Reaction of <Emphasis Type="Italic">N</Emphasis>-aryl-3-oxobutanethioamides with 2-amino-1,3-thiazole and 2-amino-1,3-benzothiazole

N-Aryl-3-oxobutanethioamides react with 2-amino-1,3-thiazole (2-amino-1,3-benzothiazole) in acetic acid to give mixtures of 7-methyl-5H-1,3]thiazolo3,2-a]pyrimidine-5-thione (2-methyl-4H-pyrimido-2,1-b]1,3]benzothiazole-4-thione) and 5-arylimino-7-methyl-5H-1,3]thiazolo3,2-a]pyrimidines (4-arylimino-2-methyl-4H-pyrimido2,1-b]1,3]benzothiazoles), whose ratio depends on the nature of the aryl substituent in the initial butanethioamide.