[C:1]1(B(O)O)[CH:6]=[CH:5][CH:4]=[CH:3][CH:2]=1.[CH2:10]([O:12][C:13]([C:15]1[N:16]=[C:17](Cl)[O:18][CH:19]=1)=[O:14])[CH3:11].C(=O)([O-])[O-].[Na+].[Na+].C(OCC)(=O)C>COCCOC.CCCCCC>[CH2:10]([O:12][C:13]([C:15]1[N:16]=[C:17]([C:1]2[CH:6]=[CH:5][CH:4]=[CH:3][CH:2]=2)[O:18][CH:19]=1)=[O:14])[CH3:11]
A mixture of phenylboronic acid (729 mg, 5.98 mmol), 2-chloro-oxazole-4-carboxylic acid ethyl ester (prepared according to the procedures described in Org. Lett. 2002, 4 (17), 2905 and J. Med. Chem. 1971, 14, 1075) (1.0 g, 5.70 mmol), Pd[PPh3]4 (329 mg, 0.285 mmol), and sodium carbonate (2M, 2 mL) in ethylene glycol dimethyl ether (10 mL) were heated at 90 degrees overnight. After cooling the reaction, solvent was removed to give the crude residue. Flash chromatography (Merck silica gel 60, 230-400 mesh, 5-45% ethyl acetate in hexane for 35 min) gave 2-phenyl-oxazole-4-carboxylic acid ethyl ester (1.03 g, 83%) as colorless oil. LCMS calcd for C12H11NO3 (m/e) 217, obsd 218 (M+H).
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