Asymmetric synthesis of α,α-difluoro-β-amino phosphonic acids using sulfinimines

Addition of diethyl lithiodifluoromethylphosphonate to enantiopure sulfinimines afforded the corresponding N-sulfinyl α,α-difluoro-β-amino phosphonates with good diastereoselectivity. A two-step deprotection involving treatment of diastereomerically pure N-sulfinyl α,α-difluoro-β-amino phosphonates with trifluoroacetic acid in EtOH followed by refluxing with 10 N HCl afforded enantiopure α,α-difluoro-β-amino phosphonic acids.