On the Role of the Solvent in the Synthesis of Spirocycles from Alkyne Cations Catalyzed by Triflic Acid: A DFT Study

The relevance of solvent molecules in the reactivity of alkyne cations has been analyzed computationally. Analysis of the possible reaction mechanisms towards competitive cyclization and elimination processes including a molecule of solvent shows the crucial role of the solvent. In dichloromethane there are no relevant discrete solvent‐cation interactions that could determine the outcome and a strong intramolecular π‐cation interaction favors the [5‐ exo ‐dig] cyclization route. On the other hand, in tetrahydrofuran or toluene solvated environments, the existence of solvent‐cation interaction via formation of a dative C−O bond or the formation of a highly stabilized triflate‐cation complex, respectively, modifies the energy profile, thus promoting the elimination pathway.