Carboxylate Catalysis: A Catalytic O-Silylative Aldol Reaction of Aldehydes and Ethyl Diazoacetate

A mild catalytic variant of the aldol reaction between ethyl diazoacetate and aldehydes is described using a combination of N,O-bis(trimethylsilyl)acetamide and catalytic tetramethylammonium pivalate as catalyst. The reaction proceeds rapidly at ambient temperature to afford the O-silylated aldol products in good to excellent yield, and the acetamide byproducts can be removed by simple filtration.

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.