A solution of 567 mg (1.09 mmol) (2S,4R)-2-(2,4,5-trifluoro-benzyloxymethyl)-4-tritylsulfanyl-pyrrolidine, 302 mg (1.09 mmol) sulfamic acid 2,4,6-trichloro-phenyl ester [Hedayatullah, M. & Hugueny, J. Phosphorus, Sulfur Silicon Relat. Elem. (1991), 61(1–2), 19–25.] and 0.15 ml triethylamine in 2 ml CH2Cl2 was heated for 1 h at reflux, evaporated and purified by flash column chromatography on silica gel with hexane/EtOAc (9:1 to 1:1) to give 286 mg (44%) (2S,4R)-2-(2,4,5-Trifluoro-benzyloxymethyl)-4-tritylsulfanyl-pyrrolidine-1-sulfonic acid amide. [Hedayatullah, M. & Hugueny, J. Phosphorus Sulfur (1985), 25(1), 33-8.] MS: 621 (M+Na+).
