Copper-catalysed photoinduced decarboxylative alkynylation: a combined experimental and computational study

Area of Science:

• Organic Chemistry
• Catalysis
• Radical Chemistry

Background:

• Redox-active esters (RAEs) are effective precursors for generating alkyl radicals.
• Alkyl radicals are valuable intermediates in carbon-carbon bond formation.
• Copper catalysis offers a versatile platform for organic transformations.

Purpose of the Study:

• To develop a novel decarboxylative cross-coupling method for synthesizing substituted alkynes.
• To utilize RAEs as alkyl radical precursors in copper-catalyzed reactions.
• To explore the photoexcitation strategy for generating alkyl radicals from RAEs.

Main Methods:

• Employing copper catalysts (CuCl and Cu(acac)2) for decarboxylative cross-coupling.
• Utilizing photoexcitation of copper acetylides with triethylamine (NEt3) as a ligand.
• Expanding the reaction scope to include aliphatic alkynes and alkynyl silanes.
• Performing Density Functional Theory (DFT) calculations to elucidate the reaction mechanism.

Main Results:

• Successfully synthesized a range of substituted alkynes from various carboxylic acids.
• Demonstrated the generation of diverse alkyl radicals from RAEs via photoexcitation.
• Achieved cross-coupling with aromatic and aliphatic alkynes, as well as alkynyl silanes.
• DFT calculations confirmed a favorable reaction pathway and highlighted the role of the acetylacetonate ligand in preventing alkyne homo-coupling.

Conclusions:

• The developed method provides a general and efficient strategy for C-C bond formation using RAEs and copper catalysis.
• Photoexcitation of copper acetylides is a key step in generating alkyl radicals for cross-coupling.
• The reaction scope is broad, accommodating various substrates and expanding synthetic possibilities.