Scheme 1. Reagents and conditions: (a) AcOH, rt, 1 h, 71% (b) NHR₁R₂, K₂CO₃, CH₃CN : H₂O (3 : 1), rt, 24 h, 55–96% (c) (i) NaH, DMF, 0 ° C-rt, 0.5 h; (ii) benzylating agent, DMF, 0 °C-rt, 2–24 h; (d) benzylating agent, K₂CO₃, acetone, reflux, 24 h, 79–98%.