Highly Efficient Access to Strained Bicyclic Ketals via Gold-Catalyzed Cycloisomerization of Bis-homopropargylic Diols

A highly efficient gold-catalyzed cycloisomerization reaction of bis-homopropargylic diols is described. The cyclizations are conducted in the presence of either AuI or AuIII catalysts in MeOH at room temperature in a very short time. The reaction conditions are compatible with functional groups, such as n-butyl, phenyl, allyl, benzyl, and alcohol groups, leading to original strained dioxabicyclo[2.2.1], -[2.2.2], or -[3.2.1] ketals in good to excellent yields.