Reaction of 2-alkyl-3-bromo-1,4-Naphthoquinone with Amines; A Novel Demethylation Reaction.
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Derivatives of 1,4-naphthoquinone are utilized as anti-fungal, antibacterial, and potential anticancer pharmaceuticals, which often show unexpected reactivities. Here we study the reactivity of 2-bromo-3-methyl-1,4-naphthoquinone toward primary and secondary amines. In the reaction with primary amines in methanol, contrary to our expectations, demethylation of 2-bromo-3-methyl-1,4-naphthoquinone generates 2-alkylamino-3-bromo-1,4-naphthoquinone as the major product. Furthermore, secondary amines such as N-ethylmethylamine gave 2-methylamino-3-bromo-1,4-naphthoquinone, presumably as the secondary reaction product. Unexpectedly, the reaction of 2-bromo-3-ethyl-1,4-naphthoquinone with primary, secondary, and tertiary amines yields very different results. In the reaction 2-bromo-3-ethyl-1,4-naphthoquinone with propylamine, for example, substitution occurs for the bromine. We believe this is due to the varying acidity between the two 2-alkyl-3-bromo-1,4-naphthoquinones. The scope and limitations of the reaction and reaction mechanism are studied.