To a mixture of 4-{4-[chloro(cyclohexyl)methyl]-5-ethylthiophen-2-yl}tetrahydro-2H-thiopyran (1.91 g) synthesized above, methyl 4-aminobenzoate (1.68 g), sodium iodide (1.66 g) and N,N-dimethylacetamide (20 mL) was added sodium carbonate (1.18 g), and the mixture was stirred overnight at 100° C. under an argon atmosphere. 1N Hydrochloric acid was added to quench the reaction, and the 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 (20% ethyl acetate/hexane) to give a white solid. To a mixture of the obtained solid, tetrahydrofuran (20 mL) and ethanol (20 mL) was added 1N aqueous sodium hydroxide solution (20 mL), and the mixture was stirred with heating under reflux overnight, and concentrated under reduced pressure. The residue was dissolved in water (60 mL), and 1N hydrochloric acid (20 mL) was added at 0° C. The resulting precipitate was collected by filtration to give the title compound (2.07 g, 84%) as a yellow solid.
