Scheme 3. Synthesis of pyrazole derivative 13. Reagents and conditions: (a) 1-Boc-4-piperidinol, DIAD, PPh3. THF, rt, 4 h, 46%; (b) hydrazine monohydrate, EtOH, reflux, 18 h, quantitative; (c) EDCI, HOBt, 2-(trimethyl-1H-pyrazol-4-yl)acetic acid,28 DIPEA, THF : DMF (4 : 1, v/v), rt, 18 h; (d) TsCl, 1,2,2,6,6-pentamethylpiperidine, DCM, rt, 3 h; (e) 10% TFA in DCM (v/v), rt, 2 h, 40% over three steps.
