A New Procedure for the Preparation of β-Keto-δ-lactones from Sugars and Their Transformation into Glycosyl Acceptors in Disaccharides Synthesis

Glycals are effective starting materials for the synthesis of enantiopure β-ketone-δ-lactones. They are easily transformed, through a two-step, one-pot reaction, into the corresponding α,α‘-dioxothiones which in turn can be quantitatively trapped with dienophiles in inverse electron-demand [4 + 2] cycloadditions. The reaction of dioxothione 8b with endo and exo glucals allowed the elaboration of a new protocol to prepare 2-thio- or 2-deoxydisaccharides stereoselectively.