Photolysis of Fused Cyclobutatriazolines: An Adventitious Route to 3,6-Di(2-pyridyl)pyridazonorbornadiene

Abstract

Ultraviolet irradiation of the triazolines (18a,b) formed by the high-pressure addition of benzyl azide to dimethyl 3,6-di(2-pyridyl)-4,5-diazatetracyclo[6.4.1.0 ^2,3 .0 ^9,12 ]trideca-3,5,7,10-tetraene-10,12-dicarboxylate (16a) and the related monoester (16b), forms 13–17% of the expected aziridine (19a,b), together with cyclobutane-cleavage products that include the hitherto unknown pyridazinonorbornadiene (2), its di-π-methane rearrangement product (21) and the corresponding triazoles (20a,b). Mechanistic pathways are discussed.