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 ß,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 ß,γ-unsaturated thioesters to α,ß-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 (k1H /k1D =1.065±0.026) with a ß,γ-deuterated substrate. Computational analysis of the mechanism provides a similar value (k1H /k1D =1.05) with a mechanism where γ-reprotonation of the enolate intermediate is rate determining.