5 ml of dimethylformamide was added to 2.5 ml of toluene, the mixture was cooled with ice, and 1.3 ml (1.4 mmol) of phosphorus oxychloride was dropwise added thereto. After the mixture was stirred under cooling with ice for 10 minutes, 2.5 g (0.7 mmol) of 4-(2,3,4-trimethoxy-6-methylbenzoyl)-3-chloro-5-methoxypyridine-N-oxide was added thereto. After the mixture was stirred under cooling with ice for 30 minutes, the temperature was recovered to room temperature, followed by stirring for 2 hours. 30 ml of water was added to the mixture to terminate the reaction, and ethyl acetate was added thereto for extraction. The organic layer was dried over anhydrous sodium sulfate, subjected to filtration and purified by silica gel column chromatography to obtain 2.0 g (yield 76%) of 4-(2,3,4-trimethoxy-6-methylbenzoyl)-2,3-dichloro-5-methoxypyridine (compound No. 193; m.p. 98-99° C.).
