Studies on Benzimidazoles and Related Compounds. V. Reaction of 2-Azido-1-methylbenzimidazole with Unsaturated Compounds

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Cycloaddition reactions of 2-azido-1-methylbenzimidazole (I) with such reagents as diphenylketene, dimethyl acetylenedicarboxylate, methyl propiolate, and N, N-diethyl-phenylethynylamine were investigated. The diester exclusively reacted with the carbonnitrogen double bond of imidazole ring to give the 1 : 1 molar adduct (IV). On the other hand, the ynamine added to azido group at C2-position and only triazole derivative (XI) was obtained. For thermal decomposition of the adduct (XI), the presence of 2-azirine compound (XIX), a four electron system, as intermediate was assumed from consideration of structures of the decomposition products (XII and XIII). Reaction of I with the ester gave a mixture of the triazolo derivative (VI) as major product and the 1 : 1 molar adduct (VII). Also, diphenylketene exothermically reacted with I and gave 2, 3-dihydro-9-methyl-3-oxo-2, 2-diphenyl-9H-imidazo[1, 2-a] benzimidazole (II).

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