A 250-mL single-neck round-bottomed flask equipped with a magnetic stirrer and reflux condenser was purged with nitrogen and charged with 10 (6.55 g, 15.7 mmol) and anhydrous methylene chloride (60 mL). To the resulting suspension phosphorous oxybromide (9.95 g, 34.3 mmol) and N,N-dimethylformamide (190 mg, 2.60 mmol) were added and the reaction was then heated at reflux for 4 h. After this time the reaction mixture was poured into a 10% aqueous potassium carbonate solution (100 mL) and methylene chloride (75 mL) was added. The resulting suspension was filtered through. Celite 521 and the layers separated. The aqueous layer was extracted with methylene chloride (2×100 mL) and the combined organic layers were dried over sodium sulfate, filtered and concentrated under reduced pressure. The resulting residue was triturated with a 2:1 solution of ethyl acetate/hexanes (10 mL) and filtered. The filter cake was washed with the 2:1 ethyl acetate/hexanes solution (20 mL) and dried to a constant weight under vacuum to afford a 50% yield (3.59 g) of 11 as a light yellow solid: mp 240-241° C., 1H NMR (500 MHz, DMSO-d6) δ 9.86 (s, 1H), 7.98 (s, 1H), 7.67 (s, 1H), 7.28 (m, 3H), 3.57 (s, 3H), 2.76 (t, 2H, J=5.5 Hz), 2.61 (t, 2H, J=5.5 Hz), 2.18 (s, 3H), 1.76 (m, 4H); MS (ESI+) m/z 458 (M+H).
