Convenient synthesis of fused heterocycles from α‐ketohydroximoyl chlorides and heterocyclic amines

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Abstract
Nitroso derivatives of imidazo[1,2‐a]pyridine (11, 13, 14), imidazo[1,2‐a]pyrimidine (15), imidazo[1,2‐a]pyrazine (16), imidazo[1,2‐b]pyrazole (17), and imidazo[1,2‐b]‐1,2,4‐triazole (19) were obtained in good yields from α‐ketohydroximoyl chlorides3and 2‐aminopyridines (4–6), 2‐aminopyrimidine (7), 2‐aminopyrazine (8), 5‐amino‐3‐phenylpyrazole (9), and 3‐amino‐2H‐1,2,4‐triazole (10), respectively. Under different conditions, the reaction of3with 3‐amino‐2H‐1,2,4‐triazole (10) and 2‐aminopyrazine (8) afforded the noncyclized substitution products18and22, respectively. The structures of the products were assigned and confirmed on the basis of their elemental analyses, spectral data, and alternate synthesis wherever possible.