Silylation of C–H bonds in aromatic heterocycles by an Earth-abundant metal catalyst

Carbon–hydrogen (C–H) bond functionalization catalysed by potassium tert-butoxide, which is abundant and inexpensive, offers a direct route to the silylation of aromatic heterocycles that both obviates the need for precious metal catalysts and overcomes the limitations of previous methods. This paper describes a new general method for converting ubiquitous carbon–hydrogen bonds into carbon–silicon bonds that both obviates the need for precious metal catalysts and overcomes several of the limitations of previous methods. The method uses inexpensive and readily available potassium tert-butoxide to catalyse the acceptorless cross-dehydrogenative coupling of aromatic heterocycles with hydrosilanes to produce synthetically versatile heteroarylsilanes in a single step. Silicon-containing molecules are of importance in drug discovery, as medical diagnostic agents and as precursors for advanced electronics materials. Heteroaromatic compounds containing carbon–silicon (C–Si) bonds are of great interest in the fields of organic electronics and photonics1, drug discovery2, nuclear medicine3 and complex molecule synthesis4,5,6, because these compounds have very useful physicochemical properties. Many of the methods now used to construct heteroaromatic C–Si bonds involve stoichiometric reactions between heteroaryl organometallic species and silicon electrophiles6,7 or direct, transition-metal-catalysed intermolecular carbon–hydrogen (C–H) silylation using rhodium or iridium complexes in the presence of excess hydrogen acceptors8,9. Both approaches are useful, but their limitations include functional group incompatibility, narrow scope of application, high cost and low availability of the catalysts, and unproven scalability. For this reason, a new and general catalytic approach to heteroaromatic C–Si bond construction that avoids such limitations is highly desirable. Here we report an example of cross-dehydrogenative heteroaromatic C–H functionalization catalysed by an Earth-abundant alkali metal species. We found that readily available and inexpensive potassium tert-butoxide catalyses the direct silylation of aromatic heterocycles with hydrosilanes, furnishing heteroarylsilanes in a single step. The silylation proceeds under mild conditions, in the absence of hydrogen acceptors, ligands or additives, and is scalable to greater than 100 grams under optionally solvent-free conditions. Substrate classes that are difficult to activate with precious metal catalysts are silylated in good yield and with excellent regioselectivity. The derived heteroarylsilane products readily engage in versatile transformations enabling new synthetic strategies for heteroaromatic elaboration, and are useful in their own right in pharmaceutical and materials science applications.