Visible-Light/Nickel-Catalyzed Carboxylation of C(sp2) Bromides via Formate Activation

Photoredox-Catalyst-Free Carboxylation of Unactivated Alkenes in DMSO: Synthesis of Polycyclic Indole Derivatives and Aliphatic Acids

A new method for the carboxylation of unactivated alkenes using CO2 radical anions in the absence of a photoredox catalyst has been developed. The photocatalyst-free approach enables the efficient synthesis of polycyclic indole derivatives and linear carboxylic acids under mild conditions from HCO2K with/without 1,4-diazabicyclo[2.2.2]octane (DABCO) in DMSO. This work demonstrates a significant advance in green chemistry, showcasing a catalyst-free approach for the functionalization of unactivated alkenes with cheap and readily available HCO2K.

Visible-Light-Mediated Ni-Catalyzed Gas-Free Carboxylation: Stereodivergent Synthesis of E- and Z-Acrylic Acids

Stereodivergent syntheses of different scaffolds from identical starting materials by switching the fewest parameters are among the most appealing synthetic technologies. Herein, a visible-light mediated Ni-catalyzed carboxylation of vinyl halides with formates has been developed, affording acrylic acids in both Z- and E-configurations from identical vinyl halides. The reaction features Ni-catalyzed gas-free carboxylation of vinyl halides by utilizing formates as a surrogate of carbon dioxide.

Mild Photochemical Reduction of Alkenes and Heterocycles via Thiol-Mediated Formate Activation

The reduction of alkenes to their respective alkanes is one of the most important transformations in organic chemistry, given the abundance of natural and commercial olefins. Metal-catalyzed hydrogenation is the most common way to reduce alkenes; however, the use of H2 gas in combination with the precious metals required for these conditions can be impractical, dangerous, and expensive. More complex substrates often require extremely high pressures of H2, further emphasizing the safety concerns associated with these hydrogenation reactions. Here we report a safe, cheap, and practical photochemical alkene reduction using a readily available organophotocatalyst, catalytic thiol, and formate. These conditions reduce a variety of di-, tri-, and tetra-substituted alkenes in good yield as well as dearomatize pharmaceutically relevant heterocycles to generate sp3-rich isosteres of benzofurans and indoles. These formal-hydrogenation conditions tolerate a broad range of functionalities that would otherwise be sensitive to typical hydrogenations and are likely to be important for industry applications.

Visible-light-driven photocatalytic carboxylation to aromatic carboxylic acids with CO2

(Hetero)aromatic carboxylic acids and their derivatives attract attention due to their role in the synthesis of several biologically active molecules, active pharmaceutical ingredients, polymers, etc. Carbon dioxide (CO2) is a prime C1 source for the synthesis of aromatic carboxylic acids because of its nontoxicity, nonflammability, abundance and renewability. Owing to the thermodynamic and chemical inertness of CO2, traditional carboxylation to aromatic carboxylic acids with CO2 is always performed under harsh reaction conditions or using stoichiometric metallic reductants. Visible-light-driven carboxylation with CO2 provides an environmentally benign, mild, and high-efficiency route for the production of aromatic carboxylic acids. This review comprehensively introduces the visible-light-driven preparation of aromatic carboxylic acids through a visible-light-driven oxidative addition and reductive elimination mechanism, binding of aryl (radical) anions which are produced by photoinduced electron transfer (PET) to CO2, binding of carbon dioxide anion radicals (CO2˙-) which are formed by PET to aryl compounds, radical coupling between CO2˙- and aryl radicals, and other mechanisms. Finally, this review provides a summary and the future work direction. This article offers a theoretical guidance for efficient synthesis of aromatic carboxylic acids via photocatalysis.