Synthetic routes to ligustrazine derivatives L1–L15, L17–L21. Reagents and Conditions: (i) anhydrous CH2Cl2, EDCI/(CH3CH2)3 N, r.t., 12 h; (ii) anhydrous DMF (L11 anhydrous CH2Cl2), EDCI/HOBt, r.t., 12 h; (iii) anhydrous DMF (L21 DMI), EDCI/HOBt, r.t., 12 h.