Copper-catalysed asymmetric radical cyanation

Catalytic asymmetric cyanation is a straightforward route to α-chiral nitriles that has previously relied on the enantioselective attack of cyanide on unsaturated electrophiles or the hydrocyanation of alkenes. More recently, such asymmetric cyanation reactions have entailed the reaction of cyanide with carbon radicals promoted by chiral copper catalysts via a radical relay process. In this Perspective, we discuss catalytic asymmetric cyanation reactions and the key carbon radicals involved, such as benzylic, allylic and propargylic radicals. In particular, we outline the control of selectivity by considering the mechanism of formation for the carbon radicals as well as the subsequent copper-catalysed radical cyanation step. The carbon radicals can be generated from a diverse range of precursors, which include C–H substrates, alkenes, esters, cyclopropanol and so on. As a consequence, copper-catalysed asymmetric radical cyanation has the potential to expand the scope of catalytic asymmetric cyanation and is expected to find broad utility in organic synthesis and the late-stage functionalization of complex molecules.