Photochemical Reaction of 2-Alkylamino-1,4-naphthoquinones: A Novel Dealkylation.

Abstract

Naphthoquinone derivatives find vast applications both in pharmaceutical and agricultural sciences, for example, as antibacterials, antifungals, antitumors and herbicides. Here we investigate the reactivity of 2-alkylamino-3-bromo-1,4-naphthoquinones under illumination. All 2-alkylamino-3-bromo-1,4-naphthoquinones we studied were found to yield 2-amino-3-bromo-1,4-naphthoquinone. The alkyl group in the alkylamino group and the solvent influence the reactivity of 2-alkylamino-3-bromo-1,4-naphthoquinone and the yield. The alkyamino groups we used were n-propylamino, isopropylamino, cyclopropylamino, n-butylamino, sec-butylamino, and tert-butylamino groups; the solvents used were methylene chloride, chloroform, and benzene. 2-Bromo-3- isopropylamino-1,4-naphthoquinone in methylene chloride, for example, was converted into 2-amino-3-bromo-1,4-naphthoquinone in a high yield (85%) upon illumination. On the other hand, 2-bromo-3-tert-butyl-1,4-naphthoquinone yielded 2-amino-3-bromo-1,4-naphthoquinone only in poor yield. We believe hydrogen abstraction by excited quinone is the critical step in the dealkylation reaction.