Copper-Catalyzed Ring-Expansion/Thiolactonization via Azidation of Internal Olefinic C-H Bond under Mild Conditions

A copper(I)-catalyzed, (diacetoxyiodo)benzene [PhI(OAc)(2)]-mediated ring-expansion/thiolactonization of alpha-oxo ketene dithioacetals was efficiently realized via azidation of the internal olefinic C-H bond with sodium azide under mild conditions. Sequential amination, ring-expansion rearrangement, and thiolactonization occurred to form aminated thiolactones in the presence of acetic anhydride as the additive, while only C-H amination to afford the unprotected enamines occurred when using ammonium sulfide as a reducing additive. The in situ generated vinyl azides were confirmed as the reactive intermediates, which were captured by phenylacetylene to produce triazoles. This protocol provides a concise route to thiolactone derivatives and unprotected enamines.