Palladium‐Catalyzed Direct B—H Oxygenation: Facile Synthesis of <i>o</i>‐Carboranofuranones^†

Comprehensive Summary 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.