N-BOC 2-ACYLOXAZOLIDINES - USEFUL PRECURSORS TO ENANTIOPURE 1,2-DIOLSVIA HIGHLY DIASTEREOSELECTIVE NUCLEOPHILIC ADDITIONS

N-Boc 2-Acyloxazolidines were synthesized from norephedrine and phenyl glycinol. This preparation involves: (i) a transformation of the above beta-amino alcohols into N-Boc 2-ethoxycarbonyloxazolidines, (ii) the formation of the corresponding Weinreb amides and, (iii) a reaction b etween these amides and organometallic reagents. Such diastereomerical ly pure heterocycles react cleanly with various nucleophilic reagents (Grignard reagents, sodium borohydride and allylsilane) to afford the corresponding alcohols. Treatment of these hydroxyoxazolidines with tr ifluoro acetic acid, followed by hydrolysis and reduction of the inter mediate alpha-hydroxy aldehydes afforded 1,2-diols. The overall transf ormation exhibited in most cases a complete diastereoselectivity which can be explained by a chelated model for the nucleophilic addition.