Hydroalkylation of Alkynyl Ethers via a Gold(I)-Catalyzed 1,5-Hydride Shift/Cyclization Sequence

A series of alkynyl ethers react with an electrophilic gold(I) catalyst to produce a range of structurally complex spiro or fused dihydrofurans and dihydropyrans via a 1,5-hydride shift/cyclization sequence. This hydroalkylation process, which is performed under practical experimental conditions, can be applied to terminal as well as ester-substituted alkynes. It allows the efficient conversion of secondary or tertiary sp³ C−H bonds into new C−C bonds by the nucleophilic addition of a vinylgold species onto an oxonium intermediate. The stereoselectivity of the cycloisomerization process toward the formation of a new five- or six-membered cycle appears to be dependent on steric factors and the alkyne substitution pattern.