Silver-Free Gold-Catalyzed Heterocyclizations through Intermolecular H‑Bonding Activation

Modulable monosulfonyl squaramides have been shown to
exert activation
of gold(I) chloride complexes through H-bonding in an intermolecular
way. Combinations of (PPh3)AuCl or IPrAuCl complexes and
an optimal sulfonyl squaramide cocatalyst bearing two 3,5-bis(trifluoromethyl)phenyl
groups efficiently catalyzed diverse heterocyclizations and a cyclopropanation
reaction, avoiding in all cases undesired side reactions. Computational
studies indicate that the Au–Cl bond breaks by transligation
to the triple bond in a ternary complex formed by the actual AuCl···HBD
catalyst and the substrate.