Studies on Heterocyclic Compounds. XXXIII. Synthesis of [1, 2, 3]-Triazolo [1, 5-α] pyridines with Nickel Peroxide

Oxidation of hydrazone derivatives of pyridine-2-carbaldehydes (XIII, XIV a) and 2-pyridyl ketones (XIV b-h) with nickel peroxide (Ni-PO) in benzene at room temperature afforded [1, 2, 3]-triazolo [1, 5-α]-pyridines (IV, XV a-h) in good yields. The starting substituted phenyl 2-pyridyl ketones (VIII a-d) were obtained by Ni-PO oxidation of the corresponding alcohols in good yields. When the substituent was p-NO2 or m-NO2 on phenyl group, the Ni-PO oxidation could not afford the ketones but the starting alcohols were recovered. The oxidation of 5-ethyl-2-hydroxymethylpyridine (IX) with Ni-PO did not give the aldehyde but nickel complex (X) was obtained. The reaction mechanisms of Ni-PO and hydrazones are discussed.