Studies on seven-membered heterocycles. XXXIII. Synthesis of fully unsaturated 1,2,5-triazepines by photochemical ring expansion of 4-azidopyridazines.

Abstract

Photolysis of the 3-methoxy-4-azidopyridazines (11) in the presence of a base such as methoxide ion and diethylamine resulted in ring-expansion to produce the 1H-1, 2, 5-triazepines (12 and 27), which were too unstable to be isolated, but tautomerized to the stable 4H-isomers (13 and 28) on further treatment with sodium methoxide and were converted to the stable 1-acetyl-1H-1, 2, 5-triazepines (14 and 29) by acetylation with acetyl chloride. The products 12-14 and 27-29 are the first examples of fully unsaturated 1, 2, 5-triazepines and were characterized by means of spectral analyses and some chemical reactions.