Indium-Mediated Diastereoselective Allylation of d- and l-Glyceraldimines with 4-Bromo-1,1,1-trifluoro-2-butene: Highly Stereoselective Synthesis of 4,4,4-Trifluoroisoleucines and 4,4,4-Trifluorovaline

A practical and efficient route for the stereoselective synthesis of (2R,3S)- and (2S,3R)-4,4,4-trifluoroisoleucines and (2R,3S)-4,4,4-trifluorovaline was developed. Indium-mediated allylation of (R)-N-benzyl-2,3-O-isopropylideneglyceraldimine 7 with 4-bromo-1,1,1-trifluoro-2-butene 4 gave the desired
homoallylic amine 8 in high diastereoselectivity (>95% de) with moderate yield. The Cbz-protected
(2R,3S)-4,4,4-trifluoroisoleucine 14 and Boc-protected (2R,3S)-4,4,4-trifluorovaline 21 were then readily
prepared from 8. In addition, following the same procedure, Cbz-protected (2S,3R)-4,4,4-trifluoroisoleucine
28, the enantiomer of 14, was prepared starting from (S)-N-benzyl-2,3-O-isopropylideneglyceraldimine
24.