A mixture of 2-(3-methoxyphenyl)-6-phenyl-1H-imidazo[4,5-b]pyridine (Compound of Example 1) (50 mg), 2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine resin (PS-BEMP, 2.2 mmol/g) (113 mg) and N,N-dimethyl formamide (2 ml) was shaken at room temperature for 30 minutes. To the mixture was added iodomethane (28 mg), and the mixture was further shaken for 1 hour. After the resin was filtered off, the filtrate was poured into water and extracted with ethyl acetate. The organic layer was washed with water and dried over MgSO4 and the solvent was distilled off under reduced pressure. The residue was subjected to silica gel column chromatography, and the fraction eluted with ethyl acetate-chloroform-hexane (1:1:4 to 1:1:0, v/v) was concentrated under reduced pressure. The resulting crystals were collected by filtration to isolate 2-(3-methoxyphenyl)-1-methyl-6-phenyl-1H-imidazo[4,5-b]pyridine (22 mg, 41%) (As a result of this reaction, a mixture of two isomers was obtained, and the isomer having higher polarity is the desired compound.)
