Asymmetric Photoinduced Giese Radical Addition Enabled by a Single Chiral-at-Metal Rhodium Complex

Chen, Liang; Hu, Liangjian; Du, Yu; Su, Weiping; Kang, Qiang

doi:10.6023/cjoc202004041

Cited by 7 publications

(9 citation statements)

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“…94 Giese-type addition of this acyl radical to the chiral iminium intermediate is the stereodetermining step for the β-acylation of cinnamaldehydes. 95 The scope of the acylation reaction revealed that a variety of substituents are tolerated (Scheme 43). 94 Aryl, alkyl as well as heteroaryl groups could be introduced from the acyl function with moderate results.…”

Section: Scheme 42 Alkyl Hantzsch Esters (He) As Radical Precursorsmentioning

confidence: 99%

“…Experiments performed with radical clocks supported a radical mechanism involving the reductive formation of α-alkoxycarbonyl radicals that undergo ring opening or ring closing faster than they react with transmetalated Co(III) complex before reductive elimination (Scheme 157). 339 Visible-light-induced enantioselective Giese addition 100 was recently achieved by Xiao by using chiral octahedral Co(II) complexes based on chiral N4 ligands and dihydropyridines as source of alkyl radical and mesityl-acridinium perchlorate (Ms-AcrClO 4 ) as photocatalyst. 340 Yields varying from 54 to 90% and ee's ranging from 83 to 92% were obtained in the presence of 8 mol % of the catalyst (Scheme 158).…”

Section: Aziridination Reactionsmentioning

confidence: 99%

“…The dihydropyridine (DHP) entity bearing an acyl group absorbs in the visible region, and it can be excited at 460 nm to serve as the photoexcited partner to give, after decomposition to pyridine derivative, an acyl radical (Scheme ). Giese-type addition of this acyl radical to the chiral iminium intermediate is the stereodetermining step for the β-acylation of cinnamaldehydes …”

Section: Organocatalyzed Enantioselective Radical Reactionsmentioning

confidence: 99%

“…Visible-light-induced enantioselective Giese addition was recently achieved by Xiao by using chiral octahedral Co(II) complexes based on chiral N4 ligands and dihydropyridines as source of alkyl radical and mesityl-acridinium perchlorate (Ms-AcrClO 4 ) as photocatalyst . Yields varying from 54 to 90% and ee’s ranging from 83 to 92% were obtained in the presence of 8 mol % of the catalyst (Scheme ).…”

Section: Chiral Transition-metal-catalyzed Asymmetric Radical Processesmentioning

confidence: 99%

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Enantioselective Radical Reactions Using Chiral Catalysts

Mondal¹,

et al. 2022

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Scheme 24 Enantioselective Radical Hydroacylation of Enals with α-Ketoacids byMerging Photoredox Catalysis with Amine Catalysis.Jang et al. exploited enantioselective tandem Michael addition/oxyamination of α,β-unsaturated aldehydes by combining asymmetric iminium catalysis using organocatalyst with photoinduced SOMO catalysis using N719/TiO2. 60 Here, TiO2 acts as a second cooperative photocatalyst along with Ru photocatalyst N719 which bound to the latter, increases the enantio-and diastereoselectivity of the process. Adamantane carboxylic acid (30 mol%) was used as an additive which promotes formation of iminium ion 2.1.48A from aldehyde 2.1.48 and chiral amine catalyst. This iminium intermediate then reacts with diethyl malonate to provide intermediate 2.1.48B which either undergoes hydrolysis to form β-substituted aldehyde 2.1.50 or photo-oxidation by the photoexcited Ru(II) dye to form enamine radical 2.1.48C. Subsequent addition of TEMPO to radical intermediate 2.1.48BC followed by hydrolysis afforded the desired product 2.1.49 (Scheme 25). This mechanism is obeying to a polar/radical crossover sequence where the first stereocontrol arises from the addition of the malonate.Recently, Bach group reported promising preliminary results of enantioselective [2+2] photocycloaddition of cinnamaldehyde in the presence of ruthenium photocatalyst and proline derived organocatalyst. 61

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Section: Scheme 42 Alkyl Hantzsch Esters (He) As Radical Precursorsmentioning

confidence: 99%

Section: Aziridination Reactionsmentioning

confidence: 99%

Section: Organocatalyzed Enantioselective Radical Reactionsmentioning

confidence: 99%

Section: Chiral Transition-metal-catalyzed Asymmetric Radical Processesmentioning

confidence: 99%

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Enantioselective Radical Reactions Using Chiral Catalysts

Mondal¹,

et al. 2022

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“…272 More recently, Su and Kang established an asymmetric Giese addition of p-aminobenzyl radicals from the corresponding carboxylic acids using chiral rhodium catalyst Λ-223b. 273 Finally, the synthesis and application of novel chiral-at-metal bis-cyclometalated indazole catalyst Λ-224 was useful in producing α-cyano radicals and controlling their facially selective addition to rhodium enolates. 274 The mechanisms and origins of enantioselectivity using this class of Rh(III) photocatalysts (Scheme 84) have been studied by Meggers and Wiest, 275 revealing a strong rate enhancement induced by the rhodium catalyst to overcome competitive racemic reactivity.…”

Section: Rhodiummentioning

confidence: 99%

Chiral Photocatalyst Structures in Asymmetric Photochemical Synthesis

et al. 2021

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Asymmetric catalysis is a major theme of research in contemporary synthetic organic chemistry. The discovery of general strategies for highly enantioselective photochemical reactions, however, has been a relatively recent development, and the variety of photoreactions that can be conducted in a stereocontrolled manner is consequently somewhat limited. Asymmetric photocatalysis is complicated by the short lifetimes and high reactivities characteristic of photogenerated reactive intermediates; the design of catalyst architectures that can provide effective enantiodifferentiating environments for these intermediates while minimizing the participation of uncontrolled racemic background processes has proven to be a key challenge for progress in this field. This review provides a summary of the chiral catalyst structures that have been studied for solution-phase asymmetric photochemistry, including chiral organic sensitizers, inorganic chromophores, and soluble macromolecules. While some of these photocatalysts are derived from privileged catalyst structures that are effective for both ground-state and photochemical transformations, others are structural designs unique to photocatalysis and offer insight into the logic required for highly effective stereocontrolled photocatalysis.

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Asymmetric Photoredox Reactions Without Photocatalysts

Wong

Melchiorre

2022

Catalytic Asymmetric Synthesis

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Asymmetric Photoinduced Giese Radical Addition Enabled by a Single Chiral-at-Metal Rhodium Complex

Cited by 7 publications

References 1 publication

Enantioselective Radical Reactions Using Chiral Catalysts

Enantioselective Radical Reactions Using Chiral Catalysts

Chiral Photocatalyst Structures in Asymmetric Photochemical Synthesis

Asymmetric Photoredox Reactions Without Photocatalysts

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