Gold-Catalyzed Addition of N-Hydroxy Heterocycles to Alkynes and Subsequent 3,3-Sigmatropic Rearrangement

Gold-catalyzed intermolecular addition of hydroxybenzotriazole derivatives to alkynes at room temperature, gives vinyl ethers 3 in high yields and with excellent regioselectivity. Unlike many other vinyl ethers, 3 can easily be purified by regular silica-gel chromatography. On heating, 3,3-sigmatropic rearrangement of 3 gives access to highly functionalized benzotriazoles. This two-step sequence represents an efficient oxygen transfer protocol which incorporates a nucleophilic oxygen atom Into an alkyne group. Reaction of 3 with an electrophilic fluorinating reagent (Selectfluor) gives a fluorinated ketone regioselectively and in high yield.