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.