A new methodology for the stereoselective synthesis of 4-substituted butenolides: Asymmetric Michael addition reaction of 2-(trimethylsilyloxy)furans to oxazolidinone enoates

Chiral Lewis acid promoted Michael addition of 2-(trimethylsilyloxy)furans to oxazolidinone enoates (2) in the presence of hexafluoroisopropanol proceeded stereoselectively to give 4-substituted butenolides in good yields. A 1:1 complex prepared in situ from Sc(OTf)(3) and 3,3'-bis(diethylaminomethyl)-1,1'-bi-2-naphthol 5b showed excellent anti-selectivity and moderate enantioselectivity, while Cu(OTf)(2)-bis(oxazoline) complex exhibited excellent enantioselectivity and moderate to good anti-selectivity. (C) 1997 Elsevier Science Ltd.