Reaction Steps
A 1 M solution of sodium bis(trimethylsilyl)amide in tetrahydrofuran (6.55 L, 6.55 mol) was added over 20 minutes to a solution of (1R,2S)-2-benzyl-1-(4-bromo-2-fluoro-phenyl)-propane-1,3-diol (1975 g, 5.82 mol) in dimethyl sulfoxide (9.88 L) at ambient temperature. The mixture was slowly heated to 60° C. under aspirator vacuum to displace the tetrahydrofuran from the reaction mixture, and then heated at 60 to 65° C. for 5 hours under aspirator vacuum at which point the reaction was judged to be complete according to thin layer chromatography (hexanes/ethyl acetate, 2:1). The reaction mixture was cooled to ambient temperature and quenched by adding water (10 L) followed by 1 N aqueous hydrochloric acid (10 L). The resulting tan suspension was filtered, washed with water (2 L), and dissolved in ethyl acetate (12 L). This solution was washed with water (two times 12 L), concentrated to a low volume, dissolved in isopropyl ether (4 L), and concentrated under atmospheric pressure at 50 to 60° C. to 1.0 L, at which point solids began to precipitate. The resulting suspension was cooled to ambient temperature, stirred for 12 hours, concentrated to one-half its volume, cooled to 0 to 5° C., and filtered giving 916 g (49%) of (3S,4R)-3-benzyl-7-bromo-chroman-4-ol as a white solid. The filtrate was concentrated to a dark oil (906 g), dissolved in isopropyl ether (1.5 L) at reflux, cooled to ambient temperature, stirred, and filtered yielding an additional 82 g of solid. The filtrate was concentrated and chromatographed on silica gel (60-230 mesh) eluting with 3:1 hexanes/ethyl acetate. Product-rich fractions were concentrated and recrystallized from isopropyl ether yielding an additional 82 g of solid. The total yield of (3S,4R)-3-benzyl-7-bromo-chroman-4-ol was 1080 g (58%): 1H NMR (400 MHz, CDCl3) δ7.29-7.33 (m, 2H), 7.21-7.25 (m, 1H), 7.15-7.19(m, 3H), 7.06-7.09 (m, 2H), 4.44 (bs, 1H), 4.21 (dd, J=2.6, 11.3 Hz, 1H), 3.97 (dd, J=4.5, 11.3 Hz, 1H), 2.68 (dd, J=6.5, 13.8 Hz, 1H), 2.51 (dd, J=9.1, 13.8 Hz, 1H), 2.18-2.23 (m, 1H), 1.85 (d, J=4.3 Hz, 1H); IR 3274 (br), 3181 (br), 1598, 1573, 1493, 1480, 1410, 1219, 1070, 1052, 1023, 859, 700 cm−1; mp 143.5-144.0° C.
