To a stirred mixture of 430 mg of 3-(2-chlorophenyl)-5-methylbenzofuran-2-carboxylic acid and 0.39 cc of diphenylphosphoryl azide in 6 cc of benzene was added dropwise 0.22 cc of triethylamine at room temperature. The resulting mixture was stirred at room temperature for 35 minutes and then heated under reflux for 15 minutes. After cooling, 0.30 cc of 2,6-diethylaniline was added, followed by refluxing for 2 hours. After cooling, water was added to the reaction mixture and extracted with chloroform. The extract was dried over magnesium sulfate, and distilled to remove the solvent. The crude product thus obtained was purified by a silica gel column chromatography (eluent: chloroform) to obtain 446 mg of compound 21.
