An Overview of a-Aminoalkyl Radical Mediated Halogen-Atom Transfer

The merging of photocatalysis with halogen-atom transfer (XAT) processes has proven to be a versatile tool for the generation of carbon-centered radicals in organic synthesis. XAT processes are unique in that they generate radicals without requiring the use of strong reductants necessary for the traditional single electron transfer (SET) activation of halides. Pathways to achieve XAT in synthetic applications can be categorized into three major sections: i) heteroatom-based activators, ii) metal-based activators, and iii) carbon-based activators among which a-aminoalkyl radicals have taken the center stage. Access to these a-aminoalkyl radicals as XAT reagents has gained significant attention in the past few years due to the robustness of the reactions, the simplicity of the reagents required, and the broadness of their applications. Generation of these a-aminoalkyl radicals is simply achieved through the single electron oxidation of tertiary amines, which after deprotonation at the a-position generates the a-aminoalkyl radicals. Due to the wide scope of tertiary amines available and the tunable nucleophilicity of a-aminoalkyl radical formed, this strategy has become an attractive alternative to heteroatom/metal-based radicals for XAT. In this minireview, we focus our attention on recent (2020-2023) developments and uses of this robust technology to mediate XAT processes.

Automated summary

The merging of photocatalysis with halogen-atom transfer processes provides a versatile tool for generating carbon-centered radicals in organic synthesis. Three major pathways for achieving XAT in synthetic applications are categorized as heteroatom-based, metal-based, and carbon-based activators, with a-aminoalkyl radicals taking the center stage. The simplicity and broad applications of a-aminoalkyl radicals as XAT reagents make them an attractive alternative to heteroatom/metal-based radicals.