Scheme 2. General synthesis of benzimidazole derivatives 12a–f. Reagents and conditions: (a) K₂CO₃, DMF, 50 °C, 6 h; (b) Boc₂O, 1 mol L⁻¹ NaOH, THF, 25 °C, 2 h; (c) Boc₂O, 2 mol L⁻¹ NaHCO₃, THF, 25 °C, 6 h; (d) ethyl diethoxyphosphoryl acetate, K₂CO₃, DMF, 78 °C, 12 h; (e) 1 mol L⁻¹ NaOH, CH₃OH, 25 °C, 30 min; (f) 10% Pd/C, H₂, C₂H₅OH, 25 °C, 7 h; (g) 1 mol L⁻¹ NaOH, CH₃OH, 25 °C, 30 min; (h) ethyl chloroformate, Et₃N, CH₂Cl₂, 0 °C, 30 min; (i) AcOH, reflux, 2 h.