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

Synthesis

Methyl 2-amino-4,5,6,7-tetrahydrobenzo[b]thiophene-3-carboxylate (Compound 1) was synthesized from cyclohexanone and methyl cyanoacetate by standard Gewald reaction. The procedure was as follows: to a stirred solution of cyclohexanone (4.91 g, 0.05 mol), methyl cyanoacetate (4.95 g, 0.05 mol), and sulfur (1.92 g, 0.06 mol) in 35 mL of ethanol, morpholine (4.4 g, 0.05 mol) was slowly added dropwise. After the dropwise addition was completed, the reaction mixture was refluxed for 3 hours. After completion of the reaction, it was cooled to room temperature and the precipitate was collected by filtration. Purification by ethanol recrystallization gave a light yellow powdery product (8.6 g, 82% yield). The melting point of the product was 128.2-129.4 °C (literature value: 128-130 °C), and mass spectrometry (GC-MS) analysis showed a m/z of 211 [M + H]+ and fragment ion peaks of 179, 151, 125, 91, 77, 65, 53.

References

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