Carbon dioxide (CO ₂), as a one-carbon synthon, has many advantages such as abundant, non-toxic, clean and so on. So the reactions using CO ₂ as a one-carbon synthon have been widely concerned in organic chemistry. Transition-metal- catalyzed reaction of unsaturated hydrocarbons with CO ₂ to produce carboxylic acid is one of the most commonly-used method to convert CO ₂, and organometallic reagents can be added to the reaction as reducing agent. This kind of reaction can be realized by the strategy of tandem reaction. In the reaction, the unsaturated hydrocarbons react with transition-metal catalysts and organometallic reagents to generate new organometallic reagents in situ first, and then complete carboxylation with CO ₂. Common organometallic reagents such as organozinc reagents, Grignard reagents, and organoaluminum reagents can all achieve this kind of carboxylation reaction. In this review, reactions are divided according to the type of unsaturated hydrocarbons, and each type can also be divided into hydrocarboxylation and carbocarboxylation. This review would introduce reaction according to this classification.

Carbon dioxide is a readily available, low-cost, abundant, non-toxic C1 source, which can potentially serve as an ideal building block in synthetic chemistry. Recently, much progress, expecially multi-component reactions (MCRs) has been achieved in construction of carbonyl-containing heterocycles through annulation by using carbon dioxide as carbonyl/carboxyl source. Herein, the advances on the annulation reaction of atmospheric CO₂ with N-, and O-nucleophiles for the constructioin of various carbonyl-containing heterocycles, including benzoxazin, cyclic carbamates, lactams, oxazolidine-2,4-diones are reviewed. In addition, the carboxylation of C-nucleophiles with CO₂ toward carboxylic acids is also summarized.

Industrial processes of fixing carbon dioxide (CO₂) lag far behind the carbon emission generated by human activity. Since CO₂ is an abundant, non-toxic, and cost-effective one carbon source, it is highly desirable to develop methodologies on converting CO₂ into valuable products for sustainable purpose. Based on the mechanistic insight of CO₂ activation by transition-metal catalyst and organocatalyst, a variety of efficient asymmetric CO₂ chemical fixation processes have been developed in recent years. This review discusses the advances of enantioselective synthesis of small molecules by asymmetric catalytic reactions with CO₂. The interaction between catalyst, CO₂ and substrate has been elaborated aiming to inspire the design of new catalytic systems for asymmetric CO₂ transformation.

Climate change and depletion of fossil fuels have drawn considerable attention. Considering carbon dioxide is both the dominant greenhouse gas and renewable C₁ source, CO₂ valorization into valuable chemicals is considered to reconcile the environment benefit and sustainable chemistry development. Unfortunately, the thermodynamic stability and kinetic inertness of CO₂ make its chemical transformation challenging. As a consequence, developing highly efficient catalytic systems and synthetic protocols is crucial for CO₂ conversion. In recent years, He's group made great progress on strategy design and catalyst development for CO₂ conversion. A series novel CO₂ conversion strategies are proposed, including CO₂ capture and in-situ transformation, hierarchical reductive functionalization of CO₂, designing thermodynamically favorable reactions by multi-component cascade reaction and photo-promoted CO₂ transformation. Concurrently, the corresponding highly efficient catalytic systems were also developed based on the reaction mechanism and thus CO₂ transformation was successfully performed under mild conditions. It is hoped that this review can arouse broad concern on CO₂ transformation and spur its further development.

A method for the selective synthesis of o-halothiobenzamide by thiolysis reaction of o-halobenzonitrile with NaHS under the action of CO₂ was explored. CO₂/H₂O/NaHS was used as a buffer system to provide a suitable pH environment, which would make HS^- attack the nitrile-based carbon selectively to produce the corresponding o-halothiobenzamide. Moreover, the buffer system also provided the additionally required hydrogen atom for the thiolysis reaction of o-haloben-zonitrile with NaHS. Further studies have found that the CO₂/Na₂S·9H₂O buffer system could also efficiently promote the thiolysis reaction of o-halobenzonitrile to form the corresponding o-halothiobenzamide. This synthetic method could be used to prepare different substituted o-halobenzonitriles, which is a simple, efficient and high atom-economic reaction.

Atom-efficient [2+2+2] cycloaddition reaction of alkynes in green solvent supercritical carbon dioxide (ScCO₂) is an environmentally friendly reaction process that conforms to the principles of green chemistry. Cyclotrimerization of terminal alkynes catalyzed by Co₂(CO)₈ in pure ScCO₂ has been studied to obtain 1,2,4-trisubstituted benzene derivatives with excellent selectivity. The reaction conditions for the cyclotrimerization were optimized, such as concentration of catalyst, CO₂ pressure, reaction temperature and time. The solubility and phase behavior of the reaction materials and catalysts in ScCO₂ medium were discussed, and the mechanism of Co₂(CO)₈ catalyzed cyclotrimerization of terminal alkynes was assumed. The reaction substrate was extended from C≡C (alkyne) to C≡N (nitrile), and the alkyne-nitrile cycloaddition reaction in ScCO₂ was preliminary explored. Our optimized catalytic system for the cyclotrimerization of terminal alkynes exhibited wide substrate scope and high product selectivity, in which no organic co-solvent or additives were added. It provided a green synthetic method for 1,2,4-trisubstituted benzenes.

A series of carboxyl group or hydroxyl group functionalized organocatalysts were synthesized and applied in three component reaction of carbon dioxide with epoxide, and aryl amines for the synthesis of 3-aryl-2-oxazolidinones. The method allows the reaction to proceed smoothly in the mild reaction conditions, together with excellent substrates scope of epoxides and aryl amines. The control experiments suggest that the cyclic carbonates are formed by the coupling of epoxides with carbon dioxide, which further react with the amino alcohol generated from epoxides and aryl amines, finally resulting in the desired products.