A Unified Explanation for Chemoselectivity and Stereospecificity of Ni-Catalyzed Kumada and Cross-Electrophile Coupling Reactions of Benzylic Ethers: A Combined Computational and Experimental Study

Enantiospecific cross-coupling of cyclic alkyl sulfones

Methods to form carbon-carbon bonds efficiently and with control of stereochemistry are critical for the construction of complex molecules. Cross-coupling reactions are among the most efficient and widely used reactions to construct molecules, with reactions enabling the retention or installation of chirality as recent additions to this powerful toolbox. Sulfones are robust, accessible organic electrophiles that have many attractive features as cross-coupling partners; however, since the first example of their use in 1979, there have been no examples of their use in enantioselective, enantiospecific or entantioconvergent cross-couplings. The high acidity of sulfones makes it unclear whether this transformation is even possible outside tertiary systems. Here we report the enantiospecific cross-coupling of cyclic sulfones and Grignard reagents. Up to 99% chirality transfer is observed despite the strong basicity of the Grignard components. In situ monitoring reveals that the cross-coupling is kinetically competitive with competing deprotonation, resulting in a highly enantioselective transformation.

Combined Computational and Experimental Study Reveals Complex Mechanistic Landscape of Brønsted Acid-Catalyzed Silane-Dependent P═O Reduction

The reaction mechanism of Brønsted acid-catalyzed silane-dependent P═O reduction has been elucidated through combined computational and experimental methods. Due to its remarkable chemo- and stereoselective nature, the Brønsted acid/silane reduction system has been widely employed in organophosphine-catalyzed transformations involving P(V)/P(III) redox cycle. However, the full mechanistic profile of this type of P═O reduction has yet to be clearly established to date. Supported by both DFT and experimental studies, our research reveals that the reaction likely proceeds through mechanisms other than the widely accepted "dual activation mode by silyl ester" or "acid-mediated direct P═O activation" mechanism. We propose that although the reduction mechanisms may vary with the substitution patterns of silane species, Brønsted acid generally activates the silane rather than the P═O group in transition structures. The proposed activation mode differs significantly from that associated with traditional Brønsted acid-catalyzed C═O reduction. The uniqueness of P═O reduction originates from the dominant Si/O═P orbital interactions in transition structures rather than the P/H-Si interactions. The comprehensive mechanistic landscape provided by us will serve as a guidance for the rational design and development of more efficient P═O reduction systems as well as novel organophosphine-catalyzed reactions involving P(V)/P(III) redox cycle.

Unveiling the Detailed Mechanism and Origins of Chemo-, Regio-, and Stereoselectivity of Rare-Earth Catalyzed Alternating Copolymerization of Polar and Nonpolar Olefins

The direct copolymerization of polar and nonpolar olefins is of great interest and significance, as it is the most atom-economical and straightforward strategy for the synthesis of functional polyolefin materials. Despite considerable efforts, the precise control of monomer-sequence and their regio- and stereochemistry is full of challenges, and the related mechanistic origins are still in their infancy to date. Herein, the mechanistic studies on the model reaction of Sc-catalyzed co-syndiospecific alternating copolymerization of anisylpropylene (AP) and styrene were performed by DFT calculations. The results suggest that the subtle balance between electronic and steric factors plays an important role during monomer insertions, and a new amino-dissociated mechanism was proposed for AP insertion at chain initiation. AP insertion follows the 2,1-si-insertion pattern, which is mainly controlled by steric factors caused by the restricted MeO···Sc interaction. As for styrene insertion, it prefers the 2,1-re-insertion manner and its regio- and stereoselectivities are influenced by steric repulsions between the inserting styrene and the polymer chain or the ligand. More interestingly, it is found that the alternating monomer-sequence is mainly determined by the "steric matching" principle, which is quantitatively expressed by the buried volume of the metal center of the preinserted species. The concept of steric pocket has been successfully applied to explain the different performances of several catalysts and other alternating copolymerization reactions. The insightful mechanistic findings and the quantitative steric pocket model present here are expected to promote rational design of new rare-earth catalysts for developing regio-, stereo-, and sequence-controlled copolymerization of specific polar and nonpolar olefins.

Nickel-Catalyzed Stereoselective Coupling Reactions of Benzylic and Alkyl Alcohol Derivatives

ConspectusNickel-catalyzed reactions of alkyl alcohol derivatives leverage the high prevalence of hydroxyl groups in natural products, medicinal agents, and synthetic intermediates to provide access to C(sp3)-rich frameworks. This Account describes our laboratory's development of stereospecific and stereoconvergent C-C bond forming reactions employing C(sp3)-O and C(sp3)-N electrophiles. In the context of development of new transformations, we also define fundamental characteristics of the nickel catalysts.Part I details the nickel-catalyzed cross-coupling reactions developed by our group which hinges on stereospecific formation of stable π-benzyl intermediates. Acyclic and cyclic ethers, esters, carbamates, lactones, and sulfonamides undergo Kumada-, Suzuki-, and Negishi-type coupling reactions to produce enantioenriched products with high fidelity of stereochemical information. We describe extension to include ring-opening reactions of saturated heterocycles to afford acyclic 1,3-fragments in high diastereomeric ratios. We also describe our advances in stereospecific nickel-catalyzed cross-electrophile coupling reactions. Tethered C-O and C-X electrophiles proved fruitful for construction of a variety of carbocyclic frameworks. We report an intramolecular cross-electrophile coupling of benzylic pivalates with aryl bromides for the synthesis of indanes and tetralins. We found that 4-halotetrahydropyrans and 4-halopiperidines readily undergo stereospecific ring contraction to afford substituted cyclopropanes. Mechanistic investigations are consistent with closed-shell intermediates, a Ni(0)/Ni(II) cycle, and an intramolecular SN2-type reaction of a key organonickel intermediate to form the cyclopropane. Building toward more complex cascade reactions, we have demonstrated that 2-alkynyl piperidines incorporate MeMgI in a dicarbofunctionalization of the alkyne to afford highly substituted vinyl cyclopropanes.In Part II we present our development of stereoconvergent reactions of alkyl alcohol derivatives. In order to expand the utility of the intramolecular XEC reaction, we sought to employ unactivated alkyl electrophiles. Specifically, alkyl dimesylates engage in intramolecular XEC reactions to form alkyl cyclopropanes. In contrast to our previous work, these reactions proceed through open-shell intermediates and favor stereoconvergent formation of the trans-cyclopropane. Enantioselective aldol reactions can be employed in syntheses of 1,3-diols which furnish enantioenriched cyclopropanes in high ee. Experimental and computational evidence reveals that MeMgI mediates formation of alkyl iodides in situ. The coupling reaction initiates with halogen atom abstraction at the secondary alkyl iodide. The alkyl Ni(II) complex then proceeds through a stereospecific SN2-type ring closure to form cyclopropane. In an effort to increase functional group compatibility in the synthesis of cyclopropanes from alkyl dimesylates we developed a zinc-mediated reaction of 1,3-dimesylates prepared from medicinal analogues. In challenging nickel-catalyzed intramolecular cross-electrophile coupling we were also able to show that vicinal carbocycles can be prepared under similar conditions, affording vicinal cyclopentyl-cyclopropyl motifs in high yield.In Part III we discuss our recent findings on the role of ligand identity in catalyst selectivity for stereospecific vs stereoablative mechanisms for oxidative addition. We demonstrate multivariable control of mechanism, where the choice of substrate and ligand work together to promote open- or closed-shell intermediates. In divergent reactions of 4-halotetrahydropyrans we observe distinct ligand preference for reactions at the C(sp3)-O center or the C(sp3)-Cl center. These findings are the source of continued investigations in our laboratory.

A Nickel-Catalyzed Cross-Electrophile Coupling Reaction of 1,3-Dimesylates for Alkylcyclopropane Synthesis: Investigation of Stereochemical Outcomes and Radical Lifetimes

Understanding mechanistic details of the nickel-catalyzed coupling reactions of Csp3 alcohol derivatives is key to developing selective reactions of this widely prevalent functional group. In this manuscript, we utilize a combination of experimental data and DFT studies to define the key intermediates, stereochemical outcome, and competing pathways of a nickel-catalyzed cross-electrophile coupling reaction of 1,3-dimesylates. Stereospecific formation of a 1,3-diiodide intermediate is achieved in situ by the Grignard reagent. The overall stereoablative stereochemical outcome is due to a nickel-catalyzed halogen atom abstraction with a radical rebound that is slower than epimerization of the alkyl radical. Finally, lifetimes of this alkyl radical intermediate are compared to radical clocks to enhance the understanding of the lifetime of the secondary alkyl radical.

Understanding the mechanism and origins of stereoconvergence in nickel-catalyzed hydroarylation of 1,3-dienes with aryl boronates

Nickel-catalyzed stereoselective hydroarylation is one of the most efficient methods to access functionalized arenes. Herein, computational studies have been applied to reveal the mechanism and origins of ligand-controlled enantioselectivity of Ni-catalyzed hydroarylation of 1,3-dienes using ethanol as the hydrogen source. DFT calculations show that the hydroarylation of (E)-diene takes place via concerted hydronickelation aided by boronate leading to an alkylnickel(II) intermediate, which further undergoes transmetallation and C-C reductive elimination to deliver the final chiral alkylarene. The hydronickelation is found to be the rate-determining step and is irreversible. The enantioselectivity is dominated by the transmetallation step, in which the ligand-substrate interactions are analyzed to unveil the source of stereocontrol. Besides, mechanistic studies demonstrate that the (Z)-diene initially reacts to offer a (S)-Z-alkyl-Ni(II) species, which preferably undergoes facile isomerization via σ-π-σ-π-σ interconversion to the (R)-E-alkyl-Ni(II) complex rather than the transmetallation step, thus ultimately generating the same (R)-alkylarene product as (E)-diene. Overall, the mechanistic understanding will be useful for the further advancement of asymmetric hydroarylation of dienes.

Enantioselective Hydroalkoxylation of 1,3-Dienes via Ni-Catalysis

As an advance in hydrofunctionalization, we herein report that alcohols add to 1,3-dienes with high regio- and enantioselectivity. Using Ni-DuPhos, we access enantioenriched allylic ethers. Through the choice of solvent-free conditions, we control the reversibility of C-O bond formation. This work showcases a rare example of methanol as a reagent in asymmetric synthesis.

Mechanistic explorations on the decarboxylative allylation of amino esters via dual photoredox and palladium catalysis

Mechanistic studies reveal that the decarboxylative allylation of amino esters via dual photoredox and palladium catalysis occurs via oxidation giving π-allyl-Pd(II) species and carboxylate, which is oxidized by *Ir(III)-catalyst offering benzyl radicals. The alkylated product is formed via an S_N2 pathway. Single-electron transfer between Pd(I)-species and Ir(II)-catalysis restores both catalysts.

Theoretical Insight on the High Reactivity of Reductive Elimination of NiIII Based on Energy- and Electron-Transfer Mechanisms

Iridium/nickel (Ir/Ni) metallaphotoredox dual catalysis overcomes the challenging reductive elimination (RE) of Ni(II) species and has made a breakthrough progress to construct a wide range of C-X (X = C, N, S, and P) bonds. However, the corresponding reaction mechanisms are still ambiguous and controversial because the systematic research on the nature of this synergistic catalysis is not sufficient. Herein, Ir^III/Ni^II and Ir^III/Ni⁰ metallaphotoredox catalysis have been theoretically explored taking the aryl esterification reaction of benzoic acid and aryl bromide as an example by a combination of density functional theory (DFT), molecular dynamics, and time-dependent DFT computations. It is found that an electron-transfer mechanism is applicable to Ir^III/Ni^II metallaphotoredox catalysis, but an energy-transfer mechanism is applicable to Ir^III/Ni⁰ combination. The Ir^III/Ni^II metallaphotoredox catalysis succeeds to construct a Ni^I-Ni^III catalytic cycle to avoid the challenging RE of Ni(II) species, while the RE occurs from triplet excited-state Ni(II) species in the Ir^III/Ni⁰ metallaphotoredox catalysis. In addition, the lower lowest unoccupied molecular orbital energy level of Ni(III) species than that of Ni(II) species accelerates RE from Ni(III) one. The triplet excited-state Ni(II) species can resemble a Ni(III) center, considering the metal-to-ligand charge transfer character to promote the RE.

Picolinamide Ligands: Nickel-Catalyzed Reductive Cross-Coupling of Aryl Bromides with Bromocyclopropane and Beyond

The arylcyclopropane motif as the combination of aryl and cyclopropyl ring systems can be found in an increasing amount of approved and investigational drugs. Herein, we have developed a mild, efficient nickel-catalyzed reductive cross-coupling protocol, featuring a simple Ni(II) precatalyst and a novel picolinamide NN₂ pincer ligand. A variety of (hetero)aryl bromides could successfully couple with cyclopropyl bromide to furnish the valued arylcyclopropanes in good to excellent yields. This method is applicable to other alkyl bromides as well. Notably, the reaction is tolerant of a broad range of functionalities including free amines. Furthermore, the synthesis of several significant intermediates of bioactive molecules was achieved in grams, proving the practicability of this method.

Synthesis of Vicinal Carbocycles by Intramolecular Nickel-Catalyzed Conjunctive Cross-Electrophile Coupling Reaction

A nickel-catalyzed intramolecular conjunctive cross-electrophile coupling reaction has been established. This method enables the synthesis of 3,5-vicinal carbocyclic rings found in numerous biologically active compounds and natural products. We provide mechanistic experiments that indicate this reaction proceeds through alkyl iodides formed in situ, initiates at the secondary electrophilic center, and proceeds through radical intermediates.

Ligand-Based Control of Nickel Catalysts: Switching Chemoselectivity from One-Electron to Two-Electron Pathways in Competing Reactions of 4-Halotetrahydropyrans

Development of nickel-catalyzed transformations would be facilitated by an improved ability to predict which ligands promote and suppress competing mechanisms. We evaluate ligand-based modulation of catalyst preference for one- or two-electron pathways employing 4-halotetrahydropyrans as model substrates that can undergo divergent reaction pathways. Chemoselectivity for one- or two-electron oxidative addition is predicted by ligand class. Phosphine-ligated nickel catalysts favor closed-shell oxidative addition. In contrast, nitrogen-ligated nickel catalysts prefer the one-electron pathway, initiating with halogen atom transfer.

Photoredox/Nickel Dual Catalysis Enables the Synthesis of Alkyl Cyclopropanes via C(sp3)-C(sp3) Cross Electrophile Coupling of Unactivated Alkyl Electrophiles

A facile synthesis of mono-, 1,1- and 1,2-disubstituted cyclopropanes via visible light-mediated photoredox/nickel dual catalysis is demonstrated. The challenging intramolecular C(sp³)-C(sp³) cross-electrophile coupling of readily available unactivated 1,3-dialkyl electrophiles was performed under mild conditions that allowed traditionally reactive functional groups to be included. Mechanistic inspection and control experiments revealed the importance of dual catalysis and that the reaction proceeds via a stepwise oxidative addition followed by an intramolecular S_N2 reaction.

Nickel-Catalyzed Kumada Cross-Coupling Reactions of Benzylic Sulfonamides

Herein, we report a Kumada cross-coupling reaction of benzylic sulfonamides. The scope of the transformation includes acyclic and cyclic sulfonamide precursors that cleanly produce highly substituted acyclic fragments. Preliminary data are consistent with a stereospecific mechanism that allows for a diastereoselective reaction.

Overcoming the Naphthyl Requirement in Stereospecific Cross-Couplings to Form Quaternary Stereocenters

The use of a simple stilbene ligand has enabled a stereospecific Suzuki-Miyaura cross-coupling of tertiary benzylic carboxylates, including those lacking naphthyl substituents. This method installs challenging all-carbon diaryl quaternary stereocenters in good yield and ee and represents an important breakthrough in the "naphthyl requirement" that pervades stereospecific cross-couplings involving enantioenriched electrophiles.

Sulfide Oxidation by 2,6-Bis[hydroxyl(methyl)amino]-4-morpholino-1,3,5-triazinatodioxomolybdenum(VI): Mechanistic Implications with DFT Calculations for a New Class of Molybdenum(VI) Complex

Sulfide oxidation is accomplished by a new class of dioxomolybdenum(VI) catalyst (1) that uses the tridentate 2,6-bis[hydroxyl(methyl)amino]-4-morpholino-1,3,5-triazine ligand to form a five-coordinate molybdenum(VI) center. Resonance Raman spectra show that the dioxo groups on the Mo(VI) oxygens readily exchange with water in an acetonitrile media that allows ¹⁸O labeling of catalyst 1. The model oxidation reaction was the conversion of thioanisole (2) to the corresponding sulfoxide with 4% of 1 using an equimolar amount of H₂O₂ in MeCN-d₃. Oxygen-18 labeling experiments with either ¹⁸O-labeled 1 or ¹⁸O-labeled H₂O₂ are consistent with a sulfide oxygenation pathway that uses a η¹-Mo(OOH) hydroxoperoxyl species (3). The hypothesized intermediate 3 is initially formed in a proton transfer reaction between 1 and H₂O₂. Oxidation is hypothesized via nucleophilic attack of the sulfide on 3 that is supported from a Hammett linear free-energy relationship for para-derivatives of 2. A Hammett reactivity constant (ρ) of -1.2 ± 0.2 was obtained, which is consistent with other ρ values found in prior sulfide oxidation reactions by group 6 complexes. An Eyring plot of the 2 oxidation by 1 gives an E_a of 63.0 ± 5.2 kJ/mol, which is slightly higher than that of a similar oxidation of 2 by the molybdenum(VI) complex, oxodiperoxo (pyridine-2-carboxylato)molybdate(VI) bis(pyridine-2-carboxylic acid) monohydrate (5). Computational modeling with density functional theory (DFT) of the complete reaction profile gave enthalpy and entropy of activations (64 kJ/mol and -120 J/mol·K, respectively) within 1 standard deviation of the experimental values, further supporting the hypothesized mechanism.

Mechanism and Selectivity Control in Ni- and Pd-Catalyzed Cross-Couplings Involving Carbon-Oxygen Bond Activation

Transition-metal-catalyzed C-O bond activation provides a useful strategy for utilizing alcohol- and phenol-derived electrophiles in cross-coupling reactions, which has become a research field of active and growing interest in organic chemistry. The synergy between computation and experiment elucidated the mechanistic model and controlling factors of selectivities in these transformations, leading to advances in innovative C-O bond activation and functionalization methods.Toward the rational design of C-O bond activation, our collaborations with the Jarvo group bridged the mechanistic models of C(sp²)-O and C(sp³)-O bond activations. We found that the nickel catalyst cleaves the benzylic and allylic C(sp³)-O bonds via two general mechanisms: the stereoinvertive S_N2 back-side attack model and the stereoretentive chelation-assisted model. These two models control the stereochemistry in a wide array of stereospecific Ni-catalyzed cross-coupling reactions with benzylic or allylic alcohol derivatives. Because of the catalyst distortion, the ligands can differentiate the competing stereospecific C(sp³)-O bond activations. The PCy₃ ligand interacts with nickel mainly through σ-donation, and the Ni(PCy₃) catalyst can undergo facile bending of the substrate-nickel-ligand angle, which favors the stereoretentive benzylic C-O bond activation. The N-heterocyclic carbene SIMes ligand has additional d(metal)-p(ligand) back-donation with nickel, which leads to an extra energy penalty for the same angle bending. This results in the preference of stereoinvertive benzylic C-O bond activation under Ni/SIMes catalysis. In addition to ligand control, a Lewis acid can increase the selectivity for stereoinvertive C(sp³)-O activation by stabilizing the S_N2 back-side attack transition state. The oxygen leaving group complexes with the MgI₂ Lewis acid in the stereoinvertive activation, leading to the exclusive stereoinvertive Kumada coupling of benzylic ethers. We also identified that the competing C(sp³)-O bond activation models have noticeable differences in charge separation. This leads to the solvent polarity control of the stereospecificity in C(sp³)-O activations. Low-polarity solvents favor the neutral stereoretentive C-O bond activation, while high-polarity solvents favor the zwitterionic stereoinvertive cleavage.In sharp contrast to the nickel catalysts, the C(sp²)-O bond activation under palladium catalysis mainly proceeds via the classic three-membered ring oxidative addition mechanism instead of the chelation-assisted mechanism. This is due to the lower oxophilicity of palladium, which disfavors the oxygen coordination in the chelation-assisted-type activation. The three-membered ring activation model selectively cleaves the weak C-O bond, resulting in the exclusive chemoselectivity of acyl C-O bond activation in Pd-catalyzed cross-coupling reactions with aryl carboxylic acid derivatives. This explains the overall acylation in the Pd-catalyzed Suzuki-Miyaura coupling with aryl esters. In collaboration with the Szostak group, we revealed that the three-membered ring model applies in the Pd-catalyzed C-O bond activation of carboxylic acid anhydride, which stimulated the development of a series of Pd-catalyzed decarbonylative functionalizations of aryl carboxylic acids.

Nickel-Catalyzed Cross-Electrophile Coupling of the Difluoromethyl Group for Fluorinated Cyclopropane Synthesis

Herein, we report a new strategy for fluorinated cyclopropane synthesis. Photocatalytic olefin difluoromethylation is coupled with a nickel-catalyzed intramolecular cross-electrophile coupling (XEC) reaction between a difluoromethyl moiety and a benzylic ether. To the best of our knowledge, this is the first example of a XEC reaction employing a difluoromethyl group as an electrophile. A plausible mechanism is highlighted, and DFT calculations are included to support the observed stereochemical outcome.

Rhodium(i)/bisoxazolinephosphine-catalyzed regio- and enantioselective amination of allylic carbonates: a computational study

DFT calculations were performed to investigate the rhodium(i)/bisoxazolinephosphine-catalyzed regio- and enantioselective amination of allylic carbonates.

Harnessing C-O Bonds in Stereoselective Cross-Coupling and Cross-Electrophile Coupling Reactions

Herein, we discuss our laboratory's research in the activation of alcohol derivatives in cross-coupling and cross-electrophile coupling reactions. Our developed methods enable the use of secondary alcohols to afford tertiary stereogenic centers, which we applied to the synthesis of pharmaceutically relevant compounds and substructures. We first discuss the synthesis of bioactive compounds via stereospecific Kumada cross-coupling reactions, followed by a discussion on the development of our stereoselective cross-electrophile coupling reaction to synthesize cyclopropanes.

Formation of trisubstituted buta-1,3-dienes and α,β-unsaturated ketones via the reaction of functionalized vinyl phosphates and vinyl phosphordiamidates with organometallic reagents

We studied the reactions of vinyl phosphates and vinyl phosphordiamidates containing an ester functional group with organometallic reagents. We found that the functionalized vinyl phosphates were smoothly converted into tri- and tetrasubstituted buta-1,3-dienes via the reaction with aryllithium reagents. Moreover, the vinyl phosphordiamidates were converted into α,β-unsaturated ketones using Grignard reagents. Based on the performed experiments, we proposed a reaction mechanism, which was confirmed by means of the isolation of key intermediates.

We studied the reactions of vinyl phosphates and vinyl phosphordiamidates containing an ester functional group with organometallic reagents.

Nickel-Catalyzed Formal Aminocarbonylation of Secondary Benzyl Chlorides with Isocyanides

Phenylacetamides represent versatile feedstocks in synthetic chemistry, widely existing in drug molecules and natural products. Herein, we disclose a nickel-catalyzed formal aminocarbonylation of secondary benzyl chlorides with isocyanides yielding α-substituted phenylacetamide with steric hindrance, which is synthetically challenging via palladium-catalyzed aminocarbonylation. The reaction features wide functional group tolerance under mild conditions, highlighted by the tolerance of various aromatic halide (-Cl, -Br, -I) and heteroaromatic rings (pyridine and pyrazine).

Nickel-Catalyzed Alkyl-Alkyl Cross-Electrophile Coupling Reaction of 1,3-Dimesylates for the Synthesis of Alkylcyclopropanes

Cross-electrophile coupling reactions of two Csp³-X bonds remain challenging. Herein we report an intramolecular nickel-catalyzed cross-electrophile coupling reaction of 1,3-diol derivatives. Notably, this transformation is utilized to synthesize a range of mono- and 1,2-disubstituted alkylcyclopropanes, including those derived from terpenes, steroids, and aldol products. Additionally, enantioenriched cyclopropanes are synthesized from the products of proline-catalyzed and Evans aldol reactions. A procedure for direct transformation of 1,3-diols to cyclopropanes is also described. Calculations and experimental data are consistent with a nickel-catalyzed mechanism that begins with stereoablative oxidative addition at the secondary center.

Access to the most sterically crowded anilines via non-catalysed C-C coupling reactions

Variously substituted 2,6-bis(1,1-diarylethyl)anilines and 2,6-bis(trityl)anilines were prepared by a three-step high-yield process. Dimethyl-2-aminoisophtalate was modified by reaction with arylmagnesium bromides, and the hydroxy-derivatives obtained were etherified. Under the non-catalysed C-C coupling protocol, the formed bis[methyl(methoxy)diaryl]anilines react with various Grignard reagents to give highly substituted products. The buried volumes around the central nitrogen atom of the prepared compounds exceed the parameters for the known most sterically hindered anilines by about 20%.

Engaging Sulfonamides: Intramolecular Cross-Electrophile Coupling Reaction of Sulfonamides with Alkyl Chlorides

The application of amine derivatives as coupling partners is rare due to the inherent strength of the C-N bond. Herein, we report the first cross-electrophile coupling reaction of unstrained benzylic sulfonamides. Nickel-catalyzed intramolecular cross-electrophile coupling reactions of acyclic and cyclic benzylic sulfonamides with pendant alkyl chlorides generate cyclopropane products. Mechanistic experiments and DFT calculations are consistent with initiation of the reaction by magnesium iodide accelerated oxidative addition of the benzylic sulfonamide. This work establishes neutral and unstrained amine derivatives as XEC partners, furnishes structural rearrangement of benzylic sulfonamides, and provides valuable information regarding catalyst design for the development of new cross-electrophile coupling reactions of carbon-heteroatom bonds.

Identification of the Active Catalyst for Nickel-Catalyzed Stereospecific Kumada Coupling Reactions of Ethers

A series of nickel complexes in varying oxidation states were evaluated as precatalysts for the stereospecific cross-coupling of benzylic ethers. These results demonstrate rapid redox reactions of precatalysts, such that the oxidative state of the precatalyst does not dictate the oxidation state of the active catalyst in solution. These data provide the first experimental evidence for a Ni⁰ -Ni^II catalytic cycle for a stereospecific alkyl-alkyl cross-coupling reaction, including spectroscopic analysis of the catalyst resting state.