A solution of trifluoromethanesulfonic acid anhydride (3.5 g, 2.1 ml, 12.4 mmol, 2 eq.) in anhydrous methylene chloride (10 ml) is added dropwise to a stirred solution of sodium 3-(4-chlorophenyl)-2-isopropyl-8-methoxy-4-oxo-4H-chromen-7-olate (2.28 g, 6.22 mmol; prepared by treating 3-(4-chlorophenyl)-7-hydroxy-2-isopropyl-8-methoxy-chromen-4-one with a molar equivalent of sodium hydride in dry tetrahydrofuran), pyridine (2 g, 2.1 ml, 25.5 mmol, 4.1 eq.) and 4-dimethylaminopyridine (0.076 g, 0.62 mmol, 0.1 eq.) in anhydrous methylene chloride (60 ml) at 0° C. After stirring overnight, the solution is washed with 1M HCl solution. The organic phase is dried over anhydrous magnesium sulfate and filtered, and the solvent is removed by evaporation in vacuo to afford the title compound as a brown foam. The product is used in the next step without further purification.
