Emerging Strategies for C–H Silylation

Iridium and rhodium catalyses enable undirected remote C(sp2)–H silylation of (hetero)arenes under predominantly steric control and mild conditions. Direct silylation of rather unreactive C(sp3)–H bonds was disclosed by employing transition-metal catalysis. The sila-Friedel–Crafts reaction was finally achieved by removal of protons from the reaction mixture in the form of dihydrogen gas. This way, acid-promoted protodesilylation was successfully suppressed. Boron-based Lewis acids enable the metal-free C(sp2)–H silylation in the form of an electrophilic aromatic substitution (SEAr). Silicon-containing molecules are of great academic and industrial interest with widespread applications in several research areas such as materials science, medicinal chemistry, and complex-molecule synthesis. C–Si bond formation by direct C–H functionalization is a modern synthetic approach toward highly valuable compounds that offers a superior step and atom economy in contrast to conventional procedures involving at least one prefunctionalized reaction partner. In this review, we summarize the different strategies for C–H silylation. Organized by their reaction mechanism, a representative selection of recent methodologies is introduced and compared with regard to their substrate scope, functional-group tolerance, and regioselectivity. Silicon-containing molecules are of great academic and industrial interest with widespread applications in several research areas such as materials science, medicinal chemistry, and complex-molecule synthesis. C–Si bond formation by direct C–H functionalization is a modern synthetic approach toward highly valuable compounds that offers a superior step and atom economy in contrast to conventional procedures involving at least one prefunctionalized reaction partner. In this review, we summarize the different strategies for C–H silylation. Organized by their reaction mechanism, a representative selection of recent methodologies is introduced and compared with regard to their substrate scope, functional-group tolerance, and regioselectivity. a process which transforms a prochiral molecule into a chiral one by loss of one or more symmetry elements. a functional group in the vicinity of the reaction center, which generates attractive substrate–reagent interaction and controls the trajectory of the incoming reagent. This phenomenon is also described as the complex-induced proximity effect (CIPE). functionalization of arenes in which a substituent (typically hydrogen) is replaced by an incoming electrophile. The reaction proceeds through a cationic σ-complex (Wheland intermediate). functionalization of arenes by attack of a free radical. a pentadienyl anion derivative embedded into a six-membered ring that is formed as a reactive intermediate (anionic σ-complex) in the reaction of a nucleophile and a sufficiently electron-deficient (hetero)arene. in a most general sense, a reaction in which a functional group (leaving group) is replaced by an incoming nucleophile. the acid-promoted substitution of a silyl group for a hydrogen atom. the negative value of the enthalpy change for the gas-phase reaction of a chemical compound and a proton. the preference of a direction in which a chemical bond is formed or broken. Regioselective reactions discriminate different potentially reactive positions in a molecule. the characteristic of having a stereogenic unit, such as a center, axis, or plane, which results in stereoisomerism. the conversion of a silyl group into an alcohol by oxidative degradation of the C–Si bond using either peroxy acids or hydrogen peroxide as an oxidant. formation of an adduct in which the binding ligand has a hapticity of 1 so that it coordinates only through one atom. an adduct that is formed by the attack of an electrophile, nucleophile, or radical at a ring carbon of an arene. A new σ-bond is formed by disruption of the original conjugated π-system.