To a solution of sodium hydride (60% in oil, 816 mg) and methyl iodide (4.9 ml) in tetrahydrofuran (50 ml), which was heated at 50°-60° C., was added dropwise a solution of (2S,4R)-4-(tert-butyldimethylsilyloxy)-1-(tert-butoxycarbonyl)-2-hydroxymethylpyrrolidine (5.2 g) in tetrahydrofuran (10 ml). After stirring for two hours, the reaction mixture was poured into a mixture of water and ethyl acetate, the organic layer was separated, washed in turn with saturated aqueous sodium sulfite and brine, dried over magnesium sulfate. Evaporation of the solvent gave an oil, which was chromatographed on silica gel (200 ml) eluting with a mixture of hexane and ethyl acetate (4:1, V/V) to give (2S,4R)-4-(tert-butyldimethylsilyloxy)-1-(tert-butoxycarbonyl)-2-methoxymethylpyrrolidine (4.5 g).
