Fused Catechol Ethers from Gold(I)-Catalyzed Intramolecular Reaction of Propargyl Ethers with Acetals

Selective gold(I)-catalyzed rearrangement of aromatic methoxypropynyl acetals leads to fused catechol ethers (1,2-dialkoxynapthalenes) in excellent yields. Furthermore, this process extends to the analogous heterocyclic and aliphatic substrates. Alkyne activation triggers nucleophilic addition of the acetal oxygen that leads to an equilibrating mixture of oxonium ions of similar stability. This mixture is "kinetically self-sorted" via a highly exothermic cyclization. Selective formation of 1,2-dialkoxy naphthalenes originates from chemoselective aromatization of the cyclic intermediate via 1,4-elimination of methanol.