Mesoionic Purinone Analogs. V. Synthesis of Mesoionic Thiazolo[3,2-a]-s-triazine-5,7-diones, Mesoionic 1,3,4-Thiadiazolo[3,2-a]-s-triazine-5,7-diones, and Their Monothione Derivatives

Mesoionic 8-alkylthiazolo- and -1,3,4-thiadiazolo[3,2-a]-s-triazine-5,7-diones have been prepared by the reactions of 2-alkylaminothiazoles (3) or 2-alkylammo-l,3,4-thiadiazoles with phenoxycarbonyl isocyanate. Mesoionic 8-alkylthiazolo[3,2-a]-s-triazin-5-one-7-thiones and -7-one-5-thiones are obtained from the reaction of 3 with phenoxycarbonyl isothiocyanate and ethoxycarbonyl isothiocyanate, respectively. These mesoionic xanthine analogs react readily with amines and are easily hydrolyzed in water.