To a stirred solution of 10.0 g. (0.45 mol.) of 6,7-dimethoxy-2-methyl-4-oxo-1,2,3,4-tetrahydroquinoline in 76 ml. of pyridine, at 0° C., was added, dropwise, during a 30 minute period, 45 ml. of benzyl chloroformate. Stirring was continued for 15 minutes, and then an additional 10 ml. of benzyl chloroformate was added. After a further 10 minutes, a further 10 ml. of benzyl chloroformate was added. The reaction mixture was heated on a steam bath for 30 minutes, cooled to room temperature and then poured into a mixture of 950 ml. of chloroform and 300 ml. of water. The separated chloroform layer was washed successively with dilute hydrochloric acid, saturated sodium bicarbonate, and water, and then it was dried (MgSO4) and concentrated to dryness in vacuo. The residue was an oil which solidified after trituration with ehtyl acetate-hexane. The resulting solid was then recrystallized from the same solvent system, giving 11.4 g. of the title compound, m.p. 127.5°-129.5° C. (71% yield). Further recrystallization of a small portion of the product from ethyl acetate-hexane raised the melting point to 128.5°-130° C.
