2,2-Dimethoxypropane → 7-(2,2-Dimethyl-1,3-dioxolan-4-yl)chroman-4-one

To a mixture of 7-(1,2-dihydroxyethyl)chroman-4-one (Preparation 60A, 0.950 g, 4.56 mmol) and 2,2-dimethoxypropane (1.68 mL, 13.7 mmol) in acetone (20 mL) at room temperature was added (1R)-(−)-camphorsulfonic acid (0.212 g, 0.913 mmol). The reaction mixture was stirred at room temperature overnight. The reaction mixture was quenched with a saturated aqueous solution of sodium bicarbonate and concentrated under reduced pressure. The aqueous residue was diluted with ethyl acetate, washed with a saturated aqueous solution of sodium bicarbonate, and brine. The organic layer was collected, and the aqueous layer was extracted with ethyl acetate. The combined organic layers were dried over anhydrous sodium sulfate and concentrated to give the crude product as a dark oil, which was purified by flash silica gel chromatography using a 20% mixture of ethyl acetate and hexane to afford 7-(2,2-dimethyl-1,3-dioxolan-4-yl)chroman-4-one (0.657 g, 2.65 mmol, 58% yield) as a clear, colorless oil. The product had an HPLC ret. time=2.14 min.−Column: Chromolith SpeedROD 4.6×50 mm (4 min.); Solvent A=10% MeOH, 90% H2O, 0.1% TFA; Solvent B=90% MeOH, 10% H2O, 0.1% TFA. LC/MS M+1=248.9.