Synthetic applications of electro/photochemical halogen atom transfer (XAT)-driven carbon radical chemistry

Abstract

Organohalides are indispensable and widely used building blocks in organic synthesis and drug discovery due to their structural versatility, accessibility, and synthetic flexibility. The halogen atom transfer (XAT)-based strategy for generating carbon radicals from organohalides and further forming a variety of carbon–carbon and carbon–heteroatom bonds represents a powerful tool for constructing complex molecules. This approach overcomes the limitations posed by the highly negative potentials and high bond dissociation energies of organohalides, which enables the activation of inert carbon–halogen bonds under mild conditions, thus expanding the range and improving the tolerance of functional groups. In recent years, many photoredox-catalysed approaches have been reported, with advancements in energy transfer and electrochemistry leading to the development of mild methods for further functionalising organohalides and constructing complex molecules in the XAT process. This tutorial review summarises the recent advancements in research on XAT strategies for haloalkanes from the perspective of various relayed radicals such as aryl, alkyl, silyl, and boryl radicals. Detailed analysis of XAT processes of organohalides promoted by photocatalysis (energy transfer and electron donor–acceptor complex-mediated processes), electrocatalysis, and other catalytic processes is provided. Additionally, this review briefly discusses future research directions and development prospects in this field.