Arylbiguanide (1) and 2-guanidinobenzimidazole (2) were reacted with diethyl azodicarboxylate (3) to give dihydro-s-triazine (6) and dihydrobenzimidazo [1, 2-a]-s-triazine (9), respectively. The reactions of 1 and 2 with dimethyl acetylenedicarboxylate (4) in alcohol provided the corresponding imidazolinylideneacetylguanidines (10 and 12), which were converted to alkyl imidazolidinylideneacetates (11 and 13) by alcoholysis. The compounds 10 and 12 underwent acid-catalyzed ring conversion to pyrimidine compounds (15 and 16).