Photochemical dealkylation of 2-alkylamino-3-halogeno-1,4-naphthoquinones
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We studied the photochemical reactivity of 2-alkylamino-3-bromo-1,4-naphthoquinones, 2-alkylamino-3-chloro-1,4-naphthoquinones, and 2-alkylamino-1,4-naphthoquinones. In general, 2-alkylamino-3-bromo-1,4-naphthoquinones and 2-alkylamino-3-chloro-1,4-naphthoquinones undergo dealkylation when exposed to UV light. The dealkylation products are 2-amino-3-bromo-1,4-naphthoquinone and 2-amino-3-chloro-1,4-naphthoquinone, respectively. The rate of dealkylation is affected by the nature of the alkyl group in the alkylamino substituent, and 2-alkylamino-3-halogeno-1,4-naphthoquinones with a more substituted α-carbon dealkylate faster than those with less substituted α-carbons. In addition to the 2-amino-3-halogeno-1,4-naphthoquinone product, we also identified 2-butanone as another product of the dealkylation of 2-bromo-3-sec-butylamino-1,4-naphthoquinone. Similarly, 3-pentanone was identified as another product of the dealkylation of 2-bromo-3-(3-pentylamino)-1,4-naphthoquinone. On the other hand, none of the 2-alkylamino-1,4-naphthoquinones were dealkylated when irradiated.