PHOTOINDUCED MOLECULAR-REARRANGEMENTS - SOME INVESTIGATIONS OF THE PHOTOCHEMICAL BEHAVIOR OF 3-(ACYLAMINO)-1,2,5-OXADIAZOLES (FURAZANS)

Mechanistic investigations of the photochemical behavior of some 3-(ac ylamino)-1,2,5-oxadiazoles (furazans) are reported. Irradiations of 3- (aroylamino)-4-methyl- and 3-(acetylamino)-4-phenylfurazans at lambda = 254 nm in methanol, and in methanol containing pyrrolidine, are cons idered. Photochemical processes follow different routes depending on t he actual chromophore in the photoreaction. In the irradiation of 3-(a roylamino)-4-methylfurazans, two photochemical pathways involving a di fferent multiplicity of excited states are suggested: cleavage of the ring O(1)-N(5) bond via a singlet excited state (developing into nitri le oxides or carbodiimides, from which final products arise), or preli minary ring-closure involving the aroylamino group via a triplet excit ed state, respectively. In the irradiation of 3-(acetylamino)-4-phenyl furazan, photolytic intermediates arising from the cleavage of both th e O(1)-N(2) and O(1)-N(5) bonds develop into the final products by rea ction with the nucleophilic species present.