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 beta,gamma-unsaturated alpha-ketophosphonates. The corresponding 5,6-dihydro-4H-pyran-2-ylphosphonates were obtained in good ee values (up to 94% ee).