2-Carbomethoxyaminobenzimidazole in the synthesis of 2-oxo-1,2,3,4-tetrahydropyrimido-[1,2-a]benzimidazole and its derivatives

A one-step method was developed for the preparation of 2-oxo-1,2,3,4-tetrahydropyrimido1,2-a]benzimidazole and its 3-methyl, 4-methyl, 4,4-dimethyl, and 4-phenyl derivatives by heating 2-carbomethoxyaminobenzimidazole with acrylic, methacrylic, crotonic, and cinnamic acids at 140–200°C. A possible scheme for the formation of the indicated compounds is presented.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1389–1393, October, 1977.