scholarly journals Cobalt-catalyzed deoxygenative triborylation of allylic ethers to access 1,1,3-triborylalkanes

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Wei Jie Teo ◽  
Xiaoxu Yang ◽  
Yeng Yeng Poon ◽  
Shaozhong Ge
Keyword(s):  
Building Blocks ◽  
Mechanistic Studies ◽  
Deuterium Labeling ◽  
Bond Forming ◽  
Carbon Carbon Bond ◽  
Synthetic Utility ◽  
Reaction Proceeds ◽  
Site Selective ◽  
And Control ◽  
Allylic Ethers

Abstract Polyborylated organic compounds have been emerging as versatile building blocks in chemical synthesis. Here we report a selective cobalt-catalyzed deoxygenative 1,1,3-triborylation reaction of allylic ethers with pinacolborane to prepare 1,1,3-triborylalkane compounds. With naturally abundant and/or synthetic cinnamic methyl ethers as starting materials, we have achieved the synthesis of a variety of 1,1,3-triborylalkanes (25 examples). The synthetic utility of these 1,1,3-triborylalkanes is demonstrated through site-selective allylation, protodeborylation, and consecutive carbon-carbon bond-forming reactions. Mechanistic studies including deuterium-labeling and control experiments suggest that this 1,1,3-triborylation reaction proceeds through initial cobalt-catalyzed deoxygenative borylation of allylic ethers to form allylic boronates followed by cobalt-catalyzed 1,1-diborylation of the resulting allylic boronates.

scholarly journals The Eschenmoser coupling reaction under continuous-flow conditions

2011 ◽  
Vol 7 ◽  
pp. 1164-1172 ◽  
Author(s):  
Sukhdeep Singh ◽  
J Michael Köhler ◽  
Andreas Schober ◽  
G Alexander Groß
Keyword(s):  
Continuous Flow ◽  
Elevated Temperatures ◽  
Reaction Times ◽  
Coupling Reaction ◽  
Flow Chemistry ◽  
Flow Conditions ◽  
Reaction Conditions ◽  
Bond Forming ◽  
Carbon Carbon Bond ◽  
Reaction Proceeds

The Eschenmoser coupling is a useful carbon–carbon bond forming reaction which has been used in various different synthesis strategies. The reaction proceeds smoothly if S-alkylated ternary thioamides or thiolactames are used. In the case of S-alkylated secondary thioamides or thiolactames, the Eschenmoser coupling needs prolonged reaction times and elevated temperatures to deliver valuable yields. We have used a flow chemistry system to promote the Eschenmoser coupling under enhanced reaction conditions in order to convert the demanding precursors such as S-alkylated secondary thioamides and thiolactames in an efficient way. Under pressurized reaction conditions at about 220 °C, the desired Eschenmoser coupling products were obtained within 70 s residence time. The reaction kinetics was investigated and 15 examples of different building block combinations are given.

scholarly journals Cu/Pd-catalyzed borocarbonylative trifunctionalization of alkynes and allenes: synthesis of β-geminal-diboryl ketones

2021 ◽  
Author(s):  
Yang Yuan ◽  
Fu-Peng Wu ◽  
Anke Spannenberg ◽  
Xiao-Feng Wu
Keyword(s):  
Organic Synthesis ◽  
Functional Group ◽  
Building Blocks ◽  
Mechanistic Studies ◽  
Efficient Strategy ◽  
New Class ◽  
Reaction Proceeds

AbstractFunctionalized bisboryl compounds have recently emerged as a new class of synthetically useful building blocks in organic synthesis. Herein, we report an efficient strategy to synthesize β-geminal-diboryl ketones enabled by a Cu/Pd-catalyzed borocarbonylative trifunctionalization of readily available alkynes and allenes. This reaction promises to be a useful method for the synthesis of functionalized β-geminal-diboryl ketones with broad functional group tolerance. Mechanistic studies suggest that the reaction proceeds through borocarbonylation/hydroboration cascade of both alkynes and allenes.

scholarly journals Syntheses and Reactions of Pyrroline, Piperidine Nitroxide Phosphonates

Molecules ◽  
2020 ◽  
Vol 25 (10) ◽  
pp. 2430
Author(s):  
Mostafa Isbera ◽  
Balázs Bognár ◽  
József Jekő ◽  
Cecilia Sár ◽  
Kálmán Hideg ◽  
...  
Keyword(s):  
Antioxidant Activity ◽  
Antioxidant Capacity ◽  
Organic Compounds ◽  
Organophosphorus Compounds ◽  
Building Blocks ◽  
Phosphorus Compounds ◽  
Substitution Reactions ◽  
Carbon Bond ◽  
Bond Forming ◽  
Carbon Carbon Bond

Organophosphorus compounds occupy a significant position among the plethora of organic compounds, but a limited number of paramagnetic phosphorus compounds have been reported, including paramagnetic phosphonates. This paper describes the syntheses and further transformations of pyrroline and piperidine nitroxide phosphonates by well-established methods, such as the Pudovik, Arbuzov and Horner-Wadsworth-Emmons (HWE) reactions. The reaction of paramagnetic α-bromoketone produced a vinylphosphonate in the Perkow reaction. Paramagnetic α-hydroxyphosphonates could be subjected to oxidation, elimination and substitution reactions to produce various paramagnetic phosphonates. The synthesized paramagnetic phosphonates proved to be useful synthetic building blocks for carbon-carbon bond-forming reactions in the Horner-Wadsworth-Emmons olefination reactions. The unsaturated compounds achieved could be transformed into various substituted pyrroline nitroxides, proxyl nitroxides and paramagnetic polyaromatics. The Trolox® equivalent antioxidant capacity (TEAC) of new phosphonates was also screened, and tertiary α-hydroxyphosphonatate nitroxides exhibited remarkable antioxidant activity.

scholarly journals Asymmetric Redox-Neutral Radical Cyclization Catalyzed by Flavin-Dependent ‘Ene’-Reductases

2019 ◽  
Author(s):  
Michael Black ◽  
Kyle F. Biegasiewicz ◽  
Andrew J. Meichan ◽  
Daniel G. Oblinsky ◽  
bryan kudish ◽  
...  
Keyword(s):  
Ground State ◽  
Radical Cyclization ◽  
Radical Cyclizations ◽  
Single Electron Transfer ◽  
Mechanistic Studies ◽  
Neutral Radical ◽  
Bond Forming ◽  
Substrate Reduction ◽  
Reaction Proceeds ◽  
Transfer Mechanisms

<p>Flavin-dependent ‘ene’-reductases (EREDs) are exquisite catalysts for effecting stereoselective reductions. While these reactions typically proceed through a hydride transfer mechanism, we recently found that EREDs can also catalyze reductive dehalogenations and cyclizations via single electron transfer mechanisms. Here we demonstrate that these enzymes can catalyze redox-neutral radical cyclizations to produce enantioenriched oxindoles from a-haloamides. This transformation is a C–C bond forming reaction currently unknown in nature and one for which there are no catalytic asymmetric examples. Mechanistic studies indicate the reaction proceeds via the flavin semiquinone/quinone redox couple, where ground state flavin semiquinone provides the electron for substrate reduction and flavin quinone oxidizes the vinylogous a-amido radical formed after cyclization. This mechanistic manifold was previously unknown for this enzyme family, highlighting the versatility of EREDs in asymmetric synthesis.</p>

scholarly journals Site-Selective Allylic C-H Amination with Aliphatic Amines

2021 ◽  
Author(s):  
Shengchun Wang ◽  
Yiming Gao ◽  
Demin Ren ◽  
He Sun ◽  
Linbin Niu ◽  
...  
Keyword(s):  
Hydrogen Atom ◽  
Building Blocks ◽  
Hydrogen Atom Transfer ◽  
Allylic Amines ◽  
Allylic Amination ◽  
Alkyl Amines ◽  
Reaction Proceeds ◽  
Bond Options ◽  
A Site ◽  
Site Selective

Abstract The direct coupling of olefins and alkyl amines represents the most efficient and atom-economical approach to prepare aliphatic allylamines which are fundamental building blocks. However, the method that achieves this goal while exhibiting exquisite control over the site at which the amine is introduced remains elusive. Herein, we report that the combination of a photocatalyst and a cobaloxime enables site-selective allylic C–H amination of olefins with secondary alkyl amines to afford allylic amines, eliminating the need for oxidants. This reaction proceeds by a radical-based mechanism distinct from those of existing allylic amination reactions. It affords the product resulting from cleavage of the stronger, primary allylic C–H bonds over other weaker allylic C–H bond options. DFT calculations reveal that this selectivity originates from a cobaloxime-promoted hydrogen atom transfer (HAT) process. Our method is compatible with a broad scope of alkenes, and can be extended to achieve a site- and diastereoselective amination of natural terpenes.

scholarly journals Teaching an old carbocation new tricks: Intermolecular C–H insertion reactions of vinyl cations

Science ◽  
2018 ◽  
Vol 361 (6400) ◽  
pp. 381-387 ◽  
Author(s):  
Stasik Popov ◽  
Brian Shao ◽  
Alex L. Bagdasarian ◽  
Tyler R. Benton ◽  
Luyi Zou ◽  
...  
Keyword(s):  
Theoretical Studies ◽  
Computational Studies ◽  
Mechanistic Studies ◽  
Insertion Reactions ◽  
Bond Forming ◽  
The Past ◽  
Carbon Carbon Bond ◽  
Transition Structures ◽  
The Subject ◽  
Experimental And Theoretical Studies

Vinyl carbocations have been the subject of extensive experimental and theoretical studies over the past five decades. Despite this long history in chemistry, the utility of vinyl cations in chemical synthesis has been limited, with most reactivity studies focusing on solvolysis reactions or intramolecular processes. Here we report synthetic and mechanistic studies of vinyl cations generated through silylium–weakly coordinating anion catalysis. We find that these reactive intermediates undergo mild intermolecular carbon-carbon bond–forming reactions, including carbon-hydrogen (C–H) insertion into unactivated sp3 C–H bonds and reductive Friedel-Crafts reactions with arenes. Moreover, we conducted computational studies of these alkane C–H functionalization reactions and discovered that they proceed through nonclassical, ambimodal transition structures. This reaction manifold provides a framework for the catalytic functionalization of hydrocarbons using simple ketone derivatives.

Carbon-carbon bond-forming reactions of zinc homoenolate of esters. A novel three-carbon nucleophile with general synthetic utility

1987 ◽  
Vol 109 (26) ◽  
pp. 8056-8066 ◽  
Author(s):  
Eiichi Nakamura ◽  
Satoshi Aoki ◽  
Kouichi Sekiya ◽  
Hiroji Oshino ◽  
Isao Kuwajima
Keyword(s):  
Carbon Bond ◽  
Bond Forming ◽  
Carbon Carbon Bond ◽  
Synthetic Utility ◽  
Bond Forming Reactions

scholarly journals Asymmetric Redox-Neutral Radical Cyclization Catalyzed by Flavin-Dependent ‘Ene’-Reductases

2019 ◽  
Author(s):  
Michael Black ◽  
Kyle F. Biegasiewicz ◽  
Andrew J. Meichan ◽  
Daniel G. Oblinsky ◽  
bryan kudish ◽  
...  
Keyword(s):  
Ground State ◽  
Radical Cyclization ◽  
Radical Cyclizations ◽  
Single Electron Transfer ◽  
Mechanistic Studies ◽  
Neutral Radical ◽  
Bond Forming ◽  
Substrate Reduction ◽  
Reaction Proceeds ◽  
Transfer Mechanisms

<p>Flavin-dependent ‘ene’-reductases (EREDs) are exquisite catalysts for effecting stereoselective reductions. While these reactions typically proceed through a hydride transfer mechanism, we recently found that EREDs can also catalyze reductive dehalogenations and cyclizations via single electron transfer mechanisms. Here we demonstrate that these enzymes can catalyze redox-neutral radical cyclizations to produce enantioenriched oxindoles from a-haloamides. This transformation is a C–C bond forming reaction currently unknown in nature and one for which there are no catalytic asymmetric examples. Mechanistic studies indicate the reaction proceeds via the flavin semiquinone/quinone redox couple, where ground state flavin semiquinone provides the electron for substrate reduction and flavin quinone oxidizes the vinylogous a-amido radical formed after cyclization. This mechanistic manifold was previously unknown for this enzyme family, highlighting the versatility of EREDs in asymmetric synthesis.</p>

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