Highly Diastereo- and Enantioselective Cu-Catalyzed [3 + 3] Cycloaddition of Propargyl Esters with Cyclic Enamines toward Chiral Bicyclo[n.3.1] Frameworks

A new Cu-catalyzed asymmetric [3 + 3] cycloaddition of propargyl esters with cyclic enamines is reported. With a combination of Cu­(OAc)2·H2O and a chiral tridentate ferrocenyl-P,N,N ligand as the catalyst, perfect endo selectivities (endo/exo > 98/2) and excellent enantioselectivities (up to 98% ee) for endo cycloadducts were achieved under mild conditions. This method provides a simple and efficient approach for the synthesis of optically active bicyclo­[n.3.1] frameworks.