Amine oxidation. Part VI. Metal-ion induced dehydrative cyclisation, reduction, and reductive fragmentation of arylethyldimethylamine N-oxides

Abstract

The treatment of 3,4-dimethoxy-NN-dimethylphenethylamine N-oxide with iron(II) ion gives some or all of the following products, depending upon the conditions: the corresponding tertiary and secondary amines, 1,2,3,4-tetrahydro-6,7-dimethoxy-2-methylisoquinoline, and 3,4-dimethoxybenzyl alcohol. Factors which govern the course of the reaction (especially the temperature, the concentration of the reagents, and the presence of pyridine) have been examined, and the studies have been extended to the use of titanium(III) in place of iron(II) ion and to the reactions of related N-oxides. The results are consistent with the mediation of an aminium radical cation ArCH₂-CH₂NMe₂[graphic omitted] in the formation of each type of product; its one-electron reduction by iron(II) or titanium(III) ion gives the tertiary amine, its one-electron oxidation by iron(III) ion gives secondary amine and (under suitable conditions) the cyclised product, and it undergoes homolysis to the radical ArCH₂·whence non-basic products are derived.