Reagents and conditions: (a) HCl, 80 °C, 1 h; (b) i: BnONH2, MeOH, reflux, 1 h; ii: NaBH3CN, MeOH, HCl, rt, 1 h; (c) AcCl, TEA, CH2Cl2, rt, 18 h; (d) i: TMSBr, CH2Cl2, 0 °C, 30 min; ii: H2O, rt, 18 h; (e) RBr or RCl, TEA, DMF or DMPU, 60 °C, 6 h; (f) H2, 10% Pd/C, MeOH.