N,N-diisopropylethylamine (0.13 ml, 0.76 mmol) was dropwise added to a solution of allyl (5R,6S)-2-diphenoxyphosphoryloxy-6-[(R)-1-hydroxyethyl]-1-carbapen-2-em-3-carboxylate (369 mg, 0.76 mmol) and (2R,4S)-N-allyloxycarbonyl-4-mercapto-2-(2-pyrrolidon-3-ylmethyl)pyrrolidine (216 mg, 0.76 mmol) in acetonitrile (5.6 ml) under cooling with ice. The reaction mixture solution was stirred at the same temperature for one hour and further stirred at 5° C. for 16 hours. Ethyl acetate (60 ml) was added to the reaction solution. The mixture was washed sequentially with a saturated sodium hydrogen carbonate aqueous solution and a saturated sodium chloride aqueous solution, then dried over anhydrous sodium sulfate and concentrated. The residue was purified by silica gel flash column chromatography (Wakogel™ C-300, 40 ml, acetone-ethyl acetate 2:3). The fraction containing the desired product was concentrated to obtain allyl (5R,6S)-2-[(2R,4S)-N-allyloxycarbonyl-2-(2-pyrrolidon-3-ylmethyl)pyrrolidin-4-ylthio]-6-[(R)-1-hydroxyethyl]-1-carbapen-2-em-3-carboxylate (303 mg, yield: 76.7%) in the form of foam.
