Copper-Catalyzed Azide-Ynamide Cyclization to Generate alpha-Imino Copper Carbenes: Divergent and Enantioselective Access to Polycyclic N-Heterocycles

摘要

Here an efficient copper-catalyzed cascade cyclization of azide-ynamides via alpha-imino copper carbene intermediates is reported, representing the first generation of alpha-imino copper carbenes from alkynes. This protocol enables the practical and divergent synthesis of an array of polycyclic N-heterocycles in generally good to excellent yields with broad substrate scope and excellent diastereoselectivities. Moreover, an asymmetric azide-ynamide cyclization has been achieved with high enantioselectivities (up to 98:2 e.r.) by employing BOX-Cu complexes as chiral catalysts. Thus, this protocol constitutes the first example of an asymmetric azide-alkyne cyclization. The proposed mechanistic rationale for this cascade cyclization is further supported by theoretical calculations.