~~~~~ 5-Amino-4-(cyanoformimidoyl) -1 H-imidazole (3) has been prepared in good yield by the basecatalysed cyclisation of (Z) -N-(2-amino-l,2-dicyanovinyl)formamidine. Compound (3) reacts with ketones, R1COR2 [R' = R2 = Et, Me, Bu, -(CH2)5-, PhCH,; R1 = Me, R2 = Ph] to give 2,2-disubstituted-6-carbamoyl-l,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[l,5-c)imidazole derivatives, which have been isolated when R1 = R2 = Et, Bu, and PhCH,; when R' = R2 = Ph the only product isolated is tentatively assigned the imidazo[l,5-c] imidazole structure. In the reaction with acetylacetone the 1,Zdihydropurine intermediate is unstable and loses acetone to give 2-methyl-6-carbamoylpurine. The aldehydes RCHO [R = Me, Et, (4-MeCH=CH- , c-C,H,O] also react readily with (3) at room temperature to give the corresponding 6-carbamoyl-182-dihydropurine derivatives, which can be isolated when R = Me or Et; these oxidise in solution to afford the corresponding 6-carbamoylpurines.We have reported previously' that the amidinium salt (l), obtained from reaction between N-methylacetonitrilium triffate and diaminomaleonitrile (DAMN), cyclises on treatment 'H NMR spectra were recorded on Hitachi-Perkin-Elmer R24B (60 MHz) or Bruker XL300 (300 MHz) instruments, 13C NMR