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J Org Chem. 2009 Aug 7;74(15):5510-5. doi: 10.1021/jo900654y.

Oxazoline-oxazinone oxidative rearrangement. divergent syntheses of (2S,3S)-4,4,4-trifluorovaline and (2S,4S)-5,5,5-Trifluoroleucine.

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The Department of Chemistry and Biochemistry and Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA.


Stereoselective syntheses of the valuable fluorinated amino acids (2S,3S)-4,4,4-trifluorovaline and (2S,4S)-5,5,5-trifluoroleucine have been achieved starting from 4,4,4-trifluoro-3-methylbutanoic acid by using a conceptually simple transformation: conversion to a chiral oxazoline, SeO2-promoted oxidative rearrangement to the dihydro-2H-oxazinone, and face-selective hydrogenation of the C=N bond, followed by hydrogenolysis-hydrolysis. The transformation is limited by the tendency of the intermediate beta-trifluoromethyldihydrooxazinone to undergo imine-enamine isomerization. Both amino acids were obtained as configurationally pure hydrochloride salts identical in all respects with those in literature reports.

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