Pivaloyl chloride (6.73 gm, 55.8 mmol) was slowly added to a solution of (E)-hex-3-enedioic acid (4.00 gm, 27.8 mmol) and NMM (5.64 gm, 55.8 mmol) in THF (100 mL) at 0° C. The ice bath was removed and the mixture was allowed warm to rt. After 30 min the mixture was cooled back down to 0° C. In a separate vessel, a solution of n-BuLi (2.5 M in hexanes, 22.2 mL, 55.5 mmol) was slowly added to a −78° C. solution of (S)-4-benzyloxazolidin-2-one (Evans chiral auxiliary) (9.84 gm, 55.5 mmol) in THF (100 mL). The mixture was allowed to stir at −78° C. for 45 min. The mixture containing the activated di-acid was cooled to −78° C. and then cannulated into the mixture containing the lithiated Evans chiral auxiliary. Upon addition the reaction mixture turned reddish in color. The dry ice/acetone bath was removed and the mixture was allowed to warm to rt. After 2 hr at rt, the reaction mixture was quenched by addition of saturated aqueous NH4Cl (50 mL). The mixture was partitioned between water and a small amount of EtOAc. The aqueous phase was isolated and extracted with EtOAc. All organic phases were combined, washed with saturated aqueous NaCl, dried over MgSO4 and concentrated. The crude product was purified using silica gel chromatography (ISCO system) eluting with a gradient of 0-10% MeOH/DCM to give (E)-1,6-bis((S)-4-benzyl-2-oxooxazolidin-3-yl)hex-3-ene-1,6-dione (3.06 g, 6.62 mmol, 23.8% yield) as a white solid.
