First Iridium-Catalyzed Highly Enantioselective Hydrogenation of β-Nitroacrylates
摘要:
The first highly chemo- and enantioselective hydrogenation of beta-nitroacrylates was accomplished with an iridium catalyst (Ir-4) with yields and enantioselectivities of up to 96% and 98% ee, respectively. The resulting alpha chiral beta-nitro propionates are attractive building blocks for the synthesis of chiral beta(2)-amino acids, which are the core scaffolds of bioactive natural products, pharmaceuticals, and beta-peptides.
Readily available hydrogen bond catalysts for the asymmetric transfer hydrogenation of nitroolefins
作者:Jakob F. Schneider、Markus B. Lauber、Vanessa Muhr、Domenic Kratzer、Jan Paradies
DOI:10.1039/c1ob05059a
日期:——
focuses on readily accessible thiourea hydrogen bond catalysts derived from amino acids, whose steric and electronic features are modulated by their degree of substitution at the carbinol carbon center. These catalysts were applied in the asymmetric transfer hydrogenation of nitroolefins furnishing the chiral products in up to 99% yield and 86% enantiomeric excess. The proposed catalyst's mode of action
optimized an enantioselective Michael reaction of malononitrile with β,β‐disubstituted nitroalkenes. This reaction was catalyzed by a cinchona alkaloid derived thiourea catalyst, producing products of high yields (up to 98 %) and stereoselectivities (up to 93 % ee). One of the adducts was used as an intermediate for the synthesis of dihydropyrrole derivative bearing a synthetically valuable quaternary chiral
octahedral iridium complex, an exceptionally active hydrogen-bond-mediated asymmetric catalyst was developed and its mode of action investigated by crystallography, NMR, computation, kinetic experiments, comparison with a rhodium congener, and reactions in the presence of competing H-bond donors and acceptors. Relying exclusively on weak forces, the enantioselective conjugate reduction of nitroalkenes
Metal‐templated organocatalysis: The enantioselective formation of an all‐carbon quaternarystereocenter is catalyzed by the ligand sphere of an inert bis‐cyclometalated iridium complex (see picture). In this complex, the metal‐centered chirality serves as the sole source for the effective asymmetric induction.
Epi-quinine-catalyzed asymmetric nitro-Michaeladdition of furanones to β,β,-disubstituted nitroalkenes is described. The reaction proceeded smoothly with 1–5 mol % loadings of epi-quinine catalysts at room temperature, giving the corresponding Michael adducts in high yields (72–93%) with extremely high diastereo- and enantioselectivities (>98/2 dr, syn major; 95–99% ee). This reaction provides an