Using trichloromethyl substituent as convenient leaving group for the synthesis of interesting bi-heterocyclic compounds, a series of 6-methyl-and 7-alkyl (aryl)-5H-thiazolo [3, 2-a] pyrimidin-5-ones, where alkyl= methyl, n-propyl, isopropyl, isobutyl, n-hexyl, isopentyl and aryl= phenyl, 4-toluyl, 4-chlorophenyl, 4-bromophenyl, 4-methoxyphenyl was obtained from a simple and regiospecific reaction of 4-alkoxy-1, 1, 1-trichloro-3-alken-2-ones with 2- ...