Asymmetric Synthesis of Diethyl α-Amino-α-Alkyl-Phosphonates by Alkylation of the Chiral Schiff Base Derived from (+)-Ketopinic Acid and Diethylaminomethyl Phosphonate
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.
Diethyl alpha-amino-alpha-alkyl-phosphonates are obtained in good to high enantiomeric excesses by alkylation of chiral phosphonoglycine equivalents embodying the camphor skeleton. The chelating effects in the alkylation step play an important role in enhancing the diastereoselectivity of the reaction as substantiated by semiempirical calculations (AM1).
SCHOLLKOPF U.; SCHUTZE R., LIEBIGS ANN. CHEM.,(1987) N 1, 45-49