Highly Regio- and Stereoselective Three-Component Nickel-Catalyzed syn-Hydrocarboxylation of Alkynes with Diethyl Zinc and Carbon Dioxide

Enantioselective Synthesis of Chiral Carboxylic Acids from Alkynes and Formic Acid by Nickel-Catalyzed Cascade Reactions: Facile Synthesis of Profens

We report a stereoselective conversion of terminal alkynes to α-chiral carboxylic acids using a nickel-catalyzed domino hydrocarboxylation-transfer hydrogenation reaction. A simple nickel/BenzP* catalyst displayed high activity in both steps of regioselective hydrocarboxylation of alkynes and subsequent asymmetric transfer hydrogenation. The reaction was successfully applied in enantioselective preparation of three nonsteroidal anti-inflammatory profens (>90 % ees) and the chiral fragment of AZD2716.

Rhodium-Catalyzed meta-Selective C-H Carboxylation Reaction of 1,1-Diarylethylenes via Hydrorhodation-Rhodium Migration

A meta-selective C-H carboxylation reaction of 1,1-diarylethylene derivatives with CO₂ by using a rhodium catalyst with NaOⁱ Pr as a stoichiometric reductant has been achieved. Together with hydrogenation of the ethylene moiety, a carboxyl group was introduced to the meta-position of the aryl ring with high selectivity over the ortho-positions. Experimental and computational mechanistic studies indicate that this carboxylation reaction proceeds via hydrorhodation on the ethylene moiety, followed by 1,4-rhodium migration and successive 1,2-rhodium migration on the aryl ring. The use of a bulky phosphine ligand seems to be the key to this unusual aryl-to-aryl 1,2-rhodium shift.

Light-Promoted Organic Transformations Utilizing Carbon-Based Gas Molecules as Feedstocks

Carbon-based gas molecules are readily available feedstocks and are widely used in industry as building blocks or fuels. However, their application in the synthesis of fine chemicals has been hampered due to operational complexity, poor reaction efficiency and selectivity. Recent development of photoredox-promoted transformations using such gaseous reagents has received considerable attention from the synthetic community. In this review, efforts in developing light-promoted organic transformations using carbon-based natural gases as C1 or C2 feedstocks and to overcome the associated challenges are briefly summarized.

Light-Mediated Carboxylation Using Carbon Dioxide

Carbon dioxide is a green and sustainable one-carbon source, which could be utilized in the production of various fine chemicals. In recent studies, the light-mediated carboxylation employing CO₂ has received considerable attention. The photocarboxylation of substrates with CO₂ to build novel C-C bonds is introduced in this Minireview. The article is arranged based on the light-driven reactive intermediates, including CO₂ radical anion, substrate radical anions, carbanions, and M-C species. Most of the cases are under the topic of photoredox catalysis, with single electron transfer as the main driving force. Some non-catalytic examples are also discussed to provide more mechanistic insights.

Exploration of New Biomass-Derived Solvents: Application to Carboxylation Reactions

A range of hitherto unexplored biomass-derived chemicals have been evaluated as new sustainable solvents for a large variety of CO2 -based carboxylation reactions. Known biomass-derived solvents (biosolvents) are also included in the study and the results are compared with commonly used solvents for the reactions. Biosolvents can be efficiently applied in a variety of carboxylation reactions, such as Cu-catalyzed carboxylation of organoboranes and organoboronates, metal-catalyzed hydrocarboxylation, borocarboxylation, and other related reactions. For many of these reactions, the use of biosolvents provides comparable or better yields than the commonly used solvents. The best biosolvents identified are the so far unexplored candidates isosorbide dimethyl ether, acetaldehyde diethyl acetal, rose oxide, and eucalyptol, alongside the known biosolvent 2-methyltetrahydrofuran. This strategy was used for the synthesis of the commercial drugs Fenoprofen and Flurbiprofen.

Carboxylation Reactions with Carbon Dioxide Using N-Heterocyclic Carbene-Copper Catalysts

The development of versatile catalyst systems and new transformations for the utilization of carbon dioxide (CO₂ ) is of great interest and significance. This Personal Account reviews our studies on the exploration of the reactions of CO₂ with various substrates by the use of N-heterocyclic carbene (NHC)-copper catalysts. The carboxylation of organoboron compounds gave access to a wide range of carboxylic acids with excellent functional group tolerance. The C-H bond carboxylation with CO₂ emerged as a straightforward protocol for the preparation of a series of aromatic carboxylic esters and butenoates from simple substrates. The hydrosilylation of CO₂ with hydrosilanes provided an efficient method for the synthesis of silyl formate on gram scale. The hydrogenative or alkylative carboxylation of alkynes, ynamides and allenamides yielded useful α,β-unsaturated carboxylic acids and α,β-dehydro amino acid esters. The boracarboxylation of alkynes or aldehydes afforded the novel lithium cyclic boralactone or boracarbonate products, respectively. The NHC-copper catalysts generally featured excellent functional group compatibility, broad substrate scope, high efficiency, and high regio- and stereoselectivity. The unique electronic and steric properties of the NHC-copper units also enabled the isolation and structural characterization of some key intermediates for better understanding of the catalytic reaction mechanisms.

Construction of a visible light-driven hydrocarboxylation cycle of alkenes by the combined use of Rh(i) and photoredox catalysts

A visible light driven catalytic cycle for hydrocarboxylation of alkenes with CO₂ was established using a combination of a Rh(i) complex as a carboxylation catalyst and [Ru(bpy)₃]²⁺ (bpy = 2,2'- bipyridyl) as a photoredox catalyst. Two key steps, the generation of Rh(i) hydride species and nucleophilic addition of π-benzyl Rh(i) species to CO₂, were found to be mediated by light.

NHC-Ag/Pd-Catalyzed Reductive Carboxylation of Terminal Alkynes with CO2 and H2 : A Combined Experimental and Computational Study for Fine-Tuned Selectivity

Reductive carboxylation of terminal alkynes utilizing CO₂ and H₂ as reactants is an interesting and challenging transformation. Theoretical calculations indicated it would be kinetically possible to obtain cinnamic acid, the reductive carboxylation product, from phenylacetylene in a CO₂ /H₂ system with an N-heterocyclic carbene (NHC)-supported Ag/Pd bimetallic catalysts through competitive carboxylation/hydrogenation cascade reactions in one step. These calculations were verified experimentally with a poly-NHC-supported Ag/Pd catalyst. By tuning the catalyst composition and reaction temperature, phenylacetylene was selectively converted to cinnamic acid, hydrocinnamic acid, or phenylpropiolic acid in excellent yields.

Cu-Catalyzed Alkylative Carboxylation of Ynamides with Dialkylzinc Reagents and Carbon Dioxide

Alkylative carboxylation of ynamides with CO2 and dialkylzinc reagents using a N-heterocyclic carbene (NHC)-copper catalyst has been developed. A variety of ynamides, both cyclic and acyclic, undergo this transformation under mild conditions to afford the corresponding α,β-unsaturated carboxylic acids, which contain the α,β-dehydroamino acid skeleton. The present alkylative carboxylation formally consists of Cu-catalyzed carbozincation of ynamides with dialkylzinc reagents with the subsequent nucleophilic carboxylation of the resulting alkenylzinc species with CO2 . Dialkylzinc reagents bearing a β-hydrogen atom such as Et2 Zn and Bu2 Zn still afford the alkylated products despite the potential for β-hydride elimination. This protocol would be a desirable method for the synthesis of highly substituted α,β- dehydroamino acid derivatives due to its high regio- and stereoselectivity, simple one-pot procedure, and its use of CO2 as a starting material.

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.

CO2-activation for γ-butyrolactones and its application in the total synthesis of (±)-heteroplexisolide E

An efficient nickel(0)-catalyzed highly regio- and stereoselective hydrocarboxylation of homopropargylic alcohols with ZnEt(2) in the presence of CO(2) (1 atm, balloon) to synthesize α-alkylidene-γ-butyrolactones is described. The catalyst is highly active and can be applied for the synthesis of (optically active) mono- or bicyclic α-alkylidene-γ-butyrolactones with excellent regio- and stereoselectivity and good functional group tolerance. The potential of the reaction has been demonstrated in the first synthesis of (±)-heteroplexisolide E.