A Metal-Free Synthesis of N-Aryl Carbamates under Ambient Conditions

The first chemo- and site-selective process for the formation of N-aryl-carbamates from cyclic organic carbonates and aromatic amines is reported. The reactions proceed smoothly under extremely mild reaction conditions using TBD (triazabicyclodecene) as an effective and cheap organocatalyst, thus providing a sustainable and new methodology for the formation of a wide variety of useful N-aryl carbamate synthons in good to excellent yields. Computational investigations have been performed and show the underlying reason for the observed unique reactivity as related to an effective proton-relay mechanism mediated by the bicyclic guanidine base. By relay: The previously unknown site-selective attack of arylamines on cyclic carbonates to deliver N-aryl carbamates as the principal product is reported. The organocatalyst TBD guides an effective proton-relay process, thus mediating a chemoselective formation of the carbamate target under extremely mild reaction conditions. The new methodology represents a sustainable, cheap, and attractive process towards these important N-aryl carbamate synthons.