Copper‐Catalyzed and Proton‐Directed Selective Hydroxymethylation of Alkynes with CO 2

Skeletal Formation of Carbocycles with CO2: Selective Synthesis of Indolo[3,2-b]carbazoles or Cyclophanes from Indoles, CO2, and Phenylsilane

The catalytic reactions of indoles with CO2 and phenylsilane afforded indolo[3,2-b]carbazoles, where the fused benzene ring was constructed by forming two C-H bonds and four C-C bonds with two CO2 molecules via deoxygenative conversions. Nine-membered cyclophanes made up of three indoles and three CO2 molecules were also obtained, where the cyclophane framework was constructed by forming six C-H bonds and six C-C bonds. These multicomponent cascade reactions giving completely different carbocycles were switched simply by choosing the solvent, acetonitrile or ethyl acetate.

Atropisomeric Carboxylic Acids Synthesis via Nickel-Catalyzed Enantioconvergent Carboxylation of Aza-Biaryl Triflates with CO2

Upgrading CO2 to value-added chiral molecules via catalytic asymmetric C-C bond formation is a highly important yet challenging task. Although great progress on the formation of centrally chiral carboxylic acids has been achieved, catalytic construction of axially chiral carboxylic acids with CO2 has never been reported to date. Herein, we report the first catalytic asymmetric synthesis of axially chiral carboxylic acids with CO2, which is enabled by nickel-catalyzed dynamic kinetic asymmetric reductive carboxylation of racemic aza-biaryl triflates. A variety of important axially chiral carboxylic acids, which are valuable but difficult to obtain via catalysis, are generated in an enantioconvergent version. This new methodology features good functional group tolerance, easy to scale-up, facile transformation and avoids cumbersome steps, handling organometallic reagents and using stoichiometric chiral materials. Mechanistic investigations indicate a dynamic kinetic asymmetric transformation process induced by chiral nickel catalysis.

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.

Synthesis of Enamines, Aldehydes, and Nitriles from CO2: Scope of the One-Pot Strategy via Formamides

Tetrabutylammonium acetate (TBAA) and Cu(OAc)2 worked as a binary catalytic system for the solvent-free N-formylation of amines with CO2 and PhSiH3. This catalysis making C-H and C-N bonds with CO2 was coupled with the C-C bond-forming reactions to achieve the one-pot synthesis of enamines, aldehydes, and nitriles. The X-ray crystal structure of a Cu(OAc)2-TBAA complex was also revealed.

Metal-Free Hydroxymethylation of Indole Derivatives with Formic Acid as an Alternative Way to Indirect Utilization of CO2

The selective N-alkylation of indole substrates remains an ongoing research challenge for the relative attenuated nucleophilicity toward nitrogen. Herein, we developed the hydroxymethylation of indole derivatives to afford N-alkylated indole products with formic acid. This metal-free process was promoted by the organic base 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) using phenylsilane as the reductant under mild conditions. Besides, this strategy represents an alternative way for indirect utilization of CO₂, considering the facile hydrogenation of CO₂ to produce HCOOH.

Chemodivergent Synthesis of One-Carbon-Extended Alcohols via Copper-Catalyzed Hydroxymethylation of Alkynes with Formic Acid

The development of selective catalytic reactions that utilize easily available reagents for the efficient synthesis of alcohols is a long-standing goal of chemical research. Here an intriguing strategy for the chemodivergent copper-catalyzed hydroxymethylation of alkynes with formic acid and hydrosilane has been developed. By simply tuning the amount of formic acid and reaction temperature, distinct one-carbon-extended primary alcohols, that is, allylic alcohols and β-branched alkyl alcohols, were produced with high levels of Z/E-, regio-, and enantioselectivity.

Selective Production of Linear Aldehydes and Alcohols from Alkenes using Formic Acid as Syngas Surrogate

Performing carbonylation without the use of carbon monoxide for high-value-added products is an attractive yet challenging topic in sustainable chemistry. Herein, effective methods for producing linear aldehydes or alcohols selectively with formic acid as both carbon monoxide and hydrogen source have been described. Linear-selective hydroformylation of alkenes proceeds smoothly with up to 88 % yield and >30 regioselectivity in the presence of single Rh catalyst. Strikingly, introducing Ru into the system, the dual Rh/Ru catalysts accomplish efficient and regioselective hydroxymethylation in one pot. The present processes utilizing formic acid as syngas surrogate operate simply under mild condition, which opens a sustainable way for production of linear aldehydes and alcohols without the need for gas cylinders and autoclaves. As formic acid can be readily produced via CO₂ hydrogenation, the protocols represent indirect approaches for chemical valorization of CO₂ .

CuH-Catalyzed Regio- and Enantioselective Hydrocarboxylation of Allenes: Toward Carboxylic Acids with Acyclic Quaternary Centers

We report a method to prepare α-chiral carboxylic acid derivatives, including those bearing all-carbon quaternary centers, through an enantioselective CuH-catalyzed hydrocarboxylation of allenes with a commercially available fluoroformate. A broad range of heterocycles and functional groups on the allenes were tolerated in this protocol, giving enantioenriched α-quaternary and tertiary carboxylic acid derivatives in good yields with exclusive branched regioselectivity. The synthetic utility of this approach was further demonstrated by derivatization of the products to afford biologically important compounds, including the antiplatelet drug indobufen.

C-Methylenation of anilines and indoles with CO2 and hydrosilane using a pentanuclear zinc complex catalyst

The one-step C-methylenation of anilines and indoles with CO2 and phenylsilane was catalyzed by a pentanuclear ZnII complex to give diarylmethanes via geminal C-H and C-C bond formation. It is proposed that the zinc-hydride complex generated in situ is a catalytically active species and that bis(silyl)acetal is a key intermediate. When aniline was used as a substrate, both the C-methylenation and N-methylation proceeded.