3-Hydroxy-3-(4-naphth-2-ylphenyl)piperidine (Preparation 7, 1.24 g, 4.09 mmol), 3-hydroxy-3, 4-bis(ethoxycarbonyl)butanoic acid (Preparation 1, 1.01 g, 4.09 mmol), EDC, (0.785 g, 4.09 mmol), 1-hydroxybenzotriazole (HOBT, 0.055 g, 2.05 mmol) and triethylamine (570 μL, 8.18 mmol) in THF or methylene chloride (150 mL) is stirred under argon overnight. The reaction mixture is diluted with CH2Cl2 or ethyl acetate and washed with water or 5% aqueous hydrochloric acid, saturated aqueous sodium bicarbonate, and brine. The organic layer is then dried over MgSO4 or Na2SO4, filtered and concentrated. The crude product is purified by flash chromatography (using 60% ethyl acetate in hexane in this instance) to yield the diester intermediate, ethyl 4-[3-hydroxy-3-(4-naphth-2-yl-phenyl)piperidin-1-ylcarbonyl]-3-hydroxy-3-ethoxycarbonylbutanoate (1.63 g, 75%) as a foam solid.
