3-Amino-4,5,6,7-tetrahydro-benzo[b]thiophene-2-carboxylic acid methyl ester

Synthesis

1263199-68-3

119205-38-8

Ethyl methyl-S-(2-cyanocyclohex-1-enyl)sulfonate (9) (0.17 g, 0.78 mmol) was used as the starting material and it was mixed with freshly distilled anhydrous THF (3 mL). Potassium tert-butoxide (0.09 g, 0.78 mmol) was subsequently added and the reaction mixture was heated to reflux for 30 min. The reaction progress was monitored by thin layer chromatography (TLC) (eluent: petroleum ether/ethyl acetate, 5:1). After completion of the reaction, the mixture was concentrated under reduced pressure, dissolved by addition of dichloromethane (25 mL) and washed with distilled water (2 x 20 mL), and the organic phase was dried over anhydrous magnesium sulfate. After evaporation of the solvent, the resulting oil was dried under high vacuum (10^-1 mbar). After refrigeration overnight, the light yellow solid product methyl 3-amino-4,5,6,7-tetrahydrobenzo[b]thiophene-2-carboxylate (135 mg, 80% yield) was obtained. The product was characterized as follows: melting point 70-73 °C; 1H NMR (CDCl3) δ: 1.82 (m, 4H, H5, H6), 2.30 (m, 2H, H7), 2.67 (m, 2H, H4), 3.79 (s, 3H, COOCH3), 5.36 (br s, 2H, NH2); 13C NMR (CDCl3) δ. 21.9, 22.6 (2CH2, C5, C6), 23.1 (CH2, C4), 25.8 (CH2, C7), 51.1 (COOCH3), 97.3 (CAr), 126.2 (CAr), 143.5 (CAr), 152.6 (CAr), 165.4 (COOCH3); IR (KBr) ν: 768 , 1072, 1095, 1130, 1198, 1263, 1300, 1342, 1448, 1493, 1568, 1604, 1668, 1734 (ester), 2858, 2933, 3361 (NH2), 3464 (NH2) cm^-1 ; MS (EI, 70 eV) m/z (%): 32 ( 80), 40 (10), 45 (10), 65 (10), 77 (15), 91 (15), 118 (15), 151 (65), 179 (90), 211 (M+, 100), 212 (M+H+, 10); HRMS-FAB: m/z [M+H]+ calcd for C10H13NO2S. 211.0667; found: 211.0745.

References