Reaction Steps
Under N2 atmosphere and cooling with an ice bath, 3,4-dihydro-2H-pyran (33.86 g, 0.40 mol) was added dropwise to a stirred solution of 206d (88.0 g, 0.32 mol) and p-toluenesulfonic acid hydrate (0.05 g, 0.03 mmol) in CH2Cl2 (700 mL). After the addition, the reaction mixture was allowed to warm to room temperature and stirred overnight. The solution was filtered through aluminum oxide (160 g) and the aluminum oxide was washed with CH2Cl2 (800 mL). The filtrate was concentrated in vacuo and purified by flash chromatography on silica gel (hexanes/ethyl acetate=10/1) to give 207d (80.0 g, 70%) as an oil. 1H NMR (CDCl3): δ 7.40-7.14 (m 10H), 4.53 (t, 1H, J=3.4), 4.49 (t, 1H, J=3.4), 3.82 (d, 1H, J=9.4), 3.81 (t, 1H, J=9.4), 3.76-3.60 (m, 2H), 3.44 (m, 2H), 3.36 (d, 2H, J=9.4), 3.33 (t, 4H, J=7.0), 1.90-1.42 (m, 14H), 1.79 (t, 4H, J=6.8), 1.37 (s, 6H), 1.34-1.10 (m, 6H). 13C NMR (CDCl3=77.0 ppm): δ 145.67, 127.91, 127.91, 126.39, 126.37, 125.7, 98.95, 98.81, 76.11, 76.07, 62.78, 61.77, 61.66, 41.88, 41.78, 37.93, 37.75, 33.50, 33.44, 30.59, 30.44, 25.41, 25.37, 22.77, 22.71, 22.62, 19.65, 19.23, 19.15. HRMS (LSIMS, nba): Calcd for C15H28BrO2 (MH+): 355.1272, found: 355.1272.
