Cyclization Cascade Reaction of Aldehydes and Acyl‐Stabilized Sulfur Ylides for the Access to Multisubstituted 2 H ‐Pyrans

Herein, we report a novel cyclization reaction of aldehydes and acyl‐stabilized sulfur ylides for access to multisubstituted 2 H ‐pyrans rather than the classic epoxide products, in which a key 1‐oxatriene intermediate leading to 2 H ‐pyrans via oxa‐6π‐electrocyclization was generated in situ from one molecular aldehyde and three molecular acyl‐stabilized sulfur ylides through an acid‐ and base‐mediated cascade process. The reaction displays broad substrate scope, good functional group tolerance, and mild reaction conditions. Additionally, the condensation reaction of the multisubstituted 2 H ‐pyran products with hydrazine hydrate led to the easy formation of a wide array of 5 H ‐pyrano[3,4‐ d ]pyridazines.