Enantioselective Copper-Catalyzed Electrophilic Sulfenylation of Cyclic Imino Esters

Catalyzed Asymmetric Michael Additions of 1-Pyrroline Esters with β-Fluoroalkyl Alkenyl Imides and Azodicarboxylates

The asymmetric Michael addition reactions of 1-pyrroline esters with β-fluoroalkyl alkenyl imides and dialkyl azodicarboxylates catalyzed by the AgOAc/Ph-phosferrox or CuOAc/(R)-BINAP complex have been developed. A series of chiral 1,5,5-trisubstituted pyrroline ester derivatives have been obtained in 53%-90% yields with 80%-99% ee's and all > 20:1 dr. The gram-scale synthesis and synthetic application of the chiral trifluoromethylated 1-pyrroline adducts were exhibited: the pyrrolizidin-3-one analogue was first synthesized with 94% ee and > 20:1 dr through two steps of hydrolysis and reductive cyclization; the pyrrolidine and lactam derivatives were also successfully provided under the reducing conditions of NaBH3CN and Pd/C─H2, respectively.

Enantioselective Pd- and Cu-Catalyzed Hydrofunctionalization of Methylenecyclopropanes via a Distal C-C Bond Cleavage

The enantioselective ring-opening reactions of methylenecyclopropanes (MCPs) involving C-C bond activation via oxidative addition of transition metals have been rarely reported. Here, we disclose a Pd/Cu-catalyzed enantio- and regioselective coupling between cyclic imino esters and MCPs to produce α-allylated 2H-pyrrole derivatives. In this reaction, azomethine ylide formed by a chiral copper catalyst with ketimine ester would serve as a nucleophile to react with activated MCPs via palladium catalysis. This bimetallic catalyst system exhibited a broad substrate scope and high regio- and enantioselectivities.

Stereoselective Electrophilic Sulfenylation of β,β-Disubstituted Enesulfinamides: Asymmetric Construction of Less Accessible Acyclic α,α-Disubstituted α-Sulfenylated Ketimines

Current methods for the asymmetric α-sulfenylation of carbonyls cannot be applied to acyclic carbonyls that have two similar substituents at the α-position. This research demonstrated that the electrophilic sulfenylation of geometry-defined acyclic β,β-disubstituted enesulfinamides using S-aryl or S-alkyl benzenethiosulfonates can be highly stereoselective. This process results in enantioenriched α,α-disubstituted α-sulfenylated ketone surrogates with sulfur-containing acyclic tetrasubstituted carbon stereocenters bearing two electronically and sterically similar substituents (e.g., methyl and ethyl). Furthermore, by employing the corresponding stereoisomers of enensulfinamides, any of the four stereoisomers of α-sulfenylated ketimines can be selectively accessed.

Enantio- and Diastereoselective Copper-Catalyzed Synthesis of Chiral Aziridines with Vicinal Tetrasubstituted Stereocenters

A Cu-catalyzed coupling of cyclic imino esters with 2H-azirines has been developed to synthesize novel optically active aziridines in high yields with excellent levels of diastereo- and enantioselectivities under mild conditions. This novel protocol features a broad substrate scope and good functional group compatibility, and it enriches the existing reaction type of rapid synthesis of optically active aziridines bearing vicinal tetrasubstituted stereogenic carbon centers.