Scheme 1. Reagents and conditions: (i) berberine, 20 mm Hg, 190 °C, 15 min, CH₃CH₂OH–HCl; (ii) CH₃OH, NaBH₄, rt, 4 h; (iii) (a) HMTA/TFA, 120 °C, 3 h; (b) 10% H₂SO₄, 90–100 °C, 2 h; (iv) CH₃CH₂OH, CH₃COOH, reflux, 5 h; (v) alkyl bromides and halobenzyl halides, K₂CO₃, DMF, 80 °C.