[Na].[S:2]([C:6]1[CH:13]=[CH:12][CH:11]=[CH:10][C:7]=1[CH:8]=[O:9])(O)(=[O:4])=[O:3].S(Cl)([Cl:16])=O>CN(C)C=O.C(OCC)C.O>[CH:8]([C:7]1[CH:10]=[CH:11][CH:12]=[CH:13][C:6]=1[S:2]([Cl:16])(=[O:4])=[O:3])=[O:9]To a solution of 2-sulfobenzaldehyde sodium salt (2.0 g, 9.6 mmol) in 0.8 mL of dry N,N-dimethylformamide was added thionyl chloride (7.0 mL, 96 mmol) under nitrogen at 0° C. After being stirred at 100° C. for 3 min, the reaction mixture was diluted with diethyl ether and water at 0° C., successively. The separated organic layer was washed with water, brine, and dried over MgSO4. After filtration, the filtrate was concentrated in vacuo to obtain crude 2-formylbenzenesulfonyl chloride (0.75 g). To a solution of the above product, pyridine (0.57 mL, 7.0 mmol), and N,N-dimethylaminopyridine (21 mg, 0.17 mmol) in 3.5 mL of dry dichloromethane was added dimethylamine/ethanol solution (0.62 mL, 5.6 M, 3.5 mmol) at 0° C. After being stirred at room temperature overnight, the reaction mixture was diluted with ethyl acetate. The solution was washed with 1N HCl, saturated NaHCO3 aqueous solution, brine, and dried over MgSO4. After filtration, the filtrate was concentrated in vacuo, and the residue was purified with silica gel column chromatography (hexane/ethyl acetate=80/20 to 50/50) to obtain the title compound as a colorless oil (280 mg, 2 steps 14%).
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