Aryl Boronic esters are important coupling partners in metal-catalyzed cross-coupling reactions as well as a variety of synthetic transformations. Their utility comes from their mild nucleophilicity, high stability, and low toxicity. Traditional methods to synthesize aryl boron reagents require the use of highly reactive reagents such as <i>n-</i>BuLi or stoichiometric amounts of organometallic species such as Grignard reagents. Catalytic methods using transition-metals such as palladium or copper exist, but these methods often lead to competitive homo-coupling byproducts and often require harsh reaction conditions. The major catalytic hurdle within current palladium-catalyzed methodologies is the activation and transmellation step of the diboron reagents, which leads to the use of high reaction temperatures to achieve the desired transformations. On the other hand, copper-catalyzed transformations are mainly limited at the oxidative addition step. Therefore, we surmized that using a combination of palladium and copper in a dual-metal catalysis approach would enable facile oxidative addition of palladium to the aryl iodides, while the copper catalyst would generate a Cu–Bpin species that readily transmetallates. Reaction conditions using aryl iodides with bis(pinacolato)diboron have been optimized and generate the desired borylated product in good to excellent yields. Substrate scope, functional group compatibility and mechanistic work will be presented.

Borylation of aryl iodides using a Pd/Cu dual catalysis

2019 Spring National Meeting

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