Selective photorearrangement of 1-(2-naphthoyl)aziridine to 2-(2-naphthyl)-2-oxazoline by polybromobenzenes

Abstract

Photoreactions of 1-(2-naphthoyl)aziridine (1) in the presence of various brominated hydrocarbons (4a–f) in deaerated benzene solution have been studied at room temperature. The selective photorearrangement of (1) to 2-(2-naphthyl)-2-oxazoline (2) was promoted by 1,3,5-tribromobenzene (4a) and 1,4-dibromobenzene (4b). The nonpolar solvent benzene favoured selective photorearrangement, compared with polar acetonitrile. The series of brominated hydrocarbons (4a–e) but not CH₃(CH₂)₂Br (4f) formed 1 : 1 ground-state complexes with (1). The fluorescence emission of (1) was quenched efficiently by (4a–f). The fluorescence-quenching rate constant (k_q) increased on increasing the half-wave reduction potential (E^Red_½) of (4a–f). The photosensitized triplet reaction of (1) did not give (2) but a small amount of oligomer. The reciprocal of the quantum yield for the photorearrangement (Φ^–1) was proportional to that of the concentration of non-complexed (4a){([4a)]_free)^–1}.