Reactions of 2-chloro-3-methyl-1,4-naphthoquinone with Alkylamines

Abstract

The reactivity of 2-chloro-3-methyl-1,4-naphthoquinone with alkylamines is studied here. In the reaction with alkylamines, we found 2-bromo-3-methyl-1,4-naphthoquinone, an analog of 2-chloro-3-methyl-1,4-naphthqouinone, exclusively yielded 2- alkylamino-3-bromo-1,4-naphthoquinone through demethylation. Similarly as 2-bromo-3-methyl-1,4-naphthoquinone, 2-chloro-3-methyl-1,4-naphthoquinone in methanol yields 2-alkylamino-3-chloro-1,4-naphthoquinone as the major product with primary alkylamines such as propylamine, isopropylamine, cyclopropylamine, ethylamine and methylamine through demethylation. Different from the reactions of 2-bromo-3-methyl-1,4-naphthoquinone, however, 2-chloro-3-methyl-1,4-naphthoquinone produces another product, 2-alkylamino-3-methyl-1,4-naphthoquinone, in which the primary amine substitutes for the chlorine. Since a halogen such as chlorine and bromine is a good leaving group, the substitution of the halogen was originally expected for both 2-chloro-3-methyl-1,4-naphthoquinone and 2-bromo-3-methyl-1,4-naphthqouinone with reactions with primary alkylamine. The unusual demethylation reaction is caused by the acidic nature of the ?-proton of 2-halogeno-3-methyl-1,4-naphthoquinone. We studied the effect of the solvent, by systematically changing the polarity from water to hexane. In less polar solvent, the main product 2-alkylamino-3-chloro-1,4-naphthoquinone was yielded more favorably. We have also identified a new product while studying the solvent effect.