To a cooled solution (0° C.) of #196 (4.0 g, 9.4 mmol, 1 eq.) in dichloromethane (40 mL) was added dropwise pyridine (2.95 g, 37.6 mmol, 4 eq.) followed by a solution of pentafluorophenyl trifluoroacetate (3.9 g, 13.6 mmol, 1.4 eq.) in dichloromethane (5 mL). The mixture was stirred at room temperature for one hour, and the solvent was concentrated in vacuo. The residue was purified by silica gel chromatography (Gradient: 1 to 10% methanol in dichloromethane) to afford compound #197 (4.5 g, 81.2% (over three steps) as white solid.
