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 (8) in high diastereomeric and enantiomeric purity.