To a solution of the product from step 2 (2.0 g, 6.82 mmol) in anhydrous DMF (50 mL) was added dry K2CO3 (4.6 g, 33 mmol) and allowed to stir for 15 min. Propargyl bromide (1.214 g, 10.20 mmol) in anhydrous DMF (10 mL) was added and the reaction mixture stirred at 50° C. for 6 h, then at rt for 48 h. The reaction mixture was concentrated, taken up in EtOAc, washed with water, dried over anhydrous MgSO4 and the solvent removed in vacuo. The product was purified by silica gel flash chromatography using EtOAc/hexane to obtain the title compound (2.0 g, 88%).
