Synthesis of N-alkylated-2-(1,3-diphenyl-1H-pyrazol-4-ylsulfanyl)-1H-benzimidazoles by Vilsmeir-Haack reaction and by condensation with DMF-DMA

摘要

2-(1H-Benzimidazol-2-ylsulfanyl)-1-phenylethanone 3 on condensation with phenyl hydrazine under acidic conditions gives the corresponding hydrazone derivative which when subjected to Vilsmeir Hack formylation followed by alkylation under phase transfer catalyst (PTC) conditions gives N-alkylated-2-(1,3-diphenyl-1H-pyrazol-4-ylsulfanyl)-1H-benzimidazole 7a-d. Alternatively 7a-d can also be prepared by treatment of 3 with DMF-DMA at RT for 3 hr giving 2-(1H-benzimidazol-2-ylsulfanyl)-3-dimethylamino-l-phenylpropenone 10 followed by condensation with phenyl hydrazine under acidic conditions and subsequent alkylation with an alkylating agent under PTC conditions. Compound 3 itself has been prepared from the well known benzimidazole thiol 1 by condensation with phenacyl bromide 2.