Toluene (45 ml), p-toluenesulfonic acid monohydrate (21.0 mg, 111 μmol) were added to N-(2-bromo-5-cyano-3,3′-dihydroxy-6-methylbiphenyl-4-yl)-2,2-dimethylpropionamide (I-16) (446 mg, 1.11 mmol), followed by refluxing with a Dean-Stark condenser for 3 hours. After cooling, water (50 ml) was added to the reaction liquid, the product was extracted with ethyl acetate (50 ml×2). The organic layer was washed with saturated brine (50 ml), dried over anhydrous magnesium sulfate, concentrated under reduced pressure, the residue was purified by silica gel column chromatography (n-hexane:ethyl acetate=3:1) to obtain the entitled compound (404 mg, 95%) as a colorless solid.
