A mixture of 1.99 g of hydrochloride (racemic form) of 4,5,6,7-tetrahydrobenzimidazole-5-carboxylic acid, 0.15 ml of dimethyl formamide and 20 ml of thionyl chloride was refluxed for three hours. The resultant reaction solution was distilled to dryness under a reduced pressure. The residue consequently formed was added to a solution of 2.07 g of (+)-3-(3-hydroxyphenyl)indoline in 75 ml of tetrahydrofuran. This reaction solution was stirred at room temperature for 12 hours, then weakly alkalinized by addition of the saturated aqueous sodium bicarbonate solution, and extracted with chloroform. The chloroform layer was dried over anhydrous magnesium sulfate and then distilled. The residue was refined by silica gel column chromatography to obtain 2.00 g of 5-[{3-(3-hydroxyphenyl)indolin-1-ylcarbonyl}]-4,5,6,7-tetrahydrobenzimidazole (56.8%) as an epimer mixture.
