General procedure for the synthesis of methyl 7-methoxy-4-oxo-1,4-dihydroquinoline-6-carboxylate from methyl 4-((2,2-dimethyl-4,6-dioxo-1,3-dioxan-5-yl)methylamino)-2-methoxybenzoate: 5-((3-methoxy-4-methoxycarbonyloxyanilino)methylene-2,2-dimethyl-1,3-dioxane-4, 6-dione (10 g, 29.8 mmol) was suspended in DOWTHERM A (125 ml) and heated to 180-190 °C within 30 min. The raw material dissolved at 100°C and carbon dioxide began to be released at about 180°C. Heating was continued for 30 minutes and then stopped. As the reaction mixture cooled, the product gradually precipitated. When the temperature drops to 40°C, ether is added and the mixture is stirred for 30 minutes. The solid product was collected by filtration, washed with ether and dried under vacuum to afford 7-methoxy-6-methoxycarbonyl-1,4-dihydroquinolin-4-one (5.56 g, 80% yield). The structure of the product was confirmed by 1H NMR spectroscopy: (DMSO-d6) δ 3.80 (s, 3H); 3.85 (s, 3H); 5.95 (d, 1H); 7.00 (s, 1H); 7.85 (d, 1H); 8.40 (s, 1H); 11.6 (br s, 1H); MS-ESI: 234 [MH]+.
![4-[(2,2-Dimethyl-4,6-dioxo-[1,3]dioxan-5-ylidenemethyl)-amino]-2-methoxy-benzoic acid methyl ester](/CAS/20180703/GIF/205448-64-2.gif)
