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Synthesis of the ligustrazine-triterpenes derivatives 1a–4a, 1b–4b. Reagents and Conditions: (a) Benzene, reflux, 10 h; (b) CCl4, N-bromobutanimide (NBS), hv, reflux, 12 h; (c) N,N-Dimethylformamide (DMF), K2CO3, N2, 85 °C, 1.5 h; (d) H2O, KMnO4, 37 °C, 6 h; and (e) dry CH2Cl2, EDCI, DMAP, 12 h.
