Organocatalytic Access to Enantioenriched Dihydropyran Phosphonates via an Inverse-Electron-Demand Hetero-Diels–Alder Reaction

The enantioselective inverse-electron-demand
hetero-Diels–Alder
reaction of the remote olefin functionality in dienamines has been
developed by the simultaneous activation of α,β-unsaturated
aldehydes and acyl phosphonates. The dual activation is based on an
organocatalyst that activates both the α,β-unsaturated
aldehyde, through dienamine formation, and the acyl phosphonate by
hydrogen-bonding. The enantioselective reaction results in the formation
of dihydropyran frameworks with three contiguous stereogenic centers.
Different substitution patterns are possible for both the heterodiene
and the dienophile, and the target products are obtained in good yields
and up to 92% ee. The potential of the reaction is demonstrated by
transformation of the products into valuable and complex synthons.