To a solution of acid from Step 6 (1.0 g, 2.3 mmol) in THF (20 mL) at 0° C. was added KHMDS (0.64M/toluene, 4.0 mL, 2.6 mmol) followed by pivaloyl chloride (0.31 mL, 2.6 mmol). After 30 rain at 0° C., the solution was cooled to -78° C., and a cloudy solution of (R)-4-isopropyl oxazolidinone (0.35 g, 2.7 mmol) and BuLi (1.6M/hexane, 1.7 mL, 2.7 mmol) in THF (20 mL) was added via double-tipped needle. After 10 min at -78° C., the reaction was warmed to 0° C. for 1 h, at which point it was quenched by the addition of saturated NH4Cl solution. Following EtOAc/H2O work-up, the two diastereomers were obtained by flash chromatography (1:5 EtOAc/hexane). isomer A=0.55 g, isomer B =0.52 g.
