Pd2dba3/Bippyphos: A Robust Catalyst System for the Hydroxylation of Aryl Halides with Broad Substrate Scope

A mixture of tris(dibenzylideneacetone)dipalladium(0) (Pd2dba3) and 5-(di-tert-butylphosphino)-1,3,5-triphenyl-1H-[1,4]bipyrazole (Bippyphos) is shown to be a robust and efficient catalyst system for the hydroxylation of structurally diverse (hetero)aryl halides under mild conditions and with broad substrate scope. Included in this reactivity survey is the successful synthesis of substituted benzofurans and related heteroatomic derivatives, which are formed via the hydroxylation of 2-haloalkynylarenes. Notably, a significant number of the reactions reported herein proceed at room temperature, and we have demonstrated that it is possible to conduct reactions on the benchtop under air using unpurified solvents with negligible loss in reactivity versus related transformations conducted under inert atmosphere conditions. We also report herein the first crystallographically characterized (Bippyphos)Pd(II) complex, which confirms the ability of this synthetically useful ligand to adopt a bidentate binding motif in a manner similar to Buchwald's biarylphosphine ligand class.