Intramolecular hydroarylation of alkynes catalyzed by platinum or gold: Mechanism and endo selectivity

Article abstract of DOI:10.1002/chem.200401069

The cyclization of differently substituted aryl alkynes with Pt ^II or Au^I catalysts proceeds by endo-dig pathways. When Ag^I was used to generate reactive cationic Au^I catalysts, 2H-chromenes dimerize to form cyclobutane derivatives by a Ag ^I-catalyzed process. A DFT study on the cycliza-tion mechanism shows a kinetic and thermodynamic preference for 6-endodig versus 5-exo-dig cyclizations in Pt^II-catalyzed processes. Calculations indicate that although Friedel-Crafts and the cyclopropanation processes via metal cyclopropyl carbenes show very similar activation energies, platinum cyclopropyl carbenes are the stationary points with the lowest energy.