Tf2O‐Promoted Synthesis of Ureas, Carbamates and Thiocarbamate via Lossen Rearrangement: A Mechanistic Insight

Herein, we report triflic anhydride mediated synthesis of ureas starting from hydroxamic acids. The scope of triflic anhydride was also expanded to encompass carbamates. In addition, this reaction is applicable to activation of hydroxamic acid derivative of dipeptide giving α‐uriedopeptidomimetics in good yield. The mechanistic study of reaction was carried out by DFT. This study is important because it demonstrates that Tf2O has the potential to be effective when used on a substrate that possesses amide bond. A broad substrate scope and mild conditions render this protocol a promising approach to the synthesis of diverse types of ureas. A new and feasible synthetic method for ureas, carbamates and thiocarbamate from hydroxamic acid and Tf2O via Lossen rearrangement has been developed. The use of Tf2O was chemoselective with hydroxamate group with broad substrate applicability and good functional group tolerance. Further pathway of the mechanism was analysed through computational studies.