A silylative reduction of quinolines to synthetically versatile tetrahydroquinoline molecules involving the formation of a C(sp(3))-Si bond exclusively β to nitrogen is described. Triarylborane is a highly efficient catalyst (up to 1000 turnovers), and silanes serve as both a silyl source and a reducing reagent. The present procedure is convenient to perform even on a large scale with excellent stereoselectivity. Mechanistic studies revealed that the formation of a 1,4-addition adduct is rate-limiting while the subsequent C(sp(3))-Si bond-forming step from the 1,4-adduct is facile.

Silylative reduction of nitriles was studied under transition metal-free conditions by using B(C6F5)3 as a catalyst with hydrosilanes as a reductant. Alkyl and (hetero)aryl nitriles were efficiently converted to primary amines or imines under mild conditions. The choice of silanes was found to determine the selectivity: while a full reduction of nitriles was highly facile, the use of sterically bulky silanes allowed for the partial reduction leading to N-silylimines.

Tris(pentafluorophenyl)borane-catalyzed silylative reduction of pyridines has been developed giving rise to the formation of sp(3) C-Si bonds selectively beta to the nitrogen atom of azacyclic products. Depending on the position and nature of pyridine substituents, structurally diverse azacycles are obtained with high selectivity under the borane catalysis. Mechanistic studies elucidated the sequence of hydrosilylation in this multiple reduction cascade: 1,2- or 1,4-hydrosilylation as an initial step depending on the substituent position, followed by selective hydrosilylation of enamine double bonds eventually affording β-silylated azacyclic compounds.

The conversion of renewable biomass resources to synthetically valuable chemicals is highly desirable, but remains a formidable challenge in regards to the substrate scope and reaction conditions. Here we present the development of tris(pentafluorophenyl)borane–catalysed conversion of furans via ring-opening and closing cascade processes to afford silicon-functionalized synthetic chemicals under transition metal-free conditions. The furan ring-opening with hydrosilanes is highly efficient (TON up to 2,000) and atom-economical without forming any byproduct to give rise to α-silyloxy-(Z)-alkenyl silanes. Additional equivalents of silane smoothly induce a subsequent B(C6F5)3-catalysed cyclization of initially formed olefinic silane compounds to produce anti-(2-alkyl)cyclopropyl silanes, another versatile synthon being potentially applicable in the synthesis of natural products and pharmacophores.