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Synlett 2005(13): 2110-2112  
DOI: 10.1055/s-2005-871947
LETTER
© Georg Thieme Verlag Stuttgart · New York

A Direct and Efficient Stereoconservative Procedure for the Selective Oxidation of N-Protected β-Amino Alcohols

Marta Ocejo, Jose L. Vicario, Dolores Badía*, Luisa Carrillo, Efraim Reyes
Departamento de Química Orgánica II, Facultad de Ciencia y Tecnología, Universidad del País Vasco-Euskal Herriko Unibertsitatea, P.O. Box 644, 48080 Bilbao, Spain
Fax: +34(94)6012748; e-Mail: qopbaurm@lg.ehu.es;
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Publication History

Received 6 May 2005
Publication Date:
12 July 2005 (online)

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Abstract

An efficient, very simple and eco-friendly procedure has been developed for the synthesis of highly enantioenriched α-amino aldehydes by IBX-mediated oxidation of the corresponding β-amino alcohols. The procedure has been applied to a wide range of ­substrates with different side chains and protecting groups showing that the final aldehydes can be obtained in very high yields and with no racemization at the stereogenic center present in the starting compounds.

Key words

amino aldehydes - amino alcohols - oxidations - iodine - green chemistry

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Representative Experimental Procedure. IBX (2.40 g, 8.57 mmol) was added to a solution of the β-amino alcohol 5a (0.50 g, 2.86 mmol) in EtOAc (40 mL) and the mixture was refluxed for 2 h opened to the atmosphere. The mixture was cooled to r.t., filtered and the solvent was removed under reduced pressure to afford α-amino aldehyde 1a pure as its 1H NMR spectrum indicated. For correct characterization purposes, the crude mixture was purified by short path flash column chromatography (hexanes-EtOAc, 8:2) affording pure product as a white solid (0.44 g, 2.54 mmol, 89% yield). All spectral data of compounds 1a-l were in agreement with those previously reported.16

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N-Boc-phenylglycinal is known to racemize under basic conditions (see ref. 8a) and during flash chromatography purification on SiO2 (ref. 1e) but in our hands we have not observed racemization at all.