A new route to 1-oxo-1,2-dihydropyrimido[1,6-a]benzimidazole-4-carboxylates from ethyl 2-(benzimidazol-2-yl)-3-(dimethylamino)acrylate using solvent-free conditions

摘要

Ethyl 2-(Benzimidazol-2-yl)-3-(dimethylamino)acrylate (3) has been used as starting material to develop a mild, efficient solvent-free preparation of ethyl 1-oxo (or thioxo)-1,2- dihydro-pyrimido[1,6-a]benzimidazol-4-carboxylates 6 (X = 0, S) from a variety of isocyanates 4b-d and isothiocyanates 4a,e,f, in yields ranging from 52 to 82%. The synthesis of the starting benzimidazole 3 (82% yield) without solvent, assisted by focused microwave irradiation, is also reported. [References: 23]