0.19 g (0.0047 mole) of sodium hydride (as a 60% w/w dispersion in mineral oil) and 0.89 g (0.0063 mole) of methyl iodide were added, in that order, to a solution of 1.2 g (0.0031 mole) of 1-t-butoxycarbonyl-3-dibenzylamino-4-hydroxypyrrolidine [prepared as described in Step (1) above] dissolved in 10 ml of tetrahydrofuran. The mixture was then stirred at room temperature for 5 hours. At the end of this time, water was added to the reaction mixture, which was then extracted with ethyl acetate. The ethyl acetate extract was washed with water, dried and concentrated by evaporation under reduced pressure. The residue was subjected to column chromatography through silica gel, eluted with a 5:95 by volume mixture of ethyl acetate and toluene, to give 0.99 g of 1-t-butoxycarbonyl-3-dibenzylamino-4-methoxypyrrolidine as a colorless oil.
