Double Ring-Closing Approach for the Synthesis of 2,3,6,7-Substituted Anthracene Derivatives

A method for the synthesis of 2,3,6,7-substituted
anthracene derivatives,
one of the most challenging anthracene substitution patterns to obtain,
is presented. The method is exemplified by the preparation of 2,3,6,7-anthracenetetracarbonitrile
and employs a newly developed, stable, protected 1,2,4,5-benzenetetracarbaldehyde
as the precursor. The precursor can be obtained in two scalable synthetic
steps from 2,5-dibromoterephthalaldehyde and is converted into the
anthracene derivative by a double intermolecular Wittig reaction under
very mild conditions, followed by a deprotection and intramolecular
double ring-closing condensation reaction.