Study on the Reaction of 2-Bromo-3-Methoxy-1,4-Naphthoquinone with Secondary Amines and the Subsequent Dealkylation
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Here we study the reactivity of 2-bromo-3-methoxy-1,4-naphthoquinone with secondary amines. In general, secondary amines react with 2-bromo-3-methoxy-1,4-naphthoquinone by substituting at the 3-methoxy position. The reactivity of an amine with the quinone is inversely proportional to the increasing size of the alkyl groups on the amine. In the reaction of 2-bromo-3-methoxy-1,4-naphthoquinone with methylethylamine, 3-N-methylethylamino-2-bromo-1,4-naphthoquinone is obtained in good yield. Diisopropylamine, on the other hand, fails to yield a substitution product with 2-bromo-3-methoxy-1,4-naphthoquinone. The substitution product, 2-N-alkylalkylamino-3-bromo-1,4-naphthoquinone, is often found to further derive to a dealkylation product. For example, 2-bromo-3-N-methylpropylamino-1,4-naphthoquinone, as the primary product of 2-bromo-3-methoxy-1,4-naphthoquinone with methylpropylamine, was found to form 2-bromo-3-N-methylamino-1,4-naphthoquinone as the major dealkylation product by dealkylation of the propyl group in the presence of excess amine. A higher alkyl group in a secondary amine is more likely to be dealkylated.