Brønsted acid-promoted cyclizations of 1-siloxy-1,5-diynes.

We have developed the first HNTf2-promoted 5-endo-dig cyclizations of 1-siloxy-1,5-diynes, which proceed with concomitant formation of C-Hal bonds as a result of halide abstraction from a halocarbon by the intermediate alkenyl cation. This process is enabled by a chemoselective activation of the more electron-rich siloxy alkyne moiety of the diyne cyclization precursor and represents an efficient and highly diastereoselective method for assembly of a range of beta-halo enones.