Diastereoselective Hydrolysis of Asymmetric P–Cl Species and Synthesis of Optically Pure ( R P )‐(–)‐Menthyl H‐Phenylphosphinate

Phenyl dichlorophosphine reacted with ( L )‐(–)‐menthol to afford two diastereomers of menthyl phenylphosphinate ( R P )‐ 1a /( S P )‐ 1a′ in up to 89:11 dr . Compound ( R P )‐ 1a was isolated in 58 % yield (60 g) and > 99:1 dr . An HCl‐promoted diastereoselective hydrolysis of the P–Cl species was found to be involved in the reaction. On the basis of this, a mixture of 1a / 1a′ with 50:50 dr was converted to a mixture enriched in 1a with 88:12 dr by treatment with phosphorus trichloride.