Ammonium Chloride → (2S,3R)-1-tert-Butoxycarbonyl-3-(3-hydroxypropyn-1-yl)-2-phenylpiperidin-3-ol

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O-Trimethylsilylpropargyl alcohol (24.51 ml, 20.47 g, 160 ml) was added slowly to a cooled (−10° C.) solution of ethylmagnesium bromide. (1M in tetrahydrofuran, 160 ml, 160 mmol). The mixture was stirred at 0° C. for 20 minutes, then at room temperature for 2 hours. The mixture was cooled to −10° C. and a solution of (2S)-1-tert-butoxycarbonyl-2-phenylpiperidin-3-one (Description 1; 42.3 g) in tetrahydrofuran (200 ml) was added dropwise over 30 minutes (Internal temperature below −5° C.). The mixture was stirred at room temperature for 14 hours, poured into water (300 ml) and saturated aqueous ammonium chloride (300 ml) and extracted with ethyl acetate (2×300 ml). The combined organic fractions were washed with brine (300 ml), dried (MgSO4) and the solvent was evaporated under reduced pressure. The residue was dissolved in ethyl acetate (500 ml) and a solution of tetrabutylammonium fluoride (1M in tetrahydrofuran, 160 ml, 160 mmol) was added dropwise. The mixture was stirred at room temperature for 30 minutes, water (300 ml) was added, and the layers were separated. The aqueous layer was extracted with ethyl acetate (2×300 ml) and the combined organic fractions were washed with water (300 ml) and brine (300 ml), dried (MgSO4) and the solvent was evaporated under reduced pressure to give the crude title compound as an orange oil (45 g). The crude material was purified by flash column chromatography on silica gel, eluting with hexane/ethyl acetate (90:10 increasing to 25:75) to give the title compound as an amber oil (32.2 g). 1H NMR (CDCl3) δ 753-755 (2H, m), 7.19-7.35 (3H, m), 5.56 (1H, s), 4.27 (2H, s), 3.99-4.03 (1H, m), 3.25 (1H, br s), 2.77-2.81 (1H, m), 2.77 (1H, br s), 2.12-2.20 (1H, m), 1.91-1.99 (2H, m), 1.77-1.83 (1H, m), and 1.39 (9H, s).

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