Ru-catalysed C-H arylation of indoles and pyrroles with boronic acids - Scope and mechanistic studies

The Ru-catalysed C2-H arylation of indoles and pyrroles by using boronic acids under oxidative conditions is reported. This reaction can be applied to tryptophan derivatives and tolerates a wide range of functional groups on both coupling partners, including bromides and iodides, which can be further derivatised selectively. New indole-based ruthenacyclic complexes are described and investigated as possible intermediates in the reaction. Mechanistic studies suggest the on-cycle intermediates do not possess a para-cymene ligand and that the on-cycle metalation occurs through an electrophilic attack by the Ru centre. High tolerance: An oxidative, Ru-catalysed, and highly selective C-H arylation of indoles and pyrroles is accomplished by using boronic acids (see picture; pym=2-pyrimidyl). The reaction tolerates a wide range of functional groups, including aryl iodides and tryptophan derivatives. New indole-based ruthenacycles are described and their role in the mechanism is investigated.