A 6- endo -dig Thiolative Cyclization of Yne-Ynamides: Access to Thiodihydropyridin-2-ones.

A straightforward regioselective intramolecular 6- endo -dig cyclization of yne-tethered ynamide is herein developed. The reaction involves an intramolecular enolate attack of ketene- N,O -acetals, generated in situ from yne-ynamide and methanesulfonic acid, to the alkyne moiety activated by a sulfonium cation. The transformation enables access to structurally diverse 5-(arylthio)-3,6-dihydropyridin-2(3 H )-ones with broad functional group compatibility. The recovery of S-protecting groups and synthetic applications of the products make the transformation useful.