Synthesis of 5-amino-4-(cyanoformimidoyl)-1H-imidazole: a reactive intermediate for the synthesis of 6-carbamoyl-1,2-dihydropurines and 6-carbamoylpurines

Abstract

5-Amino-4-(cyanoformimidoyl)-1H-imidazole (3) has been prepared in good yield by the base-catalysed cyclisation of (Z)-N-(2-amino-1,2-dicyanovinyl)formamidine. Compound (3) reacts with ketones, R¹COR²[R¹= R²= Et, Me, Bu, –(CH₂)₅–, PhCH₂; R¹= Me, R²= Ph] togive2,2-disubstituted-6-carbamoyl-1,2-dihydropurines as the major products, together with minor amounts of compounds believed to be novel 7-amino-1-carbamoyl-3,3-disubstituted 3H-imidazo[1,5-c]imidazole derivatives, which have been isolated when R¹= R²= Et, Bu, and PhCH₂; when R¹= R²= Ph the only product isolated is tentatively assigned the imidazo[1,5-c]imidazole structure. In the reaction with acetylacetone the 1,2-dihydropurine intermediate is unstable and loses acetone to give 2-methyl-6-carbamoylpurine. The aldehydes RCHO [R = Me, Et, (E)-MeCHCH–, c-C₄H₄O] also react readily with (3) at room temperature to give the corresponding 6-carbamoyl-1,2-dihydropurine derivatives, which can be isolated when R = Me or Et; these oxidise in solution to afford the corresponding 6-carbamoylpurines.