Mechanistic Studies and Improvement of Coinage Metal-CatalyzedTransformation of Alkynyloxiranes to Furans: An AlcoholAddition-Cyclization-Elimination Cascade

摘要

In the presence of alcohol Ag or Au salts or complexes catalyze the conversion of alkynyloxiranes tosubstituted furans. Both catalysts are effective, and a large furan diversity can be obtained in high yieldwith one or the other catalyst. Mechanistic studies revealed that a cascade pathway and not thesometimes reported direct intramolecular nucleophilic addition of oxirane oxygen atom to inter-mediate acetylene-metal π-complex occurs. Under the defined conditions, the intermediate forma-tion of epoxide opening products has been identified. Depending on the catalyst, one orboth of the latter cyclized to dihydrofurans, and further elimination of the alcohol led to the corres-ponding furans. These results highlight the duality between oxophilicity and alkynophilicity of Ag or Ausalts.