To a solution of N-isoamyl-N-(6-trifluoromethanesulfonyloxy naphthalene-2-sulfonyl)-D-valine tert-butyl ester (1.1 g, 1.89 mmol) in N,N-dimethylformamide (20 mL) is added lithium chloride (0.40 g, 9.5 mmol), tetramethyl tin (0.525 mL, 3.79 mmol), and bistriphenylphosphino palladium dichloride (0.066 g, 0.095 mmol). The reaction is heated to 80° C. for 16 h. The reaction is allowed to cool to ambient temperature and filtered through Celite. The filtrate is poured over water and extracted three times with dichloromethane. The combined organic extracts were washed with brine, dried over sodium sulfate, and concentrated in vacuo. The residue is purified by column chromatography (4% hexanes-ethyl acetate) to afford the title compound as a white solid (0.41 g, 50% yield).
