Access to (bridged) bicyclic ureas through azocarboxamide-enabled enantioselective 1,2-diamination of α-branched cyclic ketones

Abstract

Chiral bicyclic ureas are important multi-nitrogen-containing polycyclic frameworks and valuable building blocks in organic synthesis. Although many racemic synthetic methods have been reported, their catalytic asymmetric synthesis remains challenging and elusive. Herein, we report the azocarboxamide-enabled enantioselective 1,2-diamination of α-branched cyclic ketones. Under mild conditions, a wide range of fused bicyclic ureas bearing vicinal N-containing quaternary stereocenters have been prepared in good yield with excellent enantioselectivity. Notably, when α-carbethoxy cyclic ketones are used as substrates, the reaction proceeds through a cascade of 1,2-diaminization/lactonization, which leads to the formation of highly crowded and structurally unique bridged bicyclic ureas.