A chiral synthesis of (2<i>S</i>, 3<i>S</i>)‐phenylalanine‐3‐²H via boronic esters

Abstract

Abstract Reduction of (s)‐pinanediol ( S )[(phenyl) (chloro)‐methyl]boronate (1) with lithium triethylborodeuteride yielded ( s )‐pinanediol ( R )‐[(phenyl)methyl]boronate‐α‐ 2 H (2). The chiral purity of 2 was measured via peroxidic oxidation to ( S )‐benzyl alcohol‐α‐ 2 H (3), which was analyzed with an NMR chiral shift reagent. (Dichloro‐methyl)lithium converted 2 to ( s )‐pinanediol (1 S ,2 S )‐1‐chloro‐2‐phenylethylboronate‐2‐ 2 H (4), which with sodium azide yielded ( s )‐pinanediol (1 R ,2 S )‐1‐azido‐2‐phenylethylboronate‐2‐ 2 H (5). (Dichloromethyl) lithium with 5 yielded ( s )‐pinanediol (1 S , 2 S ,3 S )‐1‐chloro‐2‐azido‐3‐phenylpropylboronate‐3‐ 2 H (6), which was oxidized by sodium chlorite to (2 S ,3 S )‐2‐azido‐3‐phenylacetic acid‐3‐ 2 H (7). Hydrogenation of 7 yielded (2 S ,3 S )‐phenylalanine‐3‐ 2 H (8) in high diastereomeric and enantiomeric purity.