[Synthesis]
General procedure for the synthesis of ethyl 7-methoxy-1-naphthylacetate from agomelatine impurity 21: To a solution of anhydrous dichloromethane (45 mL, 15 v/v) containing ethyl acetate-2-(2-methoxynaphthalen-8-yl)acetate (3 g, 12.1 mmol) was slowly added 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ. 4.15 g, 18.2 mmol). After the addition was completed, the reaction mixture was stirred continuously at 25-30 °C for 12 hours. Upon completion of the reaction, the mixture was separated by filtration and the precipitated solid was washed with dichloromethane (30 mL, 10 v/v). The organic phases were combined and washed sequentially with saturated sodium bicarbonate solution (15 mL, 3 x 5 volume), water (15 mL, 3 x 5 volume) and brine (15 mL, 3 x 5 volume). The organic layer was dried over anhydrous sodium sulfate and subsequently concentrated under reduced pressure to remove the solvent to give a brown crude product. The crude product was purified by chromatography on a 100-200 mesh silica gel column with hexane solution of 20% ethyl acetate as eluent to give a final colorless oily product (2.59 g, 87.3% yield). The product was purified by IR (KBr, νmax, cm-1): 2981,2937,2834,1733,1627,1601,1511,1469,1450,1260,1213,1159,133,832; 1H NMR (400 MHz, CDCl3): δ 7.75 (d, J=8.4 Hz, 1H). 7.71 (d, J=8.0 Hz, 1H), 7.38 (d, J=7.2 Hz, 1H), 7.30 (t, J=8.0 Hz, 2H), 7.16 (dd, J1=2.4 Hz, J2=8.8 Hz, 1H), 4.15 (q, J=7.2 Hz, 2H), 4.0 (s, 2H), 3.93 (s, 3H), 1.2 (t, J=7.2 Hz, 3H); 13C NMR (100 Hz, DMSO-d6): δ171.1,157.46,132.99,130.01,129.79,128.74,128.37,127.25,123.02,117.88,117.88,102.76,60.23, 54.94,14.0; EI-MS, m/z (%): 245 (M+1,100), 171 (17) for characterization confirmation. |