Development of Chemoselective Suzuki-Miyaura Coupling Reactions

An efficient Pd-catalyzed cross-coupling reaction of phenylboronic acids and benzyl carbonates was developed, producing diarylmethanes.Benzyl acetates could also be used as coupling partners instead of benzyl carbonates, affording diarylmethanes in comparable yields.This reaction can be conducted under air atmosphere without any care for moisture and oxygen.The ester function showed an intermediate reactivity between chloro and bromo groups.This property facilitated the selective synthesis of diverse (benzyl)biphenyls by successive Suzuki-Miyaura coupling reactions using bromo-and chloro-substituted benzyl esters with two types of boronic acids.Two reaction conditions were developed to accomplish the substrate switchable Suzuki-Miyaura coupling of benzyl derivatives and arylboronic acid derivatives.Under Conditions for Esters, benzyl esters such as carbonates and acetates reacted with arylboronic acids to afford the corresponding diarylmethanes.However, the benzyl halides did not react under the same conditions.On the other hand, benzyl halides such as bromides and chlorides furnished diarylmethanes under Conditions for Halides, under which benzyl ester substrates did not react.This switching system was tested using the intermolecular/intramolecular competitive reactions, during which the desired products could be synthesized by selecting the appropriate reaction conditions.