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-(acylamino)-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 considered. Photochemical processes follow different routes depending on the actual chromophore in the photoreaction. In the irradiation of 3-(aroylamino)-4-methylfurazans, two photochemical pathways involving a different multiplicity of excited states are suggested: cleavage of the ring O(1)-N(5) bond via a singlet excited state (developing into nitrile oxides or carbodiimides, from which final products arise), or preliminary ring-closure involving the aroylamino group via a triplet excited state, respectively. In the irradiation of 3-(acetylamino)-4-phenylfurazan, photolytic intermediates arising from the cleavage of both the O(1)-N(2) and O(1)-N(5) bonds develop into the final products by reaction with the nucleophilic species present.