Asymmetric Strecker Synthesis of alpha-Arylglycines

A practically simple three-component Strecker reaction for the asymmetric synthesis of enantiopure alpha-arylglycines has been developed. Addition of a range of aryl-aldehydes to a solution of sodium cyanide and (S)-1-(4-methoxyphenyl)ethylamine affords highly crystalline (S,S)-alpha-aminonitriles that are easily obtained in diastereomerically pure form. Heating the resultant (S,S)-alpha-aminonitriles in 6 M aqueous HCl at reflux resulted in cleavage of their chiral auxiliary fragments and concomitant hydrolysis of their nitrile groups to afford enantiopure (S)-alpha-arylglycines. The enantiopurities of these (S)-a-arylglycines were determined via derivatization of their corresponding methyl esters with 2-formylphenylboronic acid and (S)-BINOL, followed by (1)H NMR spectroscopic analysis of the resultant mixtures of diastereomeric iminoboronate esters.