To a solution of the compound of step 1 (2.52 g, 6.66 mmol) in 45 ml of acetone were added potassium carbonate (5.522 g, 39.96 mmol) and iodomethane (1.24 ml, 19.98 mmol) and the solution was stirred at room temperature overnight. The mixture was filtered and the filtrate was concentrated to dryness. The residue was dissolved in EA, washed twice with brine, dried over sodium sulfate, filtered and evaporated under reduced pressure. The residue was purified by chromatography on silica gel (cyclohexane/EA, 100:0, then 85:15) to give 2.334 g of the title compound as a colorless oil.
