445 mg of 7-(2-(1,4-dioxa-8-azaspiro[4.5]decan-8-yl)ethyl)-6-methoxyquinoline was dissolved in 10 ml of methanol. Thereafter, 100 mg of 10% palladium carbon was added to the reaction solution. The obtained mixture was stirred for 6 hours under a 4 kg/cm2 of hydrogen atmosphere. Palladium carbon was removed by filtration, followed by concentration under a reduced pressure. The reaction solution was stirred under the same conditions for 10 hours 3 times, followed by concentration under a reduced pressure. A saturated sodium bicarbonate aqueous solution was added to the residue, followed by extraction with chloroform. The extract was dried over magnesium sulfate and then concentrated under a reduced pressure, so as to obtain 459 mg of 7-(2-(1,4-dioxa-8-azaspiro[4.5]decan-8-yl)ethyl)-6-methoxy-1,2,3,4-tetrahydroquinoline. This compound was used in the following reaction without further purification.
