Regiodivergent Cobalt-Catalyzed Diels–Alder Reactions for the Synthesis of Bifunctional Building Blocks and Their Suzuki-Cross-Coupling Polymerizations

Abstract

Reaction sequences started by a ruthenium-catalyzed enyne cross-metathesis of bromo-substituted phenylacetylenes with ethane, followed by a regiodiverse cobalt-catalyzed Diels–Alder reaction with phenyl alkynyl pinacolboronic esters, and DDQ oxidation gave the desired bifunctional terphenyl derivatives in good yields and regioselectivities. These terphenyl derivatives which were decorated with solubility promoting alkyl-substituents were subsequently subjected to Suzuki polycondensations generating soluble poly(phenylene)s of high molecular weight. Even challenging sterically hindered ortho-bromo-substituted arene moieties could be applied successfully in the Suzuki polycondensations. The regiodivergent cobalt-catalyzed step could be used in a divergent synthesis of poly(phenylene)s with different architectures starting from identical educts. Modifications in the starting materials, which can be easily introduced, will allow the flexible generation of more complex polymers in the future.