Directing Effects of Silyl and Germyl Groups in Transition-Metal-Catalyzed Allylic Substitution

Transition-metal-catalyzed allylic substitution is a well-established strategy for the formation of carbon-carbon and carbon-heteroatom bonds. However, most methods remain incompatible with unsymmetrical 1,3-disubstituted allylic electrophiles as regioselectivity becomes difficult to control when the substituents are electronically and sterically similar. Achieving simultaneous control over the enantio- and regioselectivity as well as the alkene geometry poses an even greater challenge. To address this, sterically and electronically influential main-group elements such as carbon's heavier homologues silicon and germanium have been strategically incorporated. These metalloids can steer the bond formation away from their proximity enabling the formation of a single regioisomer while also serving as versatile linchpins for further functionalization. This Concept summarizes the key advancements made in the field since the discovery of the allylic substitution with a particular focus on silyl- and germyl-directed strategies that have expanded the synthetic utility of this highly valuable transformation.