Direct α-heteroarylation of amides (α to nitrogen) and ethers through a benzaldehyde-mediated photoredox reaction

Abstract

A benzaldehyde-mediated photoredox reaction for the α-heteroarylation of amides (α to nitrogen) and ethers through cross-dehydrogenative coupling (CDC).

Direct C−H Carbamoylation of Nitrogen‐Containing Heterocycles

“…However, the yield was low and a significant amount of side products were generated. We rationalized that visible light could mediate decomposition of persulfate as proposed by Ji and co‐workers, generating the sulfate radical anion responsible of oxidizing the oxamate, and consequently leading to the desired carbamoylation reaction (see Scheme , propagation)…”

“…Varying the electronics of the substituents on the nitrogen atom and were delighted to obtain the desired products in often excellent yields. Indeed, N ‐alkyl and N , N ′‐dialkyl carbamoyl groups were perfectly tolerated and no activation of the C−H bonds adjacent to nitrogen was observed . Sterically encumbered amines, which are very often problematic to couple even using the most elaborate coupling reagents, proceeded uneventfully (Figure , products 13 and 19 ).…”

Photochemical Hydroacylation of Michael Acceptors Utilizing an Aldehyde as Photoinitiator

“…The Based on examples in literature, the benzoyl radicals eems to be the initiator,a lthoughe xamples of ketyl radicals to promote the HATe vent are also known. [25,26] An energy-transfer mechanism, an EDAc omplex mechanism, or direct interaction of triplet benzaldehyde with one of the reagents seems unlikely to be the dominantm echanism, according to our experi-ments.T he moderate quenching of 4-cyanobenzaldehydeb y diethylm aleate is owing to the parasitic reactiono fcis-trans isomerization to fumarate. Also, as ingle-electron-transfer mechanism or ab enzoyl peroxide radical-initiated process (benzoyl radicalc oupled with oxygen) have also been ruled out as the dominant pathway.N evertheless, further validation of the mechanism is still ongoing by our team.…”

“…Based on examples in literature, the benzoyl radical seems to be the initiator, although examples of ketyl radicals to promote the HAT event are also known . An energy‐transfer mechanism, an EDA complex mechanism, or direct interaction of triplet benzaldehyde with one of the reagents seems unlikely to be the dominant mechanism, according to our experiments.…”

Neue Entwicklungen auf dem Gebiet der Minisci‐Reaktion

“…[79] 2016 zeigten DiRocco,Krska und Mitarbeiter bei Merck, dass ein Methanol-Persäure-System die Hydroxymethylierung von Heteroarenen ermçglicht. [83] Bemerkenswert ist, dass dabei die Abstraktion eines Wasserstoffatoms von einer a-C-H-Bin- Ravelli, Ryu und Mitarbeiter nutzten 2017 in einem dualen Photoredox/HAT-Katalyseansatz die Abstraktion eines Wasserstoffatoms von aktivierten und unaktivierten C-H-Bindungen fürM inisci-Reaktionen (Schema 25). Das resultierende a-Hydroxymethylradikal wird anschließend an Heteroarene addiert (Schema 23).…”