Facile Synthesis of Carboxamide-Substituted 1,3,4-Thiadiazines and 5,6-Dihydro-4H-1,3,4-Thiadiazin-5-Ols

Novel 2-carboxamide-substituted 1,3,4-thiadiazines and 5,6-dihydro-4H-1,3,4-thiadiazin-5-ols were synthesized by the reaction of oxamic acid thiohydrazides with phenacyl bromides. This reaction was performed using an equimolar mixture of thiohydrazide and alpha-bromoacetophenones in methanol under basic conditions. The ratio of products obtained in the cyclocondensation was found to be strongly dependent on the substitution pattern and reaction conditions.