N-Vinyl-2-oxazolidinones:  Efficient Chiral Dienophiles for the [4 + 2]-Based de Novo Synthesis of New N-2-Deoxyglycosides

Under smooth Eu(fod)3-catalyzed conditions, the inverse-electron demand hetero-Diels−Alder reactions between enantiopure N-vinyl-2-oxazolidinones 1a−f and representative β,γ-unsaturated α-ketoesters proceed with a high degree of endo and facial diastereoselectivity. The elucidation of the stereostructure of these adducts, performed by X-ray analysis or chemical correlation, shows that the endo-selective cycloaddition process is facially controlled in favor of the (2S,4S)-adduct when starting from a (4S)-dienophile or vice versa. The specific interest of the adducts 10a−e, derived from (E)-4-tert-butoxymethylene pyruvic acid methyl ester 9, has been exemplified by the two-step and highly stereoselective transformation of these adducts into the new and valuable N-2-deoxyglycosyl-oxazolidinones 12a−e, isolated in a pure diastereo- and enantiomeric form.