Enantiospecific and Iterative Suzuki–Miyaura Cross-Couplings

Photogeneration of α-Bimetalloid Radicals via Selective Activation of Multifunctional C1 Units

Light-driven strategies that enable the chemoselective activation of a specific bond in multifunctional systems are comparatively underexplored in comparison to transition-metal-based technologies, yet desirable when considering the controlled exploration of chemical space. With the current drive to discover next-generation therapeutics, reaction design that enables the strategic incorporation of an sp3 carbon center, containing multiple synthetic handles for the subsequent exploration of chemical space would be highly enabling. Here, we describe the photoactivation of ambiphilic C1 units to generate α-bimetalloid radicals using only a Lewis base and light source to directly activate the C-I bond. Interception of these transient radicals with various SOMOphiles enables the rapid synthesis of organic scaffolds containing synthetic handles (B, Si, and Ge) for subsequent orthogonal activation. In-depth theoretical and mechanistic studies reveal the prominent role of 2,6-lutidine in forming a photoactive charge transfer complex and in stabilizing in situ generated iodine radicals, as well as the influential role of the boron p-orbital in the activation/weakening of the C-I bond. This simple and efficient methodology enabled expedient access to functionalized 3D frameworks that can be further derivatized using available technologies for C-B and C-Si bond activation.

Simultaneous Stereoinvertive and Stereoselective C(sp3)-C(sp3) Cross-Coupling of Boronic Esters and Allylic Carbonates

With increasing interest in constructing more three-dimensional entities, there has been growing interest in cross-coupling reactions that forge C(sp3)-C(sp3) bonds, which leads to additional challenges as it is not just a more difficult bond to construct but issues of stereocontrol also arise. Herein, we report the stereocontrolled cross-coupling of enantioenriched boronic esters with racemic allylic carbonates enabled by iridium catalysis, leading to the formation of C(sp3)-C(sp3) bonds with single or vicinal stereogenic centers. The method shows broad substrate scope, enabling primary, secondary, and even tertiary boronic esters to be employed, and can be used to prepare any of the four possible stereoisomers of a coupled product with vicinal chiral centers. The new method, which combines the simultaneous enantiospecific reaction of a chiral nucleophile with the enantioselective reaction of a chiral electrophile in a single process, offers a solution for stereodivergent cross-coupling of two C(sp3) fragments.

Palladium-Catalyzed Cascade Heck Coupling and Allylboration of Iododiboron Compounds via Diboryl Radicals

Geminal bis(boronates) are versatile synthetic building blocks in organic chemistry. The fact that they predominantly serve as nucleophiles in the previous reports, however, has restrained their synthetic potential. Herein we disclose the ambiphilic reactivity of α-halogenated geminal bis(boronates), of which the first catalytic utilization was accomplished by merging a formal Heck cross-coupling with a highly diastereoselective allylboration of aldehydes or imines, providing a new avenue for rapid assembly of polyfunctionalized boron-containing compounds. We demonstrated that this cascade reaction is highly efficient and compatible with various functional groups, and a wide range of heterocycles. In contrast to a classical Pd(0/II) scenario, mechanistic experiments and DFT calculations have provided strong evidence for a catalytic cycle involving Pd(I)/diboryl carbon radical intermediates.

Isolation and Reactivity of Arylnickel(II) Complexes in Nickel-Catalyzed Borylation of Aryl Fluorosulfates

Aryl fluorosulfates have emerged as versatile SuFExable substrates, harnessing the reactivity of the S-F bond. In this study, we unveil their alternative synthetic utility in nickel-catalyzed borylation via C-O bond activation. This method highlights mild reaction conditions, a broad substrate scope, and moderate functional group tolerance, rendering it a practical and appealing approach for synthesizing a diverse array of aryl boronate esters. Furthermore, computational analysis sheds light on the reaction pathways, uncovering the participation of LNi(0) and LNi(II)ArX species. This insight is supported by the 31P NMR reaction monitoring along with isolation and single-crystal X-ray structural elucidation of well-defined arylnickel(II) intermediates obtained from the oxidative addition of aryl fluorosulfates. A comprehensive investigation, merging experimental and computational approaches, deepens our understanding of the alternative reactivity of SuFExable substrates.

Synthesis and study of antibiofilm and antivirulence properties of flavonol analogues generated by palladium catalyzed ligand free Suzuki-Miyaura coupling against Pseudomonas aeruginosa PAO1

The Suzuki-Miyaura coupling is one of the ubiquitous method for the carbon-carbon bond-forming reactions in organic chemistry. Its popularity is due to its ability to undergo extensive coupling reactions to generate a broad range of biaryl motifs in a straightforward manner displaying a high level of functional group tolerance. A convenient and efficient synthetic route to arylate different substituted flavonols through the Suzuki-Miyaura cross-coupling reaction has been explained in this study. The arylated products were acquired by the coupling of a variety of aryl boronic acids with flavonols under Pd(OAc)2 catalyzed reaction conditions in a ligand-free reaction strategy. Subsequently, the antibiofilm and antivirulence properties of the arylated flavonols against Pseudomonas aeruginosa PAO1 were studied thoroughly. The best ligands for quorum sensing proteins LasR, RhlR, and PqsR were identified using molecular docking study. These best fitting ligands were then studied for their impact on gene expression level of P. aeruginosa by RT-PCR towards quorum sensing genes lasB, rhlA, and pqsE. The downregulation in the gene expression with the effect of synthesized flavonols endorse the antibiofilm efficiency of the compounds.

Orthogonal sp3-Ge/B Bimetallic Modules: Enantioselective Construction and Enantiospecific Cross-Coupling

In this study, a series of enantioenriched sp3-Ge/B bimetallic modules were successfully synthesized via an enantioselective copper-catalyzed hydroboration of carbagermatrane (Ge)-containing alkenes. Orthogonal cross-coupling selectivity under different Pd-catalyzed conditions was achieved in an enantiospecific manner. Notably, the chiral secondary Ge exhibited a remarkable transmetallation ability prior to primary or secondary Bpin. The effectiveness of this Ge/B bimetallic strategy was further demonstrated through the development of new functional small molecules with Aggregation-Induced Emission (AIE) and Circularly Polarized Luminescence (CPL) performance. This represents the first successful example of synthesis of enantioenriched alkylgermanium reagents that permit enantiospecific cross-coupling reactions.

Rapid, Homogenous, B-Alkyl Suzuki-Miyaura Cross-Coupling of Boronic Esters

A rapid, anhydrous Suzuki-Miyaura cross-coupling of alkylboronic esters with aryl halides is described. Parallel experimentation revealed that the combination of AntPhos, an oxaphosphole ligand, neopentyldiol alkylboronic esters, and potassium trimethylsilanolate (TMSOK) enables successful cross-coupling. In general, reactions proceed in under 1 h with good yields and high linear/branched (l/b) selectivities. Crucially, two literature examples which previously took >20 h to reach completion were accomplished in a fraction of the time with the method described herein. Mechanistic studies revealed that the reaction proceeds through a stereoretentive pathway and identified the boronic ester skeleton as a predominant pathway for deleterious protodehalogenation.

Enantioselective Copper-Catalyzed Ring-Opening Diboration of Arylidenecyclopropanes to Access Chiral Skipped 1,4- and 1,3-Diboronates

Two enantioselective approaches to synthesize chiral skipped diboronate compounds have been developed, relying on copper-catalyzed one-pot asymmetric ring-opening diboration of arylidenecyclopropanes. A wide range of arylidenecyclopropanes react smoothly with HBpin in the presence of CuOAc and (R)-DTBM-Segphos, affording chiral 1,4-diboronates with high enantioselectivity (up to 99% ee). Meanwhile, a variety of arylidenecyclopropanes react selectively with HBpin and B2pin2 in the presence of CuOAc and (S,S)-Ph-BPE with the sequential addition of MeOH, providing chiral 1,3-diboronates with high enantioselectivity (up to 98% ee). These enantioenriched 1,3- and 1,4-diboronates can undergo various enantiospecific transformations with minimal loss of their enantiopurity. Mechanistic studies reveal that these two diboration processes start with CuH-catalyzed ring-opening hydroboration of arylidenecyclopropanes to form a mixture of Z/E-homoallyl boronate intermediates, which subsequently undergo enantioselective CuH-catalyzed second hydroboration or Cu-Bpin-catalyzed protoboration to produce chiral 1,4-diboronates or 1,3-diboronates, respectively.

A sustainable metal-free and additive-free olefination route to N-heteroazaarenes from methyl-substituted heterocycles and amines

A green and sustainable metal-free, additive-free olefination approach is proposed for the facile synthesis of various unsaturated N-heteroazaarenes from simple methyl-substituted heteroarenes and amines. The developed protocol employs only air as the sole oxidant and provides a useful strategy for obtaining various E-selective conjugated heterocyclic olefins. This provides a useful strategy for application in generating grams of a variety of unsaturated N-heteroazaarenes (up to 20.33 grams) and the synthetic imaging agents of STB-8 (2.40 gram) with high regioselectivity in one pot.

A General Method to Access Sterically Encumbered Geminal Bis(boronates) via Formal Umpolung Transformation of Terminal Diboron Compounds

General methods for the preparation of geminal bis(boronates) are of great interest due to their widespread applications in organic synthesis. While the terminal gem-diboron compounds are readily accessible, the construction of the sterically encumbered, internal analogues has remained a prominent challenge. Herein, we report a formal umpolung strategy to access these valuable building blocks. The readily available 1,1-diborylalkanes were first converted into the corresponding α-halogenated derivatives, which then serve as electrophilic components, undergoing a formal substitution with a diverse array of nucleophiles to form a series of C-C, C-O, C-S, and C-N bonds. This protocol features good tolerance to steric hindrance and a wide variety of functional groups and heterocycles. Notably, this strategy can also be extended to the synthesis of diaryl and terminal gem-diboron compounds, therefore providing a general approach to various types of geminal bis(boronates).

Controllable Regiodivergent Alkynylation of 1,3-Bis(Boronic) Esters Activated by Distinct Organometallic Reagents

1,3-Bis(boronic) esters can be readily synthesized from alkylBpin precursors. Selective transformations of these compounds hold the potential for late-stage functionalization of the remaining C-B bond, leading to a diverse array of molecules. Currently, there are no strategies available to address the reactivity and, more importantly, the controllable regiodivergent functionalization of 1,3-bis(boronic) esters. In this study, we have achieved controllable regiodivergent alkynylation of these molecules. The regioselectivity has been clarified based on the unique chelation patterns observed with different organometallic reagents. Remarkably, this methodology effectively addresses the low reactivity of 1,3-bis(boronic) esters and bridges the gap in radical chemistry, which typically yields only the classical products formed via stable radical intermediates. Furthermore, the compounds synthesized through this approach serve as potent building blocks for creating molecular diversity.

Nickel Chain-Walking Catalysis: A Journey to Migratory Carboboration of Alkenes

ConspectusChain-walking offers extensive opportunities for innovating synthetic methods that involve constructing chemical bonds at unconventional sites. This approach provides previously inaccessible retrosynthetic disconnections in organic synthesis. Through chain-walking, transition metal-catalyzed alkene difunctionalization reactions can take place in a 1,n-addition (n ≠ 2) mode. Unlike classical 1,2-regioselective difunctionalization reactions, there remains a scarcity of reports regarding migratory patterns. Moreover, the range of olefins utilized in these studies is quite limited.About five years ago, our research group embarked on a project aimed at developing valuable migratory difunctionalization reactions of alkenes through chain-walking. Our focus was on carboboration of alkenes utilizing nickel catalysis. The reaction commences with the migratory insertion of an olefin into a Ni-Bpin species. Subsequently, a thermodynamically stable alkyl nickel complex is generated through a chain-walking process. This complex then couples with a carbon-based electrophile, leading to the formation of an alkylboron compound. It is worth highlighting that the success of these transformations relies significantly on the utilization of a bisnitrogen-based ligand and LiOMe as a B2pin2 activator. Synthetically, these migratory carboboration reactions establish a robust platform for the rapid and efficient synthesis of a wide range of structurally diverse organoboron compounds, which are not facially accessed by conventional methods. The incorporation of a versatile boron group introduces a wealth of possibilities for subsequent diversifications, significantly enhancing the value of the resulting products and allowing for the creation of a broader range of valuable derivatives and applications.This Account provides a comprehensive overview of our research efforts and advancements in the field of migratory carboboration of unactivated alkenes using nickel catalysis. We begin by outlining the development of a series of 1,1-regioselective carboboration reactions of terminal alkenes. A significant focus is placed on the initial integration of boronate, which not only triggers the formation of thermodynamically stable metal species but also exerts control over remote stereochemistry in reactions involving substituted methylenecyclohexenes. Continuing our exploration, remarkable success is achieved in 1,3-regio- and cis-stereoselectivity when dealing with cyclic alkenes. Remarkably, nickel chain-walking catalysis enables heterocyclic alkenes to be viable coupling partners within our transformations. Moreover, it grants us the ability to achieve regioselectivity for cyclohexenes that was previously unattainable, thus expanding the horizons of regiochemical control in these reactions. Lastly, we present the evolution of ligand-modulated regiodivergent carboboration of allylarenes. By gaining insights into the underlying mechanisms driving regiodivergence, we lay a strong foundation for tackling challenges related to selecting specific sites in chain-walking reactions, especially when dealing with multiple stable factors. We anticipate that our findings, coupled with the mechanistic insights we've gained, will not only advance the realm of nickel chain-walking catalysis but also contribute to the broader understanding of selectivity control in reactions of this nature. This advancement will also catalyze the synthesis of intricate functional molecules, contributing to the creation of complex and valuable compounds in the realm of organic chemistry.

Construction of α-Halogenated Boronic Esters via Visible Light-Induced C-H Bromination

α-Halogenated boronic esters are versatile building blocks that can be diversified into a wide variety of polyfunctionalized molecules. However, their synthetic potential has been hampered by limited preparation methods. Herein, we report a visible light-induced C-H bromination reaction of readily available benzyl boronic esters. This method features high yields, mild conditions, simple operation, and good functional group tolerance. The analogous chlorides and iodides can be accessed via Finkelstein reaction. Synthesis of halogenated geminal diborons has also been demonstrated.

Stereospecific Acylative Suzuki–Miyaura Cross-Coupling: General Access to Optically Active α-Aryl Carbonyl Compounds

A novel strategy for the stereospecific Pd-catalyzed acylative cross-coupling of enantiomerically enriched alkylboron compounds has been developed. The protocol features an extremely high level of enantiospecificity to allow facile access to synthetically challenging and valuable chiral ketones and carboxylic acid derivatives. The use of a sterically encumbered and electron-rich phosphine ligand proved to be crucial for the success of the reaction. Furthermore, on the basis of experimental and computational studies, a unique mechanism for the transmetalation, assisted by the noncovalent interactions of the C(sp³)-based organoboron reagent, has been identified.

Enantioselective Suzuki cross-coupling of 1,2-diboryl cyclopropanes

Herein, we describe the catalytic enantioselective cross-coupling of 1,2-bisboronic esters. Prior work on group specific cross coupling is limited to the use of geminal bis-boronates. This desymmetrization provides a novel approach to prepare enantioenriched cyclopropyl boronates with three contiguous stereocenters, that could be further derivatized through selective functionalization of the carbon-boron bond. Our results suggest that transmetallation, which is the enantiodetermining step, takes place with retention of stereochemistry at carbon.

Unified synthesis of multiply arylated alkanes by catalytic deoxygenative transformation of diarylketones

A deoxygenative transformation of diarylketones leading to multiply arylated alkanes was developed. Diarylketones were reacted with diphenylphosphine oxide resulting in a phospha-Brook rearrangement, followed by palladium-catalyzed cross-couplings or a Friedel-Crafts type alkylation to afford the corresponding multiply arylated alkanes. A variety of diarylketones can be converted to multiply arylated alkanes such as diarylmethanes, tetraarylethanes, and triarylmethanes by reduction, dimerization, and arylation in one pot. Furthermore, a one-pot conversion from arylcarboxylic acids to diarylmethanes and tetraarylethanes, and a synthesis of tetraarylmethane and triphenylethane using sequential coupling reactions are also presented.

Ruthenium Complexes Bearing α-Diimine Ligands and Their Catalytic Applications in N-Alkylation of Amines, α-Alkylation of Ketones, and β-Alkylation of Secondary Alcohols

New Ru(II) complexes encompassing α-diimine ligands were synthesized by reacting ruthenium precursors with α-diimine hydrazones. The new ligands and Ru(II) complexes were analyzed by analytical and various spectroscopic methods. The molecular structures of L₁ and complexes 1, 3, and 4 were determined by single-crystal XRD studies. The results reveal a distorted octahedral geometry around the Ru(II) ion for all complexes. Moreover, the new ruthenium complexes show efficient catalytic activity toward the C-N and C-C coupling reaction involving alcohols. Particularly, complex 3 demonstrates effective conversion in N-alkylation of aromatic amines, α-alkylation of ketones, and β-alkylation of alcohols.

Design of Hemilabile N,N,N-Ligands in Copper-Catalyzed Enantioconvergent Radical Cross-Coupling of Benzyl/Propargyl Halides with Alkenylboronate Esters

The enantioconvergent radical C(sp³)-C(sp²) cross-coupling of alkyl halides with alkenylboronate esters is an appealing tool in the assembly of synthetically valuable enantioenriched alkenes owing to the ready availability, low toxicity, and air/moisture stability of alkenylboronate esters. Here, we report a copper/chiral N,N,N-ligand catalytic system for the enantioconvergent cross-coupling of benzyl/propargyl halides with alkenylboronate esters (>80 examples) with good functional group tolerance. The key to the success is the rational design of hemilabile N,N,N-ligands by mounting steric hindrance at the ortho position of one coordinating quinoline ring. Thus, the newly designed ligand could not only promote the radical cross-coupling process in the tridentate form but also deliver enantiocontrol over highly reactive alkyl radicals in the bidentate form. Facile follow-up transformations highlight its potential utility in the synthesis of various enantioenriched building blocks as well as in the late-stage functionalization for drug discovery.

Hydroelementation of diynes

This review highlights the hydroelementation reactions of conjugated and separated diynes, which depending on the process conditions, catalytic system, as well as the type of reagents, leads to the formation of various products: enynes, dienes, allenes, polymers, or cyclic compounds. The presence of two triple bonds in the diyne structure makes these compounds important reagents but selective product formation is often difficult owing to problems associated with maintaining appropriate reaction regio- and stereoselectivity. Herein we review this topic to gain knowledge on the reactivity of diynes and to systematise the range of information relating to their use in hydroelementation reactions. The review is divided according to the addition of the E-H (E = Mg, B, Al, Si, Ge, Sn, N, P, O, S, Se, Te) bond to the triple bond(s) in the diyne, as well as to the type of the reagent used, and the product formed. Not only are the hydroelementation reactions comprehensively discussed, but the synthetic potential of the obtained products is also presented. The majority of published research is included within this review, illustrating the potential as well as limitations of these processes, with the intent to showcase the power of these transformations and the obtained products in synthesis and materials chemistry.

Saturated Boronic Acids, Boronates, and Trifluoroborates: An Update on Their Synthetic and Medicinal Chemistry

This review discusses recent advances in the chemistry of saturated boronic acids, boronates, and trifluoroborates. Applications of the title compounds in the design of boron-containing drugs are surveyed, with special emphasis on α-amino boronic derivatives. A general overview of saturated boronic compounds as modern tools to construct C(sp³ )-C and C(sp³ )-heteroatom bonds is given, including recent developments in the Suzuki-Miyaura and Chan-Lam cross-couplings, single-electron-transfer processes including metallo- and organocatalytic photoredox reactions, and transformations of boron "ate" complexes. Finally, an attempt to summarize the current state of the art in the synthesis of saturated boronic acids, boronates, and trifluoroborates is made, with a brief mention of the "classical" methods (transmetallation of organolithium/magnesium reagents with boron species, anti-Markovnikov hydroboration of alkenes, and the modification of alkenyl boron compounds) and a special focus on recent methodologies (boronation of alkyl (pseudo)halides, derivatives of carboxylic acids, alcohols, and primary amines, boronative C-H activation, novel approaches to alkene hydroboration, and 1,2-metallate-type rearrangements).

Arylketones as Aryl Donors in Palladium-Catalyzed Suzuki-Miyaura Couplings

Herein, we report the arylation, alkylation, and alkenylation of aryl ketones via a palladium-catalyzed Suzuki-Miyaura cross-coupling reaction. The use of the pyridine-oxazoline ligand is the key to the cleavage of the unstrained C-C bond. The late-stage arylation of aryl ketones derived from drugs and natural products demonstrated the synthetic utility of this protocol.

Late-Stage Functionalization of the Periphery of Oligophenylene Dendrimers with Various Arene Units via Fourfold C-H Borylation

Late-stage functionalization of the periphery of oligophenylene dendrimers was efficiently achieved via site-selective C-H activation of a preconstructed, readily accessible dendron. By fourfold iridium-catalyzed C-H borylation followed by Suzuki-Miyaura cross-coupling, various arene units were introduced into the end points of the 1,3,5-phenylene-based hydrocarbon dendron. Coupling of the modified dendrons with a core unit, such as 2,6-dibromobenzoic acid derivatives, afforded the periphery-functionalized dendrimers that also have an endohedral functionality at the core position.

Catalytic Chemo- and Enantioselective Transformations of gem-Diborylalkanes and (Diborylmethyl)metallic Species

Chemo- and stereoselective transformations of polyborylalkanes are powerful and efficient methods to access optically active molecules with greater complexity and diversity through programmed synthetic design. Among the various polyborylalkanes, gem-diborylalkanes have attracted much attention in organic chemistry as versatile synthetic handles. The notable advantage of gem-diborylalkanes lies in their ability to generate two key intermediates, α-borylalkyl anions and (gem-diborylalkyl) anions. These two different intermediates can be applied to various enantioselective reactions to rapidly access a diverse set of enantioenriched organoboron compounds, which can be further manipulated to generate various chiral molecule libraries via stereospecific C(sp³)-B bond transformations.In this Account, we summarize our recent contributions to the development of catalytic chemo- and stereoselective reactions using gem-diborylalkanes as versatile nucleophiles, which can be categorized as follows: (1) copper-catalyzed enantioselective coupling of gem-diborylalkanes with electrophiles and (2) the design and synthesis of (diborylmethyl)metallic species and their applications to enantioselective reactions. Since Shibata and Endo reported the Pd-catalyzed chemoselective Suzuki-Miyaura cross-coupling of gem-diborylalkanes with organohalides in 2014, Morken and Hall subsequently developed the first enantioselective analogous reactions using TADDOL-derived chiral phosphoramidite as the supporting ligand of a palladium catalyst. This discovery sparked interest in the catalytic enantioselective coupling of gem-diborylalkanes with electrophiles. Our initial studies focused on generating chiral (α-borylmethyl)copper species by enantiotopic-group-selective transmetalation of gem-diborylalkanes with chiral copper complexes and their reactions with various aldimines and ketimines to afford syn-β-aminoboronate esters with excellent enantio- and diastereoselectivity. Moreover, we developed the enantioselective allylation of gem-diborylalkanes that proceeded by reaction of in situ-generated chiral (α-borylalkyl)copper and allyl bromides. Mechanistic investigations revealed that the enantiotopic-group-selective transmetalation between gem-diborylalkanes and the chiral copper complex occurred through the open transition state rather than the closed transition state, thereby effectively generating chiral (α-borylmethyl)copper species. We also utilized (diborylmethyl)metallic species such as (diborylmethyl)silanes and (diborylmethyl)zinc halides in catalytic enantioselective reactions. We succeeded in developing the enantiotopic-group-selective cross-coupling of (diborylmethyl)silanes with aryl iodides to afford enantioenriched benzylic 1,1-silylboronate esters, which could be used for further consecutive stereospecific transformations to afford various enantioenriched molecules. In addition, we synthesized (diborylmethyl)zinc halides for the first time by the transmetalation of isolated (diborylmethyl)lithium and zinc(II) halides and their utilization to the synthesis of enantioenriched gem-diborylalkanes bearing a chiral center at the β-position via an iridium-catalyzed enantioselective allylic substitution process. In addition to our research efforts, we also include key contributions by other research groups. We hope that this Account will draw the attention of the synthetic community to gem-diboryl compounds and provide guiding principles for the future development of catalytic enantioselective reactions using gem-diboryl compounds.

Nickel-Catalyzed Arylation of C(sp3)-O Bonds in Allylic Alkyl Ethers with Organoboron Compounds

A nickel-catalyzed cross-coupling of allylic alkyl ethers with organoboron compounds through the cleavage of the inert C(sp³)-O(alkyl) bonds is described. Several types of allylic alkyl ethers can be coupled with various boronic acids or their derivatives to give the corresponding products in good to excellent yields with wide functional group tolerance and excellent regioselectivity. The gram-scale reaction and late-stage modification of biologically active compounds further prove the practicality of this synthetic method.

Synthesis of Arylpalladium(II) Boronates: Confirming the Structure and Chemical Competence of Pre-transmetalation Intermediates in the Suzuki-Miyaura Reaction

Palladium(II) boronates are recognized as fundamental pre-transmetalation intermediates in Suzuki-Miyaura cross-couplings. While these typically transient species have been detected and studied spectroscopically, it is conspicuous that they have never been isolated since this important reaction was discovered over forty years ago. This study reports the synthesis of a family of unprecedented arylpalladium(II) boronates that are, by design, kinetically stable at ambient temperature, both in solution and in the solid state. These properties enabled unambiguous crystallographic confirmation of their structure for the first time and their chemical competence in a Suzuki-Miyaura reaction was demonstrated.

(Z)-Selective Hydrosilylation and Hydroboration of Terminal Alkynes Enabled by Ruthenium Complexes with an N-Heterocyclic Carbene Ligand

Metal-catalyzed trans-1,2-hydrosilylations and hydroborations of terminal alkynes that generate synthetically valuable (Z)-alkenylsilanes and (Z)-alkenylboranes remain challenging due to the (E)-selective nature of the reactions and the formation of the thermodynamically unfavorable (Z)-isomer. The development of new, efficient catalytic systems for the (Z)-selective hydrosilylation and hydroboration of terminal alkynes is thus highly desirable from a fundamental perspective as it would deepen our understanding of the metal-catalyzed (Z)-selective hydrosilylation and hydroboration of terminal alkynes. This personal account describes our research for developing a ruthenium complex that can efficiently catalyze the hydrosilylation and hydroboration of terminal alkynes, and for exploring the factors controlling (Z)-selectivity of the reactions. Our effort into the activation of B-protected boronic acids, R-B(dan) (dan=naphthalene-1,8-diaminato), that was believed not to participate in Suzuki-Miyaura cross-coupling, is also discussed.

Nickel-Catalyzed Guerbet Type Reaction: C-Alkylation of Secondary Alcohols via Double (de)Hydrogenation

Acceptorless double dehydrogenative cross-coupling of secondary and primary alcohols under nickel catalysis is reported. This Guerbet type reaction provides an atom- and a step-economical method for the C-alkylation of secondary alcohols under mild, benign conditions. A broad range of substrates including aromatic, cyclic, acyclic, and aliphatic alcohols was well tolerated. Interestingly, the C-alkylation of cholesterol derivatives and the double C-alkylation of cyclopentanol with various alcohols were also demonstrated.

One-Pot Dual C-C Coupling Reaction via Site Selective Cascade Formation by PdII -Cryptate of an Amino-Ether Heteroditopic Macrobicycle

Selectivity of aryl iodo over ethynyl iodo toward the Suzuki cross coupling reaction is explored by utilizing a palladium complex of amino-ether heteroditopic macrobicycle. Subsequently, unreacted ethynyl iodide undergoes homocoupling reaction in the same catalytic atmosphere, thereby representing a cascade dual C-C coupling reaction. Furthermore, this approach is extended for novel one-pot synthesis of unsymmetrical 1,3-diynes.

Enantioselective Hydroalkenylation of Olefins with Enol Sulfonates Enabled by Dual Copper Hydride and Palladium Catalysis

The catalytic enantioselective synthesis of α-chiral olefins represents a valuable strategy for rapid generation of structural diversity in divergent syntheses of complex targets. Herein, we report a protocol for the dual CuH- and Pd-catalyzed asymmetric Markovnikov hydroalkenylation of vinyl arenes and the anti-Markovnikov hydroalkenylation of unactivated olefins, in which readily available enol triflates can be utilized as alkenyl coupling partners. This method allowed for the synthesis of diverse α-chiral olefins, including tri- and tetrasubstituted olefin products, which are challenging to prepare by existing approaches.

Nickel-Catalyzed Asymmetric Hydroarylation of Vinylarenes: Direct Enantioselective Synthesis of Chiral 1,1-Diarylethanes

The enantioselective hydroarylation of vinylarenes catalyzed by a chiral, non-racemic nickel catalyst is presented as a facile method to generate chiral 1,1-diarylethanes. These reactions proceed via formation of a chiral, non-racemic nickel benzyl intermediate. Transmetalation with arylboron nucleophiles and subsequent reductive elimination enable the formation of a variety of chiral 1,1-diarylethanes. The 1,1-diarylethane products from reactions of arylboronic acids containing electron-donating substituents are formed with typically greater than 90% ee, while the 1,1-diarylethanes generated from reactions of arylboronic acids containing electron-withdrawing groups are generated with typically less than 80% ee. These results are consistent with the rate of transmetalation with an arylboron nucleophile playing a key role in the enantioselectivity of these hydroarylation reactions. This mechanistic insight has led to the development of reactions of neo-pentylglycolate esters of arylboronic acids with vinylarenes that occur with higher enantioselectivities based on increased rates of transmetalation.

The Stereochemical Course of Pd-Catalyzed Suzuki Reactions Using Primary Alkyltrifluoroborate Nucleophiles

Using deuterium-labeled stereochemical probes, we show that primary alkyltrifluoroborate nucleophiles undergo transmetalation to palladium exclusively via a stereoretentive pathway and that the resulting stereospecificity is broadly independent of electronic and steric effects. This stands in stark contrast to the stereochemical course of transmetalation for secondary alkyltrifluoroborates, which varies between net stereoretention and net stereoinversion depending upon the electronic properties of the supporting phosphine ligand, the electronic properties of the aryl electrophile, and the steric properties of the alkylboron nucleophile. In this study, we additionally show that the stereochemical course of transmetalation for secondary alkylboron reagents can be under reagent steric control, while no such steric control exists for analogous primary alkylboron nucleophiles. The combined study reveals fundamental mechanistic differences between transmetalations of primary and secondary alkylboron reagents in Pd-catalyzed Suzuki reactions.

Nickel-Catalyzed, Stereospecific C-C and C-B Cross-Couplings via C-N and C-O Bond Activation

Highly enantioenriched benzylic and allylic amines and alcohols are readily available via asymmetric synthesis and in complex natural products. The development of mild, nickel-catalyzed cross-couplings of their derivatives has advanced the tools available for the preparation of a range of highly enantioenriched products, including those with quaternary stereocenters. This perspective focuses on cross-couplings with convenient and functional group-tolerant organoboron reagents and highlights the discoveries of activating groups and conditions that have led to high-yielding and highly stereospecific reactions. Emphasis is placed on mechanistic understanding, particularly with regards to controlling inversion vs. retention pathways. Limitations and opportunities for future developments are also highlighted.

Efficient microwave-assisted Suzuki–Miyaura cross-coupling reaction of 3-bromo pyrazolo[1,5-a]pyrimidin-5(4H)-one: towards a new access to 3,5-diarylated 7-(trifluoromethyl)pyrazolo[1,5-a]pyrimidine derivatives

A convenient and efficient synthetic route to C3-arylated 7-trifluoromethylpyrazolo[1,5-a]pyrimidin-5-one derivatives has been reported starting from 3-bromo-7-(trifluoromethyl)pyrazolo[1,5-a]pyrimidin-5-one through a Suzuki–Miyaura cross-coupling reaction. The arylation (heteroarylation) strategy can be performed using a wide variety of aryl and heteroaryl boronic acids and requiring a tandem catalyst XPhosPdG2/XPhos to avoid the debromination reaction. These optimized conditions were successfully extended to the synthesis of 7-, 8- and 9-arylated pyrimido[1,2-b]indazol-2-ones from their corresponding brominated starting materials. Furthermore, the second C-5 arylation of C3-arylated pyrazolo[1,5-a]pyrimidin-5-ones was achieved under standard Suzuki–Miyaura cross-coupling conditions, after activating the C–O bond of the lactam function with PyBroP, giving access to a small library of 3,5-diarylated 7-(trifluoromethyl)pyrazolo[1,5-a]pyrimidines in good to excellent yields. The interest of this approach has been highlighted by the synthesis of a known anti-inflammatory agent. Additionally, a preliminary biological evaluation has revealed that a number of derivatives display micromolar IC₅₀ values against monoamine oxidase B, an important target in the field of neurodegenerative disorders.

A convenient and efficient synthetic route to C3-arylated 7-trifluoromethylpyrazolo[1,5-a]pyrimidin-5-one derivatives has been reported starting from 3-bromo-7-(trifluoromethyl)pyrazolo[1,5-a]pyrimidin-5-one through a Suzuki–Miyaura cross-coupling reaction.