Sodium hydride → 2-Cyclobutylsulfanyl-nicotinic acid

2-Mercapto-nicotinic acid (0.1 g, 0.64 mmol) was dissolved in DMF (2 mL), and the solution was cooled to 0˜5° C. NaH (0.13 g, 3.2 mmol) was added slowly thereto, and the mixture was stirred at 0˜5° C. for 30 minutes. Bromo-cyclobutane (0.12 mL, 1.28 mmol) was added thereto, and the mixture was stirred at 55˜65° C. for 3 hours, and then stirred at room temperature for 12 hours. After the termination of the reaction, the reactant was concentrated under reduced pressure. The residue was diluted with water, and then 3N HCl was used to adjust the pH of the solution to 2˜3. The solution was extracted with EtOAc. The organic layer was dried with MgSO4 and concentrated under reduced pressure to obtain the title compound, which was used in the next step without a separate purification process.