Description Application Cyclopropenimines are a highly effective new class of Brønsted base catalysts, the so-called “superbases” for organocatalysis. Due to the prevalence of chemical reactions involving proton transfer as a key mechanistic event, Brønsted bases have become indispensable tools for the practice of organic synthetic chemistry. This is one of a suite of Brønsted catalysts reported by Tristan Lambert and co-workers available through Sigma-Aldrich. Other Notes Cyclopropenimine Superbases: Competitive Initiation Processes in Lactide Polymerization