COMU: A Safer and More Effective Replacement for Benzotriazole‐Based Uronium Coupling Reagents

We describe a new family of uronium‐type coupling reagents that differ in their iminium moieties and leaving groups. The presence of the morpholino group in conjunction with an oxime derivative—especially ethyl 2‐cyano‐2‐(hydroxyimino)acetate (Oxyma)—had a marked influence on the solubilities, stabilities, and reactivities of the reagents. Finally, the new uronium salt derived from Oxyma (COMU) performed extremely well in the presence of only 1 equiv of base, thereby confirming the effect of the hydrogen bond acceptor in the reaction. COMU also showed a less hazardous safety profile than the benzotriazole‐based HDMA and HDMB, which exhibited unpredictable autocatalytic decompositions. Furthermore, the Oxyma moiety contained in COMU suggests a lower risk of explosion than in the case of the benzotriazole derivatives.