D-XYLOSE DERIVED OXAZOLIDIN-2-ONES AS CHIRAL AUXILIARIES IN STEREOSELECTIVE ACYLATIONS AND HALOGENATIONS

Chiral N-acylated oxazolidin-2-ones readily available from D-xylose ha ve been demonstrated to undergo highly diastereoselective acylation re actions via their lithium imide enolates to afford beta-keto imides. T hese are easily purified and exhibit surprisingly high stability towar ds epimerization. The glyco-oxazolidin-2-ones can also be used in dias tereoselective halogenation reactions via their boron enolates to get alpha-halogenated products. These and the branched N-acyl compounds ca n be hydrolyzed allowing isolation of the desired halogenated and rami fied carboxylic acids and return of the auxiliaries for reuse. (C) 199 7, Elsevier Science Ltd.