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

• Published in: European journal of organic chemistry 2024-09, Vol.27 (33), p.n/a
• Main Authors: Cózar, Abel, Arrieta, Ana, Cossío, Fernando P.
• Format: Article
• Language: English
• Subjects: Alkynes; Cations; Chemical synthesis; Cyclization reaction; DFT; Dichloromethane; Elimination reaction; Reaction mechanisms; Solvent effects; Solvents; Tetrahydrofuran; Toluene; Triflic acid
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.202400347

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. Not merely a spectator. The competitive cyclization/elimination mechanisms of an alkyne cation to yield either a spiroketone or and enyne have been studied computationally. Analysis of the respective reaction coordinates shows the crucial role of one discrete molecule of solvent that determines the experimentally observed outcome.