Metal-Free Photocatalytic Synthesis of exo-Iodomethylene 2-Oxazolidinones: An Alternative Strategy for CO2 Valorization with Solar Energy

Iridium-Catalyzed, Copper-Induced Reductive Cyclization of NO2-Pyrrolarenes with CO2 as a Single-Carbon Source

A new catalytic conversion type of nitro substrate with CO2 as a single-carbon source is presented, wherein a great collection of azaheterocycles is generated by a newly established iridium-catalyzed, copper-induced reductive system. This catalytic procedure handily employs poly(methylhydrosiloxane) (PMHS) as the reductant to simultaneously realize the dual reduction of the highest oxidation-state nitro and CO2 units in one operation. Elaborate mechanistic studies illustrate the essential role of the iridium catalyst in reducing the NO2 moiety as well as the double functions of the copper additive in the subsequent formylation and C-H cyclization steps.

Visible-light-induced bifunctionalisation of (homo)propargylic amines with CO2 and arylsulfinates

An unprecedented carboxylative sulfonylation of (homo)propargyl amines with CO2 and sodium arylsulfinates under visible light irradiation has been developed with high efficiency. This ruthenium-catalysed photochemical protocol offers broad substrate scope giving 2-oxazolidinones and 2-oxazinones bearing alkyl sulfones in good yields under ambient reaction conditions. An in situ double bond isomerisation occurs in tandem. A mechanistic rationale for these radical-initiated carboxylative cyclisations involving sulfinyl radicals is presented, supported by control and quenching experiments.

Advancements and Challenges in Reductive Conversion of Carbon Dioxide via Thermo-/Photocatalysis

Carbon dioxide (CO₂) is the major greenhouse gas and also an abundant and renewable carbon resource. Therefore, its chemical conversion and utilization are of great attraction for sustainable development. Especially, reductive conversion of CO₂ with energy input has become a current hotspot due to its ability to access fuels and various important chemicals. Nowadays, the controllable CO₂ hydrogenation to formic acid and alcohols using sustainable H₂ resources has been regarded as an appealing solution to hydrogen storage and CO₂ accumulation. In addition, photocatalytic CO₂ reduction to CO also provides a potential way to utilize this greenhouse gas efficiently. Besides direct CO₂ hydrogenation, CO₂ reductive functionalization integrates CO₂ reduction with subsequent C-X (X = N, S, C, O) bond formation and indirect transformation strategies, enlarging the diverse products derived from CO₂ and promoting CO₂ reductive conversion into a new stage. In this Perspective, the progress and challenges of CO₂ reductive conversion, including hydrogenation, reductive functionalization, photocatalytic reduction, and photocatalytic reductive functionalization are summarized and discussed along with the key issues and future trends/directions in this field. We hope this Perspective can evoke intense interest and inspire much innovation in the promise of CO₂ valorization.

Palladium-catalyzed carboxylative cyclization of propargylic amines with aryl iodides, CO2 and CO under ambient pressure

A palladium-catalyzed four-component carboxylative cyclization comprising propargylic amines, aryl iodides, CO₂ and CO was developed. By selecting Et₃N and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as the base, respectively, both terminal and internal propargylic amines proceeded well facilitated by Pd(PPh₃)₂Cl₂, affording the functionalized 2-oxazolones in moderate yields. This protocol enlarges the product diversity based on CO₂ conversion and simultaneously provides a cooperative transformation route for both CO₂ and CO.

Non-Noble-Metal Metal-Organic-Framework-Catalyzed Carboxylative Cyclization of Propargylic Amines with Atmospheric Carbon Dioxide under Ambient Conditions

The coupling reaction of propargylic amines and carbon dioxide (CO₂) to synthesize 2-oxazolidinones is an important reaction in industrial production, and yet harsh reaction conditions and noble-metal catalysts are often required to achieve high product yields. Herein, one novel noble-metal-free three-dimensional framework, [Mg₃Cu₂I₂(IN)₄(HCOO)₂(DEF)₄]_n (1), assembled by magnesium and copper clusters was synthesized and applied to this reaction. Compound 1 displays excellent solvent stability. Importantly, 1, acting as heterogeneous catalyst, can highly catalyze the cyclization of propargylic amines with CO₂ under atmospheric pressure at room temperature, which can be recycled at least five times without an obvious decrease of the catalytic activity. NMR spectroscopy, coupled with ¹³C-isotope- and deuterium-labeling experiments, clearly clarifies the mechanism of this catalytic system: CO₂ was successfully captured and converted to the product of 2-oxazolidinones, the C≡C bond of propargylic amines can be effectively activated by 1, and proton transfer was involved in the reaction process. Density functional theory calculations are further conducted to uncover the reaction path and the crucial role of compound 1 during the reaction.

Ultrathin mesoporous graphitic carbon nitride nanosheets with functional cyano group decoration and nitrogen-vacancy defects for an efficient selective CO2 photoreduction

Graphitic carbon nitrides have CO₂ photoreduction ability, but their activities are limited by the low potential and mobility of photogenerated carriers. Herein, ultrathin mesoporous graphitic carbon nitride nanosheets (CNNS) synchronously decorated with functional cyano groups and nitrogen vacancies were prepared by a facile molten salt route. The CNNS presented unprecedentedly excellent gas-phase CO₂ photoreduction performance under visible light irradiation without any co-catalyst or a sacrificial agent, and have a CH₄-yielding rate of 23.0 μmol g^-1 h^-1 and a selectivity of 97.9%. This boosted performance can be attributed to the synergistic effect of cyano group decoration, abundant nitrogen vacancies and extremely high surface area, which improve electron storage, charge carrier mobility, CO₂ affinity, and optimize the energy band structure. This work demonstrates that a structural optimization combined with defect design of carbon nitride framework is a powerful approach to improve the photocatalytic activity, providing an accessible way to design highly efficient carbon-based photocatalysts.

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.

Utilization of CO2 Feedstock for Organic Synthesis by Visible-Light Photoredox Catalysis

CO₂ is a highly abundant, green, and sustainable carbon feedstock. Despite its kinetic inertness and thermodynamic stability, the development of various catalytic techniques has enabled the conversion of CO₂ to value-added products such as carboxylic acids, amino acids, and heterocyclic compounds, where visible-light photocatalysis has emerged to be an efficient promoter of these processes. This Minireview covers the progress in the areas of CO₂ incorporation onto organic matters based on the combined venture of renewable resources of CO₂ and light energy with significant emphasis on the last three years' developments.

A metal-free visible-light-promoted phosphorylation/cyclization reaction in water towards 3-phosphorylated benzothiophenes

A metal-free visible-light-induced phosphorylation/cyclization reaction was developed in water at room temperature for the synthesis of 3-phosphorylated benzothiophenes.