Synthesis of asymmetrically disubstituted anthracenes

Abstract

We have developed synthetic pathways toward differently substituted hydroxyanthracenes (anthrols) with the aim to investigate their photochemical reactivity in dehydration reactions. Although the syntheses of anthracenes substituted at positions 9,10 are well known, reports for the synthesis of anthracenes with different substitution patterns are scarce. Herein we review known and report novel synthetic pathways toward anthrols with substituents at 1,2-, 2,3-, and 2,6- positions. We present two synthetic approaches: (i) building of the anthracene tricyclic fused ring system from the appropriate benzene derivatives, and (ii) reduction of the corresponding anthraquinones.Reduction of 2-hydroxyanthracene-1-carbaldehyde to the corresponding alcohol yields rather unexpected 1,1′-methylenedianthracen-2-ol, whose proposed mechanism of formation is supported by experimental observations and calculations.