To a solution of (R)—N-naphthalene-2-sulfonyl (3-oxo-cyclohepty)glycine ethyl ester (1.05 g, 2.61 mmol) in tetrahydrofuran-ethanol (20 mL, 1:1) at 0° C. is added sodium borohydride (0.147 g, 3.88 mmol) and the reaction is stirred at 0° C. for 1 hour. The reaction was quenched at 0° C. with citric acid (10% aqueous), and the solvents were removed in vacuo. The residue was dissolved in water and extracted three times with ethyl acetate. The combined organic extracts were washed with brine, dried over magnesium sulfate, and concentrated in vacuo. The residue is purified by column chromatography (50% hexanes-ethyl acetate) to afford the title compound as a white solid (0.90 g, 85% yield). LCMS (m/z): 406.14 (M+1), 404.13 (M−1).
