Functionalization of alkenes has been well investigated by chemists, thus it has been extensively applied in organic synthesis and industries. In the past few decades, transition‐metal, such as ...palladium, rhodium, gold, iridium, copper and iron, catalyzed functionalization reactions of alkenes have been significantly developed and played vital roles in synthesis. The difunctionalization of alkenes are appealing as an important alternative to the traditional approaches for the construction of useful carbon centers, particularly carbon quaternary centers, which commonly existed as structural motifs in numerous natural products, pharmaceuticals, and biologically active molecules. This account will summarize our recent advances in the intermolecular difunctionalization of alkenes, and also highlight the scope and limitations as well as the mechanisms of these difunctionalization reactions. In general, in this account the difunctionalization of alkenes starting from dicarbofunctionalization will be discussed. Then carboheterofunctionalization of alkenes will be intensively reviewed, and diheterofunctionalization will also be highlighted.
This personal account introduces the recent advances in difunctionalization of alkenes. These reactions are classified by the chemical bond formation, including C−C, C−N, C−O and other carbon‐heteroatom bond formation. This review highlights the scope and limitations, as well as the mechanisms of these functionalization reactions.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
A new metal‐free radical 5‐exo‐dig cyclization of phenol‐linked 1,6‐enynes with O2, 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO), and tBuONO is described. With this general method, carbonylated ...benzofurans can be accessed through incorporation of two oxygen atoms into the product from O2 and TEMPO through dioxygen activation and oxidative cleavage of the NO bond, respectively.
Benzofurans are obtained by the tBuONO‐initiated radical 5‐exo‐dig cyclization of enynes under mild and metal‐free conditions. The two oxygen atoms that constitute the newly formed carbonyl groups of the benzofuran system originate from O2 and 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO), respectively.
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A new metal‐free oxidative radical 2+2+1 carbocyclization of benzene‐linked 1,n‐enynes with two C(sp3)H bonds adjacent to the same heteroatom is described. This method achieves two C(sp3)H ...oxidative functionalizations and an annulation, thus providing efficient and general access to a variety of fused five‐membered carbocyclic hydrocarbons.
An oxidative functionalization of two C(sp3)H bonds adjacent to a same heteroatom for the 2+2+1 carbocyclization with benzene‐linked 1,n‐enynes is presented. This method successfully proceeds using a radical mechanism and provides straightforward access to a variety of fused five‐membered carbocyclic hydrocarbons. TBPB=tert‐butyl perbenzoate.
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Radical‐initiated difunctionalization of alkenes is one of the most important methods in organic synthesis and medicinal chemistry, which can be applied to synthesize value complex compounds as well ...as structural motifs that found in bioactive natural products and pharmaceuticals. In recent years, impressive progress have been made in this area with ideal silver catalysis. Here, we summarize recent advances in silver‐mediated radical difunctionalization of alkenes for the formation of diverse bonds, including 1) two‐component radical difunctionalization reactions enabled by an intramolecular cyclization process toward various cyclic compounds and 2) three‐component radical difunctionalization reactions leading to complex linear compounds. These silver‐mediated radical alkene difunctionalization transformations are general initiated by different radicals, such as carbon‐, oxygen‐, sulfur‐, phosphinyl‐, and halogen‐center radicals, followed by terminated with nucleophiles to form two new bonds in a single reaction.
Ag catalysis: Recent advances in the silver‐mediated intermolecular radical 1,2‐difunctionalization of alkenes are summarized. These reaction are classified by the substrate type and radical regents. Two new C−C/C−C bonds, C−C/C−X bonds (X=F, O, S…) and C−X/C−X bonds (X=O, Br, I…) could be constructed in a single reaction.
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For straightforward access to various substituted 1,1-diarylalkanes a photoredox-catalyzed and copper-promoted 1,2-alkylarylation reaction of styrenes has been developed, which uses α-carbonyl alkyl ...bromides and N,N-disubstituted anilines as functionalization reagents. In this radical difunctionalization reaction, α-carbonyl alkyl bromides, including primary-, secondary- and tertiary-α-bromoalkyl ketone esters, malonic esters and cycloalkane were transformed to the corresponding 1,1-diarylalkanes in moderate to good yields at room temperature. Notably, this transformation provided a new route for the C-H alkylation of N,N-disubstituted anilines with high para-selectivity beyond the typical Friedel-Crafts alkylation.
The first iron‐catalyzed 1,2‐difunctionalization of styrenes and conjugated alkenes with silanes and either N or C, using an oxidative radical strategy, is described. Employing FeCl2 and ...di‐tert‐butyl peroxide allows divergent alkene 1,2‐difunctionalizations, including 1,2‐aminosilylation, 1,2‐arylsilylation, and 1,2‐alkylsilylation, which rely on a wide range of nucleophiles, namely, amines, amides, indoles, pyrroles, and 1,3‐dicarbonyls, thus providing a powerful platform for producing diverse silicon‐containing alkanes.
Iron clad: By employing FeCl2 and di‐tert‐butyl peroxide (DTBP), divergent alkene 1,2‐difunctionalization reactions, including 1,2‐aminosilylation, 1,2‐arylsilylation, and 1,2‐alkylsilylation, are achieved by using different nucleophiles. The method provides straightforward and practical access to 1‐amino‐2‐silylalkanes and other functionalized silicon‐containing alkanes with broad substrate scope and high selectivity.
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A simple three-component 1,2-bromoesterification of alkenes with acids and N-bromosuccinimide under electrochemical oxidative conditions is described. This transformation enables the construction of ...β-bromoalkyl esters via oxidative C–Br/C–O difunctionalization, where a variety of alkenes, including styrenes and cycloolefins, were well tolerated to react efficiently with a wide range of acids, such as aromatic acids, aliphatic acids, and amino acids.
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IJS, KILJ, NUK, PNG, UL, UM
Owing to their easy availability and cheapness, simple alkyl chlorides are good raw materials for introducing complex polychlorinated groups. Polychlorinated hydrocarbons units, such as di‐ or ...trichloromethyl groups, not only widely found in pesticide and bioactive molecule, but also can be as a precursor to converted into different functional groups such as −COOH, −CHO and −CO. The direct polychloroalkylation reaction by using simple alkyl chlrides has been considered to be an important tool for synthesizing complex polychlorinated compounds. This review summarizes recent developments, especially free radical strategies, in the polychloroalkylation of different substrates (such as 2‐acylpyridines, benzyl tertiary amines, alkenes, imine and 1,n‐enynes). We hope that this review provides a new perspective on this field and also provides a reference to develop environmentally friendly and sustainable methods.
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Görtler vortices developed in laminar boundary layer experience remarkable changes when the flow is subjected to compressibility effects. In the present study, five
$\mathit{Ma}$
numbers, covering ...incompressible to hypersonic flows, at
$\mathit{Ma}=0.015$
, 1.5, 3.0, 4.5 and 6.0 are specified to illustrate these effects. Görtler vortices in subsonic and moderate supersonic flows (
$\mathit{Ma}=0.015$
, 1.5 and 3.0) are governed by the conventional wall-layer mode (mode W). In hypersonic flows (
$\mathit{Ma}=4.5$
, 6.0), the trapped-layer mode (mode T) becomes dominant. This difference is maintained and intensifies downstream leading to different scenarios of secondary instabilities. The linear and nonlinear development of Görtler vortices which are governed by dominant modal disturbances are investigated with direct marching of the nonlinear parabolic equations. The secondary instabilities of Görtler vortices set in when the resulting streaks are adequately developed. They are studied with Floquet theory at multiple streamwise locations. The secondary perturbations become unstable downstream following the sequence of sinuous mode type I, varicose mode and sinuous mode type II, indicating an increasing threshold amplitude. Onset conditions are determined for these modes. The above three modes can each have the largest growth rate under the right conditions. In the hypersonic cases, the threshold amplitude
$A(u)$
is dramatically reduced, showing the significant impact of the thermal streaks. To investigate the parametric effect of the spanwise wavenumber, three global wavenumbers (
$B=0.5$
, 1.0 and
$2.0\times 10^{-3}$
) are specified. The relationship between the dominant mode (sinuous or varicose) and the spanwise wavenumber of Görtler vortices found in incompressible flows (Li & Malik, J. Fluid Mech., vol. 297, 1995, pp. 77–100) is shown to be not fully applicable in high-speed cases. The sinuous mode becomes the most dangerous, regardless of the spanwise wavelength when
$\mathit{Ma}>3.0$
. The subharmonic type can be the most dangerous mode while the detuned type can be neglected, although some of the sub-dominant secondary modes reach their peak growth rates under detuned states.
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