Silylboranes as new tools in organic synthesis

Abstract

New reactivities of silylboranes are described with their applications to organic synthesis. The silylboranes add to unsaturated organic compounds such as alkynes, alkenes, 1,3-dienes, and allenes in the presence of nickel, palladium, and platinum catalysts. Reactions with isocyanide proceed in the absence of catalysts, giving 1,1-addition products. The silaborations proceed in highly regio- and stereoselective manners, leading to the formation of organic compounds bearing silyl and boryl groups. Silaborations accompanied by regioselective C-C bond cleavage in three-membered rings take place in the reactions of methylenecyclopropane and vinylcyclopropane derivatives. Unsaturated organic molecules, e.g., 1,3-diene and aldehyde, undergo silaborative C-C coupling reactions in the presence of transition-metal catalysts. Enantioselective silaboration of terminal alienes and silaborative C-C cleavage of mejo-methylenecyclopropanes have been achieved. Silaborations in which the stereochemical course, i.e., cis and trans stereoselectivities, is governed by the ligand have been established in platinum-catalyzed intramolecular silaborations of alkenes. Synthetic applications of the silaboration products through Suzuki-Miyaura coupling, one-carbon homologation, oxidation, allylation, and Rhcatalyzed conjugate addition are also described. Synthesis of silylboranes, including those having heteroatom functional groups at the silicon atoms, is summarized. © 2009 The Chemical Society of Japan.