Highly Diastereo- and Enantioselective Cu-Catalyzed 3 + 3 Cycloaddition of Propargyl Esters with Cyclic Enamines toward Chiral Bicyclon.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)·H(2)O 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 bicyclon.3.1 frameworks.