Mechanistic Support for Intramolecular Migrative Cyclization of Propargyl Sulfones Provided by Catalytic Asymmetric Induction with a Chiral Counter Cation Strategy

We previously reported an intramolecular migrative cyclization of propargylsufones and sulfonylalkynamides giving oxa- and azacycles, respectively. To confirm the postulated reaction mechanism, the reaction was conducted with chiral nucleophiles such as N-heterocyclic carbenes, phosphines, and pyridines, or with sulfinate anions and chiral cations. As expected, migrative cyclization proceeded to give the enantiomerically enriched products. These results strongly support the postulated mechanism and provide the first example of the asymmetric version of this reaction