To a dichloromethane solution (30 ml) of 4-chloro-4'-methylmercaptomethylbenzophenone hydrazone (1.5 g) and 4-(N,N-dimethylamino)pyridine (1.2 g), isobutyl chlorocarbonate (0.8 g) was dropwise added under cooling with ice and subsequently stirred at a room temperature for 20 hours. The reaction mixture was then successively washed with 2N hydrochloric acid, water and an aqueous saturated sodium chloride solution, and dried over anhydrous magnesium sulfate. After distilling off the solvent, the crude product was purified by silica gel column chromatography (developing solvent: ethyl acetate:n-hexane=1:4) to obtain 4-chloro-4'-methylmercaptomethylbenzophenone isobutoxycarbonyl hydrazone (0.5 g) as an isomer mixture.
