Methanesulfonate → 3-[[1-(Benzoylamino)-3-methylbutyl]methylphenylsilyl]propanoic acid

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To a solution of 49 (0.7 g, 1.91 mmol) in acetone (22 mL) was added 0.23 mL (2 mol %) of a 4 wt % solution of OsO4 in water and Jones reagent (2.43 mL, 6.49 mmol). After stirring the mixture for 24 h at rt, 2-propanol (0.5 mL) was added followed by NaHSO3 (0.2 g). The mixture was diluted with water (50 mL) and stirred until a dark-green, homogeneous solution was produced. This solution was diluted further with water (90 mL) and extracted with six 50-mL portions of EtOAc. The combined organic extracts were washed with saturated aqueous NaCl and dried over Na2SO4. Concentration gave a colorless solid of crude 50 as a mixture of diastereomers. This product was used in the next reaction without further purification: Rf=0.20 (1/9 EtOAc:hexane); 1H NMR (300 MHz, CDCl3) δ 7.67–7.62 (m, 2H), 7.54–7.52 (m, 2H), 7.48–7.37 (m, 6H), 5.79 and 5.73 (two doublets due to diastereomers, J=10.0 Hz, 1H), 4.25–4.13 (m, 1H), 2.44–2.34 (m, 2H), 1.64–1.57 (m, 1H), 1.49–1.38 (m, 1H), 1.34–1.21 (m, 3H), 1.03, 0.98, 0.90 and 0.84 (four doublets due to diastereomers, J=6.6 Hz, 6H), 0.40 (s, 3H); MS (FAB) m/e (rel. intensity) 384 (MH+, 62), 315 (7), 312 (8), 311 (27), 310 (100), 307 (19), 306 (88), 255 (10), 253 (22); HRMS (FAB) calcd for C22H30NO3Si: 384.1995, found: 384.1995.

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