Enantioselective catalytic β-amination through proton-coupled electron transfer followed by stereocontrolled radical–radical coupling

Zhou, Zijun; Li, Yanjun; Han, Bowen; Gong, Lei; Meggers, Eric

doi:10.1039/c7sc02031g

Cited by 80 publications

(57 citation statements)

References 99 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Moreover, the resulting enoyl radical anions feature persistency caused by Rh complexation, and by using a chiral Rh complex, asymmetric induction can be achieved. This chemistry was developed by Meggers (Figure ) . With a photoredox catalyst, carbamate 127 is oxidized to an N‐centered radical 129 , and α,β‐unsaturated ketone 126 is reduced to the enoyl radical 130 , which is stabilized by a chiral Rh complex as the Lewis acid.…”

Section: Radical–metal Crossover Reactionsmentioning

confidence: 99%

“…This chemistry was developed by Meggers ( Figure 35). [196] With ap hotoredox catalyst, carbamate 127 is oxidized to an N-centered radical 129,a nd a,b-unsaturated ketone 126 is reduced to the enoyl radical 130,which is stabilized by achiral Rh complex as the Lewis acid. These two radicals combine (see 131)togive,after protonation, the b-aminoketone 128 in high stereoselectivity.T he high cross-coupling selectivity is ensured by the longer lifetime of the enoyl radical 130.I n as imilar transformation, radicals 130 were shown to selectively combine with a-oxoketyl radicals.…”

Section: Rhodiummentioning

confidence: 99%

See 1 more Smart Citation

The Persistent Radical Effect in Organic Synthesis

2019

View full text Add to dashboard Cite

Radical–radical couplings are mostly nearly diffusion‐controlled processes. Therefore, the selective cross‐coupling of two different radicals is challenging and not a synthetically valuable transformation. However, if the radicals have different lifetimes and if they are generated at equal rates, cross‐coupling will become the dominant process. This high cross‐selectivity is based on a kinetic phenomenon called the persistent radical effect (PRE). In this Review, an explanation of the PRE supported by simulations of simple model systems is provided. Radical stabilities are discussed within the context of their lifetimes, and various examples of PRE‐mediated radical–radical couplings in synthesis are summarized. It is shown that the PRE is not restricted to the coupling of a persistent with a transient radical. If one coupling partner is longer‐lived than the other transient radical, the PRE operates and high cross‐selectivity is achieved. This important point expands the scope of PRE‐mediated radical chemistry. The Review is divided into two parts, namely 1) the coupling of persistent or longer‐lived organic radicals and 2) “radical–metal crossover reactions”; here, metal‐centered radical species and more generally longer‐lived transition‐metal complexes that are able to react with radicals are discussed—a field that has flourished recently.

show abstract

Section: Radical–metal Crossover Reactionsmentioning

confidence: 99%

Section: Rhodiummentioning

confidence: 99%

The Persistent Radical Effect in Organic Synthesis

2019

View full text Add to dashboard Cite

show abstract

“…Merging bis‐cyclometallated chiral Rh(III) complexes and α,β‐unsaturated acyl‐imidazoles 1 under photoredox conditions gave a straightforward alternative route for highly enantioselective β‐functionalization of such substrates. Alkyl radicals generated from organotrifluoroborates, nitrogen‐centered radicals obtained through proton‐coupled electron transfer (PCET), and α‐amino radicals supplied from tertiary amine derivatives allowed the formation of C−C and C−N bonds at the β‐position of 1 in an impressive enantiocontrol. Additionally, remote, unactivated δ‐C(sp 3 )−H bonds of N ‐alkyl amides were also prone to radical formation and reaction under Rh(III)‐photoredox catalysis (Scheme ) …”

Section: Metal‐centered Chirality Catalysismentioning

confidence: 99%

Acyl‐Imidazoles: A Privileged Ester Surrogate for Enantioselective Synthesis

et al. 2019

View full text Add to dashboard Cite

Since the first report by Evans in asymmetric Friedel-Crafts reactions, the use of acyl-imidazoles has blossomed as powerful ester/amide surrogates. The imidazole scaffold indeed displays stability and special activation features allowing both better reactivity and selectivity in traditional ester/amide functionalizations: α-(enolate chemistry), β-(conjugate additions), α,β-(cyclo-additions) or γ/δ-(vinylogous). An overview of the contemporary and growing interest in acyl-imidazoles in metal-and organo-catalyzed transformations (bio-hybrid catalytic systems will be fully described in a back-to-back Minireview) will be highlighted. Moreover, post-functionalization expediencies are also going to be discussed in this Minireview. Scheme 1. Synthesis of acyl-imidazoles by Okamoto and co-workers.Scheme 2. Synthesis of α,β-unsaturated acyl-imidazoles. . α-Alkylation of 2-naphthylmethyloxy acyl-imidazoles through PTC catalysis. NPM = 2-naphthylmethyl.Scheme 47. Chemo-and enantioselective oxidative cycloetherification of 2acyl-imidazoles with chiral quaternary ammonium salts. (please, change the chemdraw scheme 47; a new one is given) Scheme 48. Organocatalyzed enantioselective conjugate addition of aryl trifluoroborate to α,β-unsaturated 2-acyl 1-methylimidazole. 2 3 4 5 6 7 8

show abstract

“…103 Chalcones we shown to undergo reductive dimerization when treated with Ru II (bpy) 3 (PF 6 ) 2 photoredox catalyst, Sm(OTf) 3 Lewis acid and Hünig's base as the terminal reductant. Sm(III)-stabilized anion radical 46.2 was proposed to dimerize to generate dienolate 46.3 .…”

Section: Reactions Of Enones and Cyclopropylketones Via Ketyl Radicalmentioning

confidence: 96%

Recent developments in transition-metal photoredox-catalysed reactions of carbonyl derivatives

2017

View full text Add to dashboard Cite

Single-electron reduction of C=O and C=N bonds of aldehydes, ketones, and imines results in the formation of ketyl and α-aminoalkyl anion radicals, respectively. These reactive intermediates are characterized by an altered electronic character with respect to their parent molecules and undergo a diverse range of synthetically useful transformations, which are not available to even-electron species. This Review summarizes the reactions of ketyl and α-aminyl radicals generated from carbonyl derivatives under transition-metal photoredox-catalysed conditions. We primarily focus on recent developments in the field, as well as give a brief overview of catalytic enantioselective transformations that provide means to achieve precise stereocontrol over the reactivity of ion radicals.

show abstract

Enantioselective catalytic β-amination through proton-coupled electron transfer followed by stereocontrolled radical–radical coupling

Abstract: The catalytic asymmetry conjugate addition of carbamates to α,β-unsaturated 2-acyl imidazoles is accomplished using visible-light-induced proton-coupled electron transfer.

Cited by 80 publications

References 99 publications

The Persistent Radical Effect in Organic Synthesis

The Persistent Radical Effect in Organic Synthesis

Acyl‐Imidazoles: A Privileged Ester Surrogate for Enantioselective Synthesis

Recent developments in transition-metal photoredox-catalysed reactions of carbonyl derivatives

Contact Info

Product

Resources

About