Chemical Transformation of Protoberberines. III. Convenient Synthesis of 8-Methoxyberberinephenolbetaine by Photooxygenation of Berberine. A Novel Conversion of Berberine into (±)-Ophiocarpine, (±)-Epiophiocarpine, (±)-α-Hydrastine, and (±)-β-Hydrastine

Abstract

Photooxygenation of berberine (5) in methanol in the presence of sodium methoxide and rose bengal afforded the 8, 14-dimethoxy-13-oxoberbine (12), which, on being heated in methanol, readily yielded 8-methoxyberberinephenolbetaine (6), a key intermediate to phthalideisoquinoline alkaloids, (±)-α- and (±)-β-hydrastine (7 and 8). Reduction of 6 with sodium borohydride furnished mostly (±)-ophiocarpine (9) and a little (±)-epiophiocarpine (10).