Density functional calculations and experiments have been carried out to unravel the mechanism of a silver-mediated furan formation by oxidative coupling. Various possible reaction paths were considered and the most favorable channel has been identified on the basis of the calculated solvent-corrected Gibbs free-energy profiles. The mechanism represented by this route consists of a radical and a subsequent ionic route. The silver cation has a double role in the mechanism: it is the oxidant in the radical steps and the catalyst for the ionic steps, which is in accordance with the experimental observations. The two most important aspects of the optimal route are the formation of a silver-acetylide, reacting subsequently with the enolate radical, and the aromatic furan-ring formation in a single step at the latter, ionic segment of the reaction path. Our findings could explain several experimental observations, including the "key-promoter role" of silver, the preference for ionic cyclization, and the reduced reactivity of internal acetylides. Radical or ionic mechanism? Both. The detailed mechanism of a silver-mediated furan formation by oxidative C-H/C-H activation has been revealed by DFT calculations and additional experiments. The reaction path starts with a radical C-C coupling process. Then, an aromatic cyclization occurs featuring an ionic mechanism, which completes the furan formation. Silver plays crucial roles in the reaction: it is an oxidant and a catalyst simultaneously.
- C-H activation
- density functional calculations
- radical reactions
ASJC Scopus subject areas
- Organic Chemistry