- N-Boc 2-acyloxazolidines: Useful precursors to enantiopure 1,2-diols via highly diastereoselective nucleophilic additions
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N-Boc 2-Acyloxazolidines were synthesized from norephedrine and phenylglycinol. This preparation involves: (i) a transformation or the above β-amino alcohols into N-Boc 2-ethoxycarbonyloxazolidines, (ii) the formation of the corresponding Weinreb amides and, (iii) a reaction between these amides and organometallic reagents. Such diastereomerically pure heterocycles react cleanly with various nucleophilic reagents (Grignard reagents, sodium borohydride and allylsilane) to afford the corresponding alcohols. Treatment of these hydroxyoxazolidines with trifluoro acetic acid, followed by hydrolysis and reduction of the intermediate α-hydroxy aldehydes afforded 1,2-diols. The overall transformation exhibited in most cases a complete diastereoselectivity which can be explained by a chelated model for the nucleophilic addition.
- Agami, Claude,Couty, Francois,Lequesne, Christelle
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- A new access to enantiopure β-hydroxylated piperidines from N-Boc-2- acyloxazolidines. Application to the synthesis of (-)-desoxoprosopinine and (+)-pseudoconhydrine
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The synthesis of (-)-desoxoprosopinine and (+)-pseudoconhydrine were achieved from a common oxazolidine precursor. The three stereocenters present in (-)-desoxoprosopinine as well as the two stereocenters of (+)- pseudoconhydrine were created in highly stereoselective ways. The stereoselectivity observed during the reduction of the ketone moiety in the starting oxazolidine was dependent on the occurrence of a chelated intermediate. The others stereocenters arose from stereoselective reductions or alkylations of intermediate iminium ions.
- Agami, Claude,Couty, Francois,Lam, Hubert,Mathieu, Helene
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p. 8783 - 8796
(2007/10/03)
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