Hydrogen-Bond-Donor Coupled Electron Transfer Enabled Copper-Catalyzed Asymmetric Radical Alkynylation with a Planar...

H-bonding noncovalent interactions can efficiently facilitate electron transfer in many biological processes and organic transformations, enabling the activation of inert chemical bonds. As a prominent example, utilizing H-bonding interaction, proton coupled electron transfer (PCET), wherein both the proton and electron are transferred, has been well applied in synthetic transformations. However, as proton transfer is required, reductive PCET is generally not applicable to basic conditions and has not been implemented in the transition-metal catalyzed radical asymmetric coupling─a versatile tool for constructing complex molecules. In contrast to PCET, in a hydrogen-bond-donor coupled electron transfer (HCET) process, only electrons but no proton are transferred. This key distinction makes HCET applicable under basic conditions. Utilizing the HCET strategy, we report the copper-catalyzed asymmetric radical alkynylation of readily available yet less reactive alkyl chlorides, with the presence of a new tridentate f-PNN ligand featuring planar chirality. Mechanistic studies indicate that the HCET effect between the H-bonding catalyst and the alkyl chloride plays a vital role in the activation of the C-Cl bond. The catalytic system is highly effective in the asymmetric alkynylation of diverse benzyl chlorides with alkynes (excellent yield and ee), opening the door for HCET enabled transition-metal catalyzed radical coupling of inert chemical bonds under basic conditions.