Quinones. Part 14. Attempted synthesis of 9,10-dimethyl-2,6-anthraquinone. Desmotropic formation of secondary ortho-anthraquinoles instead of 1,2-anthrahydroquinones

Abstract

In connection with PMO calculations on the reactivity of quinones, we attempted to synthesize 9,10-dimethyl-2,6-anthraquinone 3a by oxidising 2,6-dihydroxy-9,10-dimethylanthracene 2. Even under exclusion of water, only addition products of water to 3a, viz. the secondary ortho-anthraquinols 1,6-dihydroxy-9,10-dimethylanthracen-2(1H)-one 4 and 2,6-dihydroxy-9,10-dimethylanthracen-1(2H)-one 6, could be isolated. The fully aromatic tautomer of compounds 4 and 6, 1,2,6-trihydroxy-9,10-dimethylanthracene 5 could not be detected. Acyloins 4 and 6 represent the first examples of secondary ortho-anthraquinoles.