PHOTOCHEMICAL GENERATION, PHOTOCHROMISM AND PHOTOCYCLIZATION OF 2-NORBORNADIENYL SUBSTITUTED BENZO-1,3-OXAZOLES

Under UV-irradiation (365 nm) of their solutions Schiff bases (I) unde rgo the oxidative photocyclization to give 2-(3'-aryl-norbornadien-2-y l)-benzo-1,3-oxazoles (H) (lambda(max) = 337 nm, hexane), which then c onvert to the quadricyclane isomers (III) (lambda(max) = 287 nm). The back thermal reaction proceeds on heating the solution (tau(1/2)(70 de grees C) = 2340 s). Under prolonged UV-irradiation a further (2 pi+2 p i+2 pi) photocyclization of the triene moiety of(TT) followed by 1,5-s igmatropic migration of a hydrogen atom occurs. The resulting photopro duct (IV) possesses by an intense fluorescence (lambda(max)(fl)=390 nm ).