Ruthenium-Catalyzed Alkylation of Cyclopropanols with Sulfoxonium Ylides via C-C Bond Cleavage: Formation of Diverse 1,5-Diketones

Synthesis ◽  
2021 ◽  
Author(s):  
Xin Huang ◽  
Jianglian Li ◽  
Hua He ◽  
Kaichuan Yan ◽  
Ruizhi Lai ◽  
...  
Keyword(s):  
Bond Cleavage ◽  
Mechanistic Studies ◽  
Cyclization Reactions ◽  
Good Efficiency ◽  
Migratory Insertion

A novel ruthenium-catalyzed alkylation of cyclopropanols with sulfoxonium ylides has been developed, which afford diverse 1,5-diketones with good efficiency and broad substrate scope. To illustrate the synthetic utilities of obtained 1,5-diketones, aldol and cyclization reactions have been investigated. The preliminary mechanistic studies suggest that this process involves a sequential C-C activation and carbene migratory insertion.

Mechanistic Study and Development of Catalytic Reactions of Sm(II)

2018 ◽  
Author(s):  
Sandepan Maity ◽  
Robert Flowers
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Proton Donor ◽  
Catalytic Reactions ◽  
Mechanistic Study ◽  
Mechanistic Studies ◽  
Cyclization Reactions ◽  
Mechanistic Approach ◽  
Donor Source

Despite the broad utility and application of SmI<sub>2</sub>in synthesis, the reagent is used in stoichiometric amounts and has a high molecular weight, resulting in a large amount of material being used for reactions requiring one or more equivalents of electrons. We report mechanistic studies on catalytic reactions of Sm(II) employing a terminal magnesium reductant and trimethyl silyl chloride in concert with a non-coordinating proton donor source. Reactions using this approach permitted reductions with as little as 1 mol% Sm. The mechanistic approach enabled catalysis employing HMPA as a ligand, facilitating the development of catalytic Sm(II) 5-<i>exo</i>-<i>trig </i>ketyl olefin cyclization reactions.

scholarly journals Controlling Non-Native B12 Reactivity and Catalysis in the Transcription Factor CarH

2021 ◽  
Author(s):  
Xinhang Yang ◽  
Benjamin H. R. Gerroll ◽  
Yuhua Jiang ◽  
Amardeep Kumar ◽  
Yasmine S. Zubi ◽  
...  
Keyword(s):  
Transcription Factor ◽  
Vitamin B12 ◽  
Transcription Regulation ◽  
Bond Cleavage ◽  
Oxidative Addition ◽  
Mechanistic Studies ◽  
Organic Transformations ◽  
Carbon Bond ◽  
Wide Range ◽  
Hydride Elimination

Vitamin B12 derivatives catalyze a wide range of organic transformations, but B12-dependent enzymes are underutilized in biocatalysis relative to other metalloenzymes. In this study, we engineered a variant of the transcription factor CarH, called CarH*, that catalyzes styrene C-H alkylation with improved yield and selectivity relative to B12 itself. While the native function of CarH involves transcription regulation via AdoCbl Co(III)-carbon bond cleavage and β-hydride elimination to generate 4’,5’-didehydroadenosine, CarH*-catalyzed styrene alkylation proceeds via non-native oxidative addition and olefin addition coupled with a native-like β-hydride elimination. Mechanistic studies on this reaction echo findings from earlier studies on AdoCbl homolysis under strong cage conditions to suggest that CarH* can enable non-native radical chemistry with improved selectivity relative to B12 itself. These findings lay the groundwork for the development of B12-dependent enzymes as catalysts for a wide range of non-native transformations.

scholarly journals Light-Driven Depolymerization of Native Lignin Enabled by Proton- Coupled Electron Transfer

2019 ◽  
Author(s):  
Suong Nguyen ◽  
Phillip Murray ◽  
Robert Knowles
Keyword(s):  
Electron Transfer ◽  
Visible Light ◽  
Bond Cleavage ◽  
Direct Conversion ◽  
Alkoxy Radical ◽  
Radical Intermediate ◽  
Polymer Backbone ◽  
Good Efficiency ◽  
Chemical Reagents ◽  
Proton Coupled Electron Transfer

<div><p>Here we report a catalytic, light-driven method for the redox-neutral depolymerization of native lignin biomass at ambient temperature. This transformation proceeds via a proton-coupled electron-transfer (PCET) activation of an alcohol O–H bond to generate a key alkoxy radical intermediate, which then drives the <i>β</i>-scission of a vicinal C–C bond. Notably, this depolymerization is driven solely by visible light irradiation, requiring no stoichiometric chemical reagents and producing no stoichiometric waste. This method exhibits good efficiency and excellent selectivity for the activation and fragmentation of <i>β</i>-O-4 linkages in the polymer backbone, even in the presence of numerous other PCET-active functional groups. DFT analysis suggests that the key C–C bond cleavage reactions produce non-equilibrium product distributions, driven by excited-state redox events. These results provide further evidence that visible-light photocatalysis can serve as a viable method for the direct conversion of lignin biomass into valuable arene feedstocks.</p></div>

I2/TBHP-Promoted Approach to α-Keto Esters from Trifluoromethyl β-Diketones and Alcohols via C–C Bond Cleavage

Synlett ◽  
2017 ◽  
Vol 28 (15) ◽  
pp. 2018-2023 ◽  
Author(s):  
Xiang Fang ◽  
Xueyan Yang ◽  
Tongle Shao ◽  
Jun Zhou ◽  
Chen Jin ◽  
...  
Keyword(s):  
Oxidative Coupling ◽  
Bond Cleavage ◽  
Bond Formation ◽  
Coupling Reaction ◽  
Mechanistic Studies ◽  
Metal Free ◽  
Oxidation Pathway ◽  
Keto Esters ◽  
Oxidative Coupling Reaction

A metal-free oxidative coupling reaction of trifluoromethyl β-diketones with alcohols for the synthesis of α-keto esters in good to excellent yields has been developed. Preliminary mechanistic studies suggest that an I2/TBHP promoted sequential iodination, C–C bond cleavage, C–O bond formation and oxidation pathway is involved in this reaction.

scholarly journals A [3+2] Cyclization of Siloxyalkynes and Isocyanides for the Synthesis of Oxazoles

Synlett ◽  
2018 ◽  
Vol 30 (04) ◽  
pp. 515-518
Author(s):  
An Wu ◽  
Jianwei Sun
Keyword(s):  
Catalytic System ◽  
Mechanistic Studies ◽  
Cyclization Reactions ◽  
Aromatic Heterocycles ◽  
Mechanistic Insight

A mild and efficient [3+2] cyclization of siloxyalkynes for the synthesis of aromatic heterocycles is developed. It is a new addition to the cyclization reactions of these versatile species. In the presence of TBAF as promoter, siloxyalkynes react with electron-withdrawing isocyanides to form a range of oxazole products. In this reaction, siloxyalkynes contribute the C–O unit for the cyclization, which is different from previous typical examples where it is a two-carbon contributor. Mechanistic studies provided insights into the mechanism, which involves a ketene intermediate. Based on the mechanistic insight, an alternative catalytic system was also demonstrated to be effective for the same transformation.

Synthesis of 2, 5‐Diamino‐ p— benzoquinones via Aerobic Oxidative C(sp 2 )‐C(sp 2 ) Bond Cleavage and Mechanistic Studies

2020 ◽  
Vol 5 (8) ◽  
pp. 2545-2550
Author(s):  
Anandavally Asha ◽  
Jaice Ravindran ◽  
Subhadra Suma ◽  
Cherumuttathu H. Suresh ◽  
Ravi S. Lankalapalli
Keyword(s):  
Bond Cleavage ◽  
Mechanistic Studies
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