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

A straightforward regioselective intramolecular 6--dig cyclization of yne-tethered ynamide is herein developed. The reaction involves an intramolecular enolate attack of ketene--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)-ones with broad functional group compatibility. The recovery of S-protecting groups and synthetic applications of the products make the transformation useful.