Reductive elimination of alkoxy group in anthraquinone derivatives

Abstract

Anthraquinone derivatives are constantly in a focus of synthetic chemists due to a diversity of valuable biological, photochemical and redox properties. However, quinone core limits applicability of chemical transformations making a search for new methods of modification of anthraquinones highly demanded. A convenient approach of regioselective reductive α-alkoxy group cleavage of anthraquinone derivatives was developed and evaluated. Most effectively transformation goes via a zinc reduction of quinone moiety and prototropic rearrangement in acidic media followed by the alkoxy group elimination. Strong donors in β-position of anthraquinone core are crucial for transformation and provide the elimination exclusively from α-position. The method simplifies an access to some bioactive 1,3-substituted anthraquinones and was applied for synthesis of natural products, e.g., rubiadin 1-methyl ether, anthragallol 1,2-dimethyl ether, and damnacanthol.