A 31% aqueous hydrogen peroxide solution (2 ml) and hexaammonium heptamolybdate tetrahydrate (30 mg) were added to a solution of 3,6-dichloro-2-[(6-chloropyridin-3-ylthio) (pyridin-4-yl)methyl]pyridine (82 mg, 0.24 mmol) in methanol (4 ml). The resulting mixture was stirred at room temperature for 2 hours. Ethyl acetate was added to the reaction mixture. After washing with a saturated aqueous solution of sodium bicarbonate, the organic layer was dried over anhydrous sodium sulfate and filtered. The filtrate was concentrated under reduced pressure. The residue was subjected to flash chromatography on a silica gel column. A fraction obtained from the elution portion with hexane:ethyl acetate=3:2 was concentrated under reduced pressure, whereby the title compound A (41 mg, 0.098 mmol, 46%) was obtained. A fraction obtained from the elution portion with hexane:ethyl acetate=1:1 was concentrated under reduced pressure, whereby the title compound B (isomer A) (low polarity) (8 mg, 0.020 mmol, 9%) and the title compound B (isomer B) (high polarity) (8 mg, 0.020 mmol, 9%) were obtained, respectively each as a white solid.
