Carboxylate Catalyzed Isomerization of β,γ‐Unsaturated N‐Acetylcysteamine Thioesters

We demonstrate herein the capacity of simple carboxylate salts – tetrametylammonium and tetramethylguanidinium pivalate – to act as catalysts in the isomerization of β,γ‐unsaturated thioesters to α,β‐unsaturated thioesters. The carboxylate catalysts gave reaction rates comparable to those obtained with DBU, but with fewer side reactions. The reaction exhibits a normal secondary kinetic isotope effect (k (1H)/k (1D)=1.065±0.026) with a β,γ‐deuterated substrate. Computational analysis of the mechanism provides a similar value (k (1H)/k (1D)=1.05) with a mechanism where γ‐reprotonation of the enolate intermediate is rate determining.