Synthesis
Step 2: Synthesis of cyclopentylhydrazine hydrochloride
Tert-butyl N'-cyclopentylidenehydrazine formate (5.448 g, 27.48 mmol) was dissolved in a solvent mixture of anhydrous tetrahydrofuran (25 mL) and anhydrous methanol (34 mL). Under argon protection, sodium cyanoborohydride (2.044 g, 32.53 mmol) was added in batches, followed by refluxing the reaction mixture for 10 min. Upon completion of the reaction, it was cooled to room temperature, 6N hydrochloric acid (12 mL) was added, and refluxing was continued for 1.5 hours. An aliquot was analyzed by NMR and it was confirmed that some of the BOC protecting groups were still not removed. Add 6N hydrochloric acid and continue refluxing for 3 hours. At the end of the reaction, cooled to room temperature and stirred overnight. The insoluble material was removed by filtration, and the filtrate was concentrated and azeotropized with toluene three times to completely remove the water. The residue was dissolved in hot isopropanol, cooled to room temperature, diluted with ether and further cooled. The solid was collected by filtration to afford cyclopentylhydrazine hydrochloride (3.903 g, 103% yield), which could be used in subsequent reactions without further purification.
References
[1] Patent: US2007/225280, 2007, A1. Location in patent: Page/Page column 48
[2] Patent: WO2014/16789, 2014, A1. Location in patent: Page/Page column 18; 19
[3] Bioorganic and Medicinal Chemistry, 2004, vol. 12, # 2, p. 393 - 404
[4] Journal of Organic Chemistry, 1981, vol. 46, # 26, p. 5413 - 5414
[5] Patent: US2004/220186, 2004, A1. Location in patent: Page 19
