Cross-coupling reaction of oxo-pi-allylnickel complex generated from 1,3-diene under an atmosphere of carbon dioxide

Et2 Zn-Mediated Gem-Dicarboxylation of Cyclopropanols with CO2

An unprecedented Et2 Zn-mediated gem-dicarboxylation of C─C/C─H single bond of cyclopropanols with CO2 is disclosed, which provides a straightforward and efficient methodology for the synthesis of a variety of structurally diverse and useful malonic acids in moderate to excellent yields. The protocol features mild reaction conditions, excellent functional group compatibility, broad substrate scope, and facile derivatization of the products. DFT calculations confirm that the transition-metal-free transformation proceeds through a novel ring-opening/α-functionalization/ring-closing/ring-opening/β-functionalization (ROFCOF) process, and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) plays dual important roles in the transformation.

Tungsten-anisole complex provides 3,6-substituted cyclohexenes for highly diversified chemical libraries

Medicinal chemists use vast combinatorial molecular libraries to develop leads for new pharmaceuticals. The syntheses of these compounds typically rely on coupling molecular fragments through atoms with planar (sp2) geometry. These so-called flat molecules often lack the protein binding site specificity needed to be an effective drug. Here, we demonstrate a coupling strategy in which a cyclohexene is used as a linker to connect two diverse molecular fragments while forming two new tetrahedral (sp3) stereocenters. These connections are made with the aid of a tungsten complex that activates anisole toward an unusual double protonation, followed by sequential nucleophilic additions. As a result, either cis- or trans-disubstituted cyclohexenes can be prepared with a range of chemical diversity unparalleled by other dearomatization methods.

Cu-Catalyzed Asymmetric Dicarboxylation of 1,3-Dienes with CO2

Dicarboxylic acids and derivatives are important building blocks in organic synthesis, biochemistry, and the polymer industry. Although catalytic dicarboxylation with CO2 represents a straightforward and sustainable route to dicarboxylic acids, it is still highly challenging and limited to generation of achiral or racemic dicarboxylic acids. To date, catalytic asymmetric dicarboxylation with CO2 to give chiral dicarboxylic acids has not been reported. Herein, we report the first asymmetric dicarboxylation of 1,3-dienes with CO2 via Cu catalysis. This strategy provides an efficient and environmentally benign route to chiral dicarboxylic acids with high regio-, chemo-, and enantioselectivities. The copper self-relay catalysis, that is, Cu-catalyzed boracarboxylation of 1,3-dienes to give carboxylated allyl boronic ester intermediates and subsequent carboxylation of C-B bonds to give dicarboxylates, is key to the success of this dicarboxylation. Moreover, this protocol exhibits broad substrate scope, good functional group tolerance, easy product derivatizations, and facile synthesis of chiral liquid crystalline polyester and drug-like scaffolds.

Electrochemical Ring-Opening Dicarboxylation of Strained Carbon-Carbon Single Bonds with CO2: Facile Synthesis of Diacids and Derivatization into Polyesters

Diacids are important monomers in the polymer industry to construct valuable materials. Dicarboxylation of unsaturated bonds, such as alkenes and alkynes, with CO₂ has been demonstrated as a promising synthetic method. However, dicarboxylation of C─C single bonds with CO₂ has rarely been investigated. Herein we report a novel electrochemical ring-opening dicarboxylation of C─C single bonds in strained rings with CO₂. Structurally diverse glutaric acid and adipic acid derivatives were synthesized from substituted cyclopropanes and cyclobutanes in moderate to high yields. In contrast to oxidative ring openings, this is also the first realization of an electroreductive ring-opening reaction of strained rings, including commercialized ones. Control experiments suggested that radical anions and carbanions might be the key intermediates in this reaction. Moreover, this process features high step and atom economy, mild reaction conditions (1 atm, room temperature), good chemoselectivity and functional group tolerance, low electrolyte concentration, and easy derivatization of the products. Furthermore, we conducted polymerization of the corresponding diesters with diols to obtain a potential UV-shielding material with a self-healing function and a fluorine-containing polyester, whose performance tests showed promising applications.

Nickel-Catalyzed Reductive Carboxylation and Amidation Reactions

The ubiquity and importance of carboxylic acids and amides in peptides, pharmaceuticals, agrochemicals, and synthetic materials has challenged chemists to design de novo catalytic carboxylation and amidation protocols. They represent a powerful alternative to canonical oxidation of alcohols and aldehydes, hydrolysis of nitriles, transamidation reactions, or condensation techniques for the synthesis of these functional groups. Among various scenarios, the recent years have witnessed considerable advances in Ni-catalyzed reductive carboxylation and amidation reactions utilizing carbon dioxide and isocyanate counterparts. This Account aims to highlight the progress made in this arena with a historical perspective, with particular emphasis on the methodologies that have emanated from our laboratories without losing sight of the underlying principles by which these reactions operate, with the ultimate goal of allowing the transition from comprehension to prediction in this exciting field.Unlike the utilization of conventional polar yet highly reactive organometallic reagents in carboxylation or amidation reactions, the utilization of nickel catalysts has allowed the use of carbon dioxide and isocyanates with less reactive and less-polarized counterparts for the formations of carboxylic acids and amides. These less reactive groups include organic halides and pseudohalides (i.e., alkyl bromides and chlorides, esters, alcohols, and ammonium salts), unsaturated hydrocarbons (i.e., alkynes, styrenes, unactivated alkenes, and dienes) or even C-H bonds, where forging the targeted C-C bond at previously unfunctionalized C-H linkages was possible, thus giving access to densely functionalized compounds that would be difficult to access otherwise. The C-H functionalization includes chain-walking scenarios, where subtle changes in the ligand and reaction conditions marked the selectivity of the transformations, and reactions via a [1,4]-Ni shift, where selective carboxylation in aromatic rings could be achieved. Conceptuality and practicality aside, these transformations have even offered the possibility of modulating and dictating the site-selectivity pattern, thus providing not only new vistas when controlling the selectivity of bond-forming reactions at specific sites within the side chain but also new knowledge in retrosynthetic analysis when accessing carboxylic acids and amide backbones. Importantly, these techniques have shown to be particularly suited for the preparation of isotopically labeled molecules when using ¹³CO₂ or even ¹⁴CO₂, thus becoming a useful endeavor in the drug discovery pipeline. Although mechanistic understanding at the molecular level still constitutes the "Achilles heel" of these transformations, the recent empirical discoveries and the rapid adoption of these protocols by the community augurs well for the widespread utilization of reductive carboxylation and amidation reactions in both academic and industrial laboratories.

Palladium-Catalyzed Three-Component Silylalkoxylation of 1,3-Diene with Alcohol and Disilane via Oxidative Coupling

A regioselective and Z-selective three-component silylalkoxylation of 1,3-diene using various alcohols, disilane, and a catalytic Pd/Cu/1,4-benzoquinone/O₂ system is established in this Letter. The reaction generates tetra-substituted allyl silanes containing allyl ether moieties in up to 80% isolated yield and on a 1-10 mmol scale via oxidative coupling. A wide variety of substrates, including benzyl alcohol derivates, aliphatic alcohols, and bioactive compounds such as cholesterol, are suitable for use in the developed reaction system.

Nickel-Catalyzed Carboxylation of Conjugated Dienes with Carbon Dioxide and DIBAL-H for the Synthesis of β,γ-Unsaturated Carboxylic Acids

Conjugated dienes underwent Ni-catalyst-promoted 1,2-hydrocarboxylation in a 1:1 ratio with carbon dioxide under atmospheric pressure in the presence of diisobutylaluminum hydride (DIBAL-H) to give the corresponding β,γ-unsaturated carboxylic acids, without dimerization or oligomerization of the conjugated diene.

Selective α,δ-hydrocarboxylation of conjugated dienes utilizing CO2 and electrosynthesis

To date the majority of diene carboxylation processes afford the α,δ-dicarboxylated product, the selective mono-carboxylation of dienes is a significant challenge and the major product reported under transition metal catalysis arises from carboxylation at the α-carbon. Herein we report a new electrosynthetic approach, that does not rely on a sacrificial electrode, the reported method allows unprecedented direct access to carboxylic acids derived from dienes at the δ-position. In addition, the α,δ-dicarboxylic acid or the α,δ-reduced alkene can be easily accessed by simple modification of the reaction conditions.

Indium controlled regioselective 1,4-alkylarylation of 1,3-dienes with α-carbonyl alkyl bromides and N-heterocycles

A selective indium-promoted silver-mediated intermolecular oxidative 1,4-alkylarylation of 1,3-dienes with α-carbonyl alkyl bromides and N-heterocycles was reported.

Toward ideal carbon dioxide functionalization

This Perspective recapitulates recent developments of carbon dioxide utilization in carbon-carbon bond formation reactions, with an intention of paving a way toward sustainable CO2-functionalization and its tangible applications in synthetic chemistry. CO2 functionalization reactions possess intrinsic drawbacks: the high kinetic inertness and thermodynamic stability of CO2. Numerous procedures for CO2 utilization depend on energy-intensive processes (i.e. high pressure and/or temperature), often solely relying on reactive substrates, hampering its general applications. Recent efforts thus have been dedicated to catalytic CO2-utilization under ambient reaction conditions, however, it is still limited to a few activation modes and the use of reactive substrates. Herein, ideal CO2-functionalization with particular emphasis on sustainability will be discussed based on the following sub-categories; (1) metal-catalyzed 'reductive' carboxylation reaction of halides, olefins and allyl alcohols, (2) photochemical CO2-utilization, (3) redox-neutral CO2-functionalization, and (4) enantioselective catalysis incorporating CO2 to form C-CO2 bonds (excluding strain mediated reactions with epoxide- and aziridine-based substrates). Recent progress in these fields will be discussed with the proposed reaction mechanisms and selected examples, highlighting redox-neutral, umpolung, and asymmetric carboxylation to postulate ideal CO2 functionalization reactions to be developed in the near future.

Enantioselective synthesis of β-amino acid derivatives via nickel-promoted regioselective carboxylation of ynamides and rhodium-catalyzed asymmetric hydrogenation

We succeeded in the development of a new method for enantioselective synthesis of α-substituted-β-amino acid derivatives. Thus, nickel(0)-promoted carboxylation of ynamide gave the α-substituted-β-aminoacrylate derivative in a highly regioselective manner. Then, rhodium-catalyzed asymmetric hydrogenation of the α-substituted β-aminoacrylate produced the corresponding α-substituted β-amino acid derivative as an optically active form.

Synthesis of Carboxylic Acids and Esters from CO2

The achievements in the synthesis of carboxylic acids and esters from CO₂ have been summarized and discussed.

Double carboxylation of o-alkynyl acetophenone with carbon dioxide

A copper-catalyzed double carboxylation of o-alkynyl acetophenone using carbon dioxide via a carboxylation/intramolecular cyclization/second carboxylation sequence to afford 1(3H)-isobenzofuranylidene dicarboxylic esters in good yields is developed.

Investigations on the catalytic carboxylation of olefins with CO2 towards α,β-unsaturated carboxylic acid salts: characterization of intermediates and ligands as well as substrate effects

The carboxylation of olefins beyond ethylene towards α,β-unsaturated carboxylic acid salts and a detailed investigation on the critical steps in the catalysis are reported. The influence of two chelating phosphine ligands and several olefins on the elemental steps of the catalysis is shown. The work focusses on the formation of intermediate olefin complexes, lactone formation and base induced elimination of the lactone. The direct carboxylation of olefins is possible using nickel catalysts, which opens a new route towards the desired α,β-unsaturated carboxylic acid salts. The reaction works particularly well for 1,3-dienes and proceeds via the formation of allyl-carboxylates. The ability to form such allyl-type lactone complexes seems in this case to be the most challenging step towards satisfactory turnover numbers.

A computational study on the insertion of CO2 into (PSiP)palladium allyl σ-bond

The insertion of CO2 into the (PSiP)palladium-allyl bond has been investigated using DFT. Three possible modes of CO2 insertion into (PSiP)Pd-allyl bond have been calculated, that is, direct 1.2-insertion mode, metallo-ene mode, and SE2 mode. The metallo-ene mode is the most favorable via the six-membered ring transition state. The results of calculations are consistent with the regioselectivity observed experimentally. The steric and electronic effects of different phosphine substituents have been evaluated by ONIOM and energy decomposition analysis (EDA) methods. For the phosphine substituents P(i-Pr)2 and PPh2, the contribution of electronic effect is greater than that of steric effect for the CO2 insertion into (PSiP)Pd-allyl bond; while for the phosphine substituent PMe2, the contribution of steric effect is slightly greater than that of electronic effect.

Nickel-promoted highly regioselective carboxylation of aryl ynol ether and its application to the synthesis of chiral β-aryloxypropionic acid derivatives

Nickel(0)-promoted carboxylation of aryl ynol ether proceeded in a highly regioselective manner to produce α-substituted-β-aryloxyacrylic acid derivatives. The α-substituted-β-aryloxyacrylic acids were transformed into the corresponding β-aryloxypropionic acid derivative as an optically active form via rhodium-catalyzed asymmetric hydrogenation.

Bond and small-molecule activation with low-valent nickel complexes

The use of nickel compounds in low oxidation states allowed a variety of useful transformations of interest for academia, industry and in the solution of environmental issues.

Carboxylic acid derivatives via catalytic carboxylation of unsaturated hydrocarbons: whether the nature of a reductant may determine the mechanism of CO2incorporation?

Advances and recent breakthroughs in catalytic synthesis of carboxylic acids and their derivatives starting from unsaturated hydrocarbons are discussed.

Nickel-catalyzed double carboxylation of alkynes employing carbon dioxide

The nickel-catalyzed double carboxylation of internal alkynes employing carbon dioxide (CO2) has been developed. The reactions proceed under CO2 (1 atm) at room temperature in the presence of a nickel catalyst, Zn powder as a reducing reagent, and MgBr2 as an indispensable additive. Various internal alkynes could be converted to the corresponding maleic anhydrides in good to high yields. DFT calculations disclosed the indispensable role of MgBr2 in the second CO2 insertion.

Palladium-catalyzed cross-coupling reaction of diazo compounds and vinyl boronic acids: an approach to 1,3-diene compounds

A palladium-catalyzed oxidative cross-coupling of vinyl boronic acids and cyclic α-diazocarbonyl compounds has been reported. The reaction constitutes an efficient method for the synthesis of 1,3-diene compounds bearing a ring structure. Mechanistically, the reaction involves migratory insertion of palladium carbene as the key step.