ENANTIOSELECTIVE SYNTHESIS OF DIETHYL 1-HYDROXYALKYLPHOSPHONATES VIA OXAZABOROLIDINE CATALYZED BORANE REDUCTION OF DIETHYL ALPHA-KETOPHOSPHONATES

Reduction of diethyl alpha-ketophosphonates 1 with borane and B-butyloxazaborolidine 2 as catalyst afforded diethyl (S)- or (R)-1-hydroxyalkylphosphonates 3a-d or 3e-f respectively in good yields and moderate to good enantiomeric excess (53-83 ee%). Respective diethyl (R)- and (S)-1-aminoalkylphosphonates 6 were obtained in a one-pot transformation, by the Mitsunobu reaction of 1-hydroxyphosphonates 3 with hydrazoic acid, and subsequent treatment of the intermediate azides 4, with triphenylphosphine, followed by hydrolysis df the iminophosphoranes 5 with water.