Copper-Catalyzed Asymmetric Kinugasa/Michael Addition Cascade Reactions for the Synthesis of Chiral Spiro β-Lactams
作者:Yunlin Ao、Haowen Ma、Binghan Gan、Wenjing Wang、Jiehao Zhang、Wei Zhou、Xiaoqi Zhang、Qian Cai
DOI:10.1021/acs.orglett.4c01568
日期:2024.6.7
A mild copper-catalyzed asymmetric Kinugasa/Michael addition cascade process is developed. The reaction of α, β-unsaturated ester-tethered propiolamides with nitrones provides an efficient protocol for the construction of functionalized chiral 2,6-diazaspiro[3.4]octane-1,5-dione products in satisfactory yields and with high enantio- and diastereoselectivities.
Various nitrogen-bridged bicyclic skeletons are found in bioactive natural products and pharmaceuticals. The development of a new reaction to construct these molecular frameworks has attracted considerable attention in synthetic organic chemistry. We developed a novel synthetic method for obtaining a wide variety of nitrogen-bridged bicyclic compounds with a catalytic process, Rh-catalyzed formal carbenoid insertion into an amide C-N bond. Using 0.1-0.4 mol % Rh-2((NHCOBu)-Bu-t)(4) catalyst, various azabicydo[X.Y.Z]alkane derivatives were obtained in good to excellent yield, successfully demonstrating the broad substrate scope of the developed process. Experimental and computational studies to elucidate the reaction mechanism revealed that the formal insertion reaction of a carbenoid into an amide C-N bond proceeded via the formation of Rh-associated N-ylides, followed by an acyl group-selective Stevens [1,2]-shift through a concerted addition/elimination process on the sp(2)-hybridized carbon.