A solution of 252A (22 g, 81 mmol) and toluene (400 mL) was treated with (R)-1-phenylethanamine (12.5 mL, 97 mmol) and p-TsOH (1.5 g). The reaction mixture was heated to reflux with a Dean-Stark trap for 23 hours. The mixture was cooled to room temperature, washed with saturated aqueous NaHCO3 (2×200 mL) and brine (2×200 mL). The combined organic layers were dried (Na2SO4), filtered and concentrated. The crude material was filtered through a pad of silica (100% CH2Cl2) and concentrated to provide 14.7 g (yield: 49%) of Compound 252B as an oil.
