The same operation as in Reference Example 4-1) was carried out by using (2S,4S)-N-allyloxycarbonyl-2-hydroxymethyl-4-tritylthiopyrrolidine (the compound obtained in Reference Example 3-1); 1.5 g, 3.26 mmol), dimethyl sulfoxide (0.65 ml, 9.14 mmol), oxalyl chloride (0.42 ml, 4.90 mmol), triethylamine (2 ml, 14.9 mmol), N-allyloxycarbonyl-N'-(diethylphosphonoacetyl)piperazine (1.24 g, 3.92 mmol) and 60% sodium hydride (130 mg, 3.26 mmol), followed by flash column chromatographic purification on silica gel (Wakogel® C-300, 40 ml, elution with ethyl acetate) to give the title compound (1.97 g, 92.6% yield).
