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Download fileAsymmetric Induction and Enantiodivergence in Catalytic Radical C–H Amination via Enantiodifferentiative H-Atom Abstraction and Stereoretentive Radical Substitution
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posted on 29.07.2019, 04:29 authored by Kai Lang, Sebastian Torker, Lukasz Wojtas, X. Peter ZhangControl of enantioselectivity remains
a major challenge in radical
chemistry. The emergence of metalloradical catalysis (MRC) offers
a conceptually new strategy for addressing this and other outstanding
issues. Through the employment of D2-symmetric
chiral amidoporphyrins as the supporting ligands, Co(II)-based MRC
has enabled the development of new catalytic systems for asymmetric
radical transformations with a unique profile of reactivity and selectivity.
With the support of new-generation HuPhyrin chiral ligands whose cavity
environment can be fine-tuned, the Co-centered d-radicals enable to
address challenging issues that require exquisite control of fundamental
radical processes. As showcased with asymmetric 1,5-C–H amination
of sulfamoyl azides, the enantiocontrol of which has proven difficult,
the judicious use of HuPhyrin ligand by tuning the bridge length and
other remote nonchiral elements allows for controlling both the degree
and sense of asymmetric induction in a systematic manner. This effort
leads to successful development of new Co(II)-based catalytic systems
that are highly effective for enantiodivergent radical 1,5-C–H
amination, producing both enantiomers of the strained five-membered
cyclic sulfamides with excellent enantioselectivities. Detailed deuterium-labeling
studies, together with DFT computation, have revealed an unprecedented
mode of asymmetric induction that consists of enantiodifferentiative
H-atom abstraction and stereoretentive radical substitution.
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Keywords
nonchiral elementsnew-generation HuPhyrin chiral ligandsbridge lengthStereoretentive Radical Substitution Controldeuterium-labeling studiesMRCissuecavity environmentenantiodifferentiative H-atom abstractionEnantiodifferentiative H-Atom Abstractionfive-membered cyclic sulfamidesinductionHuPhyrin ligandmetalloradical catalysischiral amidoporphyrinssulfamoyl azidesDFT computationCo-centered d-radicalsD 2Asymmetric Inductionamination