Reaction Steps
To a suspension of 9 (1.0 g, 2.39 mmol, 1 equiv) in MeCN (10 mL), triethyl orthoformate (2.8 g, 19.13 mmol, 8 equiv) was added followed by 2 drops of sulfuric acid. The reaction mixture was heated at reflux for 1.5 h until starting material was disappeared (TLC). The precipitated product was filtered, washed with diethyl ether and dried under vacuum to afford 3 as pale yellow solid (0.77 g, 76%). mp: 175-177° C., IR: 1737 (C═O), 1610, 1589, 1251, 1176 cm−1. 1H NMR (400 MHz, d6-DMSO): δ=3.69 (s, 3H, OCH3), 3.70 (s, 3H, OCH3), 5.08 (s, 2H, CH2), 5.51 (s, 2H, CH2), 6.85 (d, J=8.2 Hz, 2H, Ar—H), 6.89 (d, J=8.2 Hz, 2H, Ar—H), 7.29 (d, J=8.2 Hz, 2H, Ar—H), 7.33 (d, J=8.2 Hz, 2H, Ar—H), 8.75 (s, 1H, Ar—C═N—H), 8.92 (s, 1H, Imid-H). 13C NMR (100 MHz, d6-DMSO): δ=43.4, 47.0, 55.6, 55.7, 114.4, 114.6, 128.5, 128.8, 129.2, 129.7, 129.8, 148.9, 150.3, 156.3, 159.2, 159.5, 160.2, 166.3. HRMS (FAB) Calcd for C23H20N6O3, 428.1597 (M+); observed m/z 429.1667 (M+H)+.
