Migration Of Functional Groups Research Articles

Radical Homopolymerization of Linear α‐Olefins Enabled by 1,4‐Cyano Group Migration

α‐Olefins are valued and abundant building blocks from fossil resources. They are widely used to provide small‐molecule or polymeric products. Despite numerous advantages of radical polymerization, it has been well‐documented as textbook knowledge that α‐olefins and their functionalized derivatives cannot be radically homopolymerized because of the degradative chain transfer side reactions. Herein, we report our studies on the homopolymerization of thiocyanate functionalized α‐olefins enabled by 1,4‐cyano group migration under radical conditions. By this approach, a library of ABC sequence‐controlled polymers with high molecular weights can be prepared. We can also extend this strategy to the homopolymerization of α‐substituted styrenic and acylate monomers which are known to be challenging to achieve. Overall, the demonstrated functional group migration radical polymerization could provide new possibilities to synthesize polymers with unprecedented main chain sequences and structures. These polymers are promising candidates for novel polymeric materials.

Radical Homopolymerization of Linear α-Olefins Enabled by 1,4-Cyano Group Migration.

α-Olefins are valued and abundant building blocks from fossil resources. They are widely used to provide small-molecule or polymeric products. Despite numerous advantages of radical polymerization, it has been well-documented as textbook knowledge that α-olefins and their functionalized derivatives cannot be radically homopolymerized because of the degradative chain transfer side reactions. Herein, we report our studies on the homopolymerization of thiocyanate functionalized α-olefins enabled by 1,4-cyano group migration under radical conditions. By this approach, a library of ABC sequence-controlled polymers with high molecular weights can be prepared. We can also extend this strategy to the homopolymerization of α-substituted styrenic and acylate monomers which are known to be challenging to achieve. Overall, the demonstrated functional group migration radical polymerization could provide new possibilities to synthesize polymers with unprecedented main chain sequences and structures. These polymers are promising candidates for novel polymeric materials.

E-Selective Radical Difunctionalization of Unactivated Alkynes: Preparation of Functionalized Allyl Alcohols from Aliphatic Alkynes.

Radical difunctionalization of aliphatic alkynes provides direct access to valuable multi-substituted alkenes, but achieving a high level of chemo- and stereo-control remains a formidable challenge. Herein a novel photoredox neutral alkyne di-functionalization is reported through functional group migration followed by a radical-polar crossover and energy transfer-enabled stereoconvergent isomerization of alkenes. In this sequence, a hydroxyalkyl and an aryl group are incorporated concomitantly into an alkyne, leading to diversely functionalized E-allyl alcohols. The scope of alkynes is noteworthy, and the reaction tolerates aliphatic alkynes containing hydrogen donating C─H bonds that are prone to intramolecular hydrogen atom transfer. The protocol features broad functional group compatibility, high product diversity, and exclusive chemo- and stereoselectivity, thus providing a practical strategy for the elusive radical di-functionalization of unactivated alkynes.

Distal Functional Group Migration of Unactivated Alkenes with IMDN‐Tf Reagents

AbstractThe difunctionalization of alkenes involving 1,5‐functional group migration strategies for the conversion of versatile and readily available olefins into more structurally complex molecules has been greatly studied. However, the vast majority of the reported reactions rely on strongly oxidizing conditions and oxidizing fluoroalkyl radical reagents. In contrast, few reactions with reduced radical reagents have been reported. This work describes a photo / electroredox catalytic condition for difunctional modification of unactivated olefins via a radical process using IMDN‐Tf reagents with broad substrate scope and excellent tolerance.

Mechanoredox Enabled the Difunctionalization of Unactivated Alkenes via Distal Functional Group Migration

Mechanoredox Enabled the Difunctionalization of Unactivated Alkenes via Distal Functional Group Migration

Experimental study of coal spontaneous combustion high-temperature region spreading characteristics

To solve the difficult problem of determining the change law of key point temperature and gas during the motion of high temperature area inside the coal mine seam, this study used the simulation platform of coal spontaneous combustion (CSC) development to investigate the temperature, gas concentration, functional group migration, and change rule of key points with layers in the holistic process of high-temperature region (HTR) spreading of Wen-Zhuang coalmine in Shanxi province, China. The analysis involved the dynamic change rule among temperature, oxygen consumption rate, CO, and C2H4. Finally, with the gray correlation method, the changes of the dominant functional groups released by CO and C2H4 were explored, which revealed the transport rule between the functional groups and the regional spreading in the HTR spreading process. The results show that the temperature of coal body and the rate of oxygen consumption gradually decreased with the deepening of coal layers. Among them, as the coal seam burns, the coal body will appear to “collapse”, along with the phenomenon of “re-ignition”; at the combustion point temperature of each coal layer, the activity of the oxygen-containing functional group was the largest, the activity of hydroxyl group was the smallest, and the activity of aliphatic and aromatic hydrocarbons was similar. Among them, the hydroxyl group, aromatic hydrocarbon, and oxygen-containing functional group had the same trend changing with the deepening of the layers, exhibiting a trend of first decreasing after increasing and later decreasing, and positively correlated with the ignition temperature of each layer. The trend of aliphatic hydrocarbon was opposite to the trend of other functional groups and negatively correlated with the ignition temperature of each layer. The research results of this paper can be used for disaster prevention in the HTR of mine fires, and parameters, such as indicator gases, functional groups and temperature, can be used to determine and deter the migration trend of mine fires, providing a theoretical basis for the prevention and control of high-temperature diffusion of coal spontaneous combustion.

1,2-Alkynyl Functionalization of Unactivated Alkenes via Diverse Radical-Triggered Functional Group Migration.

We have developed a transition-metal-free radical approach for 1,2-alkynyl functionalization of unactivated alkenes through the combination of 3-exo-dig cyclization with alkynyl migration triggered by in situ-generated diverse radical precursors. This strategy provides a robust toolkit to access a variety of synthetically important α-functionalized alkynyl ketones, simultaneously installing densely functionalized carbonyl, alkynyl, and other various functional groups into the alkenes. The broad substrate scope, which includes distinctly electron-donating or electron-withdrawing alkynyl migrating groups, excellent functional group compatibility, and remarkable selectivity make this protocol practical and attractive.

Docking-migration: a powerful tool for radical-mediated difunctionalization of alkenes

<p indent="0mm">Alkene difunctionalization supplies a robust tool for the conversion of simple alkenes to complex molecules by simultaneously installing two different functional groups to alkenes. In particular, radical-mediated difunctionalization of alkenes has received extensive attention from synthetic chemists, because of the inherent features of mild reaction conditions and high product diversity. By taking advantage of designed bifunctional reagents, in which a radical donor and a migrating group are tethered by a linker, the docking-migration process proceeding through consecutive radical addition to alkene and intramolecular functional group migration provides an efficient strategy for alkene difunctionalization. The approach demonstrates broad scope of alkene substrates that activated and unactivated alkenes as well as complex alkenes are suitable substrates. This account summarizes the progress from our group in alkene difunctionalization relying on the docking-migration strategy.

Computational Study on Chemoselective Difunctionalization of Unactivated Alkenes with Radical-mediated Remote Functional Group Migration.

A computational study of the radical-mediated chemoselective difunctionalization of the tertiary alcohol substituted aliphatic alkenes is carried out employing density functional theory (DFT) and high-level coupled-cluster methods, such as coupled-cluster singles and doubles with perturbative triples [DLPNO-CCSD(T)]. Our results indicate that the cyclic vinyl radical plays an important role in the progression of the reactions. Our computations demonstrated that the chemoselective difunctionalization of unactivated alkenes with radical-mediated remote functional group migration is suitable for the 5- and 6-exo-dig cyclization, as opposite to 3- and 4-exo-dig cyclization suffering from cyclic intermediate with high energy. Our results show that the migration of nitrile group is more preferable than that of alkynyl group for the molecules including both cyano group and alkynyl group. For the 5- and 6-exo-dig cyclization, the rate-determining step is the homolysis of the C-C σ-bond in the cyclic intermediate, which results in the hydroxyl alkyl radical.

Metal-free radical-mediated alkylfunctionalization of ethylene and low-boiling-point alkenes

We report a metal-free approach for radical alkylfunctionalization of gaseous ethylene and other light alkenes by remote functional group migration.

Ruthenium-catalyzed 1,3-indolyl migration within α,α-disubstituted allylic alcohols

The functional group migration strategy could facilitate the construction of complex structures from relatively simple starting materials.

Remote desaturation of hexenenitriles by radical-mediated cyano migration

We report a new reaction mode involving functional group migration, which is applied to the radical-mediated remote desaturation of hexenenitriles. The reaction proceeds through consecutive alkene sulfonylation, intramolecular cyano migration, and single-electron oxidation of benzyl radical to cation followed by deprotonation, leading to a variety of densely functionalized alkenes. The protocol features mild photocatalytic conditions, broad functional group tolerance, and high product diversity.

Merging Fluorine Incorporation and Functional Group Migration.

Fluorine incorporation by concomitant fluoroalkyl radical addition to alkene or alkyne and functional group migration (FGM) represents an ingenious and robust strategy for the synthesis of structurally diverse fluorinated compounds. This account gives an overview of related studies in our group, in which three main reaction modes are discussed: 1) radical fluoroalkylative difunctionalization of unactivated alkenes via intramolecular FGM; 2) alkene difunctionalization by docking-migration process using fluoroalkyl-containing bifunctional reagents; 3) incorporation of fluoroalkyl group into C(sp3 )-H bond via consecutive hydrogen atom transfer (HAT) and FGM. Relying on these methods, a variety of trifluoromethylation and di-/mono-fluoroalkylation reactions along with the migration of cyano, heteroaryl, oximino, formyl, alkynyl, and alkenyl groups have been accomplished under mild conditions.

Metal-free radical difunctionalization of ethylene

<h2>Summary</h2> Owing to its simplicity, ethylene, as the most abundant organic feedstock, only finds limited applications in fine chemical synthesis, resulting in molecules of modest complexity. Ethylene difunctionalization allows for the synthesis of much more complex chemicals, but it is rare and almost always relies on transition-metal catalysis. Herein, we report an unprecedented metal-free radical difunctionalization of ethylene through a functional group migration strategy. The use of sulfone-based bifunctional reagents enables straightforward access to a wide range of diheteroarylated compounds under mild conditions in a highly selective manner. The precise modulation of radical polarity and kinetic preference arising from intramolecular functional group migration guarantee the success of the cascade three-bond forming process in a controllable manner.

Study of the microstructure and oxidation characteristics of residual coal in deep mines

Residual coal is prone to spontaneous combustion under the influence of high ground temperature, and the risk increases with mining depth. This results in gradual increases in smoke and dust emissions, which seriously affect the ecological and geological environment of the mining area. To avoid spontaneous combustion of the residual coal, protect the resources and ecology of mining areas, and investigate the influence of the deep thermal environment on the microstructure and oxidation properties of coal, the pore evolution characteristics and functional group migration of coal in a thermal environment were studied by N2 adsorption and infrared spectroscopy. A temperature-programmed test system was used to simulate the low-temperature oxidation process occurring in deep coal seams, and the heat release characteristics and oxidation kinetic parameters of the index gas were calculated. The experimental results revealed that the pore oxygen storage capacities and coal oxygen contact areas of residual coal in deep mines are larger than those of coal in shallow seams. As the preheating temperature is increased, the rates of CO and CO2 production and the amount of oxygen consumed in oxidation of heat-treated coal increase. The crossing point temperature (CPT) of heat-treated coal decreases. The deep thermal environment accelerates the rate of condensation decomposition of the aliphatic hydrocarbon groups in coal and fracture of side chain hydrogen bonds connecting strong electron-absorbing groups, which increases the exothermic intensity of the oxidation process. The reaction trigger temperatures for aliphatic hydrocarbon groups, peroxyl radicals, associative hydrogen bonds and other active groups in coal are different. With increasing ambient temperature, the types of active groups in coal increase, and the contents accumulate. With an increase in the deep geothermal temperature, the oxidation activity of coal is enhanced, and the coal is more prone to spontaneous combustion. These research results provide a theoretical reference for deep coal clean mining and prevention of spontaneous combustion disasters and have a potential guiding role in environmental protection and ecological improvement of deep mining areas.

Spontaneous combustion characteristics and mechanism of water-immersed and air-dried brown coal

ABSTRACT To reveal the influential laws and mechanism of water immersion on the spontaneous combustion traits of lignite in the low-temperature oxidation stage. Raw coal (HL), water-immersed for 30 days (HL-S30), 90 days (HL-S90) and 150 days (HL-S150), were taken as the research objects. The pore evolution characteristics and functional group migration law of coal were explored by Scanning Electron Microscopy (SEM), Low-temperature Nitrogen Adsorption Test (LNAT) and Fourier Transform Infrared Spectroscopy (FTIR). The low-temperature oxidation procedure was simulated by Programmed Heating Test (PHT), and the gas release characteristics, exothermicity and ultimate spontaneous combustion parameters of the relic coal were compared. These findings demonstrated that the discriminant indexes of spontaneous combustion tendency of four specimens change periodically with temperature, but generally the spontaneous combustion intensity of HL-S30 and HL-S150 is greater than HL, and HL-S90 is the least. The micro reasons for increasing oxidation activity of HL-S30 and HL-S150 are as follows: the number of micropores of water-immersed coal is almost 3 ~ 4 times that of HL, and the pores expanded with immersion which helps to enhance the adsorption of oxygen; the content of broken aromatic hydrocarbon -C = C- reached 50%, the total amount of hydroxy -OH decreased to 2/3 of HL, while the content of carboxyl -COOH and ether-oxygen bond -C-O- of active group doubled which are beneficial to accelerate the process of free radical chain reaction, and promote the gas release and the temperature of residual coal to reach the ignition point. The research findings enrich the basic theory of spontaneous combustion traits of water-impregnated coal, which help reduce the fire accidents and hidden dangers in actual production.

Combination of radical functional group migration (FGM) and hydrogen atom transfer (HAT)

Direct functionalization of C–H bonds is a powerful synthetic tool that unlocks tremendous opportunities for late-stage elaboration of complex molecules. Recent advances of a new strategy, merging radical-mediated functional group migration (FGM) with hydrogen atom transfer (HAT), have shown great potential for site-selective C(sp³)–H bond functionalization.

Rearrangements and Migrations along the Ferrocene Periphery: On the Way to Planar‐Chiral and (Multi)Substitution Patterns

AbstractThe functionalization of ferrocenes via intramolecular rearrangements is summarized. Focus will be directed on anionic, cationic and thermal/photo‐induced processes that enable the migration of functional groups along the periphery of the ferrocene's cyclopentadienyl rings. Anionic processes include halogen dance reactions and Fries rearrangements. The metalation procedures are discussed, which are essential for a regio‐ and stereoselective proceeding. Computational studies and electrochemical data are included to discuss stereoselective processes and reactivity differences. Positioning of a positive charge in close proximity to the ferrocenyl backbone induces Pinacol, Beckmann, and remote Fries rearrangements. Activation of an alkynyl functionality facilitates alkyne/vinylidene changes. Thermal rearrangements do not require an additional charge and are induced by N2 elimination, followed by nitrene/carbene formation via Curtius and Wolff rearrangements, respectively. The latter was exemplarily used for the ring contraction of [4]‐ into [3]ferrocenophanes.

Radical trifunctionalization of hexenenitrile via remote cyano migration.

A novel radical-mediated trifunctionalization of hexenenitriles via the strategy of remote functional group migration is disclosed. A portfolio of functionalized hexenenitriles are employed as substrates. After difunctionalization of the unactivated alkenyl part via remote cyano migration, the in situ formed radical intermediate is captured by an azido radical, thus enabling the trifunctionalization. The reaction features mild conditions and broad functional group compatibility, leading to valuable products bearing multiple useful groups. This protocol further extends the scope of remote functional group migration.

Multisubstituted Cyclohexene Construction through Telescoped Radical-Addition Induced Remote Functional Group Migration and Horner-Wadsworth-Emmons (HWE) Olefination.

An efficient telescoped method for the rapid assembly of multisubstituted cyclohexenes is presented herein. The whole process nicely merges photoredox-promoted alkene difunctionalization via remote functional group migration with concomitant intramolecular Horner-Wadsworth-Emmons (HWE) olefination. The characteristic feature of this protocol resides in the fact that the follow-up requiring ketone functionality for ring-closing olefination is in situ unveiled from the otherwise inert tertiary alcohol by the preceding alkene difunctionalization.