Chiral-Boron-Complex Catalyzed Asymmetric Inverse-Electron-Demand Aza-Diels-Alder Reaction of β-Trifluoromethyl α,β-Unsaturated Ketones with Cyclic N-Sulfonyl Ketimines

Chiral-Boron Complex-Catalyzed Asymmetric [3 + 2] Cycloaddition of 2'-Hydroxychalcones with N-2,2,2-Trifluoroethylisatin Ketimines

A highly efficient asymmetric [3 + 2] cycloaddition reaction of 2'-hydroxychalcones with N-2,2,2-trifluoroethylisatin ketimines catalyzed by a (R)-3,3'-I2-BINOL-boron complex was developed. A broad range of 3,2'-pyrrolidinyl spirooxindole derivatives bearing a CF3-substituted pyrrolidine moiety with four contiguous stereocenters was prepared in high yields with excellent diastereo- and enantioselectivities (up to >20:1 dr and >99% ee). This protocol had the characteristics of mild reaction conditions, high efficiency, and excellent stereocontrol.

Recent Advances in Asymmetric Catalysis Using p-Block Elements

The development of new methods for enantioselective reactions that generate stereogenic centres within molecules are a cornerstone of organic synthesis. Typically, metal catalysts bearing chiral ligands as well as chiral organocatalysts have been employed for the enantioselective synthesis of organic compounds. In this review, we highlight the recent advances in main group catalysis for enantioselective reactions using the p-block elements (boron, aluminium, phosphorus, bismuth) as a complementary and sustainable approach to generate chiral molecules. Several of these catalysts benefit in terms of high abundance, low toxicity, high selectivity, and excellent reactivity. This minireview summarises the utilisation of chiral p-block element catalysts for asymmetric reactions to generate value-added compounds.

Chiral-Boron-Complex-Catalyzed Asymmetric [3 + 2] Cycloaddition of β-Trifluoromethyl α,β-Unsaturated Ketones with N,N'-Cyclic Azomethine Imines

The (R)-3,3'-(3,5-(CF3)2-C6H3)2-BINOL-boron-complex-catalyzed asymmetric 1,3-dipolar cycloaddition of β-trifluoromethyl α,β-unsaturated ketone with N,N'-cyclic azomethine imines was developed to afford N,N'-bicyclic pyrazolidine derivatives bearing a stereogenic carbon center containing CF3 motifs in high yields with excellent diastereo- and enantioselectivities (up to >20:1 dr, and >99% ee). This catalytic system features mild reaction conditions, high efficiency, and a broad substrate scope.