Selective Catalytic B–H Arylation of o‑Carboranyl Aldehydes by a Transient Directing Strategy

Carboranyl aldehydes are among the most useful synthons in derivatization of carboranes. However, compared to the utilization of carboranyl carboxylic acids in selective B–H bond functionalizations, the synthetic application of carboranyl aldehydes is limited due to the weakly coordinating nature of the aldehyde group. Herein, the direct arylation of o-carboranyl aldehydes has been developed via Pd-catalyzed cage B–H bond functionalization. With the help of glycine to generate a directing group (DG) in situ, a series of cage B­(4,5)-diarylated- and B(4)-monoarylated-o-carboranyl aldehydes were obtained in good to excellent yields with high selectivity. A wide range of functional groups are tolerated. The aldehyde group in the B–H arylated products could be readily removed or transformed into o-carboranyl methanol. A plausible catalytic cycle for B–H arylation was proposed based on control experiments and stoichiometric reactions, including the isolation of a key bicyclic palladium complex.