Asymmetric cyclopropanation of chiral (1-dimethoxyphosphoryl-2-phenyl)vinyl p-tolyl sulfoxide: a new synthesis of enantiomerically pure 2-amino-3-phenyl-1-cyclopropane-phosphonic acid—a constrained analog of phaclofen

E-(S)-(1-Dimethoxyphosphoryl-2-phenyl)vinyl p-tolyl sulfoxide 3 was found to undergo cyclopropanation with sulfur ylides [dimethyl(oxo)sulfonium methylide, diphenyl sulfonium isopropylide and ethyl (dimethylsulfuranylidene)acetate (EDSA)] in a highly diastereoselective manner. The major diastereomer obtained in the reaction of E-(S)-3 with EDSA was converted into enantiopure (2R)-amino-(3R)-phenyl-(1R)-cyclopropane-phosphonic acid, a constrained analog of the GABAB antagonist, phaclofen.