Enantioselective Nickel-Electrocatalyzed Reductive Propargylic Carboxylation with CO2.

The exploitation of carbon dioxide (CO2) as a sustainable, plentiful, and harmless C1 source for the catalytic synthesis of enantioenriched carboxylic acids has long been acknowledged as a pivotal task in synthetic chemistry. Herein, we present a current-driven nickel-catalyzed reductive carboxylation reaction with CO2 fixation, facilitating the formation of C(sp3)-C(sp2) bonds by circumventing the handling of moisture-sensitive organometallic reagents. This electroreductive protocol serves as a practical platform, paving the way for the synthesis of enantioenriched propargylic carboxylic acids (up to 98% enantiomeric excess) from racemic propargylic carbonates and CO2. The efficacy of this transformation is exemplified by its successful utilization in the asymmetric total synthesis of (S)-arundic acid, (R)-PIA, (S)-chizhine D, (S)-cochlearin G, and (S,S)-alexidine, thereby underscoring the potential of asymmetric electrosynthesis to achieve complex molecular architectures sustainably.

Electroreductive Dicarboxylation of Unactivated Skipped Dienes with CO2.

Carboxylation of easily available alkenes with CO2 is highly important to afford value-added carboxylic acids. Although dicarboxylation of activated alkenes, especially 1,3-dienes, has been widely investigated, the challenging dicarboxylation of unactivated 1,n-dienes (n>3) with CO2 remains unexplored. Herein, we report the first dicarboxylation of unactivated skipped dienes with CO2 via electrochemistry, affording valuable dicarboxylic acids. Control experiments and DFT calculations support the single electron transfer (SET) reduction of CO2 to its radical anion, which is followed by sluggish radical addition to unactivated alkenes, SET reduction of unstabilized alkyl radicals to carbanions and nucleophilic attack on CO2 to give desired products. This reaction features mild reaction conditions, broad substrate scope, facile derivations of products and promising application in polymer chemistry.

Photocatalytic Carboxylation of C-N Bonds in Cyclic Amines with CO2 by Consecutive Visible-Light-Induced Electron Transfer.

Visible-light photocatalytic carboxylation with CO2 is highly important. However, it still remains challenging for reluctant substrates with low reduction potentials. Herein, we report a novel photocatalytic carboxylation of C-N bonds in cyclic amines with CO2 via consecutive photo-induced electron transfer (ConPET). It is also the first photocatalytic reductive ring-opening reaction of azetidines, pyrrolidines and piperidines. This strategy is practical to transform a variety of easily available cyclic amines to valuable ß-, γ-, δ- and ϵ-amino acids in moderate-to-excellent yields. Moreover, the method also features mild and transition-metal-free conditions, high selectivity, good functional-group tolerance, facile scalability and product derivations. Mechanistic studies indicate that the ConPET might be the key to generating highly reactive photocatalysts, which enable the reductive activation of cyclic amines to generate carbon radicals and carbanions as the key intermediates.

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 Asymmetric Reductive Carbo-Carboxylation of Alkenes with CO2.

Reductive carboxylation of organo (pseudo)halides with CO2 is a powerful method to provide carboxylic acids quickly. Notably, the catalytic reductive carbo-carboxylation of unsaturated hydrocarbons via CO2 fixation is a highly challenging but desirable approach for structurally diverse carboxylic acids. There are only a few reports and no examples of alkenes via transition metal catalysis. We report the first asymmetric reductive carbo-carboxylation of alkenes with CO2 via nickel catalysis. A variety of aryl (pseudo)halides, such as aryl bromides, aryl triflates and inert aryl chlorides of particular note, undergo the reaction smoothly to give important oxindole-3-acetic acid derivatives bearing a C3-quaternary stereocenter. This transformation features mild reaction conditions, wide substrate scope, facile scalability, good to excellent chemo-, regio- and enantioselectivities. The method highlights the formal synthesis of (-)-Esermethole, (-)-Physostigmine and (-)-Physovenine, and the total synthesis of (-)-Debromoflustramide B, (-)-Debromoflustramine B and (+)-Coixspirolactam A; thereby, opening an avenue for the total synthesis of chiral natural products with CO2 .

Visible-Light Photoredox-Catalyzed Ring-Opening Carboxylation of Cyclic Oxime Esters with CO2.

The carboxylation of cyclic oxime esters with carbon dioxide via visible-light photoredox catalysis is demonstrated for the first time. A variety of cyclic oxime esters undergo ring-opening C-C bond cleavage and carboxylation to give cyanoalkyl-containing carboxylic acids in moderate to good yields. Moreover, this methodology features mild reaction conditions (room temperature, 1 atm), wide substrate scope, good functional group tolerance as well as facile derivations of products. Mechanistic studies indicate that the benzylic radicals and anions might be the key intermediates.

Construction of Unsymmetrical Triphenylenes from Electron-Rich Biphenyls and Diaryliodonium Salts via Copper-Catalyzed Multiple C-H Arylation.

An efficient protocol to synthesize unsymmetrical triphenylenes from electron-rich biphenyls and diaryliodonium salts via Cu catalysis was developed. A variety of unsymmetrical triphenylenes with diversified functional groups were synthesized according to this method. This transformation went through multiple direct C-H arylations from easily produced starting materials with high step-economy. The gram-scale synthesis of triphenylenes and their facile transformation into diverse functional organic molecules were illustrated.