Preparation of Chiral<i>N</i>-Vinyl Oxazolidinones by a Simple General Procedure
作者:Robert Dhal、Catherine Gaulon、Gilles Dujardin
DOI:10.1055/s-2003-41443
日期:——
A high yielding, general, and practical procedure for the N-vinylation of 2-oxazolidinones via TMSOTf-promoted dehydroalkoxylation of N,O-acetals is described.
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
R' = Me, Ar, CH2 Ar) and beta,gamma-unsaturated alpha-ketoesters (R = Ar) afforded heteroadducts with high levels of endo and facialselectivities. A complete reversal of facial differentiation was achieved by varying the Lewis acid, leading to the stereoselective formation of either endo-alpha or endo-beta adducts. [reaction: see text].
新的β-取代的N-乙烯基-1,3-恶唑烷-2-酮(具有R'= Me,Ar,CH2 Ar)与β,γ-不饱和α-酮酸酯([4 + 2]酸催化的杂环加成)之间( R = Ar)提供具有高水平的内和面选择性的杂加合物。通过改变路易斯酸可以完全逆转面部分化,从而导致内-α或内-β加合物的立体选择性形成。[反应:请参见文字]。