Scheme 2. Synthetic Route for Compounds 9–11.

Reagents and conditions: (a) Trifluoroacetic anhydride, DCM, rt, 4 h; (b) ClSO₃H, 150 °C, 16 h; (c) 4-piperidinol, DIPEA, MeCN, rt, overnight; (d) 3,4,5-trifluoroaniline, HATU, DIPEA, DMF, rt–50 °C, overnight; (e) LiOH·H₂O, THF:H₂O, 50 °C, 48 h; (f) 1 N NaOH aqueous solution, MeOH, 30 °C, 2 h; (g) 35% formaldehyde aq solution, NaCNBH₃, AcOH, MeCN, 0 °C, 1 h.