Photochemical hydroxymethylation of protoberberine alkaloids. Total synthesis of (±)-solidaline

The introduction of a hydroxymethyl group at the C-8 position of berberinium salts was readily achieved by photoaddition of methanol. The resulting photoproducts were isolated as tetrahydroprotoberberine derivatives. By combining this photochemical reaction with the oxidation of the photoproduct, the synthesis of (±)-solidaline starting from palmatine chloride was accomplished for the first time.