Scheme 1. Synthesis of Benzamidine Derivatives 1a–d.

Reagents and conditions. (i) PhtN^–K⁺, DMF, rt, 20 h; (ii) PhtNH, Ph₃P, DIAD, THF, 0 °C then rt, 20 h; (iii) K₂CO₃, CH₃CN, 80 °C, 24 h; (iv) N₂H₄·H₂O, EtOH, 80 °C, 12 h; (v) for 7a, 7c, and 7d, EDC·HCl, DMAP, CH₃CN, 80 °C, 20 h; for 7b, PyBOP, DIPEA, DMF, rt, 18 h; (vi) NH₂OH·HCl, ^tBuOK, DMSO, rt, 4 days; (vii) (1) Ac₂O, AcOH, 15 min, (2) H₂, 5% Pd–C, AcOH, rt, 12 h.