Acetoxy-ketones => vinyl esters

Reductions. Nelson et a/. selectively reduced enol acetates, vinyl chlorides, and x,/i-unsaturated aldehydes to the corresponding olefins. The reagent also reduces a-acetoxy ketones to the respective ketones. Ketones and esters arc not reduced. The... 

Diels-Alder reactions carbohydrates.2 This 3,y-unsaturated a-keto ester undergoes Diels-Alder reactions with electron-rich dienophiles to provide protected sugars. The thermal and pressure-promoted reaction of 1 with ethyl vinyl ketone provides the endo-adduct 2, which can be converted in two steps into the ethyl (3-mannopyranoside 3. The same reaction of 1 with (Z)-l-acetoxy-2-benzy-loxyethylene is even more endo-selective, and gives the endo-adduct 4, which can be converted into a derivative of benzyl DL-mannopyranoside. 

---