In(III) and Hf(IV) Triflate-Catalyzed Hydration and Catalyst-free Hydrohalogenation of Aryl Acetylenes in Liquid Sulfur Dioxide

[Image: see text] The use of liquid sulfur dioxide as a reaction solvent to promote chemical transformations of alkynes has been explored. First, a combination of liquid SO(2) and In(OTf)(3) or Hf(OTf)(4) as a catalyst allows to perform hydration of aryl alkynes under mild conditions without a direct addition of Brønsted acid. Second, novel catalyst-free conditions for the synthesis of α-vinyl iodides, bromides, and chlorides from aryl alkynes have been developed in liquid SO(2) using group I and II metal halides and ammonium iodide as the halide ion sources.