Chemical transformation of protoberberines. I. Conversion of tetrahydroberberine and dihydroberberine into noroxyhydrastinine by photooxygenation.

Simple and biomimetic conversions of tetrahydroberberine (1) and dihydroberberine (6) into noroxyhydrastinine (3), an isoquinolone alkaloid, are described. Photooxygenation of 1 afforded berberal (2), 3, and O-methylpseudopianic acid (4). The same products were obtained more efficiently by photooxygenation of 6.