Photolysis of 4-azidopyridines (7a-e) in the presence of methoxide ions resulted in ring expansion to give 5-methoxy-6H-1, 4-diazepines (10a-e), presumably via the azirine intermediates 8 derived from the initially formed singlet pyridylnitrenes. Treatment of the 6H-1, 4-diazepine (10a) with benzoyl chloride, acetyl chloride, or ethyl chloroformate in pyridine afforded the corresponding 1-acyl-1H-1, 4-diazepines (21a-c), whose structures were confirmed by means of thermal and photochemical reactions.