Oxazoline−Oxazinone Oxidative Rearrangement. Divergent Syntheses of (2<i>S</i>,3<i>S</i>)-4,4,4-Trifluorovaline and (2<i>S</i>,4<i>S</i>)-5,5,5-Trifluoroleucine
作者:Julie A. Pigza、Tim Quach、Tadeusz F. Molinski
DOI:10.1021/jo900654y
日期:2009.8.7
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,