Direct C–H Arylation of Thiophenes at Low Catalyst Loading of a Phosphine-Free Bis(alkoxo)palladium Complex

An efficient phosphine-free direct
C–H arylation of thiophenes
at the α-position has been developed at low catalyst loading
of bis­(alkoxo)palladium complex (Cat.I, 0.1–0.2
mol %). The developed synthetic method can be applied to the synthesis
of α-aryl/heteroaryl thiophenes from aryl or heteroaryl bromides
in good to excellent yields and is compatible with the substrates
bearing electron-donating or electron-withdrawing groups. The reactivities
of the 2- and 5-positions of thiophenes are equivalent and not dependent
on steric hindrance under optimal conditions. This condition can also
be applied to other heterocyclic moieties such as benzothiophene,
benzofuran, and pyrrole with high conversion yields.