Carboxyzincation Employing Carbon Dioxide and Zinc Powder: Cobalt-Catalyzed Multicomponent Coupling Reactions with Alkynes

Mechanistic Insights into the Ni-Catalyzed Reductive Carboxylation of C-O Bonds in Aromatic Esters with CO2 : Understanding Remarkable Ligand and Traceless-Directing-Group Effects

The mechanism of the Ni⁰ -catalyzed reductive carboxylation reaction of C(sp² )-O and C(sp³ )-O bonds in aromatic esters with CO₂ to access valuable carboxylic acids was comprehensively studied by using DFT calculations. Computational results revealed that this transformation was composed of several key steps: C-O bond cleavage, reductive elimination, and/or CO₂ insertion. Of these steps, C-O bond cleavage was found to be rate-determining, and it occurred through either oxidative addition to form a Ni^II intermediate, or a radical pathway that involved a bimetallic species to generate two Ni^I species through homolytic dissociation of the C-O bond. DFT calculations revealed that the oxidative addition step was preferred in the reductive carboxylation reactions of C(sp² )-O and C(sp³ )-O bonds in substrates with extended π systems. In contrast, oxidative addition was highly disfavored when traceless directing groups were involved in the reductive coupling of substrates without extended π systems. In such cases, the presence of traceless directing groups allowed for docking of a second Ni⁰ catalyst, and the reactions proceed through a bimetallic radical pathway, rather than through concerted oxidative addition, to afford two Ni^I species both kinetically and thermodynamically. These theoretical mechanistic insights into the reductive carboxylation reactions of C-O bonds were also employed to investigate several experimentally observed phenomena, including ligand-dependent reactivity and site-selectivity.

Visible-Light-Driven Alkyne Hydro-/Carbocarboxylation Using CO2 via Iridium/Cobalt Dual Catalysis for Divergent Heterocycle Synthesis

We present herein the first visible-light-driven hydrocarboxylation as well as carbocarboxylation of alkynes using CO₂ via an iridium/cobalt dual catalysis. Such transformations provide access to various pharmaceutically important heterocycles in a one-pot procedure from readily available alkynes. Coumarins, 2-quinolones, and 2-benzoxepinones were directly accessed through a one-pot alkyne hydrocarboxylation/alkene isomerization/cyclization sequence in which the Ir photocatalyst serves a dual role to promote single-electron transfer in alkyne hydrocarboxylation and energy transfer in the subsequent alkene isomerization. Moreover, an unprecedented cobalt carboxylation/acyl migration cascade enables alkyne difunctionalization to introduce γ-hydroxybutenolides with high efficiency. We expect that this cascade strategy will inspire new perspectives for alkyne and alkene difunctionalization.

Regio- and Stereoselective Anti-Carbozincation of Alkynyl Ethers Using ZnBr2 toward (Z)-β-Zincated Enol Ether Synthesis

(Z)-β-Aryloxyalkenylzincs are synthesized stereoselectively via anti-carbozincation among alkynyl ethers, silyl ketene acetals, and ZnBr₂. X-ray analysis revealed the structure of the zinc species is a mononuclear two-coordinate dialkenylzinc that is transformed into functionalized enol ethers as a single isomer in the reaction of various electrophiles.

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.

Synthesis of 2-aryloxy butenoates by copper-catalysed allylic C–H carboxylation of allyl aryl ethers with carbon dioxide

2-Aryloxy butenoates were efficiently synthesized by deprotonative alumination of ally aryl ethers and subsequent Cu-catalysed carboxylation with CO₂.

CO2 as a C1 Source: B(C6F5)3-Catalyzed Cyclization of o-Phenylene-diamines To Construct Benzimidazoles in the Presence of Hydrosilane

The catalytic construction of benzimidazoles using CO₂ as a carbon source represents a facile and sustainable approach to obtaining these valuable compounds. Herein, we describe the B(C₆F₅)₃-catalyzed synthesis of benzimidazoles via cyclization of o-phenylenediamines with CO₂ and PhSiH₃. This metal-free catalytic route achieves the desired products in high yield under convenient reaction conditions and is applicable to a broad substrate scope. A plausible mechanism for the reaction involving a frustrated Lewis pair pathway is proposed based on spectroscopic characterization (e.g., ¹³C NMR) of the reaction intermediates.

Mechanism of the Palladium-Catalyzed Synthesis of Münchnones: The Role of Ligands in N-Acyl Iminium Salt Carbonylation

The palladium-catalyzed carbonylative coupling of imines, acid chlorides, and dipolarophiles can provide efficient routes to prepare nitrogen-containing heterocycles. One challenge in developing this reaction, and in the creation of more active catalyst systems, is the lack of data on how this complex transformation proceeds. To address this, we report here the results of our mechanistic studies on this system, and in particular the formation of mesoionic münchnones. This includes the synthesis of key catalytic intermediates, model reactions, and kinetic studies that support the role of these compounds in catalysis. Together, these studies provide a clear picture of the impact of catalyst structure, ligands, and palladium nanoparticles on facilitating the carbonylation of in situ generated iminium salts, and suggest an avenue for the creation of more active catalyst systems.