General procedure for the synthesis of pyridine-3-methylidenehydrazine (1-(3-pyridyl)methylhydrazine) from 3-pyridinecarboxaldehyde: Hydrazine (1.05 mL, 46.7 mmol) was slowly added to a solution of methanol (100 mL) containing 3-pyridinecarboxaldehyde (5 g, 46.7 mmol). The reaction mixture was stirred continuously for 1 hour at room temperature. Subsequently, the air in the reaction system was replaced with nitrogen and 10% Pd/C catalyst (200 mg) was added. The nitrogen was again replaced with hydrogen and the reaction mixture was stirred overnight at room temperature under hydrogen atmosphere. Upon completion of the reaction, the solid catalyst was removed by filtration and the filtrate was concentrated under reduced pressure to give the crude product pyridine-3-methylenehydrazine (Example 85A). This crude product can be used directly in the subsequent reaction without further purification. Yield: 5.2 g (91% yield). Mass spectrometry (DCI) analysis result: m/z 124 ([M+H]+).
