Sterically Crowded Heterocycles. X. A New Mechanistic Approach to the Ferricyanide Oxidation of 4,6'-Disubstituted 1-(Pyridin-2'-yl)-2,6-diphenylpyridinium Salts

The oxidations of the title perchlorates, bearing the sterically diverse 6'-substituents (H, Me, Et, i-Pr, n-Bu, t-Bu and Ph) in two series with the same 4-substituents (Ph and t-Bu) lead to pairs of isomeric 3',5-disubstituted (Z)-1'-phenyl-3'-(2-phenylimidazo[1,2-a]pyridin-3-yl)prop-2'- en-1'-ones and 3,6'-disubstituted [5-phenyl-1-(6'-pyridin-2'-yl)-1H-pyrrol-2-yl](phenyl)methanones except where the both variable substituents are t-Bu and then only pyrrolic product is formed. Considering steric interactions of the substituents in some intermediate and/or transition states a multistep mechanism for the oxidative transformation is proposed and supported by model PM3-PECI calculations of some radical intermediates.

Download Full-text

[3,3] Sigmatropic Rearrangement of Some Fluorinated 1,5-Hexadienes

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc20021517 ◽

2002 ◽

Vol 67 (10) ◽

pp. 1517-1532 ◽

Cited By ~ 5

Author(s):

William R. Dolbier ◽

Keith W. Palmer ◽

Feng Tian ◽

Piotr Fiedorow ◽

Andrzej Zaganiaczyk ◽

...

Keyword(s):

Experimental Data ◽

Ab Initio ◽

Transition States ◽

Activation Parameters ◽

Sigmatropic Rearrangement ◽

Semiempirical Methods ◽

Cope Rearrangement ◽

Computational Studies ◽

Stepwise Mechanism ◽

Radical Intermediates

Fluorine atoms incorporated into 1,5-hexadiene molecule should influence the kinetic as well as the thermodynamic parameters of [3,3] sigmatropic rearrangement (Cope rearrangement). Within few decades is has been documented that this transformation proceeds in a concerted manner, rather than stepwise with some radical intermediates involved. Few new terminally fluorinated 1,5-hexadienes (compounds 3, 5A, 7, 9 and 5B) have been synthesized. The activation parameters of rearrangement have been determined and compared with those known for hydrocarbon analogues. While systems developing chair-like transition states (compounds 3 and 5) showed close similarity with hydrocarbon analogues (compound 1), those developing boat-like transition states (compounds 7, 9 and 5B) may proceed through radical stepwise mechanism. Computational studies of the transition states were carried out, showing that only ab initio methods (MP2 and especially DFT) can give approximate correlation with experimental data, whereas in the case of hydrocarbon analogues even simple semiempirical methods (AM1) were reliable enough to reproduce experimental results.

Download Full-text

THE INFLUENCE OF HAEMOGLOBIN-S AND G6PD DEFICIENCY ON THE ACTIVITY OF THE 17β-HYDROXYSTEROID DEHYDROGENASE OF INTACT HUMAN ERYTHROCYTES

Acta Endocrinologica ◽

10.1530/acta.0.0750793 ◽

1974 ◽

Vol 75 (4) ◽

pp. 793-800

Author(s):

A. O. Sogbesan ◽

O. A. Dada ◽

B. Kwaku Adadevoh

Keyword(s):

Enzyme Activity ◽

Dehydrogenase Activity ◽

Sex Steroids ◽

G6pd Deficiency ◽

Incubation Medium ◽

Hydroxysteroid Dehydrogenase ◽

G6pd Activity ◽

Reverse Transformation ◽

Oxidative Transformation ◽

Haemoglobin S

ABSTRACT The 17β-hydroxysteroid dehydrogenase activity in intact erythrocytes of Nigerian patients, in particular with regard to haemoglobin genotypes and G6PD* activity was studied. The G6PD activity of the erythrocyte did not affect the oxidative transformation of testosterone to androstenedione and of oestradiol to oestrone. The reduction (reverse transformation) was inhibited in G6PD-deficient erythrocytes but this inhibition was offset by the addition of 0.025 m glucose to the incubation medium. The per cent oxidation transformation of testosterone was higher in Hb-AA than in Hb-SS erythrocytes. It is suggested that the differences may be a result of either lower enzyme activity in the Hb-SS erythrocytes or of differences in the uptake and possibly binding of sex steroids by intact Hb-SS and Hb-AA erythrocytes.

Download Full-text

Oxidation of Aromatic Secondary alcohol by Polymer Supported Reagent: A Kinetic and Mechanistic Approach

Indian Journal Of Applied Research ◽

10.15373/2249555x/may2013/190 ◽

2011 ◽

Vol 3 (5) ◽

pp. 589-591

Author(s):

Vilas Y Sonawane ◽

Keyword(s):

Secondary Alcohol ◽

Mechanistic Approach ◽

Polymer Supported

Download Full-text

Visible Light-Promoted Catalytic Ring-Opening Isomerization of 1,2-Disubstituted Cyclopropanols to Linear Ketones

10.26434/chemrxiv.11467845.v1 ◽

2019 ◽

Author(s):

Marharyta V. Laktsevich-Iskryk ◽

Nastassia A. Varabyeva ◽

Volha V. Kazlova ◽

Vladimir N. Zhabinskii ◽

Vladimir A. Khripach ◽

...

Keyword(s):

Visible Light ◽

Functional Groups ◽

Ring Opening ◽

Radical Intermediates ◽

Reaction Proceeds

In this article, we report a photocatalytic protocol for the isomerization of 1,2-disubstituted cyclopropanols to linear ketones. The reaction proceeds via radical intermediates and tolerates various functional groups.

Download Full-text

Visible Light-Promoted Catalytic Ring-Opening Isomerization of 1,2-Disubstituted Cyclopropanols to Linear Ketones

10.26434/chemrxiv.11467845 ◽

2019 ◽

Author(s):

Marharyta V. Laktsevich-Iskryk ◽

Nastassia A. Varabyeva ◽

Volha V. Kazlova ◽

Vladimir N. Zhabinskii ◽

Vladimir A. Khripach ◽

...

Keyword(s):

Visible Light ◽

Functional Groups ◽

Ring Opening ◽

Radical Intermediates ◽

Reaction Proceeds

Download Full-text

An Iron-Based Catalyst Enables The Enantioconvergent Synthesis of Chiral 1,1-Diarylalkanes Through a Suzuki-Miyaura Cross-Coupling Reaction

10.26434/chemrxiv.12582284.v1 ◽

2020 ◽

Author(s):

Chet Tyrol ◽

Nang Yone ◽

Connor Gallin ◽

Jeffery Byers

Keyword(s):

Coupling Reaction ◽

Cross Coupling ◽

Coupling Reactions ◽

Radical Intermediates ◽

Cross Coupling Reactions ◽

Cross Coupling Reaction ◽

Boronic Esters ◽

Carbon Centered Radical ◽

Iron Based ◽

High Yields

By using an iron-based catalyst, access to enantioenriched 1,1-diarylakanes was enabled through an enantioselective Suzuki-Miyaura crosscoupling reaction. The combination of a chiral cyanobis(oxazoline) ligand framework and 1,3,5-trimethoxybenzene additive were essential to afford high yields and enantioselectivities in cross-coupling reactions between unactivated aryl boronic esters and a variety of benzylic chlorides, including challenging ortho-substituted benzylic chloride substrates. Mechanistic investigations implicate a stereoconvergent pathway involving carbon-centered radical intermediates.

Download Full-text

Catalytic Enantioselective Benzylation Directly from Aryl Acetic Acids

10.26434/chemrxiv.7119887.v1 ◽

2018 ◽

Author(s):

Patrick Moon ◽

Zhongyu Wie ◽

Rylan Lundgren

Keyword(s):

Functional Group ◽

Terminal Event ◽

Radical Intermediates ◽

Carbon Carbon Bond ◽

Or Groups ◽

Reaction Proceeds ◽

Wide Availability ◽

Metal Catalyzed ◽

The Stability ◽

Acetic Acids

The stability and wide availability of carboxylic acids make them valuable reagents in chemical synthesis. Most transition metal catalyzed processes using carboxylic acid substrates are initiated by a decarboxylation event that generates reactive carbanion or radical intermediates. Developing enantioselective methodologies relying on these principles can be challenging, as highly reactive species tend to react indiscriminately without selectivity. Furthermore, anionic or radical intermediates generated from decarboxylation can be incompatible with protic and electrophilic functionality, or groups that undergo trapping with radicals. We demonstrate that metal-catalyzed enantioselective benzylation reactions of allylic electrophiles can occur directly from aryl acetic acids. The reaction proceeds via a pathway in which decarboxylation is the terminal event, occurring after stereoselective carbon–carbon bond formation. The mechanistic features of the process enable enantioselective benzylation without the generation of a highly basic nucleophile. Thus, the process has broad functional group compatibility that would not be possible employing established protocols.

Download Full-text

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

10.26434/chemrxiv.8120654 ◽

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(sp3) 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(sp3)-H bonds.

Download Full-text

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

10.26434/chemrxiv.7355069 ◽

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 SmI2in 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-exo-trig ketyl olefin cyclization reactions.

Download Full-text