Copper-catalysed synthesis of chiral alkynyl cyclopropanes using enantioconvergent radical cross-coupling of cyclopropyl halides with terminal alkynes

Abstract

Transition-metal-catalysed enantioconvergent cross-coupling reactions of highly reactive alkyl radicals often suffer from reduced chemoselectivity, mainly due to side reactions with closed-shell reactants. A strategy to overcome this challenge has yet to be identified, posing substantial limitations on the synthetic utility of this method. Here we report a method for enantioconvergent radical carbon–carbon cross-coupling of highly reactive cyclopropyl radicals with terminal alkynes, using redox state-tuned copper catalysis, under mild conditions. Key to this method is the use of hard chiral N,N,N-ligands in combination with Cu(II) salts of hard ligands/counterions, which results in elevated concentrations of Cu(II) species and thus enhanced cross-coupling reactions. This protocol not only exhibits a broad substrate scope across a wide range of both racemic cyclopropyl halide and terminal alkyne coupling partners but also provides access to useful yet synthetically challenging enantioenriched cyclopropane building blocks. The synthetic use of highly reactive alkyl radicals typically results in low chemoselectivity due to competing side reactions. Now, a redox-state-tuned copper catalytic method is reported, which enables the enantioconvergent cross-coupling of cyclopropyl radicals and terminal alkynes with high chemo- and stereoselectivity.