Enantioselective synthesis of beta-amino acids using hexahydrobenzoxazolidinones as chiral auxiliaries

Add time:08/13/2019    Source:sciencedirect.com

A practical synthetic route for the asymmetric synthesis of β2-amino acids is described. In the first step, the procedure involves the N-acylation of readily available, enantiopure hexahydrobenzoxazolidinone (4R,5R)-1 with 3-methylbutanoyl chloride 2, 4-methylpentanoic acid 3, and 3-(1-tert-butoxycarbonyl)-1H-indol-3-yl)propanoic acid 4 to afford derivatives 5a, 5b, and 5c, respectively, which were alkylated with high diastereoselectivity by means of reaction between their sodium enolates and benzyl bromoacetate. Removal of the chiral auxiliary from the alkylated products followed by hydrogenation and hydrolysis gave β2-amino acids (S)-10a, (S)-10b, and (S)-10c, which were N-protected with Fmoc. Enantiomeric (R)-10a–c were similarly prepared from the isomeric hexahydrobenzoxazolidinone (4S,5S)-1; thus, the route presented here provides access to both enantiomers of valuable highly enantioenriched β2-amino acids.

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