Dicyanoketene ethylene acetal (1) reacted with substituted guanidines to yield o-aminocyanopyrimidines, which reacted with N,N-dimethylformamide dimethyl acetal to afford N,N-dimethylamino-methyleneaminopyrimidine derivatives. A new approach to pyrimido[4,5-d]pyrimidines from o-aminocyanopyrimidine and N-dichloromethylenedialkyliminum chorides followed by cyclization with ammonium hydroxide was reported.