Reaction Steps
To a solution of azide 47 (2.75 g, 9.57 mmol) in ethyl ether (100 mL) at 0° C. was added dropwise over 5 min lithium aluminum hydride (1 M in ether, 47.8 mmol), and the mixture was allowed to warm to rt over 10 min. After stirring for 30 min under argon; the mixture was cooled to 0° C. and diluted with ether (100 mL). This mixture was quenched with saturated aqueous Na2SO4 solution until evolution of hydrogen had ceased. The mixture was dried with solid Na2SO4 and filtered. The residue was extracted with ether (50 mL) and the organic extracts combined. Concentration gave crude amine 48 as a colorless oil. This amine was dissolved in CH2Cl2 (60 mL) and Et3N (5 mL), and the solution was cooled to 0° C. To this solution was added dropwise over min benzoyl chloride (1.34 g, 9.57 mmol), and the mixture was allowed to warm to rt. After stirring overnight under argon, the reaction mixture was quenched with saturated aqueous NaHCO3 (20 mL). The organic layer was isolated and the aqueous layer extracted twice with 50-mL portions of CH2Cl2. The combined organic extracts were washed with saturated aqueous NaCl, dried over Na2SO4, and concentrated. Flash chromatography over silica gel (1/9 EtOAc:hexane) gave a sticky colorless solid of 49 as a mixture of diastereomers (2.6 g, 74%): Rf=0.20 (1/9 EtOAc:hexane); 1H NMR (300 MHz, CDCl3) δ 7.69-7.60 (m, 2H), 7.56-7.54 (m, 2H), 7.48-7.37 (m, 6H), 5.95-5.80 (m, 1H), 5.57 (d, J=9.9 Hz, 1H), 5.0 (d, J=17.0 Hz, 1H), 4.90 (d, J=8.6 Hz, 1H), 4.24-4.13 (m, 1H), 2.17-2.07 (m, 2H), 1.68-1.55 (m, 1H), 1.44-1.24 (m, 2H), 1.07-0.99 (m, 2H), 0.93 (d, J=6.4 Hz, 3H), 0.85 and 0.84 (two doublets due to diastereomers, J=6.6 Hz, 3H), 0.40 and 0.39 (two singlets due to diastereomers, 3H); 13C NMR (75 MHz, CDCl3) δ 166.7, 140.9, 135.0, 134.7, 134.5, 134.34, 134.31, 131.1, 131.0, 130.5, 129.64, 129.61, 128.8, 128.54, 1128.0, 126.6, 113.3, 113.2, 40.5, 40.4, 37.2, 36.9, 27.5, 25.1, 23.6, 21.2, 11.3, 10.7, −6.7, −7.4; IR (neat) 3279 (m, br), 3064 (m), 2954 (s), 2919 (m), 2867 (m), 1787 (w), 1727 (w), 1628 (s), 1577 (m), 1536 (s), 1487 (m), 1427 (m), 1323 (m), 1252 (m), 1110 (m), 994 (m), 902 (m), 791 (m), 699 (s) cm−1; MS (FAB) m/e (rel. intensity) 366 (MH+, 11), 365 (9), 364 (5), 350 (6), 322 (11), 311 (11), 310 (34), 290 (10), 289 (26), 288 (100), 253 (8); HRMS (FAB) calcd for C23H31NOSi: 365.2175 (MH+−1), found: 365.2172. Anal. Calcd for C23H31NOSi: C, 75.56; H, 8.55; N; 3.83. Found: C, 75.18; H, 8.41; N, 3.72.
