ALKYLATION STUDIES ON PYRAZOLYL AND ISOXAZOLYL BENZIMIDAZOLES

摘要

2-Acetylbenzimidazole (1) on heating with dimethyl formamide dimethyl acetal gave 1-(1H-benzimidazolyl)-3-dimethylaminopropenone (2) which on reaction with hydrazine hydrate gave 2-(1 H-pyrazolyl)-1 H-benzimidazole (3). The reaction of 3 with DMS/DES/ PhCH2CI in CH3CN containing K2CO3 as base and triethylbenzylammonium chloride (TEBAC) as phase trasfer catalyst (PTC) resulted in the formation of 2-(3-pyrazolyl)-1-substitutedbenzimidazole (4). Alkylation of 1 with DMS/DES/PhCH2CI under PTC conditions gave the previously known 1-substituted -2-acetyl benzimidazoles (5) which with DMF-DMA gave 1-substituted-2-(2-benzimidazolyl)-3-dimethylaminopropenone (6). The latter could also be obtained from 2 by alkylation under PTC conditions. Treatment of 6 with hydrazine hydrate in methanol yielded 4. Reaction of 2 with hydroxylammonium chloride yielded 1H-(2-benzimidazolyl)-3-isoxazole (8) which on alkylation under PTC conditions gave 1-substituted (2-benzimidazolyl)-3-isoxazole (9). The latter could also be obtained from 6 by treatment with hydroxylammonium chloride.