Reaction Steps
In a 10 mL flask with 4-benzyloxy-but-2-enoic acid ethyl ester (0.1 g, 0.45 mmol) inside, dry CH2Cl2 3 mL was added under argon. This was cooled to 0° C., TMSOTf (0.08 mL, 0.45 mmol) was added drop by drop. After stirring for 10 min, ethyl α-fluoro silyl enol ether (0.08 g, 0.45 mmol) was added dropwisely at 0° C. This was left stirring at 0° C. for 1.5 hr, at room temperature for 5 hr and refluxing for 25 hr. After cooling to room temperature, H2O was added and the aqueous phase was extracted with CH2Cl2 three times and the combined organic phase was dried over MgSO4 and the solvent was evaporated to give an oily product which was purified by silica gel flash chromatography (Hexane:EtOAc=6:1, Rf=0.42) to give 87.7 mg (59.3%) of the product. 1H NMR (CDCl3, 400 MHz): δ 1.18-1.32 (m, 6H), 2.32-2.54 (m, 2H), 2.77-2.98 (m, 1H), 3.44-3.57 (m, 2H), 4.07-4.30 (m, 4H), 4.45-4.54 (m, 2H), 4.96-5.09 (dd, J=48, 3.2, 1H, minor isomer), 5.10-5.22 (dd, J=48, 3.2, 1H, major isomer), 7.24-7.36 (m, 5H). 13C NMR (CDCl3, 100 MHz): δ 14.23, 30.96-31.02 (d, J=6.0), 32.63, 38.51-38.70 (d, J=19), 60.87, 61.73, 67.94-67.99 (d, J=5.0), 68.60-68.63 (d, J=3.0), 73.29-73.35 (d, J=6.0), 86.96-88.81 (d, J=185), 87.54-89.40 (d, J=186), 127.77, 127.87, 128.54, 137.99-138.04 (d, J=5.0), 168.92-169.42 (t, J=25.8), 171.80-171.85 (d, J=5.0). MS (FAB): expected for C17H23FO5 (M+H)+ 327.36. Found 327.16020. IR (neat) νmax 2983, 2938, 2907, 2872, 1760, 1734, 1455, 1374, 1208, 1183, 1090, 1029, 739, 699.
