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Prepared according to the literature:
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5
gem
-Difluorocyclopropenyl Ketone 2a: α,β-Acetylenic ketone 1a (0.73 g, 3.55 mmol), NaF (19 mg, 10 mol%), and DG (2 mL) were added under a N2 atmosphere to a Schlenk tube charged with a magnetic stirring bar and a pressure-equalized dropping funnel. After the mixture was heated to about 120 °C (oil bath), TFDA (2.71 g, 3 equiv) was added dropwise. The mixture was stirred at this temperature for about 3 h. Then the mixture was cooled to r.t. and purified by flash column chromatography on silica gel; yield: 0.67 g (89%) [recovered 1a: 0.12 g (conversion 83%)]; solid; mp, 80-85 °C. IR (film): 1759, 1681, 1650, 1597,1577, 1494, 1450, 1313, 1299, 1226 cm-1. 1H NMR (CDCl3, 300 MHz): d = 8.15-8.18 (m, 2 H), 8.01-8.05 (m, 2 H), 7.52-7.72 (m, 6 H). 19F NMR (CDCl3, 282 MHz): δ = -103.74 (s, 2 F). MS: m/z (%) = 256 (M+, 11.37), 228 (6.99), 151 (6.11), 105 (100), 77 (40.21). Anal. Calcd for C16H10OF2: C, 75.00; H, 3.93; F, 14.83. Found: C, 75.06; H, 3.82; F, 14.86. X-ray crystallographic data for 2a: crystal system, monoclinic; space group, P2 (1)/n; unit cell dimensions: a = 8.4778 Å, b = 9.0567 Å, c = 17.022 Å, α = 90°, β = 103.462°, γ = 90°, Z = 4, F(000) = 528, R1 = 0.0623, wR2 = 0.1635 (all data), CCDC No. 287907.
6a
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7
Difluorinated Dihydrofuran 3c: To a solution of 2c (50 mg, 0.18 mmol) in MeOH (5 mL) was added 10% aq K2CO3 (0.1 mL). The mixture was stirred at r.t. and the progress of the reaction was monitored by 19F NMR spectroscopy. When the reaction had reached completion, H2O (10 mL) was added and the reaction was extracted with EtOAc (3 × 10 mL). The combined organic layer was dried over MgSO4. After the solvent was removed under reduced pressure, the residue was purified by flash column chromatography on silica gel; yield: 45 mg (80%); white solid. IR (film): 3117, 2935, 1650, 1616, 1579, 1515, 1494, 1452, 1343, 1285, 1271, 1149, 1071, 1047, 968, 731 cm-1. 1H NMR (CDCl3, 300 MHz): δ = 2.40 (s, 3 H), 3.39 (s, 3 H), 5.69 (s, 1 H), 7.23-7.50 (m, 7 H), 7.75-7.80 (m, 2 H). 19F NMR (CDCl3, 282 MHz): δ = -82.27 (d, J = 247 Hz, 1 F), -111.31 (d, J = 248 Hz, 1 F). MS: m/z (%) = 302 (M+, 10.13), 283 (12.21), 282 (10.24), 271 (24.50), 243 (14.40), 177 (9.80), 152 (100), 151 (65.65), 119 (59.20), 105 (93.95), 84 (99.36). Anal. Calcd for C18H16O2F2: C, 71.51; H, 5.33. Found: C, 71.52; H, 5.64.
8 X-ray crystallographic data for 3a: C17H14F2O2, M 288.28; monoclinic; space group, P2 (1)/n; unit cell dimensions: a = 13.6673 Å, b = 7.1944 Å, c = 14.8156 Å, α = 90°, β = 92.034°, γ = 90°, Z = 4, Dcalcd = 1.315 g/cm3, F(000) = 600, R1 = 0.0812, wR2 = 0.1246, CCDC No. 287908.
