Gold(I)/(III)-Catalyzed Synthesis of Cyclic Ethers; Valency-Controlled Cyclization Modes.

Strategic use of oxophilic (hard) gold(III) and π-philic (soft) gold(I) catalysts provides access to two types of cyclic ethers from propargylic alcohols. Thus, heating propargylic alcohols with an oxophilic gold(III) catalyst (AuBr3) results in cyclization to afford cyclic ethers bearing an acetylenic moiety, due to coordination of gold(III) to the oxygen of the propargylic hydroxyl group. On the other hand, propargylic alcohols with a π-philic gold(I) catalyst (Ph3PAuNTf2) induces Meyer-Schuster rearrangement to afford α,β-unsaturated ketones, which undergo gold(III)-catalyzed intramolecular oxa-Michael addition to afford cyclic ethers bearing a carbonyl group, due to coordination of gold(III) to the oxygen of the carbonyl group.