An efficient synthesis of novel pyridothieno-fused thiazolo[3,2-a]pyrimidinones viaPictet–Spengler reaction

An efficient method for the synthesis of novel fused thiazolo[3,2-a]pyrimidinones: pyrido[3″,2″:4′,5′]thieno[3′,2′:2,3]pyrido[4,5:d] [1,3]thiazolo[3,2-a]pyrimidine-5-one derivatives (5) has been developed using a Pictet–Spengler reaction between 2-(3-aminothieno [2,3-b]pyridin-2-yl)thiazolo[3,2-a]pyrimidin-4-one (3), which could be obtained from condensation of 7-(chloromethyl)-5H-thiazolo [3,2-a]pyrimidin-5-one (1) with 3-cyanopyridine-2-thione (2) viaThorpe–Ziegler isomerization, and aromatic aldehydes under NH2SO3H as catalysis in good yields.