A suspension containing 16 g of the sulfonamide of Example 3, 7.7 g of potassium carbonate and 6.7 g of n-butylisocyanate in 130 of 2-butanone was refluxed for 4 hours, then stirred overnight at room temperature. After concentrating the mixture in vacuo, the residue was diluted with about 150 ml of water and the solution was washed 1×100 ml of ethyl ether. The aqueous layer was acidified with concentrated hydrochloric acid (red to litmus paper) and the resulting suspension was filtered, then suction-dried overnight to give 20 g of the subject compound; m.p. 156°-159°. IR (nujol): 1680 cm-1 (C=O).
