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Diastereoselective Radical Aminoacylation of Olefins through N‑Heterocyclic Carbene Catalysis
Ist Teil von
Journal of the American Chemical Society, 2022-12, Vol.144 (49), p.22767-22777
Ort / Verlag
United States: American Chemical Society
Erscheinungsjahr
2022
Link zum Volltext
Quelle
MEDLINE
Beschreibungen/Notizen
There have been significant advancements in radical-mediated reactions through covalent-based organocatalysis. Here, we present the generation of iminyl and amidyl radicals via N-heterocyclic carbene (NHC) catalysis, enabling diastereoselective aminoacylation of trisubstituted alkenes. Different from photoredox catalysis, single electron transfer from the deprotonated Breslow intermediate to O-aryl hydroxylamine generates an NHC-bound ketyl radical, which undergoes diastereocontrolled cross-coupling with the prochiral C-centered radical. This operationally simple method provides a straightforward access to a variety of pyrroline and oxazolidinone heterocycles with vicinal stereocenters (77 examples, up to >19:1 d.r.). Electrochemical studies of the acyl thiazolium salts support our reaction design and highlight the reducing ability of Breslow-type derivatives. A detailed computational analysis of this organocatalytic system suggests that radical–radical coupling is the rate-determining step, in which π–π stacking interaction between the radical intermediates subtly controls the diastereoselectivity.