EXO DIASTEREOSELECTIVE DIELS-ALDER REACTIONS OF (R)-2-PHENYL-4-METHYLENE-OXAZOLIDIN-5-ONE

The thermally induced Diels-Alder reactions of (R)-2-phenyl-4-methylen e-oxazolidin-5-one 2 and substituted 1,3-cyclohexadienes and substitut ed Ig-butadienes gives exo diastereomeric Diels-Alder adducts. In some cases the initially formed adducts undergo epimerization at the amino -acetal carbon, however the stereochemical integrity of the quaternary alpha-amino acid stereogenic centre is maintained and Diels-Alder add ucts can be obtained in high enantiomeric purity (> 90% eel. The stere ochemistry of these adducts has been elucidated by single crystal X-ra y structure determinations and 2D H-1 NMR analysis.