Diethyl Malonate → Ethyl 1-benzyl-4-hydroxy-2-oxo-1,2-dihydro-1,8-naphthyridine-3-carboxylate

To a slurry of sodium hydride (60%, 0.118 g, 2.95 mmol) in anhydrous dimethylacetamide (6 mL) at 0° C. under N2 was added diethyl malonate (0.472 g, 2.95 mmol) dropwise over 5 minutes. The mixture was stirred at ambient temperature for 1 hour, reacted with the product of Example 15A (0.50 g, 1.97 mmol), and heated at 120° C. for 3 hours. The mixture was cooled to ambient temperature and partitioned between ethyl acetate and cold water, and adjusted to pH to 5 with 1 M HCl. The aqueous layer was extracted with ethyl acetate (2×100 mL) and the combined extracts were washed with brine, dried over magnesium sulfate, filtered, and concentrated under vacuum. The residue was recrystallized from methanol to give the title compound as a white solid (0.439 g, 68%). MS (ESI+) m/z 325.0 (M+H)+, 347.0 (M+Na)+; 1H NMR (300 MHz, DMSO-d6) δ 1.30 (t, J=7.17 Hz, 3H), 4.32 (q, J=7.23 Hz, 2H), 5.55 (s, 2H), 7.23 (m, 5H), 7.37 (dd, J=7.91, 4.60 Hz, 1H), 8.45 (dd, J=7.91, 2.02 Hz, 1H), 8.71 (dd, J=4.78, 1.84 Hz, 1H), 13.00 (s, 1H).