An efficient method for the synthesis of thieno[3′,2′:2,3]pyrido-[4,5-d]-thiazolo[3,2-a]pyrimidinones

An efficient method for the preparation of thieno[3′,2′:2,3]pyrido-[4,5-d]thiazolo[3,2-a]pyrimidin-5-ones 5 is described. The key intermediate, 7-(3-amino-4-cyano-5-phenylaminothieno-2-yl)-5H-thiazolo[3,2-a]pyrimidin-5-one (3), was synthesized from 7-chloro methyl-5H-thiazolo[3,2-a]pyrimidin-5-one (1) with potassium-(2,2-dicyano-1-phenylaminoethen-1-yl)thiolate (2) by Thorpe-Ziegler isomerization. Subsequent reaction of the intermediate amine with aromatic aldehydes via Pictet-Spengler reaction provided thieno-pyridine fused thiazolo[3,2-a]pyrimidines under p-TsOH as catalyst in good yields.