Alkylboron and -silicon Compounds

Abstract

Alkylboron and -silicon compounds are such key reagents in organic synthesis that it is virtually impossible to undertake any major synthesis without employing either. Hydroboration is one of the most studied reactions in organic synthesis, being the most important type of electrophilic addition to a double bond that can be carried out with high stereoselectivity. There is now a variety of amine complexes of diborane that are sufficiently reactive to provide viable alternatives to the traditional diborane reagents, as well as many documented examples of successful asymmetric syntheses that employ achiral and homochiral alkylboron reagents. Asymmetric methods of hydroboration are augmented by catalytic hydrosilylation procedures with useful and practical solid-supported variants beginning to emerge. Silicon-based protecting groups such as silyl ethers, of which there are new examples, continue to play more than just a spectator role in organic synthesis. Methods for their introduction and selective removal, stability profiles, and compatibilities with other functional groups have been studied extensively. Silyl-based linkers, especially those that are traceless, are effective for solid-supported reactions including combinatorial strategies. The high stereoselectivities achievable by alkylboron and -silicon reagents coupled with better reagent recycling will counterbalance any concerns over atom economy.