A solution of 1.1 eq. of 20, 1.1 eq. of pyridine, and 0.07 eq. of DMAP in CH2Cl2 was cooled to 0° C. While stirring, a solution of 1.0 eq. of 59 in CH2Cl2 was added. The reaction solution was allowed to warm to rt. After a time sufficient for reaction completion, the reaction solution was concentrated by rotary evaporation and 1.0 M HCl was added. The acidified solution was extracted with EtOAc. The combined organic extracts were washed with saturated aqueous NaHCO3, followed by drying over MgSO4 and filtering. The filtrate was rotary evaporated and the crude material was purified by flash chromatography on silica gel using a mixture of EtOAc-hexanes as eluant to give 60.
