Cationic 1,3‐diazadienes in annulation reactions. Synthesis of pyrimidine, thiadiazinedioxide and triazine derivatives

Abstract

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 .