A solution of bromine (0.166 mL, 0.0032 mol) in 1 mL of CCl4 was added dropwise to a stirred solution of 20 (1.0 g, 0.0032 mol) and pyridine (0.314 mL, 0.0039 mol) in dry CHCl3 (30 mL) at 0° C. The reaction mixture was stirred at 0° C. for 1 h and then neutralized with 10 mL of a mixture of sodium bicarbonate-sodium:thiosulfate (1:1). The organic layer was separated and further extracted with dichloromethane (3×10 mL) and the combined organics dried and concentrated in vacuo. The residue was subjected to flash chromatography (30% EtOAc-70% hexanes) to give 0.97 g (78%) of the desired material 21. 1H NMR CDCl3 8.9 (s, 1H), 8.55 (d, 1H), 8.4 (d, 1H), 8.0 (d, 1H), 7.9 (d, 1H), 7.4 (dd, 1H), 7.2 (s, 1H), 0.9 (s, 9H), 0.5 (s, 6H).
