A solution of 17.9 g (30 mmol) of p-nitrobenzyl(4R,5S,6S)-3-(diphenoxy-phosphoryloxy)-6-[(1R)-1-hydroxyethyl]-4-methyl-7-oxo-1-aza-bicyclo[3.2.0]hept-2-ene-2-carboxylate in 150 ml of acetonitrile was added into a flask and the reaction mixture was cooled below −10° C. Then diisopropylethylamine (8 mL) and a solution of the intermediate (I-1) prepared by Intermediate Example 1 (10.1 g, 31 mmol) in 100 mL of acetonitrile were added and the reaction mixture was stirred at 0° C. for 15 hours. After the completion of the reaction, ethyl acetate (400 mL) was added to the reaction mixture for dilution and the mixture was washed successively with water and saturated brine. The organic layer was dried and concentrated to give 14.7 g (yield: 73.1%) of p-nitrobenzyl (4R,5S,6S)-3-[(2S,4S)-2-formyl[[furan-2-ylmethyl]amino]-1-(tert-butoxycarbonyl)pyrrolidine-4-yl]thio-6-[(1R)-1-hydroxyethyl]-4-methyl-7-oxo-1-aza-bicyclo[3.2.0]hept-2-ene-2-carboxylate, which is the intermediate II-1.
