Hypervalent silicon as a reactive site in selective bond-forming processes

Silicon is a truly exceptional element as it serves as a reactive site for an almost infinite number of transformations pertinent to synthetic organic chemistry. Importantly, the intertwined relationship of the valency at silicon and its chemical reactivity represents the key to a profound understanding and the design of novel reactions. Thus, these so-called hypervalent silanes are crucial intermediates in silicon-based carbon-carbon bond-forming reactions, whereby tetravalent silanes are conventionally employed in carbon-silicon bond-forming processes. This review aims at a detailed discussion of these mechanistic aspects illustrated with some synthetically significant developments in modern organosilicon chemistry. Recent advances in silicon-mediated, organocatalytic C(sp(3))-C(sp(3)) bond formation directed towards the preparation of aldol and aldol-like products are covered. Silicon-based transition-metal-catalyzed C(sp(n))-C(sp(2)) bond formations involving hypervalent silicon intermediates are also included. These seemingly dissimilar reactions will be comparatively juxtaposed.