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Redox Active N-Heterocyclic Carbenes in Oxidative NHC Catalysis
Sara Bacaicoa1, Simon Stenkvist1, Henrik Sundén1
1University of Gothenburg, Medicinaregatan 19, 413 90 Gothenburg, Sweden.
Organic Letters
|March 29, 2024
Summary
A novel hybrid N-heterocyclic carbene (NHC) catalyst with a linked quinone enables efficient internal oxidations. This redox-active catalyst facilitates aerobic regeneration, producing carboxylic esters with high yields and water as the only byproduct.
Area of Science:
- Organic Chemistry
- Catalysis
- Green Chemistry
Background:
- N-heterocyclic carbenes (NHCs) are versatile catalysts in organic synthesis.
- Oxidative catalysis often requires efficient methods for intermediate oxidation.
- Developing sustainable catalytic systems with minimal waste is crucial.
Purpose of the Study:
- To introduce a novel hybrid N-heterocyclic carbene (NHC) covalently linked to a quinone.
- To investigate the utility of this hybrid NHC in oxidative catalysis, specifically for intramolecular oxidations.
- To explore aerobic regeneration of the redox-active NHC catalyst for sustainable synthesis.
Main Methods:
- Synthesis of a novel NHC-quinone hybrid molecule.
- Application of the hybrid NHC as a catalyst in oxidative transformations.
- Utilizing aerobic conditions for catalyst regeneration.
- Analysis of reaction products, including carboxylic esters.
Main Results:
- The hybrid NHC effectively promotes intramolecular electronic flow for the oxidation of the Breslow intermediate to acyl azolium.
- Aerobic regeneration of the redox-active NHC catalyst was successfully achieved.
- Carboxylic esters were synthesized with high efficiencies, up to 99%.
- Water was identified as the sole byproduct of the catalytic process.
Conclusions:
- The developed NHC-quinone hybrid represents a novel class of catalysts for internal oxidations.
- This catalytic system offers an efficient and sustainable route to carboxylic esters.
- The use of aerobic regeneration and water as a byproduct aligns with green chemistry principles.
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