Er(OTf) 3 ‐Catalyzed Multicomponent Synthesis of 3,4‐Dihydro‐2 H ‐pyran via Hetero‐Diels‐Alder Reaction under Ambient Temperature

A one‐pot synthesis of 3,4‐dihydro‐2 H ‐pyran derivatives has been achieved using substituted styrenes, aqueous formaldehyde and various β‐keto esters. This multicomponent protocol employs erbium (III) triflate as a catalyst affording 3,4‐dihydro‐2 H ‐pyran derivatives in good to excellent yields (72‐98%). Furthermore, synthesis of the bicyclic fused ring system such as 2‐aryl‐2,3,4,6,7,8‐hexahydro‐5 H ‐pyrano[2, 3‐ d ]pyridazin‐5‐one 6 was achieved from the corresponding 3,4‐dihydro‐2 H ‐pyran 4 .