Selective Silylative Reduction of Pyridines Leading to Structurally Diverse Azacyclic Compounds with the Formation of sp³ C-Si Bonds.

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.