| Abstract: | Oxidation of the alkaloids (-)tylocrebrine, (-)septicine and (±)canadine by N-bromosuccinimide gave the corresponding tetradehydroiminium salts in which the six-membered heterocyclic rings were aromatized. Evidence was provided for the preferred path of the two available alternatives. Reduction of these salts with sodium borohydride regenerated the starting bases but without the optical activity. In contrast to the simpler 1 ,2,3,4-tetrahydroisoquinolines, hydrastine gave a brominated isoquinolinium salt with the loss of dimethoxy phthalide anion. A discussion of the stoichiometry and a probable mechanism is presented. |
