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14 Five-Carbon Ring Expansion: In a 100-mL round-bottomed flask, a solution of 3c (114.4 mg, 0.386 mmol) in anhyd CH2Cl2 (40 mL) was prepared at -60 °C under Ar. To this was added 2,6-lutidine (0.13 mL) and Tf2O (0.1 mL) successively with stirring; stirring was continued for 1 h at the same temperature. A sat. aq solution of NH4Cl was added and the mixture was extracted with CH2Cl2. The organic layer was dried and the solvent was evaporated to afford an oily residue, which was chromatographed on silica gel (3 g; hexane-EtOAc, 95:5) to give 11 (43.7 mg, 69%).
15 Compound 11: Oil. IR (neat): 1657 cm-1. 1H NMR (CDCl3): δ = 1.47-1.80 (4 H, m), 2.01-2.10 (2 H, m), 2.21-2.30 (4 H, m), 2.61-2.67 (2 H, m), 5.03 (1 H, dt, J = 15.5, 7.6 Hz, CH=CH), 5.31 (1 H, dt, J = 15.5, 7.7 Hz, CH=CH), 5.90 (1 H, d, J = 16.2 Hz, CH=CHCO), 6.31 (1 H, dt, J = 16.2, 7.5 Hz, CH=CHCO). 13C NMR (CDCl3): δ = 27.28, 28.53, 30.07, 34.21, 34.45, 38.59, 128.81, 132.01, 137.38, 156.96, 202.88. HRMS: m/z calcd for C11H16O (M+): 164.1201; found: 164.1235.
16 Compound 15: Oil. IR (neat): 1658 cm-1. 1H NMR (CDCl3): δ = 0.87-0.96 (1 H, m), 0.89 (9 H, s, t-Bu), 1.15 (1 H, dddd, J = 2.3, 3.5, 12.5, 14.6 Hz), 1.54 (1 H, dt, J = 12.5, 10.0 Hz), 1.93 (1 H, ddt, J = 1.4, 9.5, 12.5 Hz), 2.07 (1 H, ddt, J = 5.6, 14.6, 2.5 Hz), 2.17-2.37 (3 H, m), 2.44-2.54 (2 H, m), 2.81 (1 H, dt, J = 2.5, 11.3 Hz), 5.08-5.20 (1 H, m, CH=CH), 5.30 (1 H, br dt, J = 15.7, 7.5 Hz, CH=CH), 5.90 (1 H, br d, J = 16.1 Hz, CH=CHCO), 6.45 (1 H, ddd, J = 6.0, 9.4, 16.1 Hz, CH=CHCO). 13C NMR (CDCl3): δ = 27.14 (3 C), 30.07, 31.07, 34.20, 34.42, 35.03 (br), 38.86, 49.56, 129.12 (br), 132.31, 136.33, 156.27, 202.97. HRMS: m/z calcd for C15H24O (M+): 220.1827; found: 220.1812
17 Compound 19: Oil. IR (neat): 1672 cm-1. 1H NMR (CDCl3): δ =1.64-1.74 (4 H, m), 2.17-2.31 (6 H, m), 2.53-2.57 (2 H, m), 5.36-5.43 (1 H, m, CH=CH), 5.52 (1 H, ddt, J = 10.5, 8.2, 1.7 Hz, CH=CH), 6.19 (1 H, dt, J = 16.2, 1.5 Hz, CH=CHCO), 6.80 (1 H, dt, J = 16.2, 6.7 Hz, CH=CHCO). 13C NMR (CDCl3): δ = 22.92, 25.10, 25.15, 28.50, 32.10, 39.81, 128.81, 129.73, 131.57, 151.11, 203.56. HRMS: m/z calcd for C11H16O (M+): 164.1201; found: 164.1221.