Ligand-Controlled Cobalt-Catalyzed Regio-, Enantio-, and Diastereoselective Oxyheterocyclic Alkene Hydroalkylation

Halogen-Atom Transfer Enabled Z-Selective Styrene Synthesis via Dual Cobalt and Photocatalysis Through Coupling of Unactivated Alkyl Iodides With Terminal Arylalkynes

An efficient Z-selective cobalt-catalyzed reductive hydroalkylation of terminal aryl alkynes with unactivated alkyl iodides has been achieved, providing a straightforward and modular route to access 1,2-disubstituted Z-styrenes. This reaction operates under mild conditions without requiring over-stoichiometric amounts of metal terminal reductants. Excellent Z/E ratios and good to excellent yields can be achieved for diverse and complex scaffolds with remarkable functional-group compatibility. One potential utility of this reaction is demonstrated by the efficient synthesis of several syn homoallylic alcohols in a one-pot two-step sequence. Control experiments strongly support that the halogen-atom transfer (XAT) process is the key to generating carbon radicals. DFT studies suggest that the catalytic system involves the Co(II)/Co(III) cycle and the steric repulsion between the Co(II) catalyst, and the alkenyl radical in radical capture by Co(II) is the dominant factor controlling the Z/E selectivity. This approach represents the first example of merging photo-XAT with cobalt-catalyzed reductive coupling of terminal aryl alkynes with unactivated alkyl iodides.

Solvent-Controlled Enantioselective Allylic C-H Alkylation of 2,5-Dihydrofuran via Synergistic Palladium/Nickel Catalysis

Enantioenriched, substituted tetrahydrofuran skeletons extensively occur in natural products, bioactive targets, and organic frameworks. The rapid and diverse synthesis of these tetrahydrofuran molecules is highly desired yet challenging. Herein, we present a practical synthetic strategy for asymmetric allylic C-H bond functionalization of oxyheterocyclic alkenes by making use of the synergistic catalysis of achiral Pd complex and chiral N,N'-dioxide-Ni(II) catalyst. Notably, the chemodivergent synthesis of allylic C-H alkylated products and hydroalkylated products was readily achieved in good outcomes via the regulation of solvents. Furthermore, the post-transformation of these functionalized 2,5-dihydrofurans provides an innovative synthetic route to access tetrahydrofuran skeleton compounds containing multiple stereocenters.

Switchable Regiodivergent Reductive Alkyl-Alkyl Coupling by Nickel Catalysis: Sorting Different Alkyl-Nickel Intermediates

Site-selective and divergent functionalizations on saturated alkyl chain at specific unfunctionalized positions is a key challenge in organic chemistry and other related areas and offers unprecedented synthetic opportunities. Herein, a ligand-controlled Ni-catalyzed site-selective and divergent alkyl-alkyl reductive coupling between two different alkyl halides has been developed. Notably, the reaction finely tunes and recognizes thermodynamic favored α-aminoalkyl radicals over β-aminoalkyl radicals, and distal ipso-alkyl radicals to deliver chemo- and position-selective alkylation of unactivated α-H and β-H of amines under reductive conditions. Moreover, the reaction selectively functionalizes one alkyl chain over two migratable alkyl chains. By just switching the catalytic parameters, α- and β-alkylation of saturated C─H bonds, and ipso-alkyl-alkyl coupling allow for rapid access to three types of branched aliphatic amine architectures from identical starting materials.

ortho-C─H Alkylation of Aryl Chlorides by a Catellani Strategy

Herein we report a general and practical palladium/norbornene catalysis system that effectively promotes difunctionalization of less reactive aryl chlorides. The key to success lies in the use of a particular norbornene (NBE) derivative as a powerful mediator that synergistically cooperates with the palladium catalyst and an electron-rich phosphine ligand. A broad spectrum of electronically diverse aryl chlorides (57 examples) delivered the corresponding ortho-C─H alkylation/ipso-olefination products in moderate to good yields. Notably, this protocol features excellent functional-group tolerance, high concentration, scalability, and late-stage functionalization of complex aryl chlorides. Furthermore, by integrating this chemistry with its counterparts involving aryl iodides and bromides, an intriguing triple-Catellani reaction sequence was developed, rapidly increasing molecular complexity and diversity. Finally, DFT calculations were performed, revealing that noncovalent C─H⋯O interactions between the XPhos ligand and the NBE mediator promote the pivotal NBE insertion step.

Enantio- and Diastereoselective Synthesis of P-Stereogenic Phospholane Oxides via Cobalt-Catalyzed Hydroalkylation

Chiral phospholane ligands and catalysts have been widely applied in asymmetric catalysis and synthesis. However, the construction of the chiral phospholane skeleton remains challenging and primarily relies on the use of chiral auxiliaries or resolution. In this work, a highly enantioselective and diastereoselective synthesis of P-stereogenic phospholane oxides has been achieved through a cobalt-catalyzed desymmetric hydroalkylation strategy. This method enables the construction of two discrete stereocenters with excellent yields and enantiomeric excesses.

Regiodivergent Hydroamidation of Alkenes via Cobalt-Hydride Catalysis

Regiodivergent hydroamin(d)ation of alkenes presents a valuable strategy for the synthesis of diverse amines or amides from a common set of starting materials, yet achieving controlled regioselectivity remains a significant challenge. In this work, we present a cobalt-catalyzed regiodivergent hydroamidation of alkenes, enabling enantioselective ipso- and migratory hydroamidation of heterocyclic alkenes. The ability to finely tune various reaction parameters allows for a seamless switch in regioselectivity. Notably, ipso- and migratory selectivity are governed by the choice of cobalt catalyst anions. Mechanistic studies reveal a neutral Co-H species mediating ipso-hydroamidation and a cationic Co-H intermediate promoting migratory hydroamidation. This protocol exhibits a broad substrate scope, high functional group tolerance, and provides an efficient pathway for synthetizing structurally diverse amides.

Selective Hydrodisulfuration of Alkenes with Dithiosulfonate

In this study, we have discovered the versatility of the dithiosulfonate reagent (ArSO2-SSR) in transition metal catalyzed selective hydrodisulfuration of unactivated alkenes. The hydrodisulfuration displays a unique Markovnikov selectivity with a Salen-cobalt complex, while an anti-Markovnikov selectivity is observed when employing a nickel/bidentate N-donor ligand. Furthermore, precise control over nickel/ligand enables the successful achievement of remote site-selective hydrodisulfuration for both internal and terminal alkenes via a chain-walking process. In these processes, silanes are employed as a hydride source. Mechanistic insights into these innovative catalytic systems are also elucidated. Experimental findings suggest that Markovnikov hydrodisulfuration is likely to proceed through radical substitution on dithiosulfonate reagents, while nickel catalyzed anti-Markovnikov selectivity and remote site-selectivity likely occur via the radical addition of the reductively formed dithiosulfonate radical anion ([ArSO2-SSR]⋅-) to alkyl Ni(II) species (alkyl-Ni(II)LnX) and subsequent reductive elimination on Ni(III) intermediate (alkyl-Ni(III)Ln(X)-SSR) as the key steps based on DFT calculation analysis.

Parametrization of κ2-N,O-Oxazoline Preligands for Enantioselective Cobaltaelectro-Catalyzed C-H Activations

Enantioselective electrocatalyzed C-H activations have emerged as a transformative platform for the assembly of value-added chiral organic molecules. Despite the recent progress, the construction of multiple C(sp3)-stereogenic centers via a C(sp3)-C(sp3) bond formation has thus far proven to be elusive. In contrast, we herein report an annulative C-H activation strategy, generating chiral Fsp3-rich molecules with high levels of diastereo- and enantioselectivity. κ2-N,O-oxazoline preligands were effectively employed in enantioselective cobalt(III)-catalyzed C-H activation reactions. Using DFT-derived descriptors and regression statistical modeling, we performed a parametrization study on the modularity of chiral κ2-N,O-oxazoline preligands. The study resulted in a model describing ligands' selectivity characterized by key steric, electronic, and interaction behaviors.

Enantioselective Cobalt-Catalyzed Remote Hydroboration of Alkenylboronates

Heteroatomic groups in alkenes typically direct thermodynamically favored chain walking of C═C bonds toward themselves, thereby facilitating C-H bond functionalization near the heteroatoms. We present herein an efficient cobalt-catalyzed contra-thermodynamic remote hydroboration of alkenylboronates with pinacolborane to synthesize chiral 1,n-diboronates. This protocol features a broad substrate scope, high functional group tolerance, and excellent enantioselectivity. Mechanistic studies indicate the involvement of a chain-walking process. Gram-scale reactions and various product derivatizations further highlight its practicality.

Nickel-Catalyzed α-selective Hydroalkylation of Vinylarenes

C(sp3) centers adjacent to (hetero) aryl groups are widely present in physiologically active molecules. Metal-hydride-catalyzed hydroalkylation of alkenes represents an efficient means of forging C(sp3)-C(sp3) bonds, boasting advantages as a wide source of substrates, mild reaction conditions, and facile selectivity manipulation. Nevertheless, the hydroalkylation of vinylarenes encounters constraints in terms of substrate scope, necessitating the employment of activated alkyl halides or alkenes containing chelating groups, remains a challenge. In this context, we report a general nickel-hydride-catalyzed hydroalkylation protocol for vinylarenes. Remarkably, this system enables α-selective hydroalkylation of both aryl and heteroaryl alkenes under an extra ligand-free condition, demonstrating excellent coupling efficiency and selectivity. Furthermore, through the incorporation of chiral bisoxazoline ligands, we have achieved regio- and enantioselective hydroalkylation of vinylpyrroles, thereby facilitating the synthesis of α-branched alkylated pyrrole derivatives.

Cobalt-Catalyzed Three-Component Alkyl Arylation of Acrylates with Alkyl Iodides and Aryl Grignard Reagents

A highly regioselective cobalt-catalyzed three-component alkyl arylation of acrylates with alkyl iodides and aryl Grignard reagents has been established. The reaction efficiently provides an alternative strategy for the construction of α-aryl esters with a broad substrate scope and good yields under mild conditions. The practical applicability of this protocol is shown by the scaled-up reaction and further transformations of the products. In addition, the preliminary mechanistic explorations demonstrated that the alkyl radicals generated by the efficient cobalt catalysis are instantaneously added to the acrylates to finally afford the desired products.

Hydrodeuteroalkylation of Unactivated Olefins Using Thianthrenium Salts

Isotopically labeled alkanes play a crucial role in organic and pharmaceutical chemistry. While some deuterated methylating agents are readily available, the limited accessibility of other deuteroalkyl reagents has hindered the synthesis of corresponding products. In this study, we introduce a nickel-catalyzed system that facilitates the synthesis of various deuterium-labeled alkanes through the hydrodeuteroalkylation of d2-labeled alkyl TT salts with unactivated alkenes. Diverging from traditional deuterated alkyl reagents, alkyl thianthrenium (TT) salts can effectively and selectively introduce deuterium at α position of alkyl chains using D2O as the deuterium source via a single-step pH-dependent hydrogen isotope exchange (HIE). Our method allows for high deuterium incorporation, and offers precise control over the site of deuterium insertion within an alkyl chain. This technique proves to be invaluable for the synthesis of various deuterium-labeled compounds, especially those of pharmaceutical relevance.

Radical alkylation and protonation induced anti-Markovnikov hydroalkylation of unactivated olefins via cobalt catalysis

Although strategies of olefin hydroalkylation continue to emerge rapidly, the precise control of the regio- or chemoselectivity and the expansion of the reaction range are still challenges. Herein, a straightforward route for cobalt-catalyzed anti-Markovnikov hydroalkylation of unactivated olefins with alkyl iodides has been achieved. The developed reaction is compatible with oxa-, aza-, cyclo- and a series of other functional groups as well as the frameworks of some bioactive compounds. Mechanism studies confirm that an alkyl radical is involved and cobalt-alkyl insertion followed by protonation with water are possible pathways in this reaction.

Photoinduced Co/Ni-cocatalyzed Markovnikov hydroarylation of unactivated olefins with aryl bromides

Transition-metal-catalyzed hydroarylation of unactivated alkenes via metal hydride hydrogen atom transfer (MHAT) is an attractive approach for the construction of C(sp2)-C(sp3) bonds. However, this kind of reaction focuses mainly on using reductive hydrosilane as a hydrogen donor. Here, a novel photoinduced Co/Ni-cocatalyzed Markovnikov hydroarylation of unactivated alkenes with aryl bromides using protons as a hydrogen source has been developed. This reaction represents the first example of photoinduced MHAT via a reductive route intercepting an organometallic coreactant. The key to this transformation was that the CoIII-H species was generated from the protonation of the CoI intermediate, and the formed CoIII-C(sp3) intermediate interacted with the organometallic coreactant rather than reacting with nucleophiles, a method which has been well developed in photoinduced Co-catalyzed MHAT reactions. This reaction is characterized by its high catalytic efficiency, construction of quaternary carbons, simple reaction conditions and expansion of the reactive mode of Co-catalyzed MHAT reactions via a reductive route. Moreover, this catalytic system could also be applied to complex substrates derived from glycosides.

Regio- and Enantioselective Hydromethylation of 3-Pyrrolines and Glycals Enabled by Cobalt Catalysis

Enantioenriched 3-methylpyrrolidine, with its unique chiral nitrogen-containing core skeleton, exists widely in various functional molecules, including natural products, bioactive compounds, and pharmaceuticals. Traditional methods for synthesizing these valuable methyl-substituted heterocycles often involve enzymatic processes or complex procedures with chiral auxiliaries, limiting the substrate scope and efficiency. Efficient catalytic methylation, especially in an enantioselective manner, has been a long-standing challenge in chemical synthesis. Herein, we present a novel approach for the remote and stereoselective installation of a methyl group onto N-heterocycles, leveraging a CoH-catalyzed asymmetric hydromethylation strategy. By effectively combining a commercial cobalt precursor with a modified bisoxazoline (BOX) ligand, a variety of easily accessible 3-pyrrolines can be converted to valuable enantiopure 3-(isotopic labeling)methylpyrrolidine compounds with outstanding enantioselectivity. This efficient protocol streamlines the two-step synthesis of enantioenriched 3-methylpyrrolidine, which previously required up to five or six steps under harsh conditions or expensive starting materials.

CoH-catalyzed asymmetric remote hydroalkylation of heterocyclic alkenes: a rapid approach to chiral five-membered S- and O-heterocycles

Saturated heterocycles, which incorporate S and O heteroatoms, serve as fundamental frameworks in a diverse array of natural products, bioactive compounds, and pharmaceuticals. Herein, we describe a unique cobalt-catalyzed approach integrated with a desymmetrization strategy, facilitating precise and enantioselective remote hydroalkylation of unactivated heterocyclic alkenes. This method delivers hydroalkylation products with high yields and excellent stereoselectivity, representing good efficiency in constructing alkyl chiral centers at remote C3-positions within five-membered S/O-heterocycles. Notably, the broad scope and good functional group tolerance of this asymmetric C(sp3)-C(sp3) coupling enhance its applicability.

Enantioselective synthesis of chiral α,α-dialkyl indoles and related azoles by cobalt-catalyzed hydroalkylation and regioselectivity switch

General, catalytic and enantioselective construction of chiral α,α-dialkyl indoles represents an important yet challenging objective to be developed. Herein we describe a cobalt catalyzed enantioselective anti-Markovnikov alkene hydroalkylation via the remote stereocontrol for the synthesis of α,α-dialkyl indoles and other N-heterocycles. This asymmetric C(sp3)-C(sp3) coupling features high flexibility in introducing a diverse set of alkyl groups at the α-position of chiral N-heterocycles. The utility of this methodology has been demonstrated by late-stage functionalization of drug molecules, asymmetric synthesis of bioactive molecules, natural products and functional materials, and identification of a class of molecules exhibiting anti-apoptosis activities in UVB-irradiated HaCaT cells. Ligands play a vital role in controlling the reaction regioselectivity. Changing the ligand from bi-dentate L6 to tridentate L12 enables CoH-catalyzed Markovnikov hydroalkylation. Mechanistic studies disclose that the anti-Markovnikov hydroalkylation involves a migratory insertion process while the Markovnikov hydroalkylation involves a MHAT process.