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

Abstract

The role of discrete 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 show the crucial role of dichloromethane (DCM) and tetrahydrofuran (THF). In the presence of DCM, a strong intramolecular p‐cation interaction between the electrophilic center and the triple bond favors the [5‐exo‐dig] cyclization route, with no direct participation of the solvent in the reaction path. On the contrary, in the presence of a discrete molecule of THF, a strong solvent–cation interaction via formation of a dative C(+)–O(THF) bond drastically modifies the energy profile, thus promoting the elimination pathway.