Asymmetric Formal [3+2] Cycloaddition Reaction of α-Aryl Isocyanoesters with N-Aryl Maleimides by Bifunctional Cinchona Alkaloids-Based Squaramide/AgSbF_6 Cooperative Catalysis

摘要

Cooperative catalysis, which combines two or more catalytic species that operate together within the same molecular environment to achieve an overall transformation through synergistic activation of reaction partners, have been shown to possess distinguished advantages in developing new chemical transformations or improving the efficiency and stereoselectivity of existing transformations. The organo/metal mixed system, as one of the three main categories of cooperative systems, has been widely used in reactions such as α-functionalization of aldehydes or imines, conjugate addition to α,β-unsaturated carbonyl compounds, and carbonyl and imine 1,2-addition via the merger of enamine or imine catalysis and metal catalysis. Moreover, cinchona alkaloid scaffolds have proven to be privileged systems in the cooperative catalysis owing to their facile preparation, excellent stereoselective induction, commercial availability, and presence of multiple sites for further functionalization. Cinchona alkaloid-derived ethers, esters, amides, and thioureas have been widely applied in nucleophilic additions of aldehydes, imines, and olefins, through their Bronsted/ Lewis basic property, to activate pro-nucleophiles via deprotonation or coordination, and ketene cycloaddition reactions by using them as Lewis basicucleophilic catalyst.