The research group of Prof. Da-Gang Yu at Sichuan University focuses on the development of strategies for CO₂ utilization and transformation in the past few years. In the area of visible-light photoredox-catalyzed carboxylations with CO₂ (Research summary: Acc. Chem. Res. 2021, 54, 2518), we have achieved umpolung carboxylations of various electrophiles (ACIE 2018, 57, 13897; JACS 2018, 140, 17338; Nat. Commun. 2021, 12, 3306). Also, we have achieved visible light-driven hydro- carbo-, thio-, phosphono-carboxylation, and dicarboxylation of alkenes with CO₂ (ACIE 2017, 56, 15416; Nat. Commun. 2019, 10, 3592; Nat. Commun. 2020, 11, 3263; ACIE 2020, 59, 21121; CCS Chem. 2020, 2, 1746; JACS 2021, 143, 2812; Nat. Catal. 2021, 4, 304; Nat. Catal. 2022, 5, 832). In our recent paper published in Nature Catalysis, we described the latest progress on this topic. The efficient merger of photocatalysis with copper catalysis enables the aminocarboxylation of alkenes with CO₂, providing efficient and practical synthetic access to valuable β-amino acids.

The conversion of CO₂ to valuable chemicals is highly desirable for sustainable development. Carboxylation with CO₂, especially difunctionalizing carboxylation of alkenes with CO₂ emerges as an exceptionally efficient approach to constructing densely functionalized carboxylic acids^1,2. Although many 1,2-difunctionalizing carboxylations of alkenes with CO₂ have been realized via transition-metal catalysis^3,4, photocatalysis^5-10, and electrochemistry¹¹, some issues remained. Firstly, existing systems have been limited to mono-catalytic strategies and a few specific reaction types. Secondly, β-selective carboxylation could give access to various bioactive carboxylic acids but it is more challenging and less accessible than widely investigated α-selective carboxylation. Thirdly, some reactions suffer from the use of sacrificial electrodes or superstoichiometric reductants.

Tackling the limitations in the current difunctionalizing carboxylations of alkenes, we believe that synergistic catalysis could unlock the previously inaccessible transformations with CO₂. Our proposal is leveraging photochemistry in the generation of the alkene radical anion species for β-selective carboxylation and metal-mediated bond-forming processes for further functionalization, which could provide a reaction platform for transformations of alkenes and CO₂. However, orthogonal difunctionalization of alkene radical anions under redox-neutral conditions^12,13 is elusive due to the following reasons. First, the generation of alkene radical anions is difficult due to the very negative reduction potentials of most alkenes, which are beyond the capabilities of most photocatalysts. Moreover, the efficient and selective trap of alkene radical anions by appropriate electrophiles is hard to achieve, and many side reactions, including SET reduction, hydrogen atom transfer (HAT), and dimerization of the in situ generated carbon radicals should be avoided. In addition, it is also challenging to achieve nice compatibility between strongly reducing photocatalysts and transition-metal catalysts under redox-neutral conditions.

In this manuscript, we report our success in realizing the aminocarboxylation of alkenes with CO₂ via visible-light photoredox and copper dual catalysis, providing efficient and practical synthetic access to valuable β-amino acids. Noteworthy, we have identified a photosensitizer derived from binaphthol with strong reducibility, which enables the single-electron activation of alkenes to generate their radical anion intermediates. Notably, the merger of photocatalysis with copper catalysis is the key to realizing such a rare redox-neutral difunctionalization of alkene radical anions. We do believe this synergistic catalysis will provide a reaction platform for the utilization of alkenes and CO₂ in chemical synthesis.

More details of this work could be found here: “Metallaphotoredox-enabled aminocarboxylation of alkenes with CO2” in Nature Catalysis.

References

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