Journal of Organic Chemistry 2009-08-07

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

Julie A Pigza, Tim Quach, Tadeusz F Molinski

Index: J. Org. Chem. 74(15) , 5510-5, (2009)

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Abstract

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.