Asymmetric Synthesis of Diethyl α-Amino-α-Alkyl-Phosphonates by Alkylation of the Chiral Schiff Base Derived from (+)-Ketopinic Acid and Diethylaminomethyl Phosphonate

The alkylation of the chiral Schiff base derived from the condensation of (+)-ketopinic acid and diethyl aminomethylphosphonate followed by hydrolysis affords diethyl (S)-α-amino-α-alkyl phosphonates with high enantiomeric excesses when benzyl or allyl halides are used in the alkylation step. An improved procedure for the preparation of diethyl aminomethylphosphonate is also reported.