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 alpha,beta-unsaturated aldehydes and acyl phosphonates. The dual activation is based on an organocatalyst that activates both the alpha,beta-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.