Reversible Carbon−Carbon Bond Formation between 1,3-Dienes and Aldehyde or Ketone on Nickel(0)

Stereoconvergent and Enantioselective Synthesis of Z-Homoallylic Alcohols via Nickel-Catalyzed Reductive Coupling of Z/E-1,3-Dienes with Aldehydes

Stereoconvergent reactions enable the transformation of mixed stereoisomers into well-defined, chiral products─a crucial strategy for handling Z/E-mixed olefins, which are common but challenging substrates in organic synthesis. Herein, we report a stereoconvergent and highly enantioselective method for synthesizing Z-homoallylic alcohols via the nickel-catalyzed reductive coupling of Z/E-mixed 1,3-dienes with aldehydes. This process is enabled by an N-heterocyclic carbene ligand characterized by C2-symmetric backbone chirality and bulky 2,6-diisopropyl N-aryl substituents. Our method achieves excellent stereocontrol over both enantioselectivity and Z-selectivity in a single step, producing chiral Z-homoallylic alcohols that are valuable in natural products and pharmaceuticals.

Palladium(0) π-Lewis Base Catalysis: Concept and Development

The development of a new catalytic strategy plays a vital role in modern organic chemistry since it permits bond formation in an unprecedented and more efficient manner. Although the application of preformed metal complexes as π-base-activated reagents have enabled diverse transformations elegantly, the concept and strategy by directly utilizing transition metals as efficient π-Lewis base catalysts remain underdeveloped, especially in the field of asymmetric catalysis. Here, we outline our perspective on the discovery of palladium(0) as an efficient π-Lewis base catalyst, which is capable of increasing the highest occupied molecular orbital (HOMO) energy of both electron-neutral and electron-deficient 1,3-dienes and 1,3-enynes upon flexible η2-complexes formed in situ and resultant π-backdonation. Thus, fruitful carbon-carbon-forming reactions with diverse electrophiles can be achieved enantioselectively in a vinylogous addition pattern, which is conceptually different from the classical oxidative cyclization mechanism. Emphasis will be given to the concept and mechanism elucidation, catalytic features, and reaction design together with perspective on the further development of this emerging field.

Aminoalcohol derivatives by nickel-catalyzed enantioselective coupling of imines and dienol ethers

The reductive coupling of dienol ethers with N-tosylimines catalyzed by Ni(0) in the presence of a VAPOL-derived phosphoramidite ligand follows an unprecedented regiochemical course; it furnishes syn-configured 1,2-aminoalcohol derivatives in good chemical yields with up to 94% ee.

Diastereodivergent and Enantioselective Synthesis of Homoallylic Alcohols via Nickel-Catalyzed Borylative Coupling of 1,3-Dienes with Aldehydes

We present the first enantioselective nickel-catalyzed borylative coupling of 1,3-dienes with aldehydes, providing an efficient route to highly valuable homoallylic alcohols in a single step. The reaction involves the 1,4-carboboration of dienes, leading to the formation of C-C and C-B bonds accompanied by the construction of two continuous stereogenic centers. Enabled by a chiral spiro phosphine-oxazoline nickel complex, this transformation yields products with exceptional diastereoselectivity, E-selectivity, and enantioselectivity. The diastereoselectivity of the reaction can be controlled by employing either (Z)-1,3-dienes or (E)-1,3-dienes.

Iridium-, Ruthenium-, and Nickel-Catalyzed C-C Couplings of Methanol, Formaldehyde, and Ethanol with π-Unsaturated Pronucleophiles via Hydrogen Transfer

In this Perspective, the use of methanol and ethanol as C1 and C2 feedstocks in metal-catalyzed C-C couplings to π-unsaturated pronucleophiles via hydrogen auto-transfer is surveyed. In these processes, alcohol oxidation to form an aldehyde electrophile is balanced by reduction of an π-unsaturated hydrocarbon to form a transient organometallic nucleophile. Mechanistically related reductive couplings of paraformaldehyde mediated by alcohol reductants or formic acid also are described. These processes encompass the first catalytic enantioselective C-C couplings of methanol and ethanol and, more broadly, illustrate how the native reducing ability of alcohols enable the departure from premetalated reagents in carbonyl addition.

Ni-catalyzed arylation of alkynes with organoboronic acids and aldehydes to access stereodefined allylic alcohols

A new, efficient and practical method for the three-component arylative coupling of aldehydes, alkynes and arylboronic acids has been developed through nickel catalysis. This transformation provides diverse Z-selective tetrasubstituted allylic alcohols without the use of any aggressive oragnometallic nucleophiles or reductants. Moreover, benzylalcohols are viable coupling partners via oxidation state manipulation and arylative coupling in one single catalytic cycle. This reaction features a direct and flexible approach for the preparation of stereodefined arylated allylic alcohols with broad substrate scope under mild conditions. The utility of this protocol is demonstrated through the synthesis of diverse biologically active molecular derivatives.

Redox-Neutral 1,4-Dicarbonfunctionalization of 1,3-Butadiene by Merging Photoredox and Nickel Catalysis

The diverse functionalization of 1,3-butadiene provides wide applicability toward the synthesis of abundant and useful allylic compounds. Here, we describe a three-component and redox-neutral assembly of readily available C═X compounds, 1,3-butadiene, and various nucleophiles by merging photoredox and nickel catalysis, enabling the rapid synthesis of structurally diverse homoallyl amines and homoallylic alcohols.

Nickel-Catalyzed Enantioselective Coupling of Aldehydes and Electron-Deficient 1,3-Dienes Following an Inverse Regiochemical Course

The nickel catalyzed reductive coupling of aldehydes with sorbate esters and related electron-deficient 1,3-dienes are known in the literature to occur at the π-bond proximal to the ester to afford aldol-type products. In stark contrast to this established path, a VAPOL-derived phosphoramidite ligand in combination with a bench-stable nickel precatalyst brokers a regiocomplementary course in that C-C bond formation proceeds exclusively at the distal alkene site to give deoxypropionate type products carrying an acrylate handle; they can be made in either anti- or syn-configured form. In addition to this enabling reverse pathway, the reaction is distinguished by excellent levels of chemo-, diastereo-, and enantioselectivity; moreover, it can be extended to the catalytic formation of F₃C-substituted stereogenic centers. The use of a dienyl pinacolboronate instead of a sorbate ester is also possible, which opens access to valuable chiral borylated building blocks in optically active form.

Nickel-Catalyzed Three-Component Cross-Electrophile Coupling of 1,3-Dienes with Aldehydes and Aryl Bromides

We herein report a Ni-catalyzed three-component cross-electrophile coupling of 1,3-dienes with aldehydes and aryl bromides using manganese metal as the reducing agent. This efficient protocol accomplishes dicarbofunctionalization of 1,3-dienes to synthesize diverse structural 1,4-disubstituted homoallylic alcohols by forming two new C-C bonds in one time. Mechanistic study suggests that an allyl-nickel(I) species is involved in the catalytic cycle.

Synthesis of oxaboranes via nickel-catalyzed dearylative cyclocondensation

We report Ni-catalyzed dearylative cyclocondensation of aldehydes, alkynes, and triphenylborane. The reaction is initiated by oxidative cyclization of the aldehyde and alkyne coupling partners to generate an oxanickelacyclopentene which reacts with triphenylborane to form oxaboranes. This formal dearylative cyclocondensation reaction generates oxaboranes in moderate-to-high yields (47–99%) with high regioselectivities under mild reaction conditions. This approach represents a direct and modular synthesis of oxaboranes which are difficult to access using current methods. These oxaboranes are readily transformed into valuable building blocks for organic synthesis and an additional class of boron heterocycles. Selective homocoupling forms oxaboroles, oxidation generates aldol products, and reduction and arylation form substituted allylic alcohols.

Oxaboranes are prepared via a nickel-catalyzed dearylative cyclocondensation reaction in up to 99% yield and excellent regioselectivity. These oxaborane products can be further transformed into a variety of synthetically useful building blocks.

A palladium catalyzed stereo-convergent aminocarbonylation of 1,3-dienes with nitroarenes: synthesis of (E,E)-dienamides

A palladium catalyzed stereo-convergent aminocarbonylation of 1,3-dienes with nitroarenes has been developed. The reaction of mixtrues of E/Z isomers of 1,3-dienes reacted with nitroarenes and produced (E,E)-dienamides with high stereoselectivities.

Highly efficient synthesis of 3,4-diarylbutadiene sulfones using Heck–Matsuda reaction

For the first time we describe a general method for the synthesis of previously not synthesized unsymmetrical 3,4-diarylbutadiene sulfones which can be stable convenient precursors for 2,3-diaryl-1,3-butadienes. Our method for arylation of butadiene sulfones via Heck–Matsuda reaction allows to obtain unsymmetrical 3,4-diarylbutadiene sulfones with a variety of alkyl, alkoxy, nitro, ethoxycarbonyl, perfluoroalkyl and halogen substituents (30 examples) in very good yields using readily available reagents and catalysts.

An efficient and facile Pd-catalyzed synthesis of 3,4-diarylbutadiene sulfones with high regioselectivity from aryldiazonium salts and butadiene sulfone was developed.

First-Row d-Block Element-Catalyzed Carbon-Boron Bond Formation and Related Processes

Organoboron reagents represent a unique class of compounds because of their utility in modern synthetic organic chemistry, often affording unprecedented reactivity. The transformation of the carbon-boron bond into a carbon-X (X = C, N, and O) bond in a stereocontrolled fashion has become invaluable in medicinal chemistry, agrochemistry, and natural products chemistry as well as materials science. Over the past decade, first-row d-block transition metals have become increasingly widely used as catalysts for the formation of a carbon-boron bond, a transformation traditionally catalyzed by expensive precious metals. This recent focus on alternative transition metals has enabled growth in fundamental methods in organoboron chemistry. This review surveys the current state-of-the-art in the use of first-row d-block element-based catalysts for the formation of carbon-boron bonds.

Catalyst Design Principles Enabling Intermolecular Alkene-Diene [2+2] Cycloaddition and Depolymerization Reactions

Aryl-substituted pyridine(diimine) iron complexes promote the catalytic [2 + 2] cycloadditions of alkenes and dienes to form vinylcyclobutanes as well as the oligomerization of butadiene to generate divinyl(oligocyclobutane), a microstructure of poly(butadiene) that is chemically recyclable. A systematic study on a series of iron butadiene complexes as well as their ruthenium congeners has provided insights into the essential features of the catalyst that promotes these cycloaddition reactions. Structural and computational studies on iron butadiene complexes identified that the structural rigidity of the tridentate pincer enables rare s-trans diene coordination. This geometry, in turn, promotes dissociation of one of the alkene arms of the diene, opening a coordination site for the incoming substrate to engage in oxidative cyclization. Studies on ruthenium congeners established that this step occurs without redox involvement of the pyridine(diimine) chelate. Cyclobutane formation occurs from a metallacyclic intermediate by reversible C(sp³)-C(sp³) reductive coupling. A series of labeling experiments with pyridine(diimine) iron and ruthenium complexes support the favorability of accessing the +3 oxidation state to trigger C(sp³)-C(sp³) reductive elimination, involving spin crossover from S = 0 to S = 1. The high density of states of iron and the redox-active pyridine(diimine) ligand facilitate this reactivity under thermal conditions. For the ruthenium congener, the pyridine(diimine) remains redox innocent and irradiation with blue light was required to promote the analogous reactivity. These structure-activity relationships highlight important design principles for the development of next generation catalysts for these cycloaddition reactions as well as the promotion of chemical recycling of cycloaddition polymers.

Nickel-Catalyzed Enantioselective Synthesis of Pre-Differentiated Homoallylic syn- or anti-1,2-Diols from Aldehydes and Dienol Ethers

Nickel catalysis allied with cyclodiphosphazane or VAPOL-derived phosphoramidite ligands provides selective access to monoprotected vicinal diols by reductive coupling of dienol ethers and aldehydes. The observed regioselectivity is unprecedented, in that the diene reacts at the least nucleophilic and most hindered C atom that is attached to the oxygen substituent rather than at the terminal position. Notably, both syn and anti diastereomers of the products can be accessed depending on the configuration of the diene partner with usually excellent diastereo- and enantioselectivity.

Copper(I)-Catalyzed Regioselective Asymmetric Addition of 1,4-Pentadiene to Ketones

By using commercially available 1,4-pentadiene as a pronucleophile, a copper(I)-catalyzed regioselective asymmetric allylation of ketones is achieved. A variety of chiral tertiary alcohols bearing a terminal (Z)-1,3-diene unit are generated in high (Z)/(E) ratio and high enantioselectivity. Both aromatic ketones and aliphatic ketones serve as suitable substrates. Furthermore, the reactions with (E)-C¹(alkyl)-1,4-dienes proceed in moderate yields with acceptable enantioselectivity but with low (Z,E)/others ratio, which demonstrates the partial isomerization of (E)-allylcopper(I) species to (Z)-allylcopper(I) species through 1,3-migration. Subsequent Heck reaction and olefin metathesis compensate for the low efficiency with C¹-1,4-dienes. The synthetic utility of the product is further demonstrated by a copper(I)-catalyzed regioselective borylation of the 1,3-diene group.

A Palladium Complex as an Asymmetric π-Lewis Base Catalyst for Activating 1,3-Dienes

Here we report that palladium(0) complexes can coordinate in a η² fashion to 1,3-dienes and significantly raise the energy of their highest occupied molecular orbital (HOMO) by donating the electrons from the d-orbitals to the empty antibonding molecular orbitals of double bonds (π*) via back-bonding. Thus, the uncoordinated double bond, as a more reactive partner on the basis of the principle of vinylogy, can directly attack imines, furnishing a formal hydrodienylation reaction enantioselectively. A chemoselective cascade vinylogous addition/allylic alkylation difunctionalization process between 1,3-dienes and imines with a nucleophilic group is also compatible, by trapping in situ formed π-allylpalladium species after initial ene addition. This π-Lewis base catalytic mode, featuring simple η²coordination, vinylogous activation, and compatibility with both conjugated neutral polyenes and electron-deficient polyenes, is elucidated by control experiments and density functional theory (DFT) calculations.

Regio- and Trans-Selective Ni-Catalyzed Coupling of Butadiene, Carbonyls, and Arylboronic Acids to Homoallylic Alcohols under Base-Free Conditions

We herein report a Ni-catalyzed three-component coupling of 1,3-butadiene, carbonyl compounds, and arylboronic acids as a general synthetic approach to 1,4-disubstituted homoallylic alcohols, an important class of compounds, which have previously not been straightforward to access. The reaction occurs efficiently using a Ni(cod)₂ catalyst without any external base and ligand at ambient temperature and allows a highly regioselective and trans-selective 1,4-dicarbofunctionalization of feedstock butadiene in a single operation. This simple and practical protocol could apply to a comprehensive scope of substrates. The neutral conditions show extraordinary tolerance for even highly base-sensitive functional groups.

Three-Component, Interrupted Radical Heck/Allylic Substitution Cascade Involving Unactivated Alkyl Bromides

Developing efficient and selective strategies to approach complex architectures containing (multi)stereogenic centers has been a long-standing synthetic challenge in both academia and industry. Catalytic cascade reactions represent a powerful means of rapidly leveraging molecular complexity from simple feedstocks. Unfortunately, carrying out cascade Heck-type reactions involving unactivated (tertiary) alkyl halides remains an unmet challenge owing to unavoidable β-hydride elimination. Herein, we show that a modular, practical, and general palladium-catalyzed, radical three-component coupling can indeed overcome the aforementioned limitations through an interrupted Heck/allylic substitution sequence mediated by visible light. Selective 1,4-difunctionalization of unactivated 1,3-dienes, such as butadiene, has been achieved by employing different commercially available nitrogen-, oxygen-, sulfur-, or carbon-based nucleophiles and unactivated alkyl bromides (>130 examples, mostly >95:5 E/Z, >20:1 rr). Sequential C(sp³)-C(sp³) and C-X (N, O, S) bonds have been constructed efficiently with a broad scope and high functional group tolerance. The flexibility and versatility of the strategy have been illustrated in a gram-scale reaction and streamlined syntheses of complex ether, sulfone, and tertiary amine products, some of which would be difficult to access via currently established methods.

Regioselective Cross-Electrophile Coupling of Epoxides and (Hetero)aryl Iodides via Ni/Ti/Photoredox Catalysis

A cross-electrophile coupling reaction of epoxides and (hetero)aryl iodides that operates via the merger of three catalytic cycles involving a Ni-, Ti-, and organic photoredox catalyst has been developed. Three distinct classes of epoxides, styrene oxides, cyclic epoxides, and terminal aliphatic epoxides, all undergo coupling in moderate to good yield and high regioselectivity with the use of three different nitrogen-based ligands for Ni under otherwise identical reaction conditions. The mild reaction conditions accommodate a broad scope of abundant and complex coupling partners. Mechanistic studies suggest that when styrene oxides are employed radical intermediates are involved via Ti-radical ring-opening of the epoxide. Conversely, for terminal aliphatic epoxides, involvement of an iodohydrin intermediate enables the formation of the unexpected linear product.

Direct use of 1,3-dienes for the allylation of ketones via catalytic hydroindation

In this study, in situ catalytically generated allylic indium from 1,3 dienes and InCl₂H was developed for use in the allylation of ketones.

Engaging Aldehydes in CuH-Catalyzed Reductive Coupling Reactions: Stereoselective Allylation with Unactivated 1,3-Diene Pronucleophiles

Recently, CuH-catalyzed reductive coupling processes involving carbonyl compounds and imines have become attractive alternatives to traditional methods for stereoselective addition because of their ability to use readily accessible and stable olefins as surrogates for organometallic nucleophiles. However, the inability to use aldehydes, which usually reduce too rapidly in the presence of copper hydride complexes to be viable substrates, has been a major limitation. Shown here is that by exploiting relative concentration effects through kinetic control, this intrinsic reactivity can be inverted and the reductive coupling of 1,3-dienes with aldehydes achieved. Using this method, both aromatic and aliphatic aldehydes can be transformed into synthetically valuable homoallylic alcohols with high levels of diastereo- and enantioselectivities, and in the presence of many useful functional groups. Furthermore, using a combination of theoretical (DFT) and experimental methods, important mechanistic features of this reaction related to stereo- and chemoselectivities were uncovered.

α-Silicon effect assisted Curtin-Hammett allylation using allylcopper reagents derived from 1,3-dienylsilanes

Cu-catalyzed stereoselective synthesis of (E)-δ-silyl-anti-homoallylic alcohols from 1,3-dienylsilane was developed. Mechanistic studies revealed that the borocupration of dienylsilane proceeded through a 1,2-addition pathway to give an allylcopper intermediate with Cu distal to the silyl group. However, the subsequent aldehyde allylation proceeded via Curtin-Hammett control to give (E)-δ-silyl-anti-homoallylic alcohols with high diastereoselectivities. This method was applied to the synthesis of the C1-9 fragment of a polyketide natural product, mycinolide IV.

CuH-Catalyzed Enantioselective Ketone Allylation with 1,3-Dienes: Scope, Mechanism, and Applications

Chiral tertiary alcohols are important building blocks for the synthesis of pharmaceutical agents and biologically active natural products. The addition of carbon nucleophiles to ketones is the most common approach to tertiary alcohol synthesis but traditionally relies on stoichiometric organometallic reagents that are difficult to prepare, sensitive, and uneconomical. We describe a mild and efficient method for the copper-catalyzed allylation of ketones using widely available 1,3-dienes as allylmetal surrogates. Homoallylic alcohols bearing a wide range of functional groups are obtained in high yield and with good regio-, diastereo-, and enantioselectivity. Mechanistic investigations using density functional theory (DFT) implicate the in situ formation of a rapidly equilibrating mixture of isomeric copper(I) allyl complexes, from which Curtin-Hammett kinetics determine the major isomer of the product. A stereochemical model is provided to explain the high diastereo- and enantioselectivity of this process. Finally, this method was applied to the preparation of an important drug, ( R)-procyclidine, and a key intermediate in the synthesis of several pharmaceuticals.

Catalytic carboboration of dienylboronate for stereoselective synthesis of (E)-γ′,δ-bisboryl-anti-homoallylic alcohols

A Cu-catalyzed stereoselective carboboration of dienylboronate for the synthesis of (E)-γ′,δ-bisboryl-anti-homoallylic alcohols was developed.

Intermolecular Metal-Catalyzed Reductive Coupling of Dienes, Allenes, and Enynes with Carbonyl Compounds and Imines

Metal-catalyzed reductive coupling has emerged as an alternative to the use of stoichiometric organometallic reagents in an increasingly diverse range of carbonyl and imine additions. In this review, the use of diene, allene, and enyne pronucleophiles in intermolecular carbonyl and imine reductive couplings are surveyed, along with related hydrogen autotransfer processes.

Recent advances in well-defined, late transition metal complexes that make and/or break C-N, C-O and C-S bonds

Chemical transformations that result in either the formation or cleavage of carbon-heteroatom bonds are among the most important processes in the chemical sciences. Herein, we present a review on the reactivity of well-defined, late-transition metal complexes that result in the making and breaking of C-N, C-O and C-S bonds via fundamental organometallic reactions, i.e. oxidative addition, reductive elimination, insertion and elimination reactions. When appropriate, emphasis is placed on structural and spectroscopic characterization techniques, as well as mechanistic data.

Nickel-catalyzed coupling reaction of alkyl halides with aryl Grignard reagents in the presence of 1,3-butadiene: mechanistic studies of four-component coupling and competing cross-coupling reactions

We describe the mechanism, substituent effects, and origins of the selectivity of the nickel-catalyzed four-component coupling reactions of alkyl fluorides, aryl Grignard reagents, and two molecules of 1,3-butadiene that affords a 1,6-octadiene carbon framework bearing alkyl and aryl groups at the 3- and 8-positions, respectively, and the competing cross-coupling reaction. Both the four-component coupling reaction and the cross-coupling reaction are triggered by the formation of anionic nickel complexes, which are generated by the oxidative dimerization of two molecules of 1,3-butadiene on Ni(0) and the subsequent complexation with the aryl Grignard reagents. The C-C bond formation of the alkyl fluorides with the γ-carbon of the anionic nickel complexes leads to the four-component coupling product, whereas the cross-coupling product is yielded via nucleophilic attack of the Ni center toward the alkyl fluorides. These steps are found to be the rate-determining and selectivity-determining steps of the whole catalytic cycle, in which the C-F bond of the alkyl fluorides is activated by the Mg cation rather than a Li or Zn cation. ortho-Substituents of the aryl Grignard reagents suppressed the cross-coupling reaction leading to the selective formation of the four-component products. Such steric effects of the ortho-substituents were clearly demonstrated by crystal structure characterizations of ate complexes and DFT calculations. The electronic effects of the para-substituent of the aryl Grignard reagents on both the selectivity and reaction rates are thoroughly discussed. The present mechanistic study offers new insight into anionic complexes, which are proposed as the key intermediates in catalytic transformations even though detailed mechanisms are not established in many cases, and demonstrates their synthetic utility as promising intermediates for C-C bond forming reactions, providing useful information for developing efficient and straightforward multicomponent reactions.

Transition metal catalysis—a unique road map in the stereoselective synthesis of 1,3-polyols

The present review summarizes recent diverse reactions employed in the formation of 1,3-polyols providing an overview of the mechanistic pathway and the enantioselectivity obtained, in terms of the properties of transition metals directly involved in the catalytic transformations and their interaction with various ligands.

Nickel-Catalyzed Chemo-, Regio- and Diastereoselective Bond Formation through Proximal C-C Cleavage of Benzocyclobutenones

The first catalytic intermolecular proximal C1-C2 cleavage of benzocyclobutenones (BCB) without prior carbonyl activation or employing noble metals has been developed. This protocol operates at room temperature and is characterized by an exquisite chemo-, regio- and diastereoselectivity profile, constituting a unique platform for preparing an array of elusive carbocyclic skeletons.

Regiocontrol in catalytic reductive couplings through alterations of silane rate dependence

Combinations of ligand, reducing agent, and reaction conditions have been identified that allow alteration in the rate- and regioselectivity-determining step of nickel-catalyzed aldehyde–alkyne reductive couplings. Whereas previously developed protocols involve metallacycle-forming oxidative cyclization as the rate-determining step, this study illustrates that the combination of large ligands, large silanes, and elevated reaction temperature alters the rate- and regiochemistry-determining step for one of the two possible product regioisomers. These modifications render metallacycle formation reversible for the minor isomer pathway, and σ-bond metathesis of the metallacycle Ni–O bond with the silane reductant becomes rate limiting. The ability to tune regiocontrol via this alteration in reversibility of a key step allows highly regioselective outcomes that were not possible using previously developed methods.

Aza-nickelacycle key intermediate in nickel(0)-catalyzed transformation reactions

Oxidative cyclization of alkynes and imines with nickel(0) is a key step in multicomponent coupling and cycloaddition reactions to give nitrogen-containing organic compounds.