scholarly journals Dearomative [4 + 3] cycloaddition of furans with vinyl-N-triftosylhydrazones by silver catalysis: stereoselective access to oxa-bridged seven-membered bicycles

2022 ◽  
Author(s):  
Zhaohong Liu ◽  
Yong Yang ◽  
Xinyu Jiang ◽  
Qingmin Song ◽  
Giuseppe Zanoni ◽  
...  
Keyword(s):  
Dft Calculations ◽  
Experimental Studies ◽  
Cope Rearrangement ◽  
Efficient Synthesis ◽  
Rhodium Catalysis ◽  
Bicyclic Compounds ◽  
Silver Catalysis ◽  
Reaction Proceeds ◽  
Functionally Diverse

Abstract The first example of dearomative [4 + 3] cycloaddition between furans and vinyl-N-sulfonylhydrazones as vinylcarbene precursors is reported. The merger of silver catalysis and easily decomposable vinyl-N-triftosylhydrazones enabled the efficient synthesis of a variety of skeletally and functionally diverse oxa-bridged seven-membered bicyclic compounds with complete and predictable stereoselectivity. The combination of experimental studies and DFT calculations disclosed that the silver-catalyzed reaction proceeds via a concerted [4 + 3] cycloaddition mechanism, rather than the generally accepted cyclopropanation / Cope rearrangement pathway by rhodium catalysis.

scholarly journals Palladium-Catalysed C–F Alumination of Fluorobenzenes: Mechanistic Diversity and Origin of Selectivity

2020 ◽  
Author(s):  
Feriel Rekhroukh ◽  
Wenyi Chen ◽  
Ryan Brown ◽  
Andrew J. P. White ◽  
Mark Crimmin
Keyword(s):  
Dft Calculations ◽  
Bond Activation ◽  
Oxidative Addition ◽  
Fluorine Content ◽  
Model Potential ◽  
Heterometallic Complex ◽  
Experimental Support ◽  
Highly Active ◽  
Reaction Proceeds ◽  
Directing Group

A palladium pre-catalyst, [Pd(PCy<sub>3</sub>)<sub>2</sub>] is reported for the efficient and selective C–F alumination of fluorobenzenes with the aluminium(I) reagent [{(ArNCMe)<sub>2</sub>CH}Al] (<b>1</b>, Ar = 2,6-di-iso-propylphenyl). The catalytic protocol results in the transformation of sp<sup>2</sup> C–F bonds to sp<sup>2</sup> C–Al bonds and provides a route into reactive organoaluminium complexes (<b>2a-h</b>) from fluorocarbons. The catalyst is highly active. Reactions proceed within 5 minutes at 25 ºC (and at appreciable rates at even –50 ºC) and the scope includes low-fluorine-content substrates such as fluorobenzene, difluorobenzenes and trifluorobenzenes. The reaction proceeds with complete chemoselectivity (C–F vs C–H) and high regioselectivities ( >90% for C–F bonds adjacent to the most acidic C–H sites). The heterometallic complex [Pd(PCy<sub>3</sub>)(<b>1</b>)<sub>2</sub>] was shown to be catalytically competent. Catalytic C–F alumination proceeds with a KIE of 1.1–1.3. DFT calculations have been used to model potential mechanisms for C–F bond activation. These calculations suggest that two competing mechanisms may be in operation. Pathway 1 involves a ligand-assisted oxidative addition to [Pd(<b>1</b>)<sub>2</sub>] and leads directly to the product. Pathway 2 involves a stepwise C–H to C–F functionalisation mechanism in which the C–H bond is broken and reformed along the reaction coordinate, allowing it to act as a directing group for the adjacent C–F site. This second mechanism explains the experimentally observed regioselectivity. Experimental support for this C–H activation playing a key role in C–F alumination was obtained by employing [{(MesNCMe)<sub>2</sub>CH}AlH<sub>2</sub>] (<b>3</b>, Mes = 2,4,6-trimethylphenyl) as a reagent in place of 1. In this instance, the kinetic C–H alumination intermediate could be isolated. Under catalytic conditions this intermediate converts to the thermodynamic C–F alumination product.

Tropylium Salt Promoted Hydroboration Reactions: Mechanistic Insights via Experimental and Computational Studies

2021 ◽  
Author(s):  
Nhan Nu Hong Ton ◽  
Binh Khanh Mai ◽  
Thanh Vinh Nguyen
Keyword(s):  
Dft Calculations ◽  
Lewis Acids ◽  
Experimental Studies ◽  
Cross Coupling ◽  
Computational Studies ◽  
Metal Free ◽  
Hydride Abstraction ◽  
Novel Method ◽  
Tropylium Salts

Abstract: Hydroboration reaction of alkynes is one of the most synthetically powerful tools to access organoboron compounds, versatile precursors for cross coupling chemistry. This type of reaction has traditionally been mediated by transition metal or main group catalysts. Herein, we report a novel method using tropylium salts, typically known as organic oxidants and Lewis acids, to efficiently promote the hydroboration reaction of alkynes. A broad range of vinylboranes can be easily accessed via this metal-free protocol. Similar hydroboration reactions of alkenes and epoxides can also be efficiently catalyzed by the same tropylium catalysts. Experimental studies and DFT calculations suggested that the reaction follows an uncommon mechanistic paradigm, which is triggered by a hydride abstraction of pinacolborane with tropylium ion. This is followed by a series of <i>in situ</i> counterion-activated substituent exchanges to generate boron intermediates that promote the hydroboration reaction.

scholarly journals Novel edaravone-based azo dyes: efficient synthesis, characterization, antibacterial activity, DFT calculations and comprehensive investigation of the solvent effect on the absorption spectra

RSC Advances ◽  
2020 ◽  
Vol 10 (59) ◽  
pp. 35729-35739
Author(s):  
Mohammad Amin Davasaz Rabbani ◽  
Behzad Khalili ◽  
Hamid Saeidian
Keyword(s):  
Antibacterial Activity ◽  
Dft Calculations ◽  
Solvent Effect ◽  
Absorption Spectra ◽  
Azo Dyes ◽  
Drug Combination ◽  
Azo Compounds ◽  
Efficient Synthesis ◽  
Comprehensive Investigation ◽  
Anions And Cations

The present study deals with designing and synthesizing novel dyes using the drug combination of edaravone and azo compounds which can be used as an indicator for anions and cations.

Manganese PNP-pincer catalyzed isomerization of allylic/homo-allylic alcohols to ketones – activity, selectivity, efficiency

2019 ◽  
Vol 9 (22) ◽  
pp. 6327-6334 ◽  
Author(s):  
Tian Xia ◽  
Brian Spiegelberg ◽  
Zhihong Wei ◽  
Haijun Jiao ◽  
Sergey Tin ◽  
...  
Keyword(s):  
Dft Calculations ◽  
Pincer Complexes ◽  
Allylic Alcohols ◽  
Deuterium Labelling ◽  
Reaction Proceeds

Manganese PNP pincer complexes are excellent catalysts for the isomerization of allylic alcohols to the ketones. The reaction proceeds via a dehydrogenation/hydrogenation mechanism as shown by DFT calculations and deuterium labelling.

Copper(II)-Promoted Oxidation/[3+2]Cycloaddition/Aromatization Cascade: Efficient Synthesis of Tetrasubstituted NH-Pyrrole from Chalcones and Iminodiacetates

Synlett ◽  
2019 ◽  
Vol 30 (12) ◽  
pp. 1442-1446 ◽  
Author(s):  
Zhang-qi Lin ◽  
Chao-dong Li ◽  
Zi-chun Zhou ◽  
Shuai Xue ◽  
Jian-rong Gao ◽  
...  
Keyword(s):  
Efficient Method ◽  
Cascade Reaction ◽  
Oxidative Cyclization ◽  
Efficient Synthesis ◽  
Reaction Conditions ◽  
Highly Efficient ◽  
Wide Range ◽  
Reaction Proceeds

A simple and highly efficient method for the preparation of tetrasubstituted NH-pyrrole from a wide range of chalcones and diethyl iminodiacetates via a Cu(OAc)2-promoted oxidation/[3+2]cycloaddition/aromatization cascade reaction has been developed. This reaction proceeds through dehydrogenations, deamination, and oxidative cyclization, affording the corresponding products in good to excellent yields. This convenient methodology for constructing tetrasubstituted NH-pyrroles has several advantages over existing methods, such as the use of easily accessible chalcones and readily available diethyl iminodiacetates, and mild reaction conditions. A wide range of substrates are tolerated.

An Efficient Synthesis of Functionalized 2H-1,3,5-Oxadiazines via Metal-Carbenoid-Induced 1,2,4-Oxadiazole Ring Cleavage

Synthesis ◽  
2020 ◽  
Vol 53 (02) ◽  
pp. 348-358
Author(s):  
Mikhail S. Novikov ◽  
Julia O. Strelnikova ◽  
Nikolai V. Rostovskii ◽  
Olesya V. Khoroshilova ◽  
Alexander F. Khlebnikov
Keyword(s):  
Ring Opening ◽  
Ring Cleavage ◽  
Efficient Synthesis ◽  
Alkyl Aryl ◽  
Diazo Esters ◽  
Reaction Proceeds

AbstractA high-yielding method for the synthesis of 2H-1,3,5-oxadiazines by rhodium(II)- or copper(II)-catalyzed reaction of 1,2,4-oxadiazoles with α-diazo esters has been developed. The reaction proceeds via attack of the metallocarbenoid on the oxadiazole N2 atom followed by ring opening/1,6-electrocyclization and enables the introduction of alkyl, aryl, oxy, and amino substituents into the 6-position and electron-withdrawing groups into the 2-position of 1,3,5-oxadiazine. The N2-attack and the N4-attack of the carbenoid cause different oxadiazole ring openings, which are controlled by the substitution at C5. The presence of a substituent at this position is a prerequisite for the N2-attack to occur, leading to the formation of 1,3,5-oxadiazines.

scholarly journals Isoxazolium N-ylides and 1-oxa-5-azahexa-1,3,5-trienes on the way from isoxazoles to 2H-1,3-oxazines

2014 ◽  
Vol 10 ◽  
pp. 1896-1905 ◽  
Author(s):  
Alexander F Khlebnikov ◽  
Mikhail S Novikov ◽  
Yelizaveta G Gorbunova ◽  
Ekaterina E Galenko ◽  
Kirill I Mikhailov ◽  
...  
Keyword(s):  
Dft Calculations ◽  
Experimental Studies ◽  
Diazo Compounds ◽  
Stationary Points ◽  
Reaction Intermediates ◽  
Reaction Conditions ◽  
Open Chain ◽  
Isoxazole Ring ◽  
Diazo Esters ◽  
Probable Reaction

Theoretical and experimental studies of the reaction of isoxazoles with diazo compounds show that the formation of 2H-1,3-oxazines proceeds via the formation of (3Z)-1-oxa-5-azahexa-1,3,5-trienes which undergo a 6π-cyclization. The stationary points corresponding to the probable reaction intermediates, isoxazolium N-ylides, were located by DFT calculations at the B3LYP/6-31G(d) level only for derivatives without a substituent in position 3 of the isoxazole ring. These isoxazolium N-ylides are thermodynamically and kinetically very unstable. According to the calculations and experimental results 2H-1,3-oxazines are usually more thermodynamically stable than the corresponding open-chain isomers, (3Z)-1-oxa-5-azahexa-1,3,5-trienes. The exception are oxaazahexatrienes derived from 5-alkoxyisoxazoles, which are thermodynamically more stable than the corresponding 2H-1,3-oxazines. Therefore, the reaction of diazo esters with 5-alkoxyisoxazoles is a good approach to 1,4-di(alkoxycarbonyl)-2-azabuta-1,3-dienes. The reaction conditions for the preparation of aryl- and halogen-substituted 2H-1,3-oxazines and 1,4-di(alkoxycarbonyl)-2-azabuta-1,3-dienes from isoxazoles were investigated.

Iridium-Catalyzed Asymmetric Umpolung Allylation of N-Fluor­enyl Imines to Prepare 1,4-Disubstituted Homoallylic Amines

Synlett ◽  
2017 ◽  
Vol 28 (16) ◽  
pp. 2051-2056 ◽  
Author(s):  
Dawen Niu ◽  
Liqiang Wan ◽  
Lan Tian ◽  
Jie Liu
Keyword(s):  
Natural Products ◽  
Cope Rearrangement ◽  
Allylic Substitution ◽  
Reaction Discovery ◽  
Homoallylic Amines ◽  
Synthetic Utility ◽  
Reaction Proceeds ◽  
Conventional Methods

The discovery and development of an Ir-catalyzed asymmetric umpolung allylation of imines is discussed here. This method produces 1,4-disubstituted homoallylic amines, a class of compounds that are difficult to access by conventional methods. This reaction proceeds through a sequence involving an allylation and a 2-aza-Cope rearrangement event. The unique mechanistic feature of this reaction could be the reason for its broad substrate scope. The products of this reaction are useful intermediates for various bioactive and natural products. Besides its immediate synthetic utility, we expect this transformation to inspire the development of other umpolung functionalizations of imines and Ir-catalyzed asymmetric allylic substitution (AAS) reactions.1 Introduction2 Reaction Discovery3 Substrate Scope4 Conclusion

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