Organocatalysis
Asymmetric organocatalysis involving double activation
Asymmetric organocatalysis contributed tremendously to the field of organic synthesis since year 2000. Considering the diversity of organocatalysts and their activation modes, chemists developed the double activation strategy, in which two distinct catalysts simultaneously interact with a single substrate, thus enabling effective transformations that might be too challenging or even unattainable under a sole catalytic system. This review summarized the asymmetric reactions via double activation catalysis involving different Lewis bases (aminocatalysts, N-heterocyclic carbenes, isothioureas, N,N-dimethyl-4-aminopyridine, tertiary amines/phosphines, or even thiols), Brønsted bases (including phase transfer catalysts), Brønsted acids, and a few examples combining organocatalysts and metal catalysts or photocatalysts were also discussed.Dynamic hydrogen bonds promote C–H functionalization driven by Cl− anion
Most of studies for hydrogen bonds focus on the static model especially between two polar atoms. In contrast, introducing the third polar atom may emerge the competitive hydrogen bonds, which would represent a distinct perspective to perturb the catalytic chemical transformation. Herein, we report quantum mechanics calculations and quasi-classical direct dynamics simulations that demonstrate a triangle form of proton accepters enabled by Cl− anion can afford diverse hydrogen bonds, which control the reactivity and selectivity of Rh catalyzed phenol functionalization.Organocatalytic asymmetric synthesis of bioactive hexahydropyrrolo[2,3-b]indole-containing tetrasubstituted allenes bearing multiple chiral elements
An organocatalytic asymmetric construction of hexahydropyrrolo[2,3-b]indole-containing tetrasubstituted allene scaffolds bearing both axial chirality and central chirality has been established via a cascade 1,8-addition/dearomatization-cyclization reaction of para-aminophenyl propargylic alcohols with tryptamines in the presence of chiral phosphoric acid (CPA), thus affording a wide range of such tetrasubstituted allenes bearing multiple chiral elements in generally good yields (up to 94%) with high diastereo- and enantioselectivities (up to 95:5 dr, 95% ee).Modular access to chiral cyclopentanes via formal [2+2+1] annulation enabled by palladium/chiral squaramide relay catalysis
An enantio- and diastereodivergent [2+2+1] annulation reaction of allyl ketones, acidic methylene compounds, and nitroalkenes to assemble highly functionalized cyclopentanes from readily available substances enabled by asymmetric relay catalysis of chiral bifunctional squaramide and palladium complex has been established. This method showcases that allyl ketones can serve as latent 1,2-dication synthons via a linear-selective allylic C–H functionalization and sequential 1,4-conjugated addition, enabling the rapid assembly of cyclopentane skeleton with a broad scope of methylene nucleophiles and nitroalkenes.
