scholarly journals Electrocatalytic Oxidative Hydrofunctionalization Reactions of Alkenes via Co(II/III/IV) Cycle

2021 ◽  
Author(s):  
Fan Yang ◽  
Yi-Chen Nie ◽  
Han-Yuan Liu ◽  
Lei Zhang ◽  
Fanyang Mo ◽  
...  
Keyword(s):  
Hydrogen Atom ◽  
Hydrogen Atom Transfer ◽  
Oxidation States ◽  
Atom Transfer ◽  
Mechanistic Studies ◽  
Pinacol Rearrangement ◽  
Chemical Oxidants ◽  
Alkene Functionalization ◽  
The Common ◽  
Space Expansion

Here we disclose a general and versatile Co(II/III/IV) electrocatalytic platform for alkene functionalization. Driven by electricity, a set of the oxidative hydrofunctionalization reactions initiated by hydrogen atom transfer were demonstrated without the need for stochiometric chemical oxidants. The scope of the reactions encompasses hydroalkoxylation, hydroacyloxylation, hydroarylation, semi-pinacol rearrangement, and deallylation. Mechanistic studies and stereochemical evidence support an ECEC process involving an electrochemically-generated organocobalt(IV) intermediate. This work presents an example of reactivity space expansion in electrocatalysis of VB12-systems by going beyond the common oxidation states of Co(I/II/III).

Catalytic Synthesis of Cyclic Guanidines via Hydrogen Atom Transfer and Radical-Polar Crossover

2020 ◽  
Author(s):  
Shunya Ohuchi ◽  
Hiroki Koyama ◽  
Hiroki Shigehisa
Keyword(s):  
Hydrogen Atom ◽  
Functional Group ◽  
Hydrogen Atom Transfer ◽  
Catalytic Synthesis ◽  
Membered Ring ◽  
Biologically Active ◽  
Atom Transfer ◽  
Powerful Method ◽  
Protective Groups ◽  
The Common

A catalytic synthesis of cyclic guanidines, which are found in many biologically active compounds and natu-ral products, was developed, wherein transition-metal hydrogen atom transfer and radical-polar crossover were employed. This mild and functional-group tolerant process enabled the cyclization of alkenyl guanidines bearing common protective groups, such as Cbz and Boc. This powerful method not only provided the common 5- and 6-membered rings but also an unusual 7-membered ring. The derivatization of the products afforded various heterocycles. We also investigated the se-lective cyclization of mono-protected or hetero-protected (TFA and Boc) alkenyl guanidines and their further derivatiza-tions.

scholarly journals Cationic DABCO-based Catalyst for Site-Selective C−H Alkylation via Photoinduced Hydrogen-Atom Transfer

2021 ◽  
Author(s):  
Akira Matsumoto ◽  
Keiji Maruoka
Keyword(s):  
Hydrogen Atom ◽  
Nitrogen Atom ◽  
Crucial Role ◽  
Active Species ◽  
Hydrogen Atom Transfer ◽  
Atom Transfer ◽  
Mechanistic Studies ◽  
Complex Molecules ◽  
Site Selectivity ◽  
Site Selective

A novel class of hydrogen-atom transfer (HAT) catalysts based on the readily available and tunable 1,4-diazabicyclo[2.2.2]octane (DABCO) structure was designed, and their photoinduced HAT catalysis ability was demonstrated. The combination of the optimal HAT catalyst with an acridinium-based organophotoredox catalyst enables highly efficient and site-selective C−H alkylation of substrates ranging from unactivated hydrocarbons to complex molecules. Notably, a HAT catalyst with additional substituents adjacent to a nitrogen atom further improved the site-selectivity. Mechanistic studies suggested that the N-substituent of the catalyst plays a crucial role, assisting in the generation of a dicationic aminium radical as an active species for the HAT process.

scholarly journals On the Mechanism of Electrochemical Generation and Decomposition of Phthalimide N-oxyl (PINO)

2021 ◽  
Author(s):  
Cheng Yang ◽  
Luke Farmer ◽  
Derek Pratt ◽  
Stephen Maldonado ◽  
Corey Stephenson
Keyword(s):  
Electron Transfer ◽  
Hydrogen Atom ◽  
Catalytic Efficiency ◽  
Hydrogen Atom Transfer ◽  
Second Order ◽  
Atom Transfer ◽  
Multiple Site ◽  
Mechanistic Studies ◽  
Electrochemical Generation ◽  
Bulk Electrolysis

Phthalimide <i>N</i>-oxyl (PINO) is a potent hydrogen atom transfer (HAT) catalyst that can be generated electrochemically from <i>N</i>-hydroxyphthalimide (NHPI). However, catalyst decomposition has limited its application. This paper details mechanistic studies of the generation and decomposition of PINO under electrochemical conditions. Voltammetric data, observations from bulk electrolysis, and <a>computational</a> studies suggest two primary aspects. First, base-promoted formation of PINO from NHPI occurs via multiple-site concerted proton-electron transfer (MS-CPET). Second, PINO decomposition occurs by at least two second-order paths, one of which is greatly enhanced by base. Optimal catalytic efficiency in PINO-catalyzed oxidations occurs in the presence of bases whose corresponding conjugate acids have <a>p<i>K</i><sub>a</sub></a>s in the range of 12-15, which strike a balance between promoting PINO formation and minimizing its decay.

Kinetic and Mechanistic Studies of Carbon-to-Metal Hydrogen Atom Transfer Involving Os-Centered Radicals: Evidence for Tunneling

2014 ◽  
Vol 136 (9) ◽  
pp. 3572-3578 ◽  
Author(s):  
Anna Lewandowska-Andralojc ◽  
David C. Grills ◽  
Jie Zhang ◽  
R. Morris Bullock ◽  
Akira Miyazawa ◽  
...  
Keyword(s):  
Hydrogen Atom ◽  
Hydrogen Atom Transfer ◽  
Atom Transfer ◽  
Mechanistic Studies

scholarly journals Cationic DABCO-based Catalyst for Site-Selective C−H Alkylation via Photoinduced Hydrogen-Atom Transfer

2021 ◽  
Author(s):  
Akira Matsumoto ◽  
Keiji Maruoka
Keyword(s):  
Hydrogen Atom ◽  
Nitrogen Atom ◽  
Crucial Role ◽  
Active Species ◽  
Hydrogen Atom Transfer ◽  
Atom Transfer ◽  
Mechanistic Studies ◽  
Complex Molecules ◽  
Site Selectivity ◽  
Site Selective

A novel class of hydrogen-atom transfer (HAT) catalysts based on the readily available and tunable 1,4-diazabicyclo[2.2.2]octane (DABCO) structure was designed, and their photoinduced HAT catalysis ability was demonstrated. The combination of the optimal HAT catalyst with an acridinium-based organophotoredox catalyst enables highly efficient and site-selective C−H alkylation of substrates ranging from unactivated hydrocarbons to complex molecules. Notably, a HAT catalyst with additional substituents adjacent to a nitrogen atom further improved the site-selectivity. Mechanistic studies suggested that the N-substituent of the catalyst plays a crucial role, assisting in the generation of a dicationic aminium radical as an active species for the HAT process.

scholarly journals On the Mechanism of Electrochemical Generation and Decomposition of Phthalimide N-oxyl (PINO)

2021 ◽  
Author(s):  
Cheng Yang ◽  
Luke Farmer ◽  
Derek Pratt ◽  
Stephen Maldonado ◽  
Corey Stephenson
Keyword(s):  
Electron Transfer ◽  
Hydrogen Atom ◽  
Catalytic Efficiency ◽  
Hydrogen Atom Transfer ◽  
Second Order ◽  
Atom Transfer ◽  
Multiple Site ◽  
Mechanistic Studies ◽  
Electrochemical Generation ◽  
Bulk Electrolysis

Phthalimide <i>N</i>-oxyl (PINO) is a potent hydrogen atom transfer (HAT) catalyst that can be generated electrochemically from <i>N</i>-hydroxyphthalimide (NHPI). However, catalyst decomposition has limited its application. This paper details mechanistic studies of the generation and decomposition of PINO under electrochemical conditions. Voltammetric data, observations from bulk electrolysis, and <a>computational</a> studies suggest two primary aspects. First, base-promoted formation of PINO from NHPI occurs via multiple-site concerted proton-electron transfer (MS-CPET). Second, PINO decomposition occurs by at least two second-order paths, one of which is greatly enhanced by base. Optimal catalytic efficiency in PINO-catalyzed oxidations occurs in the presence of bases whose corresponding conjugate acids have <a>p<i>K</i><sub>a</sub></a>s in the range of 12-15, which strike a balance between promoting PINO formation and minimizing its decay.

Direct Cyclization of Alkenyl Thioester via Transition Metal‐hydrogen Atom Transfer/radical‐polar Crossover Mechanism

2019 ◽  
Author(s):  
Shiori Date ◽  
Kensei Hamasaki ◽  
Karen Sunagawa ◽  
Hiroki Koyama ◽  
Chikayoshi Sebe ◽  
...  
Keyword(s):  
Natural Products ◽  
Hydrogen Atom ◽  
Transition Metal ◽  
Hydrogen Atom Transfer ◽  
Synthetic Method ◽  
Atom Transfer ◽  
Reaction Conditions ◽  
Hydride Hydrogen ◽  
Sulfur Heterocycles ◽  
One Step

<div>We report here a catalytic, Markovnikov selective, and scalable synthetic method for the synthesis of saturated sulfur heterocycles, which are found in the structures of pharmaceuticals and natural products, in one step from an alkenyl thioester. Unlike a potentially labile alkenyl thiol, an alkenyl thioester is stable and easy to prepare. The powerful Co catalysis via a cobalt hydride hydrogen atom transfer and radical-polar crossover mechanism enabled simultaneous cyclization and deprotection. The substrate scope was expanded by the extensive optimization of the reaction conditions and tuning of the thioester unit.</div>

Sulfamides Direct Radical-Mediated Chlorination of Aliphatic C–H Bonds

2019 ◽  
Author(s):  
Melanie Short ◽  
Mina Shehata ◽  
Matthew Sanders ◽  
Jennifer Roizen
Keyword(s):  
Hydrogen Atom ◽  
Transfer Reaction ◽  
Hydrogen Atom Transfer ◽  
Chain Propagation ◽  
Propagation Mechanism ◽  
Atom Transfer ◽  
Radical Chain ◽  
Radical Intermediates ◽  
Transfer Processes ◽  
Unusual Position

Sulfamides guide intermolecular chlorine transfer to gamma-C(sp<sup>3</sup>) centers. This unusual position-selectivity arises because accessed sulfamidyl radical intermediates engage in otherwise rare 1,6-hydrogen-atom transfer processes. The disclosed chlorine-transfer reaction relies on a light-initiated radical chain-propagation mechanism to oxidize C(sp<sup>3</sup>)-H bonds.

Sulfamides Direct Radical-Mediated Chlorination of Aliphatic C–H Bonds

2019 ◽  
Author(s):  
Melanie Short ◽  
Mina Shehata ◽  
Matthew Sanders ◽  
Jennifer Roizen
Keyword(s):  
Hydrogen Atom ◽  
Transfer Reaction ◽  
Hydrogen Atom Transfer ◽  
Chain Propagation ◽  
Propagation Mechanism ◽  
Atom Transfer ◽  
Radical Chain ◽  
Radical Intermediates ◽  
Transfer Processes ◽  
Unusual Position

Sulfamides guide intermolecular chlorine transfer to gamma-C(sp<sup>3</sup>) centers. This unusual position-selectivity arises because accessed sulfamidyl radical intermediates engage in otherwise rare 1,6-hydrogen-atom transfer processes. The disclosed chlorine-transfer reaction relies on a light-initiated radical chain-propagation mechanism to oxidize C(sp<sup>3</sup>)-H bonds.

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