Diisopropyl Ether → 2-Methoxy-4-methylquinoline

The 4-(bromomethyl)-2-methoxyquinoline obtained in Step 2 was dissolved in 7 mL of acetonitrile, and then 0.5 g (1.54 mmol) of quinine was added, and stirred for 2 hours while heated at 70° C. After stirring was completed, the solution was cooled to a normal temperature, and 20 mL of diisopropyl ether was added. Then, the solution was filtered under reduced pressure to separate a solid precipitated in the reaction solution. The resultant residual solid was washed with a mixed solvent of 5 mL of chloroform and 15 mL of diisopropyl ether. After washing, the solid was dried under reduced pressure to obtain 0.82 g of the target compound, 2-methoxy-4-methyl quinoline quininium bromide. The melting point was 181° C. to 191° C. (degradation). M+496 was confirmed by LCMS.