Stereoselective Gold(I)-Catalyzed Intermolecular Hydroalkoxlation of Alkynes

Area of Science:

• Organometallic Chemistry
• Catalysis
• Organic Synthesis

Background:

• Hydroalkoxylation reactions are crucial for synthesizing vinyl ethers.
• Developing efficient and selective catalysts for internal alkyne functionalization remains a challenge.
• Solvent-free conditions are desirable for sustainable chemical processes.

Purpose of the Study:

• To investigate the efficacy of cationic gold complexes as catalysts for the hydroalkoxylation of internal alkynes.
• To develop a highly active and stereoselective catalytic system for vinyl ether synthesis.
• To explore the application of these catalysts under solvent-free conditions.

Main Methods:

• Utilized cationic gold complexes, specifically [Au(NHC)(CH3CN)][BF4] and [{Au(NHC)}2(μ-OH)][BF4] (NHC = N-heterocyclic carbene), as catalysts.
• Performed the hydroalkoxylation of internal alkynes with primary and secondary alcohols under solvent-free conditions.
• Analyzed reaction products for yield and stereoselectivity using standard analytical techniques.

Main Results:

• Achieved excellent yields and high stereoselectivities for a broad range of (Z)-vinyl ethers.
• Demonstrated high catalytic activity with catalyst loadings as low as 200 ppm for primary alcohols.
• Observed exceptional performance metrics, including a turnover number (TON) of 35,000 and a turnover frequency (TOF) of 2188 h⁻¹.

Conclusions:

• Cationic gold-N-heterocyclic carbene complexes are highly effective catalysts for the solvent-free hydroalkoxylation of internal alkynes.
• The developed protocol offers a simple, efficient, and sustainable route to valuable (Z)-vinyl ethers.
• The methodology showcases remarkable catalytic efficiency, enabling low catalyst loadings and high productivity.