10 mg of powdered 4-chloro-3-sulfamoylbenzoyl chloride (melting point, m.p. 166° C.), prepared from 4-chloro-3-sulfamoylbenzoic acid and thionyl chloride, are introduced into 70 ml of anhydrous chlorobenzene, subsequently 6.32 g of 2-ethylbenzo[b]furan are added, and the reaction mixture is cooled to 0° C. After addition of 11.4 g of anhydrous aluminum chloride, the reaction batch is maintained at a temperature of 5° to 10° C., subsequently stirred for 5 hours at 15° C., and the mixture is then poured into a suspension of 200 g of ice and 10 ml of concentrated hydrochloric acid. After extraction with ethyl acetate and washing with water, the organic phase is stirred for 6 hours with a dilute NaHCO3 solution having a pH of 8.5, dried over magnesium sulfate, and, after evaporation, a light yellow to colorless viscous oil is obtained which crystallizes from petroleum ether. Colorless crystals, m.p. 170°-172° C. (from a small amount of methanol).
