A convenient one-pot synthesis of thiopyrano[4,3-b]pyran derivatives under LiOH·H2O/EtOH/ultrasonic conditions

Various derivatives of thiopyrano[4,3-b]pyran structure are synthesized via a multicomponent procedure starting from tetrahydro-4H-thiopyran-4-one, aromatic aldehydes, and malononitrile. Reactions take place by the use of catalytic quantities of LiOH·H2O in one pot under ultrasonic conditions and in an ethanolic medium. Isolation of products occurs by spontaneous precipitation in reaction mixtures and no cumbersome and expensive chromatographic separations are needed.