To (+)-3-hydroxy-N-(benzyloxycarbonyl)morphinan (33.0 g, 87.4 mmol) and cesium carbonate (28.5 g, 87.4 mmol) in acetone (450 mL) was added iodomethyl isopropyl carbonate (21.3 g, 87.4 mmol) (see Rigel Pharmaceuticals, Inc. US2006/247287 A1, Appl.; US2006-381215 (2006 May 2)) at room temperature. The reaction mixture was stirred vigorously at room temperature overnight. The acetone was then removed by rotary evaporation under vacuum. To the residue was added saturated NaHCO3 solution. The mixture was extracted with EtOAc (300 mL×2). The combined organics were washed with 1N HCl solution (300 mL), dried over MgSO4, filtered, and evaporated under vacuum to provide the title compound (42.0 g, 97%) as a yellow gum.
