To a 15 ml sealable vial was added a 60:40 mixture of (4R,5R)-4-(2-bromo-5-fluoropyridin-4-yl)-5-(4-fluorophenyl)oxazolidin-2-one (50 mg, 0.141 mmol) and its regioisomer in triethylamine (3 mL). To this suspension was added 3-ethynyl-5-fluoropyridine (22.17 mg, 0.183 mmol), triphenylphosphine (11.08 mg, 0.042 mmol) and copper(I) iodide (0.536 mg, 2.82 mmol). The solution was degassed with nitrogen for 20 min, then bis(triphenylphosphine)palladium(II) chloride (1.976 mg, 2.82 mmol) was quickly added and the vial was sealed, heated to 90° C., and allowed to stir overnight. The next day the suspension had turned homogeneous and the reaction was cooled to room temperature and the solvent was evaporated in vacuo. The crude residue was purified by reverse phase chromatography to isolate a single peak (4R,5R)-5-(5-fluoro-2-((5-fluoropyridin-3-yl)ethynyl)pyridin-4-yl)-4-(4-fluorophenyl)oxazolidin-2-one (18.4 mg, 0.046 mmol, 49.8% yield). This single peak was still a mixture of the regioisomers. This single peak was a 65:35 mixture of regioisomers and was subsequently purified by chiral supercritical fluid chromatography Chiralpak AD-H column, 4.6×250 mm, 5 um particle size mobile phase: 35% MeOH in CO2 (w/0.1% diethylamine) column temp: 35 C flow rate: 2 mL/min., affording 1H-NMR (CDCl3, 400 MHz) δ 8.67 (s, 1H), 8.54 (s, 1H), 8.51 (d, J=4.0, 1H), 7.79 (d, J=4.0, 1H), 7.64-7.60 (m, 1H), 7.42-7.39 (m, 2H), 7.19-7.15 (m, 2H), 6.00 (brs, 1H), 5.36 (d, J=4.0, 1H), 5.12 (d, J=4.0, 1H), LC/Mass spec. (Analytical HPLC method 2): RT=1.95 min. Mass=395.99 (MH)+.
