Synthesis
Step 2: Synthesis of 1-(5-nitropyridin-2-yl)piperazine (B-3)
Compound 1-tert-butylcarbonyl-4-(5-nitro-2-piperidinyl)piperazine (B-2, 19.45 g, 0.0631 mol) was dissolved in dichloromethane (250 mL) and cooled to 0°C. Trifluoroacetic acid (50 mL) was added slowly. The reaction mixture was stirred at room temperature for 16 hours and then concentrated under reduced pressure. The crude product was again dissolved in dichloromethane (250 mL), and the pH was adjusted to alkaline by sequentially adding 1N aqueous NaOH solution (200 mL) and 3N aqueous NaOH solution (100 mL). The organic layer was separated and the aqueous phase was extracted with dichloromethane. The organic phases were combined, dried with anhydrous magnesium sulfate, filtered and concentrated under reduced pressure to give 1-(5-nitropyridin-2-yl)piperazine (B-3, 13.13 g, 100% yield) as a yellow solid. Mass spectrometry (MS) showed the [M + 1] peak as 209.
References
[1] Patent: WO2010/59606, 2010, A2. Location in patent: Page/Page column 182
[2] Patent: WO2011/31628, 2011, A1. Location in patent: Page/Page column 67
[3] Bioorganic and Medicinal Chemistry Letters, 2013, vol. 23, # 4, p. 985 - 988
[4] Tetrahedron Letters, 2011, vol. 52, # 45, p. 5905 - 5909
[5] Patent: WO2006/94840, 2006, A1. Location in patent: Page/Page column 43-44
