Alkylation of chiral phosphonoglycine equivalents: asymmetric synthesis of diethyl α-amino-α-alkyl-phosphonates

A model was developed to rationalize the experimental results of the alkylation of chiral phosphonoglycine equivalents yielding alpha-amino-alpha-alkyl-phosphonates. The model studies, carried out using semiempirical calculations, have emphasized the role of the chelating effects in influencing the diastereoselectivity of the alkylation step. Chelation can be optimized by tuning the functionality of the substituent at carbon C-1 of the camphor skeleton, By employing 2d, as suggested by the modelling, a major improvement in the enantiomeric excesses of compounds 5 (R=CH3, C2H5) was obtained.