Several tetrazolo [1, 5-a] pyridines/2-azidopyridines undergo photochemical nitrogen elimination and ring expansion to 1, 3-diazacyclohepta-1, 2, 4, 6-tetraenes (7, 10, 13, 16, 19, 22) as well as ring cleavage to cyanovinylketenimines (8, 17, 20b) in low temperature Ar matrices. 6, 8-Dichlorotetrazolo [1, 5-a] pyridine/2-azido-3, 5-dichloropridine 6 undergoes ready exchange of the chlorine in position 8 (3) with ROH/RONa. 8-Chloro-6- ...