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Aminoalkyl radicals as halogen-atom transfer agents for activation of alkyl and aryl halides

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Science  28 Feb 2020:
Vol. 367, Issue 6481, pp. 1021-1026
DOI: 10.1126/science.aba2419

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Amines as a gateway to alkyl radicals

In recent years, photoredox catalysis driven by blue light has often been used to oxidize carbon centers adjacent to nitrogen. Constantin et al. now show that these aminoalkyl radicals can, in turn, conveniently strip iodine atoms from a variety of alkyl carbons. The new alkyl radicals that result readily undergo deuteration and couplings such as alkylation, allylation, and olefination. The upshot is that simple amines can replace more hazardous conventional reagents such as trialkyltin compounds in the homolytic activation and functionalization of halocarbons.

Science, this issue p. 1021

Abstract

Organic halides are important building blocks in synthesis, but their use in (photo)redox chemistry is limited by their low reduction potentials. Halogen-atom transfer remains the most reliable approach to exploit these substrates in radical processes despite its requirement for hazardous reagents and initiators such as tributyltin hydride. In this study, we demonstrate that α-aminoalkyl radicals, easily accessible from simple amines, promote the homolytic activation of carbon-halogen bonds with a reactivity profile mirroring that of classical tin radicals. This strategy conveniently engages alkyl and aryl halides in a wide range of redox transformations to construct sp3-sp3, sp3-sp2, and sp2-sp2 carbon-carbon bonds under mild conditions with high chemoselectivity.

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