Manganese(III) acetate mediated radical reactions leading to araliopsine and related quinoline alkaloids

Tricyclic quinoline alkaloids, including araliopsine 2, can be prepared in ‘one-pot’ by reaction of 4-hydroxy-1-methyl-2(1H)-quinoline 5 or 2,4-quinolinediol 31 with manganese(III) acetate in the presence of a variety of electron-rich alkenes. The reaction mechanism involves an initial intermolecular radical addition reaction followed by radical oxidation and cyclisation steps. Both angular and linear tricyclic alkaloids can be formed and the regioselectivity of the cyclisation is shown to depend on whether alkyl or aryl groups are attached to the alkene.