Reaction Steps
To a solution of 1,3-dithiane (6.77 g, 56.3 mmol) in THF (120 mL) at −78° C. was added dropwise over 10 min n-butyllithium (1.6 M in hexane, 50 mmol), and the solution was stirred for 2 h under argon. A solution of 31 (11.1 g, 43.3 mmol) in THF (100 mL) was added, the mixture was stirred for 3 h at −78° C., and overnight at rt. The reaction mixture was quenched with water (100 mL) and the organic layer isolated. The aqueous layer was extracted with two 100-mL portions of ethyl ether. The combined organic extracts were washed with saturated aqueous NaCl, dried over Na2SO4, and concentrated. Flash chromatography over silica gel (1/9EtOAc:hexane) gave 32 contaminated with 1,3-dithiane. The latter was removed by sublimation (54° C., 8.0 mm Hg). Recrystallization from Et2O provided pure 32 as a colorless solid (14.8 g, 96%): Rf=0.40 (1/49 EtOAc:hexane); mp 47-49° C.; 1H NMR (300 MHz, CDCl3) δ 7.66 (d, J=7.8 Hz, 4H), 7.43 (m, 6H), 5.90 (m, 1H), 5.02 (dd, J=17.1, 1.7 Hz 1H), 4.91 (dd, J=10.2, 1.7 Hz, 1H), 4.26 (s, 1H), 2.92 (t, J=11.8 Hz, 2H), 2.71 (m, 2H), 2.19 (m, 2H), 2.07 (m, 2H), 1.37 (m, 2H); 13C NMR (75 MHz, CDCl3)δ 141.1, 135.9, 132.4, 130.2, 128.0, 113.2, 32.3, 31.5, 27.5, 25.8, 10.5; IR (film) 3068 (m), 3047 (m), 2897 (s), 2840 (m), 1961 (w), 1890 (w), 1826 (w), 1639 (m), 1490 (w), 1429 (s), 1275 (m), 1112 (s), 1003 (m), 911 (s), 785 (m), 744(s), 703 (s) cm−1; MS (FAB) m/e (rel. intensity) 357 (MH+, 11), 356 (11), 355 (25), 301 (18), 279 (13), 237 (36), 227 (11), 225 (18), 221 (14), 215 (14), 213 (18), 212 (12), 211 (100), 209 (9), 207 (15); HRMS (FAB) calcd for C20H23S2Si: 355.1010 (MH+−2). found: 355. 1020. Anal. Calcd for C20H24S2Si: C, 67.36; H, 6.78. Found: C, 67.08; H, 6.78.
