p ‐Toluenesulfonic Acid‐Mediated Three‐Component Reaction “On‐Water” Protocol for the Synthesis of Novel Thiadiazolo[2,3‐ b ]quinazolin‐6(7 H )‐ones

The first p ‐toluenesulfonic acid‐mediated “on‐water” multicomponent reaction sequence for the synthesis of novel thiadiazolo[2,3‐ b ]quinazolinones from 5‐aryl‐1,3,4‐thiadiazol‐2‐amines, cyclic 1,3‐dicarbonyls and aldehydes with microwave irradiation is described. This protocol proceeds with high atom economy and leads to the generation of three rings, together with one C−C, one C=N and two C−N bonds in a single operation. This new methodology has advantages such as operational simplicity, mild conditions, broad functional group tolerance, simple work‐up procedure and applicability on a gram scale.