C(Cl)(=O)C(Cl)=O.CS(C)=O.[Br:11][C:12]1[CH:17]=[CH:16][CH:15]=[CH:14][C:13]=1[S:18]([C:21]1[CH:26]=[CH:25][C:24]([CH2:27][OH:28])=[CH:23][CH:22]=1)(=[O:20])=[O:19].C(N(CC)CC)C>ClCCl>[Br:11][C:12]1[CH:17]=[CH:16][CH:15]=[CH:14][C:13]=1[S:18]([C:21]1[CH:22]=[CH:23][C:24]([CH:27]=[O:28])=[CH:25][CH:26]=1)(=[O:20])=[O:19]To a solution of oxalyl chloride (2.7 mL, 30.58 mmol) in dichloromethane (73 mL) at −78° C. under nitrogen was added dimethylsulfoxide (4.4 mL, 56.88 mmol) over 30 minutes. The mixture was stirred vigorously for a further 30 minutes then a solution of {4-[(2-bromophenyl)sulfonyl]phenyl}methanol (Step 3, 4.0 g, 12.23 mmol) in dichloromethane (24 mL) was added over 15 minutes. The reaction was stirred at −78° C. for 1 hour. Triethylamine (11.99 mL, 85.61 mmol) was added and stirring continued at −78° C. for 1 hour then the reaction was allowed to warm to room temperature. The pale yellow solution was diluted with dichloromethane, washed with sodium hydrogencarbonate solution, water and brine, dried over MgSO4 and evaporated in vacuo. The residue was purified by flash column chromatography on silica, eluting with 30% ethyl acetate/isohexane, to give 4-[(2-bromophenyl)sulfonyl]benzaldehyde (3.41 g, 85%). δH (400 MHz, d6 DMSO): 10.09 (1H, s), 8.37 (1H, dd, J=1.7, 7.9 Hz), 8.10 (4H, s), 7.83 (1H, dd, J=1.2, 7.9 Hz), 7.75 (1H, td, J=1.4, 7.7 Hz), 7.66 (1H, td, J=1.8, 7.7 Hz).
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