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

Abstract

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)-1,2dihydro-pyrimido[1,6-a ]benzimidazol-4-carboxylates 6 (X = O, 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.

A practical multi-step synthesis of ethyl N-functionalized $$\varvec{\upbeta }$$ β -amino benzimidazole acrylate derivatives as promising cytotoxic agents

“…Typically, the mechanism of this reaction is an additionelimination [18] after the loss of dimethylamine via an aminal intermediate, which could not be isolated [13]. In previous work, we used 5 as an ambident synthon in a regioselective azaannulation with isocyanate for the preparation of 1-oxo-1,2-dihydropyrimido[1,6-a]benzimidazole-4-carboxylates using solvent-free conditions under microwave irradiation [19]. This solvent-free aza-annulation was also extended to mono N-substituted hydrazines in the synthesis of new 4-(1Hbenzimidazol-2-yl)-1,2-dihydro-(3H)-pyrazol-3-ones [20].…”