Metallaphotoredox-enabled aminocarboxylation of alkenes with CO2

CO2 conversion to valuable chemicals is of great interest in sustainable chemistry. Now, β-amino acids are synthesized by a dual catalytic strategy that enables the aminocarboxylation of alkenes using CO2, proceeding via alkene radical anion intermediates.
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Metallaphotoredox-enabled aminocarboxylation of alkenes with CO2
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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 acids1,2. Although many 1,2-difunctionalizing carboxylations of alkenes with CO2 have been realized via transition-metal catalysis3,4, photocatalysis5-10, 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 conditions12,13 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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  10. Ju, T. et al. Dicarboxylation of alkenes, allenes and (hetero)arenes with CO2 via visible-light photoredox catalysis. Catal. 4, 304−311 (2021).
  11. Zhang, W. & Lin, S. Electroreductive carbofunctionalization of alkenes with alkyl bromides via a radical-polar crossover mechanism. Am. Chem. Soc. 142, 20661−20670 (2020).
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  13. Zhang, B. et al. Enantioselective diversification of alkene radical anions. Preprint at https://doi.org/10.26434/chemrxiv-2022-qkd7j (2022).

 

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