To a mixture of cyclohexyl(3-methylthieno[2,3-b]pyridin-2-yl)methanone (1.00 g) synthesized above, methyl 4-aminobenzoate (642 mg), triethylamine (4.31 mL) and methylene chloride (20 mL) was added titanium (IV) chloride (508 μL) at 0° C., and the mixture was stirred at room temperature for 1.5 days under argon atmosphere. Saturated aqueous sodium hydrogen carbonate 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 to give a dark brown solid. To a solution (20 mL) of the obtained solid in tetrahydrofuran were added acetic acid (442 μL) and sodium cyanoborohydride (485 mg), and the mixture was stirred at room temperature for 1.5 hr. Saturated aqueous sodium hydrogen carbonate 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 (30-70% ethyl acetate/hexane) to give the title object compound (975 mg, 64%) as a pale-brown solid.
