Inverse-Electron-Demand Hetero-Diels—Alder Reaction of β,γ-Unsaturated α-Ketophosphonates Catalyzed by Prolinal Dithioacetals.

Some novel prolinal dithioacetal derivatives were studied as catalysts for the inverse-electron-demand hetero-Diels−Alder reaction of enolizable aldehydes and β,γ-unsaturated α-ketophosphonates. The corresponding 5,6-dihydro-4H-pyran-2-ylphosphonates were obtained in good ee values (up to 94% ee).