The Mechanism of the Gold-Catalyzed Intramolecular [3 + 2]-Cycloaddition of 1,6-Diynes: a DFT Study.

The gold-catalyzed [3 + 2] cycloaddition of areneyne-yne functionalities represents one of the most efficient methodologies for the construction of tricyclic ring systems under mild conditions. In the current report, a detailed mechanistic understanding of the reaction was achieved by DFT calculations. It was found that under the catalysis of gold(i), the initial cyclization occurs more favorably between the two alkynyl moieties via the 6-exo-dig pathway other than the arene-yne addition, which is the selectivity-determining step of the whole reaction and leads eventually to the [3 + 2] cycloadduct irreversibly by following the steps of arene-cation cyclization and proton transfer. Electronic and geometric factors are analyzed to better understand the calculation results.