To a solution of (2S,4S)-2-mesyloxymethyl-N-(p-nitrobenzyloxycarbonyl)-4-tritylthiopyrrolidine (9.6 g, 15.2 mmol) in THF (190 ml), thiophenol (2.34 ml, 22.8 mmol) and 1,8-diazabicyclo[5.4.0]-7-undecene (3.4 ml, 22.8 mmol) were successively added dropwise in a nitrogen stream under cooling with ice. The reaction solution was stirred at room temperature for 15 minutes and the solvent was distilled off. To the residue, ethyl acetate was added. The organic layer was washed with 1N aqueous potassium hydrogensulfate and saturated aqueous sodium chloride, dried over anhydrous sodium sulfate, and concentrated in vacuo. The resulting residue was subjected to silica gel column chromatography (Wakogel™ C-300 heptane-ethyl acetate 3:1) to give (2S,4S)-N-(p-nitrobenzyloxycarbonyl)-2-phenylthiomethyl-4-tritylthiopyrrolidine (9.24 mg, yield: 94%) as a yellow oily substance.
