Synthesis
Methylhydrazine (4.47 mL, 84.99 mmol) was added slowly and dropwise to a solution of ethyl 3-oxohexanoate (11.06 g, 84.99 mmol) in anhydrous ethanol (100 mL) at 0 °C. The reaction system was naturally warmed to room temperature with continuous stirring for 3.5 hours. Subsequently, the reaction mixture was heated to 60 °C and the reaction was continued for 10 hours and kept at reflux for 2.5 hours. Upon completion of the reaction, the mixture was concentrated to dryness using a rotary evaporator to afford intermediate 4 as a viscous pink solid (9.52 g, 100% yield). The structure of intermediate 4 was confirmed by 1H NMR (400 MHz, CDCl3) and mass spectrometry (ESI): 1H NMR (400 MHz, CDCl3) δ (ppm): 5.06 (s, 1H), 3.85 (bs, 1H), 3.32 (s, 3H), 1.94 (s, 3H); MS (ESI): m/z calculated value ( C15H9N2O) was 113.1 and the measured value was 113.2 ([M+H]+).
References
[1] Bioorganic and Medicinal Chemistry Letters, 2005, vol. 15, # 13, p. 3307 - 3312
[2] Patent: WO2016/205460, 2016, A1. Location in patent: Paragraph 0140-0141
[3] Patent: WO2016/7905, 2016, A1. Location in patent: Page/Page column 37
[4] Bioorganic and Medicinal Chemistry Letters, 2016, vol. 26, # 23, p. 5815 - 5818
[5] Patent: US4382948, 1983, A
