Functionalization Of Alkanes Research Articles

Mechanism and Selectivities of [Cu]/[M] (M=Pd, Ni) Synergistic Catalyzed Alkene Arylboration: A DFT Investigation

ABSTRACTThe transition metal–catalyzed boronation reactions are considered as one of the most effective methods for the synthesis of alkylboranes in terms of functional group compatibility and reactivity. Herein, the mechanism of synergistic catalysis of alkene arylboration by [Cu]/[M] (M=Pd, Ni) bimetallic catalysts, as well as the regioselectivity and stereoselectivity of the reactions, has been investigated by using DFT calculations. The results show that four processes are involved in the whole reaction: [Cu]‐catalyzed borylcuprization of alkene, [Pd] or [Ni]‐catalyzed oxidative addition of halogenated aryl groups, transmetalation, and reductive elimination. [Cu]/[Ni] bimetallic catalysts show the same catalytic activity as [Cu]/[Pd] catalysts and are good economic alternatives for the alkene arylboration. The cleavage of B–B bond of B2Pin2 is the rate‐determining step. The regioselectivity of the title reaction is determined by the mode of the alkene insertion into the Cu–B bond. The attacking of C atom with the more electron‐rich character in alkyne makes for the formation of the main product. The small energy barrier difference between the rotation of the Cu‐C σ bond from the syn‐9 to the anti‐9 controls the stereoselectivity. Our findings provide a thorough explanation of the experimental results and shed light on the further development of the alkene functionalization.

Radical Cation Alkene Functionalization Using Anodic Oxidation

Oxidative functionalization of alkenes is a promising molecular transformation technique, where intramolecular reactions enable the synthesis of saturated heterocycles1), which are often found in natural products and pharmaceuticals. In addition to the widely studied palladium-catalyzed oxidative functionalization of alkenes2), electrochemical3), 4) and photocatalytic5) methods have recently been developed. These one-electron oxidation-based methods have been applied to trisubstituted and tetrasubstituted alkenes with large steric hindrance, which is difficult to achieve with conventional palladium-catalyzed reactions. In many cases, these methods reported previously form rings as neutral radicals under basic conditions. On the other hand, radical cationic cyclization is relatively rare and have not yet been fully discussed. In this study, we developed an alkene oxidative functionalization using electrolysis for radical cationic cyclization.After optimizing the reaction conditions using trisubstituted alkene (1a) as a model substrate, we succeeded in obtaining the target compound (2a) in 90% yield (Scheme 1). In this reaction, a six-membered ring is formed as a byproduct, but the anion species of the supporting salt affects the reaction selectivity, and it was found that a five-membered ring was formed with high selectivity when ClO4- or TfO- were used. Furthermore, using a 1:9 mixture of highly polar CH3CN and low-polar 1,2-DCE as the reaction solvent improved the solubility and conductivity of the supporting salt, resulting in a significant increase in yield. The use of carbon felt, which has a large surface area, as the working electrode also contributed to the yield improvement by suppressing the voltage increase.For sulfonamides (1b-d) with various substituents on the aromatic ring, we were able to obtain five-membered ring compounds (2b-d) in good yields in all cases. In addition to these results, the details of the condition studies and other substrates will be discussed.1) Nakamura, I.; Yamamoto, Y. Chem. Rev. 2004, 104, 2127-2198.2) McDonald, R. I.; Liu, G.; Stahl, S, S. Chem. Rev. 2011, 111, 2981-3019.3) Xu, H.-C.; Moeller, K. D. J. Am. Chem. Soc. 2010, 132, 2839–2844.4) Huang, C.; Li, Z.-Y.; Song, J.; Xu, H.-C. Angew. Chem. Int. Ed. 2021, 60, 11237–11241.5) Reed, N. L.; Lutovsky, G. A.; Yoon, T. P. J. Am. Chem. Soc. 2021, 143, 6065-6070. Figure 1

Transition Metal Mimetic π-Activation by Cationic Bismuth(III) Catalysts for Allylic C-H Functionalization of Olefins Using C═O and C═N Electrophiles.

The discovery and utilization of main-group element catalysts that behave similarly to transition metal (TM) complexes have become increasingly active areas of investigation in recent years. Here, we report a series of Lewis acidic bismuth(III) complexes that allow for the catalytic allylic C(sp3)-H functionalization of olefins via an organometallic complexation-assisted deprotonation mechanism to generate products containing new C-C bonds. This heretofore unexplored mode of main-group reactivity was applied to the regioselective functionalization of 1,4-dienes and allylbenzene substrates. Experimental and computational mechanistic studies support the key steps of the proposed catalytic cycle, including the intermediacy of elusive Bi-olefin complexes and allylbismuth species.

Photocatalytic Functionalization of Alkenes Enabled by Polyfluoroaryl Migration

AbstractVisible light‐mediated photocatalytic approach for the radical functionalization of alkenes bearing the fluorinated aryl sulfide fragment is described. The process occurs in the presence of organic photocatalyst using sulfinates as sources of radicals. The key step of the reaction is the intramolecular 1,4‐migration of the polyfluoroaryl group. In the reaction, three new bonds are formed (two C−C and one C−S bond). The decisive role of fluorine atoms in the reaction efficiency was confirmed by DFT calculations.

Radical Fluorosulfonamidation: A Facile Access to Sulfamoyl Fluorides

AbstractRecently, the introduction of fluorosulfonyl (−SO2F) groups have attracted considerable research interests, as this moiety could often afford enhanced activities and new functions in the context of chemical biology and drug discovery. Herein, we report the design and synthesis of 1‐fluorosulfamoyl‐pyridinium (FSAP) salts, which could serve as an effective photoredox‐active precursor to fluorosulfamoyl radicals and enable the direct radical C−H fluorosulfonamidation of a variety of (hetero)arenes. This method features mild conditions, visible light, broad substrate scope, good group tolerance, etc., and a metal‐free protocol is also viable by using organic photocatalysts. Further, FSAP can also be applied to the radical functionalization of alkenes via 1,2‐difunctionalization, radical distal migration, tandem radical‐polar crossover reactions, etc. In addition, a formal C−H methylamination of (hetero)arenes by combining this radical C−H fluorosulfonamidation with subsequent hydrolysis as well as product derivatization are also demonstrated.

Radical Fluorosulfonamidation: A Facile Access to Sulfamoyl Fluorides.

Recently, the introduction of fluorosulfonyl (-SO2F) groups have attracted considerable research interests, as this moiety could often afford enhanced activities and new functions in the context of chemical biology and drug discovery. Herein, we report the design and synthesis of 1-fluorosulfamoyl-pyridinium (FSAP) salts, which could serve as an effective photoredox-active precursor to fluorosulfamoyl radicals and enable the direct radical C-H fluorosulfonamidation of a variety of (hetero)arenes. This method features mild conditions, visible light, broad substrate scope, good group tolerance, etc., and a metal-free protocol is also viable by using organic photocatalysts. Further, FSAP can also be applied to the radical functionalization of alkenes via 1,2-difunctionalization, radical distal migration, tandem radical-polar crossover reactions, etc. In addition, a formal C-H methylamination of (hetero)arenes by combining this radical C-H fluorosulfonamidation with subsequent hydrolysis as well as product derivatization are also demonstrated.

Visible-Light-Mediated Ring-Opening Geminal Dibromination of Alkenes via Alkoxy Radicals Enabled by Electron Donor-Acceptor Complex.

An electron donor-acceptor complex was utilized to generate alkoxy radicals from alcohols under mild conditions using visible light. This approach was combined with a hydroxybromination process to achieve the deconstructive functionalization of alkenes, leading to the production of geminal dibromides. Mechanistic investigations indicated the intermediacy of hypervalent iodine (III) compounds.

Hypervalent iodine-catalyzed amide and alkene coupling enabled by lithium salt activation.

Hypervalent iodine catalysis has been widely utilized in olefin functionalization reactions. Intermolecularly, the regioselective addition of two distinct nucleophiles across the olefin is a challenging process in hypervalent iodine catalysis. We introduce here a unique strategy using simple lithium salts for hypervalent iodine catalyst activation. The activated hypervalent iodine catalyst allows the intermolecular coupling of soft nucleophiles such as amides onto electronically activated olefins with high regioselectivity.

Construction of Acyclic Quaternary Carbon Stereocenters via Enantioselective Nickel Catalysis†

Comprehensive SummaryThe construction of acyclic quaternary carbon stereocenters, which are ubiquitous in many bioactive compounds, pharmaceuticals and natural products, has been a long persuit in synthetic organic chemistry. Among numerous methods, enantioselective nickel‐catalysis has attracted incremental attention in recent years. This review summarizes the recent development in the asymmetric strategies, research progress, mechanistic investigations for the generation of acyclic quaternary carbon stereocenters via enantioselective nickel catalysis. Key ScientistsIn 2006, the Zhou group and RajanBabu group realized the nickel‐catalyzed enantioselective hydrovinylation of α‐substituted styrenes and ethylene to construct acyclic quaternary carbon stereocenters (QCSs) by using spiro‐ and binaphthyl phosphoramidite ligands, respectively. In 2016, Watson developed a nickel‐catalyzed Suzuki‐Miyaura arylation to generate acyclic QCSs via chirality transfer reaction. In 2017, the Feng and the Fu group developed nickel‐catalyzed enantioselective conjugated/Michael additions to build acyclic QCSs, respectively. In 2020, the Fang group made the first success in the construction of QCSs by nickel‐catalyzed hydrocyanation of alkenes and allenes. In 2021, Gregory C. Fu and co‐workers disclosed a nickel‐catalyzed enantioselective α‐functionalization of carbonyl compounds that could form acyclic QCSs. At the same time, the Shi group constructed chiral acyclic QCSs via nickel‐catalyzed functionalization of alkenes. In 2023, Kleij and co‐workers applied a new strategy for Ni‐catalyzed regio‐ and enantioselective homoallylic coupling to construct acyclic QCSs. In the same year, Tao and co‐workers demonstrated a novel strategy that is dinickel‐catalyzed enantioselective α‐alkylation of carbonyl compounds with alkyl iodides.

Pendant Group Functionalization of Cyclic Olefin for High Temperature and High-Density Energy Storage.

High-temperature flexible polymer dielectrics are critical for high-power-density energy storage and conversion under harsh operating conditions. These types of dielectrics will need to simultaneously possess a high bandgap, dielectric constant and glass transition temperature - a substantial challenge when designing novel dielectric polymers. In this work, by varying halogen substituents of an aromatic pendant hanging off a bicyclic mainchain polymer, a class of high-temperature olefins with adjustable thermal stability are obtained, all with uncompromised large bandgaps. Halogens substitution of the pendant groups at para or ortho position of polyoxanorborneneimides (PONB) imparts it with tunable high glass transition temperature from ∼220 to 245°C, while with also moderate dielectric constant of ∼ 2.8-3.0 and high breakdown strength of ∼625-800MV/m. A high energy density of 7.1 J/cc at 200°C is achieved with p-POClNB, representing the highest reported energy density among all-organic homo-polymer dielectrics. Molecular dynamic simulations and ultrafast infrared spectroscopy were used to probe the free volume element distribution and chain relaxations of the polymers to provide insights to the dielectric thermal properties. An increase in free volume element is observed with the change in the pendant group from fluorine to bromine at the para position; however, a decrease in free volume element is observed as we change the pendant group from fluorine to chlorine at the ortho position because of the steric hindrance. Overall, the dielectric constant and band gap remain stable while the glass transition temperature changes more obviously. Consequently, by proper designing the pendant groups, the thermal stability of PONB can be improved for harsh condition electrification. This article is protected by copyright. All rights reserved.

Recent Advances in Photochemical/Electrochemical Carboxylation of Olefins with CO2

Comprehensive SummaryCO2 is an abundant, nontoxic, and renewable C1 feedstock in synthetic chemistry. Direct carboxylation of readily available olefins incorporating CO2 is regarded as a promising strategy to access high value‐added carboxylic acids as well as CO2 fixation. However, due to the thermodynamic stability and kinetic inertness of CO2 and the difficulty in controlling the regioselectivity, the carboxylation of olefins with CO2 still remains challenging. Radical‐type functionalization with olefins represented a powerful protocol and enabled the development of novel transformations in this realm. More recently, the advance of new technology, such as photoredox catalysis and the renaissance of electrochemistry in organic synthesis, offered access to unique chemical reactivities of radical precursors and provided new solutions to the functionalization of olefins. This review presents the recent advances in the radical‐type carboxylation of olefins, which has mainly been achieved through photocatalysis and electrocatalysis in the last decade. In this article, we provide a comprehensive introduction of the progress, summarize the advantages and limitations of current research, and discuss the potential outlook for further development. Key Scientists

Nickel-Catalyzed Regio- and Enantioselective Migratory Hydrocyanation of Internal Alkenes: Expanding the Scope to α,ω-Diaryl Internal Alkenes.

Metal-hydride-catalyzed migratory functionalization of alkenes witnessed extensive development in the past few years. However, the asymmetric version of this reaction has remained largely underdeveloped owing to the difficulty in simultaneous control of both regio- and stereoselectivity. In addition, exploring the wider alkene substrate scope to enable more synthetically valuable applications represents another challenge in this field. In this context, a nickel-catalyzed asymmetric hydrocyanation of internal alkenes involving a chain-walking process is demonstrated. The reaction exhibits excellent regio- and enantioselectivity, proceeds under mild reaction conditions, and delivers benzylic nitriles in high yields. Even α,ω-diaryl internal alkenes, which are known to be one of the most challenging substrates of this type, could be successfully converted to the desired products with good regio- and stereoselectivity by modifying the electronic and steric effects. Theoretical calculations suggest that the η3-benzyl coordination mode and the aryl substituent (3,5-(OMe)2C6H3) on the diphosphite ligand are both key factors in regulating regio- and enantioselectivity.

Nickel‐Catalyzed Regio‐ and Enantioselective Migratory Hydrocyanation of Internal Alkenes: Expanding the Scope to α,ω‐Diaryl Internal Alkenes

AbstractMetal‐hydride‐catalyzed migratory functionalization of alkenes witnessed extensive development in the past few years. However, the asymmetric version of this reaction has remained largely underdeveloped owing to the difficulty in simultaneous control of both regio‐ and stereoselectivity. In addition, exploring the wider alkene substrate scope to enable more synthetically valuable applications represents another challenge in this field. In this context, a nickel‐catalyzed asymmetric hydrocyanation of internal alkenes involving a chain‐walking process is demonstrated. The reaction exhibits excellent regio‐ and enantioselectivity, proceeds under mild reaction conditions, and delivers benzylic nitriles in high yields. Even α,ω‐diaryl internal alkenes, which are known to be one of the most challenging substrates of this type, could be successfully converted to the desired products with good regio‐ and stereoselectivity by modifying the electronic and steric effects. Theoretical calculations suggest that the η3‐benzyl coordination mode and the aryl substituent (3,5‐(OMe)2C6H3) on the diphosphite ligand are both key factors in regulating regio‐ and enantioselectivity.

Functionalization of Alkenes with Difluoromethyl Nitrile Oxide to Access the Difluoromethylated Derivatives.

Electron-rich, electron-deficient, and non-activated alkenes can be rapidly functionalized by in situ-generated difluoromethyl nitrile oxide. The (3+2) cycloaddition proceeds at room temperature, has broad functional group tolerance, and can be used for the late-stage modification of bioactive molecules (finasteride and carbamazepine). The obtained CF2H-isoxazolines can be easily transformed into CF2H-containing building blocks for medicinal chemistry: amines, amino acids, amino alcohols, and spirocyclic scaffolds.

Congested C(sp3)-rich architectures enabled by iron-catalysed conjunctive alkylation.

Catalytic cross-coupling by transition metals has revolutionized the formation of C-C bonds in organic synthesis. However, the challenge of forming multiple alkyl-alkyl bonds in crowded environments remains largely unresolved. Here, we report the regioselective functionalization of olefins with sp3-hybridized organohalides and organozinc reagents using a simple (terpyridine)iron catalyst. Aliphatic groups of various sizes are successfully installed on either olefinic carbon, furnishing a diverse array of products with congested cores featuring C- or heteroatom-substituted stereocenters. The method enables access to valuable but synthetically challenging C(sp3)-rich molecules, including alicyclic compounds bearing multiple contiguous stereocenters through annulation cascades. Mechanistic and theoretical studies suggest a stepwise iron-mediated radical carbometallation pathway followed by outer-sphere C-C bond formation, which potentially opens the door to a broader scope of transformations and new chemical space.

Alkene Thianthrenation Unlocks Diverse Cation Synthons: Recent Progress and New Opportunities

AbstractOxidative alkene functionalization reactions are a fundamental class of complexity‐building organic transformations. However, the majority of established approaches rely on electrophilic reagents that limit the diversity of groups that can be installed. Recent advances have established a new approach that instead relies on the transformation of alkenes into thianthrene‐derived cationic electrophiles. These linchpin intermediates can be generated selectively and undergo a diverse array of mechanistically distinct reactions with abundant nucleophiles. Taken together, this unlocks a suite of net oxidative alkene transformations that have been elusive using conventional strategies. This Minireview describes these advances and is organized around the three distinct synthons formally accessible from alkenes via thianthrenation: 1) alkenyl cations; 2) vicinal dications; 3) allyl cations. Throughout the Minireview, we illustrate how thianthrenium salts address key limitations endemic to classic alkene‐derived electrophiles and highlight the mechanistic origins of these distinctions wherever possible.

Alkene Thianthrenation Unlocks Diverse Cation Synthons: Recent Progress and New Opportunities.

Oxidative alkene functionalization reactions are a fundamental class of complexity-building organic transformations. However, the majority of established approaches rely on electrophilic reagents that limit the diversity of groups that can be installed. Recent advances have established a new approach that instead relies on the transformation of alkenes into thianthrene-derived cationic electrophiles. These linchpin intermediates can be generated selectively and undergo a diverse array of mechanistically distinct reactions with abundant nucleophiles. Taken together, this unlocks a suite of net oxidative alkene transformations that have been elusive using conventional strategies. This Minireview describes these advances and is organized around the three distinct synthons formally accessible from alkenes via thianthrenation: 1) alkenyl cations; 2) vicinal dications; 3) allyl cations. Throughout the Minireview, we illustrate how thianthrenium salts address key limitations endemic to classic alkene-derived electrophiles and highlight the mechanistic origins of these distinctions wherever possible.

Prussian Blue Analogue-Derived Co3O4 as Catalysts for Enhanced Selective Oxidation of Cyclohexane Using Molecular Oxygen.

Selective conversion of inert C-H bonds in alkanes into high-value-added functional groups (alcohols, ketones, carboxylic acids, etc.) plays a vital role in establishing a green and sustainable chemical industry. Catalytic selective oxidation of cyclohexane to KA oil (cyclohexanol and cyclohexanone) is a typical representative of alkane functionalization. In this work, hollow cage-like Co3O4 (Co3O4-C) and particle Co3O4 (Co3O4-P) were synthesized by calcining two types of Prussian blue analogues (PBAs), which were used to catalyze the selective oxidation of cyclohexane. The Co3O4-C predominantly exposed (311) crystal plane is easier to adsorb cyclohexane than Co3O4-P, which is beneficial to shorten the induction period, accelerate the reaction rate, and improve the conversion. Consequently, Co3O4-C displayed a 10% conversion of cyclohexane within 1 h, and the KA oil selectivity reached 90%. The Co3O4-P exposed (220) crystal plane has a higher molar percentage of oxygen vacancies and more active oxygen species, as well as a strong cyclohexanone adsorption capacity, which is conducive to the deep oxidation of cyclohexanone to adipic acid and other diacid products. The mechanism analysis of cyclohexane oxidation catalyzed by PBA-based Co3O4 shows that it exemplifies the feasibility to tailor the surface of catalysts by modulating the PBAs, which ultimately influences their reaction performance for accelerating the reaction and maintaining high cyclohexane conversion and KA oil selectivity.

Dynamical Origin of Rebound versus Dissociation Selectivity during Fe-Oxo-Mediated C-H Functionalization Reactions.

The mechanism of catalytic C-H functionalization of alkanes by Fe-oxo complexes is often suggested to involve a hydrogen atom transfer (HAT) step with the formation of a radical-pair intermediate followed by diverging pathways for radical rebound, dissociation, or desaturation. Recently, we showed that in some Fe-oxo reactions, the radical pair is a nonstatistical-type intermediate and dynamic effects control rebound versus dissociation pathway selectivity. However, the effect of the solvent cage on the stability and lifetime of the radical-pair intermediate has never been analyzed. Moreover, because of the extreme complexity of motion that occurs during dynamics trajectories, the underlying physical origin of pathway selectivity has not yet been determined. For the reaction between [(TQA_Cl)FeIVO]+ and cyclohexane, here, we report explicit solvent trajectories and machine learning analysis on transition-state sampled features (e.g., vibrational, velocity, and geometric) that identified the transferring hydrogen atom kinetic energy as the most important factor controlling rebound versus nonrebound dynamics trajectories, which provides an explanation for our previously proposed dynamic matching effect in fast rebound trajectories that bypass the radical-pair intermediate. Manual control of the reaction trajectories confirmed the importance of this feature and provides a mechanism to enhance or diminish selectivity for the rebound pathway. This led to a general catalyst design principle and proof-of-principle catalyst design that showcases how to control rebound versus dissociation reaction pathway selectivity.

Pd-Catalyzed Oxidative Functionalization of Alkenes, Arenes, and 1,3-Dienes Using Molecular Oxygen as the Terminal Oxidant

AbstractThis Account presents palladium-complex-catalyzed oxidative couplings mainly developed by the author’s group, including oxidative amination and silylation of terminal alkenes, direct oxidative arylation of aromatic compounds, and oxidative difunctionalization of 1,3-dienes. The catalytic cycles in these representative reactions feature re-oxidation of the palladium species with molecular oxygen as the terminal oxidant. Varying the combination of palladium catalyst and re-oxidant enables the formation of a variety of bonds through dehydrogenative cross-coupling reactions.1 Introduction2 Oxidative Amination of Terminal Alkenes3 Direct Oxidative Arylation of Aromatic Compounds4 Oxidative Silylation of Terminal Alkenes5 Oxidative Difunctionalization of 1,3-Dienes6 Conclusions and Perspectives