Palladium-Catalyzed Direct B—H Oxygenation: Facile Synthesis of o-Carboranofuranones†

Abstract

Recent advances in transition metal-catalyzed o-carborane B—H activation have led to the rapid development of various methodologies for cage boron functionalization. For catalytic cage B—H acyloxylation, intermolecular oxygenation gave products with different regioselectivities (B(3)-, B(4)-, and B(8,9)-selectivities). Herein, an efficient palladium-catalyzed direct cage B(4)–H oxygenation of o-carboranylacetic acids has been achieved, where the carboxylic group serves as not only a directing group, but also a coupling partner. A wide range of substituted o-carboranylacetic acids have been cyclized via the formation of B(4)−O bond to give the corresponding γ-lactones in modest to excellent yields. A Pd(IV) intermediate is proposed to be involved in the catalytic cycle. This work offers valuable references for the BH/OH dehydrocoupling reactions under mild conditions to produce carborane-featuring functional molecules.