Dichloromethane → 1-tert-butyl 3-ethyl 4-(2-(7-methoxy-4-methyl-2-oxoquinolin-1(2H)-yl)ethyl)piperazine-1,3-dicarboxylate

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To 3 mL of a dichloromethane solution containing 0.10 g of (7-methoxy-4-methyl-2-oxoquinolin-1(2H)-yl)acetaldehyde, 0.12 g of 1-tert-butyl 3-ethyl piperazine-1,3-dicarboxylate, 30 μl of acetic acid and 0.14 g of sodium triacetoxyborohydride were added at room temperature, and the mixture was stirred at room temperature for 1 hour and 40 minutes. The reaction mixture was added with water and chloroform. The organic layer was separated, and the aqueous layer was extracted twice with chloroform. The organic layer and the extract were combined, the resultant solution was dried over anhydrous magnesium sulfate, and the solvent was removed under reduced pressure. The residue thus obtained was purified by silica gel column chromatography [eluent; chloroform:acetone=100:1] to obtain a colorless foam, 1-tert-butyl 3-ethyl 4-(2-(7-methoxy-4-methyl-2-oxoquinolin-1(2H)-yl)ethyl)piperazine-1,3-dicarboxylate. (2) To 2.6 mL of a dichloromethane solution containing 1-tert-butyl 3-ethyl 4-(2-(7-methoxy-4-methyl-2-oxoquinolin-1(2H)-yl)ethyl)piperazine-1,3-dicarboxylate, 1.3 mL of trifluoroacetic acid was added, the mixture was stirred at room temperature for 2 hours, and the solvent was removed under reduced pressure. The residue thus obtained was added with ethyl acetate and water, and the resultant solution was adjusted to pH 1.0 with 6 mol/L hydrochloric acid. The aqueous layer was separated, and the organic layer was extracted twice with 20 mL of 0.1 mol/L hydrochloric acid. The aqueous layer and an extract were combined, thereto was added ethyl acetate, and the resultant solution was adjusted to pH 8.5 with a 5 mol/L aqueous sodium hydroxide solution. The organic layer was separated, and the aqueous layer was adjusted to pH 11.5 with a 5 mol/L aqueous sodium hydroxide solution, and extracted with ethyl acetate. The organic layer and the extract were combined, the resultant solution was washed with a saturated sodium chloride solution, and dried over anhydrous magnesium sulfate, and the solvent was removed under reduced pressure to obtain 89 mg of a colorless foam, ethyl 1-(2-(7-methoxy-4-methyl-2-oxoquinolin-1(2H)-yl)ethyl)piperazine-2-carboxylate.

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