Reaction Steps
A solution of anhydrous DMSO (0.34 mL, 0.37 g, 4.78 mmol) in dry DCM (4 mL) was added dropwise over a period of 5 minutes to a stirred solution of oxalyl chloride (1.20 mL of a 2M solution in DCM, 2.39 mmol) under a nitrogen atmosphere at −60° C. (liq N2/CHCl3). After stirring at −55° C. for 15 minutes, a slurry of the substrate 42 (962 mg, 0.80 mmol) in dry DCM (8 mL) was added dropwise over a period of 10 minutes to the reaction mixture. After stirring for a further 1 h at −55° C., a solution of TEA (1.56 mL, 1.13 g; 11.2 mmol) in dry DCM (4 mL) was added dropwise over a period of 5 minutes to the reaction mixture. The reaction mixture was allowed to warm to 0° C. and then diluted with DCM (50 mL). The organic solution was washed with cold 1N HCl (20 mL), H2O (20 mL), brine (30 mL) and dried (MgSO4). Filtration and evaporation of the solvent in vacuo afforded the crude product which was purified by flash column chromatography (50:50 v/v Hexane/EtOAc) to afford bis-ketone 43 as a foam (550 mg, 57%): 1H NMR (400 MHz, CDCl3) δ 7.25 (s, 2H), 6.76 (s, 2H), 5.82 (d, 2H, J=9.3 Hz), 5.22 (d, 2H, J=12.0 Hz), 4.32 (d, 2H, J=20.4 Hz), 4.22 (d, 2H, J=12.0 Hz), 4.17-4.08 (m, 4H), 4.03-3.89 (m, 10H), 2.96 (dd, 2H, J=19.6, 10.2 Hz), 2.56 (dd, 2H, J=19.6, 2.8 Hz), 1.99-1.92 (m, 4H), 1.72-1.64 (m, 2H), 0.86 (s, 18H), 0.24 and 0.23 (s×2, 12H); 13C NMR (100 MHz, CDCl3) δ 207.7, 168.0, 153.8, 151.0, 149.5, 127.9, 124.4, 114.1, 110.8, 95.2, 87.5, 74.8, 68.8, 58.9, 56.2, 52.9, 40.4, 28.7, 25.6, 22.8 17.8, −4.12 and −5.31.
