Abstract Triazapentadienium iodides 2 prepared from N'-thiocarbamoylformamidines 1 are efficient intermediates in heterocyclic synthesis. They react with ketenes, sulfenes, phenyl isocyanate or isothiocyanate and dimethyl acetylenedicarboxylate affording the corresponding dihydropyrimidinones 3, thiadiazinedioxides 5, triazinones 6, triazinethiones 7 and pyrimidines 9.
