The recovered intermediate (20a) (8.5 g, 33 mmol, 1.0 eq) was dissolved into 70 mL pyridine containing potassium hydroxide (2.1 g, 37 mmol, 1.1 eq) and the mixture was chilled in an ice bath. Tosyl chloride (7.1 g, 37 mmol, 1.1 eq) was added and the mixture was stirred at 0° C. for 2 hours then refrigerated overnight. The mixture was filtered and the filtrate was concentrated under reduced pressure. The recovered residue was dissolved into 300 mL EtOAc, washed with 2×200 mL 1M H3 PO4, saturated bicarbonate, and saturated aqueous NaCl. The organic was dried over MgSO4 and concentrated under reduced pressure to yield intermediate (20b) (10.3 g) as a pale brown oil.
