Diastereoselective and Enantioselective Conjunctive Cross-Coupling Enabled by Boron Ligand Design

Xanthopinacol Boronate: A Robust, Photochemically Assembled and Cleavable Boronic Ester for Orthogonal Chemistry

Organoboronic acids impact numerous fields of application from organic synthesis to drug discovery and materials science. However, their highly polar nature makes them challenging to handle, purify, and characterize. Boronic esters help overcome these issues, and pinacol esters (Bpin) have become the dominant boronic acid surrogate in organic synthesis. Despite its popularity, Bpin is not without drawbacks. Its formation from pinacol is intrinsically reversible in the presence of water or alcohols, which may cause premature release leading to losses during reactions and purification. This reversibility complicates the hydrolytic regeneration of free boronic acids, which often requires additional steps to destroy the pinacol by-product. Although other boronyl protecting groups exist, their removal requires harsh pH conditions. To address these issues, we developed xanthopinacol boronates (Bxpin), a robust protecting group for boronic acids with excellent orthogonality in various chemical reactions and mild irreversible removal under catalyzed photoredox conditions. Xpin boronates can be obtained directly by irradiation of a mixture of free boronic acid and xanthone with UV light, causing an in situ dimerization of xanthone to the required xanthopinacol. The unique attributes of xpin boronates were further studied by UV-vis spectrophotometry, X-ray crystallography, cyclic voltammetry, and various stability tests.

Ni-Catalyzed Regioselective Alkylarylation of Unactivated Alkenes in Amines Enabled by Cooperative Ligand Effects of Nitriles and Electron-Deficient Alkenes

We report a Ni-catalyzed vicinal alkylarylation of unactivated alkenes in γ,δ- and δ,ε-alkenylamines with aryl halides and alkylzinc reagents. The reaction is enabled by amine coordination and can use all primary, secondary, and tertiary amines. The reaction constructs two new C(sp3)-C(sp3) and C(sp3)-C(sp2) bonds and produces δ- and ε-arylamines with C(sp3)-branching at the γ- and δ-positions. A variety of aryl and heteroaryl iodides and both the primary and secondary alkylzinc reagents can be used as coupling carbon sources. Mechanistic studies suggest that the reaction is enabled by the cooperative effect of organic nitriles and electron-deficient alkenes (EDAs) as ligands.

Chemoselective and Stereoselective Allylation of Bis(alkenyl)boronates

Bis(alkenyl)boronates react with optically active Ir(π-allyl) species in a process that involves allylation of the more substituted olefin and 1,2-metalate shift of the less substituted olefin. The method constructs valuable enantioenriched tertiary allylic boronic esters with high chemoselectivity, enantioselectivity and diastereoselectivity. Allylic functionalization reactions transform the 1,3-stereodiad to 1,5- and 1,6-stereochemical relationships.

Stereoselective polar radical crossover for the functionalization of strained-ring systems

Radical-polar crossover of organoborates is a poweful tool that enables the creation of two C-C bonds simultaneously. Small ring systems have become essential motifs in drug discovery and medicinal chemistry. However, step-economic methods for their selective functionalization remains scarce. Here we present a one-pot strategy that merges a simple preparation of strained organoboron species with the recently popularized polar radical crossover of borate derivatives to stereoselectively access tri-substituted azetidines, cyclobutanes and five-membered carbo- and heterocycles.

The reactivity of alkenyl boron reagents in catalytic reactions: recent advances and perspectives

Recent advances focusing on novel reactivity of alkenyl boron reagents in polar or radical pathways within catalytic reactions by employing transition metal catalysis, organocatalysis have been summarized and discussed.

Asymmetric Synthesis of Chiral 1,2-Bis(Boronic) Esters Featuring Acyclic, Non-Adjacent 1,3-Stereocenters

The construction of acyclic, non-adjacent 1,3-stereogenic centers, prevalent motifs in drugs and bioactive molecules, has been a long-standing synthetic challenge due to acyclic nucleophiles being distant from the chiral environment. In this study, we successfully synthesized highly valuable 1,2-bis(boronic) esters featuring acyclic and nonadjacent 1,3-stereocenters. Notably, this reaction selectively produces migratory coupling products rather than alternative deborylative allylation or direct allylation byproducts. This approach introduces a new activation mode for selective transformations of gem-diborylmethane in asymmetric catalysis. Additionally, we found that other gem-diborylalkanes, previously challenging due to steric hindrance, also successfully participated in this reaction. The incorporation of 1,2-bis(boryl)alkenes facilitated the diversification of the alkenyl and two boron moieties in our target compounds, thereby enabling access to a broad array of versatile molecules. DFT calculations were performed to elucidate the reaction mechanism and shed light on the factors responsible for the observed excellent enantioselectivity and diastereoselectivity. These were determined to arise from ligand-substrate steric repulsions in the syn-addition transition state.

Palladium-Catalyzed Multicomponent Assembly of (Z)-Alkenylborons via Carbopalladation/Boronation/Retro-Diels-Alder Cascade Reaction

A palladium-catalyzed multicomponent cascade reaction of aryl iodides, oxanorbornadiene, and diborns to access (Z)-alkenylborons is reported. This transformation proceeds through the sequential carbopalladation/boronation/retro-Diels-Alder domino reaction. The oxanorbornadiene used in this reaction serves as an acetylene surrogate, which is generated via a retro-Diels-Alder reaction. Such a stereoselective and scalable approach has a wide range of functional group tolerance and good substrate universality.

Iridium-Catalyzed Asymmetric Difunctionalization of C-C σ-Bonds Enabled by Ring-Strained Boronate Complexes

Enantioenriched organoboron intermediates are important building blocks in organic synthesis and drug discovery. Recently, transition metal-catalyzed enantioselective 1,2-metalate rearrangements of alkenylboronates have emerged as an attractive protocol to access these valuable reagents by installing two different carbon fragments across C═C π-bonds. Herein, we report the development of an iridium-catalyzed asymmetric allylation-induced 1,2-metalate rearrangement of bicyclo[1.1.0]butyl (BCB) boronate complexes enabled by strain release, which allows asymmetric difunctionalization of C-C σ-bonds, including dicarbonation and carboboration. This protocol provides a variety of enantioenriched three-dimensional 1,1,3-trisubstituted cyclobutane products bearing a boronic ester that can be readily derivatized. Notably, the reaction gives trans diastereoisomers that result from an anti-addition across the C-C σ-bond, which is in contrast to the syn-additions observed for reactions promoted by Pd^II-aryl complexes and other electrophiles in our previous works. The diastereoselectivity has been rationalized based on a combination of experimental data and density functional theory calculations, which suggest that the BCB boronate complexes are highly nucleophilic and react via early transition states with low activation barriers.

Asymmetric Synthesis of β-Aminoboronates via Copper-Catalyzed Reductive Coupling of Vinyl Boronates with Imines

We report a copper-catalyzed asymmetric reductive coupling of vinyl boronates with imines, which directly access enantiomerically enriched β-aminoalkylboronates. Stereoselective addition of the in situ generated chiral α-borylalkyl copper to N-phosphinoyl imines provided target products in good yields with high diastereo- and enantioselectivity. Vinyl boronate with methylated acenaphthoquinone as a boron ligand was essential to efficiently spawn asymmetric products, and organic transformations of the boron moiety, along with the easily removable N-protecting group, proved their synthetic utility.

Photocatalytic Decarboxylative Coupling of Arylacetic Acids with Aromatic Aldehydes

An efficient protocol was proposed for the preparation of secondary alcohols in good to excellent yields via photoredox-catalyzed decarboxylative couplings between readily available arylacetic acids and a variety of less reactive (hetero)aromatic aldehydes. The formation of carbanion is the key intermediate in this reaction. Various substituted arylacetic acids and aldehydes were all compatible with this transformation under mild reaction conditions. Furthermore, the current protocol was successfully applied to the direct alcoholization of several drug acids.

Ni-Catalyzed Regio- and Stereoselective Alkylarylation of Unactivated Alkenes in γ,δ-Alkenylketimines

We disclose a Ni-catalyzed vicinal alkylarylation of unactivated alkenes in γ,δ-alkenylketimines with aryl halides and alkylzinc reagents. The reaction produces γ-C(sp3)-branched δ-arylketones with the construction of two new C(sp3)-C(sp3) and C(sp3)-C(sp2) bonds. Electron-deficient alkenes play crucial dual roles as ligands to stabilize reaction intermediates and to increase catalytic rates for the formation of C(sp3)-C(sp3) bonds. This alkene alkylarylation reaction is also effective for secondary alkylzinc reagents and internal alkenes, and proceeds with a complete regio- and stereocontrol, affording products with up to three contiguous all-carbon all-cis secondary stereocenters.

Catalytic Asymmetric Diarylation of Internal Acyclic Styrenes and Enamides

Enantioselective transformations of olefins are among the most important strategies for the asymmetric synthesis of organic compounds. Chemo-, diastereo-, and stereoselective control of reactions with internal acyclic alkenes for the construction of functionalized acyclic alkanes still remain a persistent challenge. Here, we report a palladium-catalyzed asymmetric regiodivergent Heck-type diarylation of internal acyclic alkenes. The 1,2-diarylation of two accessible acyclic alkenes, cinnamyl carbamates and enamides with diazonium salts and aromatic boronic acids, furnishes products containing vicinal stereogenic centers via the stereospecific formation of carbonyl coordination-assisted transient palladacycles. Moreover, the asymmetric migratory diarylation of enamides enables the formation of incontiguous stereocenters by an interrupted diastereoselective 1,3-chain-walking process. This protocol streamlines access to highly functionalized multisubstituted enantioenriched carbamates and amine derivatives which are embedded in the key biologically active motifs.

Enantioselective Synthesis of Tertiary β‐Boryl Amides by Conjunctive Cross‐Coupling of Alkenyl Boronates and Carbamoyl Chlorides

Synthesis of versatile β tert-boryl amides is accomplished by conjunctive cross-coupling of α-substituted alkenyl boron "ate" complexes and carbamoyl chloride electrophiles. This reaction can be accomplished in an enantioselective fashion using a palladium catalyst in combination with MandyPhos. The addition of water results in enhanced chemoselectivity for the conjunctive coupling product relative to the Suzuki-Miyaura cross-coupling product. Transformations of the reaction products were examined as well as application to the synthesis of (+)-adalinine.

Annulative Coupling of Vinylboronic Esters: Aryne-Triggered 1,2-Metallate Rearrangement

A stereoselective annulative coupling of a vinylboronic ester ate-complex with arynes producing cyclic borinic esters has been developed. An annulation reaction that proceeded through the formation of two C–C bonds and a C–B bond was realized by exploiting a 1,2-metallate rearrangement of boronate triggered by the addition of a vinyl group to the strained triple bond of an aryne. The generated aryl anion would then cyclize to a boron atom to complete the annulation cascade. The annulated borinic ester could be converted to boronic acids and their derivatives by oxidation, halogenation, and cross-coupling. Particularly, halogenation and Suzuki–Miyaura coupling proceeded in a site-selective fashion and produced highly substituted alkylboronic acid derivatives.

A stereoselective annulative coupling of a vinylboronic ester ate-complex with arynes producing cyclic borinic esters has been developed.

Three-component 1,2-carboamination of vinyl boronic esters via amidyl radical induced 1,2-migration

Three-component 1,2-carboamination of vinyl boronic esters with alkyl/aryl lithium reagents and N-chloro-carbamates/carboxamides is presented. Vinylboron ate complexes generated in situ from the boronic ester and an organo lithium reagent are shown to react with readily available N-chloro-carbamates/carboxamides to give valuable 1,2-aminoboronic esters. These cascades proceed in the absence of any catalyst upon simple visible light irradiation. Amidyl radicals add to the vinylboron ate complexes followed by oxidation and 1,2-alkyl/aryl migration from boron to carbon to give the corresponding carboamination products. These practical cascades show high functional group tolerance and accordingly exhibit broad substrate scope. Gram-scale reaction and diverse follow-up transformations convincingly demonstrate the synthetic potential of this method.

Recent advances in asymmetric borylation by transition metal catalysis

Chiral organoboronates have played a critical role in organic chemistry and in the development of materials science and pharmaceuticals. Much effort has been devoted to exploring synthetic methodologies for the preparation of these compounds during the past few decades. Among the known methods, asymmetric catalysis has emerged as a practical and highly efficient strategy for their straightforward preparation, and recent years have witnessed remarkable advances in this respect. Approaches such as asymmetric borylative addition, asymmetric allylic borylation and stereospecific cross-coupling borylation, have been extensively explored and well established employing transition-metal catalysis with a chiral ligand. This review provides a comprehensive overview of transition metal-catalysed asymmetric borylation processes to construct carbon-boron, carbon-carbon, and other carbon-heteroatom bonds. It summarises a range of recent achievements in this area of research, with considerable attention devoted to the reaction modes and the mechanisms involved.

Mechanism of Z-Selective Hydroalkylation of Terminal Alkynes

This paper describes a detailed mechanistic study of the silver-catalyzed Z-selective hydroalkylation of terminal alkynes. Considering the established mechanistic paradigms for Z-selective hydroalkylation of alkynes, we explored a mechanism based on the radical carbometalation of alkynes. Experimental results have provided strong evidence against the initially proposed radical mechanism and have led us to propose a new mechanism for the Z-selective hydroalkylation of alkynes based on boronate formation and a 1,2-metalate shift. The new mechanism provides a rationale for the excellent Z-selectivity observed in the reaction. A series of stoichiometric experiments has probed the feasibility of the proposed elementary steps and revealed an additional role of the silver catalyst in the protodeboration of an intermediate. Finally, a series of kinetic measurements, KIE experiments, and competition experiments allowed us to identify the turnover limiting step and the resting state of the catalyst. We believe that the results of this study will be useful in the further exploration and development of related transformations of alkynes.

Ni-Catalyzed Arylbenzylation of Alkenylarenes: Kinetic Studies Reveal Autocatalysis by ZnX2 *

We report a Ni-catalyzed regioselective arylbenzylation of alkenylarenes with benzyl halides and arylzinc reagents. The reaction furnishes differently substituted 1,1,3-triarylpropyl structures that are reminiscent of the cores of oligoresveratrol natural products. The reaction is also compatible for the coupling of internal alkenes, secondary benzyl halides and variously substituted arylzinc reagents. Kinetic studies reveal that the reaction proceeds with a rate-limiting single-electron-transfer process and is autocatalyzed by in-situ-generated ZnX2 . The reaction rate is amplified by a factor of three through autocatalysis upon addition of ZnX2 .

Nickel-Catalyzed Regioselective Alkenylarylation of γ,δ-Alkenyl Ketones via Carbonyl Coordination

We disclose a nickel-catalyzed reaction, which enabled us to difunctionalize unactivated γ,δ-alkenes in ketones with alkenyl triflates and arylboronic esters. The reaction was made feasible by the use of 5-chloro-8-hydroxyquinoline as a ligand along with NiBr2 ⋅DME as a catalyst and LiOtBu as base. The reaction proceeded with a wide range of cyclic, acyclic, endocyclic and exocyclic alkenyl ketones, and electron-rich and electron-deficient arylboronate esters. The reaction also worked with both cyclic and acyclic alkenyl triflates. Control experiments indicate that carbonyl coordination is required for the reaction to proceed.

Computational study of silver-catalyzed stereoselective hydroalkylation of alkynes: Pauli repulsion controlled Z/E selectivity

The mechanism and origin of stereoselectivity of silver-catalyzed hydroalkylation of alkynes were computationally investigated at the B3LYP-D3BJ/6-311+G(d,p)-SDD//B3LYP/6-31G(d)-LANL2DZ level. The complex of alkynyl trialkylboronate with cationic silver is a key intermediate, which triggers the rate- and stereoselectivity-determining 1,2-migration step. Energy decomposition analysis indicates that the difference of Pauli repulsion dominates the stereoselectivity.

Allenylidene Induced 1,2-Metalate Rearrangement of Indole-Boronates: Diastereoselective Access to Highly Substituted Indolines

A process to achieve 1,2-metalate rearrangements of indole boronate as a way to access substituted indolines in high diastereoselectivities is presented. The reaction involves the generation of a Cu-allenylidene, which is sufficiently electrophilic to induce the 1,2-metalate rearrangement. The scope of the reaction is evaluated as well as further transformations of the product.

Enantioselective Allylation of Alkenyl Boronates Promotes a 1,2-Metalate Rearrangement with 1,3-Diastereocontrol

Alkenyl boronates add to Ir(π-allyl) intermediates with high enantioselectivity. A 1,2-metalate shift forms a second C-C bond and sets a 1,3-stereochemical relationship. The three-component coupling provides tertiary boronic esters that can undergo multiple additional functionalizations. An extension to trisubstituted olefins sets three contiguous stereocenters.

Rate Dependence on Inductive and Resonance Effects for the Organocatalyzed Enantioselective Conjugate Addition of Alkenyl and Alkynyl Boronic Acids to β-Indolyl Enones and β-Pyrrolyl Enones

Two key factors bear on reaction rates for the conjugate addition of alkenyl boronic acids to heteroaryl-appended enones: the proximity of inductively electron-withdrawing heteroatoms to the site of bond formation and the resonance contribution of available heteroatom lone pairs to stabilize the developing positive charge at the enone β-position. For the former, the closer the heteroatom is to the enone β-carbon, the faster the reaction. For the latter, greater resonance stabilization of the benzylic cationic charge accelerates the reaction. Thus, reaction rates are increased by the closer proximity of inductive electron-withdrawing elements, but if resonance effects are involved, then increased rates are observed with electron-donating ability. Evidence for these trends in isomeric substrates is presented, and the application of these insights has allowed for reaction conditions that provide improved reactivity with previously problematic substrates.

Asymmetric Conjugate Addition of Chiral Secondary Borylalkyl Copper Species

We report the diastereo- and enantioselective conjugate addition of chiral secondary borylalkyl copper species derived from borylalkenes in situ to α,β-unsaturated diesters. In the presence of a chiral bisphosphine-ligated CuH catalyst, the conjugate addition provides a direct access to enantioenriched alkylboron compounds containing two contiguous carbon stereogenic centers in good yield with high diastereo- and enantioselectivity (up to >98:2 dr, >99:1 er) by assembling readily available starting alkenyl reagents in a single operation without using preformed organometallic reagents or chiral auxiliaries. The resulting products were used in various organic transformations. The utility of the synthetic approach was highlighted by the synthesis of (-)-phaseolinic acid.

Crystal structure of 1,2-bis-(4-fluoro-phen-yl)-1-hy-droxy-2,3,8-tri-meth-oxy-acenaphthene: formation of a five-membered intra-molecular O-H⋯O hydrogen-bonded ring

The structure of the title compound, C27H22F2O4, at 193 K has triclinic (P ) symmetry. The hy-droxy and meth-oxy groups at the 1,2-positions of the acenaphthene core display a cis configuration. Both substituents are involved in the formation of a five-membered intra-molecular O-H⋯O hydrogen-bonded ring. The 4-fluoro-phenyl rings make dihedral angles of 87.02 (7) and 51.86 (8)° with the naphthalene ring system. In the crystal, a pair of non-classical C-H⋯O hydrogen bonds forms centrosymmetric dimeric structures. The dimeric aggregates are linked in the ac plane through non-classical C-H⋯F hydrogen bonds and C-H⋯π interactions.

Rhodium-catalysed selective C-C bond activation and borylation of cyclopropanes

Transition metal (TM)-catalysed directed hydroboration of aliphatic internal olefins which facilitates the construction of complex alkylboronates is an essential synthetic methodology. Here, an efficient method for the borylation of cyclopropanes involving TM-catalysed directed C-C activation has been developed. Upon exposure to neutral Rh(i)-catalyst systems, N-Piv-substituted cyclopropylamines (CPAs) undergo proximal-selective hydroboration with HBpin to provide valuable γ-amino boronates in one step which are otherwise difficult to synthesize by known methods. The enantioenriched substrates can deliver chiral products without erosion of the enantioselectivities. Versatile synthetic utility of the obtained γ-amino boronates is also demonstrated. Experimental and computational mechanistic studies showed the preferred pathway and the origin of this selectivity. This study will enable the further use of CPAs as valuable building blocks for the tunable generation of C-heteroatom or C-C bonds through selective C-C bond activation.

Transition metal catalyzed asymmetric multicomponent reactions of unsaturated compounds using organoboron reagents

Asymmetric multicomponent reactions allow stitching several functional groups in an enantioselective and atom economical manner. The introduction of boron-based reagents as a multicomponent coupling partner has its own merits. In addition to being non-toxic and highly stable, organoboron compounds can be easily converted to other functional groups in a stereoselective manner. In the last decade several transition metal catalyzed asymmetric multicomponent strategies have been evolved using boron based reagents. This review will discuss the merits and scope of multicomponent strategies based on their difference in the reaction mechanism and transition metals involved.

Practical and Modular Construction of C(sp3)-Rich Alkyl Boron Compounds

Alkyl boronic acids and esters play an important role in the synthesis of C(sp³)-rich medicines, agrochemicals, and material chemistry. This work describes a new type of transition-metal-free mediated transformation to enable the construction of C(sp³)-rich and sterically hindered alkyl boron reagents in a practical and modular manner. The broad generality and functional group tolerance of this method is extensively examined through a variety of substrates, including synthesis and late-stage functionalization of scaffolds relevant to medicinal chemistry. The strategic significance of this approach, with alkyl boronic acids as linchpins, is demonstrated through various downstream functionalizations of the alkyl boron compounds. This two-step concurrent cross-coupling approach, resembling formal and flexible alkyl-alkyl couplings, provides a general entry to synthetically challenging high Fsp³-containing drug-like scaffolds.

Copper-Catalyzed Enantioconvergent Radical Suzuki-Miyaura C(sp3)-C(sp2) Cross-Coupling

A copper-catalyzed enantioconvergent Suzuki-Miyaura C(sp³)-C(sp²) cross-coupling of various racemic alkyl halides with organoboronate esters has been established in high enantioselectivity. Critical to the success is the use of a chiral cinchona alkaloid-derived N,N,P-ligand for not only enhancing the reducing capability of copper catalyst to favor a stereoablative radical pathway over a stereospecific S_N2-type process but also providing an ideal chiral environment to achieve the challenging enantiocontrol over the highly reactive radical species. The reaction has a broad scope with respect to both coupling partners, covering aryl- and heteroarylboronate esters, as well as benzyl-, heterobenzyl-, and propargyl bromides and chlorides with good functional group compatibility. Thus, it provides expedient access toward a range of useful enantioenriched skeletons featuring chiral tertiary benzylic stereocenters.

Synthesis of 1,3-Bis-(boryl)alkanes through Boronic Ester Induced Consecutive Double 1,2-Migration

A general and efficient approach for the preparation of 1,3-bis-(boryl)alkanes is introduced. It is shown that readily generated vinylboron ate complexes react with commercially available ICH2 Bpin to valuable 1,3-bis-(boryl)alkanes. The introduced transformation, which is experimentally easy to conduct, shows broad substrate scope and high functional-group tolerance. Mechanistic studies reveal that the reaction does not proceed via radical intermediates. Instead, an unprecedented boronic ester induced sequential bis-1,2-migration cascade is suggested.

Stereospecific 1,2-Migrations of Boronate Complexes Induced by Electrophiles

The stereospecific 1,2-migration of boronate complexes is one of the most representative reactions in boron chemistry. This process has been used extensively to develop powerful methods for asymmetric synthesis, with applications spanning from pharmaceuticals to natural products. Typically, 1,2-migration of boronate complexes is driven by displacement of an α-leaving group, oxidation of an α-boryl radical, or electrophilic activation of an alkenyl boronate complex. The aim of this article is to summarize the recent advances in the rapidly expanding field of electrophile-induced stereospecific 1,2-migration of groups from boron to sp2 and sp3 carbon centers. It will be shown that three different conceptual approaches can be utilized to enable the 1,2-migration of boronate complexes: stereospecific Zweifel-type reactions, catalytic conjunctive coupling reactions, and transition metal-free sp2 -sp3 couplings. A discussion of the reaction scope, mechanistic insights, and synthetic applications of the work described is also presented.

Difunctionalization of C-C σ-Bonds Enabled by the Reaction of Bicyclo[1.1.0]butyl Boronate Complexes with Electrophiles: Reaction Development, Scope, and Stereochemical Origins

Difunctionalization reactions of C-C σ-bonds have the potential to streamline access to molecules that would otherwise be difficult to prepare. However, the development of such reactions is challenging because C-C σ-bonds are typically unreactive. Exploiting the high ring-strain energy of polycyclic carbocycles is a common strategy to weaken and facilitate the reaction of C-C σ-bonds, but there are limited examples of highly strained C-C σ-bonds being used in difunctionalization reactions. We demonstrate that highly strained bicyclo[1.1.0]butyl boronate complexes (strain energy ca. 65 kcal/mol), which were prepared by reacting boronic esters with bicyclo[1.1.0]butyl lithium, react with electrophiles to achieve the diastereoselective difunctionalization of the strained central C-C σ-bond of the bicyclo[1.1.0]butyl unit. The reaction shows broad substrate scope, with a range of different electrophiles and boronic esters being successfully employed to form a diverse set of 1,1,3-trisubstituted cyclobutanes (>50 examples) with high diastereoselectivity. The high diastereoselectivity observed has been rationalized based on a combination of experimental data and DFT calculations, which suggests that separate concerted and stepwise reaction mechanisms are operating, depending upon the migrating substituent and electrophile used.

Chemoselective Cross-Coupling of gem-Borazirconocene Alkanes with Aryl Halides

The direct and chemoselective conversion of the carbon-metal bond of gem-dimetallic reagents enables rapid and sequential formation of multiple carbon-carbon and carbon-heteroatom bonds, thus representing a powerful method for efficiently increasing structural complexity. Herein, we report a visible-light-induced, nickel-catalyzed, chemoselective cross-coupling reaction between gem-borazirconocene alkanes and diverse aryl halides, affording a wide range of alkyl Bpin derivatives in high yields with excellent regioselectivity. This practical method features attractively simple reaction conditions and a broad substrate scope. Additionally, we systematically investigated a Bpin-directed chain walking process underlying the regioselectivity of alkylzirconocenes, thus uncovering the mechanism of the remote functionalization of internal olefins achieved with our method. Finally, DFT calculations indicate that the high regioselectivity of this reaction originates from the directing effect of the Bpin group.

Radical-Induced 1,2-Migrations of Boron Ate Complexes

1,2-Boron ate rearrangements represent a fundamental class of transformations to establish new C-C bonds while retaining the valuable boron moiety in the product. In established ionic processes, the boron ate complex is activated by an external electrophile to induce a 1,2-migration from boron to an adjacent sp 3 or sp 2 carbon atom. Recently, two complementary radical polar crossover approaches have been explored for both classes, 1,2-migrations to sp 2 and sp 3 carbon centers. This review describes the general concepts in this emerging research field and summarizes recent developments of radical-induced 1,2-migrations from boron to carbon.

Catalytic Enantioselective Synthesis of anti-Vicinal Silylboronates by Conjunctive Cross-Coupling

Chiral 1,2-bimetallic reagents are useful motifs in synthetic chemistry. Although syn-1,2-bimetallic compounds can be prepared by alkene dimetallation, anti-1,2-bimetallics are still rare. The stereospecific 1,2-metallate shift that occurs during conjunctive cross-coupling is shown to enable a practical and modular approach to the catalytic synthesis of enantioenriched anti-1,2-borosilanes. In addition to reaction development, the synthetic utility of anti-1,2-borosilanes was investigated, including applications to the synthesis of anti-1,2-diols and anti-1,2-amino alcohols.

Diastereo- and Enantioselective 1,4-Difunctionalization of Borylenynes by Catalytic Conjunctive Cross-Coupling

Enantioselective conjunctive cross-coupling of enyne-derived boronate complexes occurs with 1,4 addition of the electrophile and migrating group across the π system. This reaction pathway furnishes α-boryl allenes as the reaction product. In the presence of a chiral catalyst, both the central and axial chirality of the product can be controlled during product formation.

Site-Selective 1,2-Dicarbofunctionalization of Vinyl Boronates through Dual Catalysis

A modular, site-selective 1,2-dicarbofunctionalization of vinyl boronates with organic halides through dual catalysis is described. This reaction proceeds under mild conditions and is characterized by excellent chemo- and regioselectivity. It thus represents a complementary new technique for preparing densely functionalized alkyl boron architectures from simple and accessible precursors.