To a solution (60 mL) of 3-methylthieno[2,3-b]pyridine-2-carbaldehyde (2.07 g) synthesized above in tetrahydrofuran was added a 1.0M solution (17.6 mL) of cyclohexylmagnesium bromide in tetrahydrofuran at 0° C., and the mixture was stirred for 1 hr. Saturated aqueous ammonium chloride solution was added to quench the reaction, and the reaction mixture was extracted with ethyl acetate. The extract was washed with saturated brine, dried over magnesium sulfate, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (10-50% ethyl acetate/hexane) to give a yellow solid. To a mixture of the obtained solid, 4-methylmorpholine N-oxide (1.81 g) and acetonitrile (40 mL) was added tetrapropylammonium perruthenate (238 mg), and the mixture was stirred at room temperature for 3 hr, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (0-30% ethyl acetate/hexane) to give the title object compound (1.50 g, 85%) as a white solid.
