Ethyl (E)-3-(7-oxo-5,6,7,8-tetrahydro-1,8-naphthyridin-3-yl)acrylate → Ethyl 3-(7-oxo-5,6,7,8-tetrahydro-1,8-naphthyridin-3-yl)propionate

To a stirred solution of 49a (7.7 g, 34.3 mmol) in methanol (150 ml) was added 10% Pd/C (3 g) under nitrogen. The reaction mixture was stirred in presence of H2 gas at 20-35° C. for 16 h. The progress of the reaction was monitored by TLC. After the reaction was completed, the reaction mixture was filtered through celite and concentrated to get the desired compound as a white solid (7 g, 90.2%); 1H NMR (400 MHz, DMSO-d6) δ 10.35 (s, 1H), 7.95 (s, 1H), 7.48 (s, 1H), 4.05 (q, J=7.1 Hz, 2H), 2.83 (t, J=7.6 Hz, 2H), 2.79-2.60 (m, 4H), 2.58-2.55 (m, 2H), 1.16 (m, 3H); MS (ES) m/e 249.1 (M+H)+.