Sulfonate Derivative of HOAt (CTSOAt) as a Coupling Reagent for the Construction of C–N, C–O, and C–C Bonds

We have developed a novel recyclable coupling reagent, 3<i>H</i>-[1,2,3]triazolo[4,5-<i>b</i>]pyridin-3-yl 5-chlorothiophene-2-sulfonate (CTSOAt), in a faster and straightforward way. The reagent activates carboxylic acids by forming acyl-OAt intermediates, facilitating the synthesis of amides, esters, and peptides with good yields and excellent chirality retention. The reagent also offers the formation of ketones from carboxylic acids through Pd-catalyzed cross-coupling reactions. Enormous substrate scope, good yields, elimination of unwanted side reactions, significant suppression of racemization/epimerization, and compatibility with solid-phase peptide synthesis protocol make it highly advantageous for synthetic chemists.