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Example 5: Preparation of 4,5,6,7-tetrahydrothieno[3,2-c]pyridine hydrochloride In a 2-liter four-necked flask equipped with a thermometer and a mechanical stirrer, 2-thiophene ethylamine (100 g, 0.79 mol) was added. The reaction was dissolved in dichloromethane (600 ml) at 25°C (±5°C) and stirred for 5 to 10 minutes. Subsequently, paraformaldehyde (26.4 g, 0.88 mole) was added to the reaction system and the reaction was subjected to azeotropic reflux at 40 to 45°C for 4 to 6 hours. Upon completion of the reaction, the system was cooled to room temperature and a N,N-dimethylformamide solution (200 ml) of 7% hydrochloric acid was slowly added at 25 °C (±5 °C). The reaction mixture was continued to be stirred at 70°C (±5°C) for 4 to 6 hours. Afterwards, the reaction solution was cooled to 15 °C (±2 °C) and stirred for 8 to 10 hours to promote crystallization. The solid product was collected by filtration and washed with pre-cooled dichloromethane. Finally, the product was dried under vacuum at 30 to 40 °C to afford 4,5,6,7-tetrahydrothieno[3,2-c]pyridine hydrochloride (120 g, 99% yield).