of 6-styrylquinoxaline shows C5 site selectivity in the quinoxaline ring due to electronic effects. The solvent polarity plays an important role in the photocyclization which proceeds through the lowest 1(pi,pi*) state. A study of azulene quenching supports this mechanism. 6-Pyrazinylquinoxalinylethylene, which has nitrogen atoms in both naphthalene and benzene rings, does not undergo electrocyclic reaction due to the strong ''proximity effect'' leading to efficient S1 to T1 intersystem crossing.