A chiral synthesis of (2S,3S)-phenylalanine-3-2H via boronic esters

Reduction of (s)-pinanediol (S)-[(phenyl) (chloro)-methyl]boronate (1) with lithium triethylborodeuteride yielded (s)-pinanediol (R)-[(phenyl)methyl]boronate-α-2H (2). The chiral purity of 2 was measured via peroxidic oxidation to (S)-benzyl alcohol-α-2H (3), which was analyzed with an NMR chiral shift reagent. (Dichloro-methyl)lithium converted 2 to (s)-pinanediol (1S, 2S)-1-chloro-2-phenylethylboronate-2-2H (4), which with sodium azide yielded (s)-pinanediol (1R, 2S)-1-azido-2-phenylethylboronate-2-2H (5). (Dichloromethyl)lithium with 5 yielded (s)-pinanediol (1S, 2S, 3S)-1-chloro-2-azido-3-phenylpropylboronate-3-2H (6), which was oxidized by sodium chlorite to (2S, 3S)-2-azido-3-phenylacetic acid-3-2H (7). Hydrogenation of 7 yielded (2S, 3S)-phenylalanine-3-2H in high diastereomeric and enantiomeric purity. (author)