Synthesis of ethyl 6-aryl-4-oxo-4,6-dihydro-1(12)(13)H-pyrimido-[2′, 1′:4,5][1,3,5]triazino[1,2-a]benzimidazole-3-carboxylates

Abstract

The synthesis of ethyl 6-aryl-4-oxo-4,6-dihydro-1(12)(13)H- pyrimido[2′,1′:4,5][1,3,5]triazino[1,2-a]-benzimidazole-3- carboxylates (4a-p) was described via pyrimidine ring annulation to 4-aryl-3,4-dihydro[1,3,5]triazino[1,2-a]benzimidazole-2-amines (2a-p) which were obtained from 2-guanidinobenzimidazole (1). Tautomerism in the prepared compounds was investigated using nmr spectroscopy. Compounds 2a-p were found to be present in dimethyl sulfoxide solution predominantly as 3,4-dihydro tautomeric form. Compounds 4a-p existed in dynamic equilibrium of 1-, 12- and 13H- forms. It was found that methylation of 4a-d led to 13-methyl substituted derivatives 9a-d exclusively.