Ethyl 2‐(tert‐Butoxycarbonyloxyimino)‐2‐cyanoacetate (Boc‐Oxyma): An Efficient Reagent for the Racemization Free Synthesis of Ureas, Carbamates and Thiocarbamates via Lossen Rearrangement

Boc‐Oxyma (Ethyl 2‐(tert‐butoxycarbonyloxyimino)‐2‐cyanoacetate) has been reported previously as an efficient coupling reagent for the synthesis of amides, peptides, esters, thioesters and hydroxamic acids. It is known for its excellent racemization suppression capability, and also as an environment friendly reagent as it generates only Oxyma as solid byproduct that can be recovered easily and recycled for the synthesis of the same reagent. In this update, we report a simple, efficient, environment friendly, chemoselective and racemization free method for the synthesis of ureas, carbamates and thiocarbamates from hydroxamic acids via Lossen rearrangement by using Boc‐Oxyma. We have achieved racemization free di‐ and tri‐peptidyl ureas with very good yield by using this protocol. A rigorous mechanistic investigation is also incorporated.