Protonated Carbonic Acid and Reactive Intermediates in the Acidic Decarboxylation of Indolecarboxylic Acids

摘要

Elucidation of the mechanism for decarboxylationnof indolecarboxylic acids over a wide range of solutionnacidity reveals the importance of protonated carbonic acidn(PCA) as a reaction intermediate. In concentrated acid, theninitial addition of water to the carboxyl group of the indolecarboxylicnacid leads to a hydrated species that is capable ofnreleasing PCA upon rate-determining carbon−carbon bondncleavage. The overall process is catalytic in water and acid,nimplicating PCA as a potential carboxylating reagent in thenmicroscopic reverse reaction.