Cyclisation of an amine oxide initiated by successive redox reactions

3,4-Dimethoxy-NN-dimethylphenethylamine N-oxide reacts with iron(II) ion to give the corresponding tertiary amine, the demethylated secondary amine, and 1,2,3,4-tetrahydro-6,7-dimethoxy-2-methylisoquinoline in relative amounts which depend, in a way which has been rationalised, upon the reaction temperature and time, the presence of a base, and the concentration of iron(II).