scholarly journals Photocatalytic N-Heteroarylation of Aldehydes via Formyl C‒ H Activation

2020 ◽  
Author(s):  
Hiromu Fuse ◽  
Harunobu Mitsunuma ◽  
Motomu Kanai
Keyword(s):  
Secondary Alcohol ◽  
Acid Catalyst ◽  
Catalyst System ◽  
Hydrogen Atom Transfer ◽  
Single Electron ◽  
Thiyl Radical ◽  
Thiophosphoric Acid ◽  
Wide Range ◽  
Acyl Radicals ◽  
Spin Center

A formal C‒H addition of N-heteroaromatics to aldehydes<br>was achieved using a binary hybrid catalyst system comprising an acridinium photoredox catalyst and a thiophosphoric acid organocatalyst. The reaction proceeded through the following sequence: 1) photoredox-catalyzed single-electron oxidation of a thiophosphoric acid catalyst to generate a thiyl radical, 2) cleavage of the formyl C‒H bond of the aldehyde substrates by a thiyl radical acting as a hydrogen atom transfer catalyst to generate acyl radicals, 3) Minisci-type addition of the resulting acyl radicals to N-heteroaromatics, and 4) a spin-center shift, photoredox-catalyzed single-electron reduction, and protonation to produce secondary alcohol products. This metal-free hybrid catalysis proceeded under mild conditions for a wide range of substrates, including isoquinolines, quinolines, and pyridines as N-heteroaromatics, as well as both aromatic and aliphatic aldehydes, and tolerated various functional groups. The reaction was applicable to late-stage derivatization of drugs and their leads.

scholarly journals Photocatalytic N-Heteroarylation of Aldehydes via Formyl C‒ H Activation

2020 ◽  
Author(s):  
Hiromu Fuse ◽  
Harunobu Mitsunuma ◽  
Motomu Kanai
Keyword(s):  
Secondary Alcohol ◽  
Acid Catalyst ◽  
Catalyst System ◽  
Hydrogen Atom Transfer ◽  
Single Electron ◽  
Thiyl Radical ◽  
Thiophosphoric Acid ◽  
Wide Range ◽  
Acyl Radicals ◽  
Spin Center

A formal C‒H addition of N-heteroaromatics to aldehydes<br>was achieved using a binary hybrid catalyst system comprising an acridinium photoredox catalyst and a thiophosphoric acid organocatalyst. The reaction proceeded through the following sequence: 1) photoredox-catalyzed single-electron oxidation of a thiophosphoric acid catalyst to generate a thiyl radical, 2) cleavage of the formyl C‒H bond of the aldehyde substrates by a thiyl radical acting as a hydrogen atom transfer catalyst to generate acyl radicals, 3) Minisci-type addition of the resulting acyl radicals to N-heteroaromatics, and 4) a spin-center shift, photoredox-catalyzed single-electron reduction, and protonation to produce secondary alcohol products. This metal-free hybrid catalysis proceeded under mild conditions for a wide range of substrates, including isoquinolines, quinolines, and pyridines as N-heteroaromatics, as well as both aromatic and aliphatic aldehydes, and tolerated various functional groups. The reaction was applicable to late-stage derivatization of drugs and their leads.

scholarly journals DABCO-promoted photocatalytic C–H functionalization of aldehydes

2021 ◽  
Vol 17 ◽  
pp. 2959-2967
Author(s):  
Bruno Maia da Silva Santos ◽  
Mariana dos Santos Dupim ◽  
Cauê Paula de Souza ◽  
Thiago Messias Cardozo ◽  
Fernanda Gadini Finelli
Keyword(s):  
Hydrogen Atom ◽  
Cross Coupling ◽  
Hydrogen Atom Transfer ◽  
Direct Application ◽  
Atom Transfer ◽  
Organic Base ◽  
Aryl Bromides ◽  
Computational Calculations ◽  
Acyl Radicals ◽  
Aryl Ketones

Herein we present a direct application of DABCO, an inexpensive and broadly accessible organic base, as a hydrogen atom transfer (HAT) abstractor in a photocatalytic strategy for aldehyde C–H activation. The acyl radicals generated in this step were arylated with aryl bromides through a well stablished nickel cross-coupling methodology, leading to a variety of interesting aryl ketones in good yields. We also performed computational calculations to shine light in the HAT step energetics and determined an optimized geometry for the transition state, showing that the hydrogen atom transfer between aldehydes and DABCO is a mildly endergonic, yet sufficiently fast step. The same calculations were performed with quinuclidine, for comparison of both catalysts and the differences are discussed.

scholarly journals Dual Cobalt and Photoredox Catalysis Enabled Intermolecular Oxidative Hydrofunctionalization

2020 ◽  
Author(s):  
Han-Li Sun ◽  
Fan Yang ◽  
Wei-Ting Ye ◽  
Jun-Jie Wang ◽  
Rong Zhu
Keyword(s):  
Hydrogen Atom ◽  
Visible Light ◽  
Electrochemical Analysis ◽  
Hydrogen Atom Transfer ◽  
Redox Process ◽  
Photochemical Oxidation ◽  
Atom Transfer ◽  
Photoredox Catalysis ◽  
Wide Range ◽  
Selective Alkylation

A general protocol has been developed for the Markovnikov-selective intermolecular hydrofunctionalization based on visible-light-mediated Co/Ru dual catalysis. The key feature involves the photochemical oxidation of an organocobalt(III) intermediate derived from hydrogen atom transfer, which is supported by electrochemical analysis, quenching studies and stoichiometric experiments. This unique redox process enables the efficient branch-selective alkylation of pharmaceutically important nucleophiles (phenols, sulfonamides and various N-heterocycles) using a wide range of alkenes including moderately electron-deficient ones. Moreover, light-gated polar functionalization via organocobalt species was demonstrated.

scholarly journals Radical Biocatalysis: Using Non-Natural Single Electron Transfer Mechanisms to Access New Enzymatic Functions

Synlett ◽  
2019 ◽  
Vol 31 (03) ◽  
pp. 248-254 ◽  
Author(s):  
Todd K. Hyster
Keyword(s):  
Electron Transfer ◽  
Active Sites ◽  
Hydrogen Atom Transfer ◽  
Single Electron ◽  
Great Promise ◽  
Single Electron Transfer ◽  
Radical Intermediates ◽  
Redox Activation ◽  
Transfer Mechanisms ◽  
Ground State Electron

Exploiting non-natural reaction mechanisms within native enzymes is an emerging strategy for expanding the synthetic capabilities of biocatalysts. When coupled with modern protein engineering techniques, this approach holds great promise for biocatalysis to address long-standing selectivity and reactivity challenges in chemical synthesis. Controlling the stereochemical outcome of reactions involving radical intermediates, for instance, could benefit from biocatalytic solutions because these reactions are often difficult to control by using existing small molecule catalysts. General strategies for catalyzing non-natural radical reactions within enzyme active sites are, however, undeveloped. In this account, we highlight three distinct strategies developed in our group that exploit non-natural single electron transfer mechanisms to unveil previously unknown radical biocatalytic functions. These strategies allow common oxidoreductases to be used to address the enduring synthetic challenge of asymmetric hydrogen atom transfer.1 Introduction2 Photoinduced Electron Transfer from NADPH3 Ground State Electron Transfer from Flavin Hydroquinone4 Enzymatic Redox Activation in NADPH-Dependent Oxidoreductases5 Conclusion

Hydrogen atom transfer in metal ion complexes of the glutathione thiyl radical

2018 ◽  
Vol 429 ◽  
pp. 39-46 ◽  
Author(s):  
Michael Lesslie ◽  
Justin Kai-Chi Lau ◽  
Gardenia Pacheco ◽  
John T. Lawler ◽  
K.W. Michael Siu ◽  
...  
Keyword(s):  
Hydrogen Atom ◽  
Metal Ion ◽  
Hydrogen Atom Transfer ◽  
Thiyl Radical ◽  
Atom Transfer ◽  
Metal Ion Complexes

scholarly journals Site-selective redox isomerizations of furanosides using a combined arylboronic acid/photoredox catalyst system

2020 ◽  
Vol 11 (6) ◽  
pp. 1531-1537 ◽  
Author(s):  
Victoria Dimakos ◽  
Daniel Gorelik ◽  
Hsin Y. Su ◽  
Graham E. Garrett ◽  
Gregory Hughes ◽  
...  
Keyword(s):  
Hydrogen Atom ◽  
Ribonucleotide Reductase ◽  
Boronic Acid ◽  
Catalyst System ◽  
Hydrogen Atom Transfer ◽  
Synthetic Analog ◽  
Arylboronic Acid ◽  
System P ◽  
Combined Action ◽  
Site Selective

The combined action of boronic acid, photoredox catalyst and hydrogen atom transfer mediator enables the transformation of furanosides to 2-keto-3-deoxyfuranosides, a synthetic analog of the process catalyzed by the ribonucleotide reductase enzymes.

THE PHOTOINITIATED ADDITION OF MERCAPTANS TO OLEFINS: II. THE KINETICS OF THE ADDITION OF n-BUTYL MERCAPTAN TO 1-PENTENE

1955 ◽  
Vol 33 (5) ◽  
pp. 1034-1042 ◽  
Author(s):  
M. Onyszchuk ◽  
C. Sivertz
Keyword(s):  
Alkyl Radical ◽  
Side Reactions ◽  
Thiyl Radical ◽  
Principal Mechanism ◽  
Velocity Constant ◽  
Transfer Step ◽  
Wide Range ◽  
Detailed Kinetics ◽  
Kinetics Of

The detailed kinetics involved in the photoinitiated addition of n-butyl mercaptan to 1-pentene is presented. It has been shown that side reactions such as propagation and α-dehydrogenation are relatively negligible and the principal mechanism comprises attack by thiyl radical followed by transfer with mercaptan by the alkyl radical. The velocity constant of the attack step is estimated to be 7 × 106 and that of the transfer step 1.4 × 106 liters/mole-sec. These values together with approximate termination velocity constants are shown to explain the kinetics over a wide range of concentration.

Sign in / Sign up

Export Citation Format

Share Document