p-Toluenesulfonic acid monohydrate → Ethyl 2-(1,3-dioxo-1,3,4,5,6,7-hexahydro-isoindol-2-ylmethyl)-3-oxo-butyrate

Ethyl 3-(1,3-dioxo-1,3,4,5,6,7-hexahydro-isoindol-2-yl)-2-(2-methyl-[1,3]dioxolan-2-yl)propionate (866 mg, 2.57 mmol) was dissolved in a a solvent mixture of acetone/water (v/v=5/1), and a catalytic amount of p-toluenesulfonic acid monohydrate (190 mg, 0.76 mmol) was then added to the obtained solution. The resulting mixture was then refluxed at 80° C. for 4 days. After the reaction was completed, the reaction mixture where white solid were formed was washed with water. Acetone was removed by a vacuum evaporation, and the residue was extracted with dichloromethane. The combined organic layer was dried with anhydrous sulfate and then distilled under a reduced pressure in order to remove dichloromethane. The desired product was obtained (421 mg, 56%) by performing column chromatography (eluent: n-hexane/ethyl acetate=3/1). Rf=0.54 (eluent: n-hexane/ethyl acetate=1/1)