Our attention then turned to the enantiospecific synthesis of phosphinate esters (Scheme 4, D) employing Grignard reagents as nucleophiles in the second step. Pleasingly, and in complete contrast to our first generation method where addition of Grignard reagents were unproductive and led to the exclusive formation of byproducts, the thiazolidinone leaving group could be smoothly displaced by employing 1.1 equiv. of organomagnesium halides in THF at 0 °C for 4 h. Products derived from BnMgCl (50), vinyl-MgCl (51), 2-thiophene-MgBr ( ) could be obtained in moderate to good yields and ≥ 91% e.s. with only minor adjustments to the reaction temperature and time while the enantiospecific displacement with n-BuMgCl could be carried out on 0.5 mmol scale affording phosphinate ester 53 in 53% yield and 96:4 e.r. (95% e.s.). Both 50 and 51 were recrystallized to enantiopurity and single crystals from these samples were analyzed by X-Ray diffraction. Unlike displacement with heteroatom-based nucleophiles, displacement with Grignard reagents took place with retention of stereochemical configuration at the P(V) center. Finally, a collection of enantioenriched phosphonothioates was prepared by displacing the thiazolidinone leaving group with thiol nucleophiles (Scheme 4, E). Employing 1.0 equiv. of thiol with 1.0 equiv. of t-BuMgCl in THF at -40 °C phosphonothioates bearing cyclohexyl (54), n-propyl (55) and benzyl (56) substituents in good yields and with high enantiospecificity. X-Ray diffraction analysis of a single crystal of 56 revealed that, as with alcohols and amines, nucleophilic substitution with thiols proceeded with inversion of the P(V) stereocenter.