Chiral‐at‐Metal Rhodium(III) Complex Catalyzed Enantioselective Vinylogous Michael Addition of α , α ‐Dicyanoolefins with α , β ‐Unsaturated 2‐Acyl Imidazoles

Bipyridine-N,N'-dioxides Catalysts: Design, Synthesis, and Application in Asymmetric Synthesis of 1H-Pyrazolo[3,4-b]pyridine Analogues

A novel type of highly efficient chiral C2-symmetric bipyridine-N,N'-dioxides ligand application in catalyzing Michael addition/Cyclization of 5-aminopyrazoles with α,β-unsaturated 2-acyl imidazoles has been developed, affording the corresponding adducts in 85-97% yield with up to 99% enantioselectivity under mild conditions with a lower catalyst loading and broad scope. Remarkably, this protocol exhibits advantages in terms of reactivity and enantioselectivity, giving the fact that as low as 2.2 mol % of L1 and 2.0 mol % of Ni(OTf)2 can promote the title reaction on gram scale to afford the desired product with excellent enantioselectivity.

Dynamic Configuration on a Chiral-at-Rhodium Catalyst Featuring a Flexible Tetradentate Ligand

The unique dynamic configuration of an enantioselective chiral-at-metal catalyst based on Rh(III) and a non-chiral tetradentate ligand is described and resolved. At room temperature, the catalyst undergoes a dynamic configuration process leading to the formation of two interconvertible metal-stereoisomers, remarkably without racemization. Density functional theory (DFT) calculations indicate that this metal-isomerization proceeds via a concerted transition state, which features a trigonal bipyramidal geometry stabilized by the tetradentate ligand. Furthermore, the resolved enantiopure complex shows high catalytic enantioinduction in the Friedel-Crafts reaction, achieving enantiomeric ratios as high as 99 : 1.

Asymmetric Synthesis of Tertiary α-Hydroxylation-Cyclopentanones via Synergetic Catalysis of Chiral-at-Metal Rhodium(III) Complexes/Pyrrolidine

Catalytic and asymmetric domino Michael/aldol reaction of 1,2-dicarbonyl compounds with α,β-unsaturated ketones under the synergetic catalysis of chiral-at-metal rhodium complexes and pyrrolidine to deliver tertiary α-hydroxylation-cyclopentanones (45-89% yields with 81-99% ee and up to >20:1 dr) bearing three contiguous stereogenic centers had been established. Moreover, the scalability and practical utility of this protocol were well demonstrated by employing a gram-scale reaction and some representative transformations.

Catalytic asymmetric conjugate addition of coumarins to unsaturated ketones catalyzed by a chiral-at-metal Rh(III) complex

The first catalytic asymmetric vinylogous Michael addition of coumarins to unsaturated ketones catalyzed by chiral rhodium catalysts has been established. This strategy allowed the synthesis of a variety of highly enantioenriched compounds containing coumarin skeletons in 41-99% yields and 84-99% ee. The developed reaction enriches the chemistry of catalytic asymmetric vinylogous Michael additions of 3-cyano-4-methylcoumarins. Furthermore, the protocol showed obvious advantages in reaction enantioselectivity. When the chiral rhodium catalyst was reduced to 0.06 mol%, a Gram-level reaction was still achieved to provide the desired products with 99% ee.

Enantioselective Conjugate Addition of Boronic Acids to α,β-Unsaturated 2-Acyl Imidazoles Catalyzed by Chiral Diols

Herein, we report the enantioselective conjugate addition of organic boronic acids to α,β-unsaturated 2-acyl imidazoles using (R)-3,3'-I₂-BINOL as the catalyst. The catalytic system shows high efficiency and tolerance to alkenylboronic acids and heteroarylboronic acids. The corresponding Michael addition products were obtained in moderate to excellent yields and with moderate to excellent enantioselectivities (up to 97% ee). A gram-scale reaction was also conducted, and the desired product was obtained in high yield with no erosion in enantioselectivity. Finally, the synthetic utility of the methodology was demonstrated by transforming the 2-acyl imidazole moiety to the corresponding aldehyde, carboxylic acid, ester, and amide derivatives.

Catalytic Asymmetric Conjugate Addition of 2-Methyl-3,5-dinitrobenzoates to Unsaturated Ketones

Asymmetric catalytic vinylogous Michael addition of 2-methyl-3,5-dinitrobenzoates to unsaturated ketones catalyzed by chiral rhodium catalysts has been established. This strategy allowed the synthesis of a variety of optically pure compounds containing imidazole and 3,5-dinitrobenzene skeletons in 64-98% yields with 88-98% ee. The developed reaction not only represents highly asymmetric catalytic enantioselective vinylogous Michael addition employing 2-methyl-3,5-dinitrobenzoates as a building block but also enriches the chemistry of catalytic asymmetric vinylogous Michael addition of 2-methyl-3,5-dinitrobenzoates. Furthermore, the protocol showed obvious advantages in reaction activity and enantioselectivity. When the chiral rhodium catalyst was reduced to 0.06 mol %, the gram-level reaction was still achieved to provide the desired product with 95% ee.

Direct Catalytic Asymmetric Vinylogous Michael addition to Construct an All-Carbon Quaternary Center with 3-Alkenyl-oxindoles

The first highly enantioselective asymmetric vinylogous Michael addition of α,α-dicyanoalkenes with 3-alkenyl-oxindoles catalyzed by chiral-at-metal complexes to deliver 3,3′-disubstituted oxindole bearing an all-carbon quaternary stereocenter had been developed. In the...

Construction of chiral chroman skeletons via catalytic asymmetric [4 + 2] cyclization of ortho-hydroxyphenyl-substituted para-quinone methides catalyzed by a chiral-at-metal rhodium complex

Construction of chiral chroman skeletons via catalytic asymmetric [4 + 2] cyclization of ortho-hydroxyphenyl-substituted p-QMs catalyzed by a chiral-at-metal rhodium complex.

Recent Development of Bis-Cyclometalated Chiral-at-Iridium and Rhodium Complexes for Asymmetric Catalysis

The field of asymmetric catalysis has been developing to access synthetically efficacious chiral molecules from the last century. Although there are many sustainable ways to produce nonracemic molecules, simplified and unique methodologies are always appreciated. In the recent developments of asymmetric catalysis, chiral-at-metal Lewis acid catalysis has been recognized as an attractive strategy. The catalysts coordinatively activate a substrate while serving the sole source of chirality by virtue of its helical environment. These configurationally stable complexes were utilized in a large number of asymmetric transformations, ranging from asymmetric Lewis acid catalysis to photoredox and electrocatalysis. Here we provide a comprehensive review of the current advancements in asymmetric catalysis utilizing iridium and rhodium-based chiral-at-metal complexes as catalysts. First, the asymmetric transformations via LUMO and HOMO activation assisted by a chiral Lewis acid catalyst are reviewed. In the second part, visible-light-induced asymmetric catalysis is summarized. The asymmetric transformation via the electricity-driven method is discussed in the final section.

Cooperative Lewis Acid Catalysis for the Enantioselective C(sp3)-H Bond Functionalizations of 2-Alkyl Azaarenes

Herein, we describe the enantioselective C(sp³)-H bond functionalizations of 2-alkyl azaarenes using a cooperative dual Lewis acid catalysis. An achiral Lewis acid activates the unactivated azaarene partner without the need for a strong base. Orthogonally, a chiral-at-metal Lewis acid catalyst enables LUMO lowering and induces chirality. This method tolerates a range of complex molecular scaffolds and exhibits good to excellent yields and selectivity while accepting a wide variety of functional groups.

Asymmetric catalysis with a chiral-at-osmium complex

The first example of a chiral osmium catalyst is reported in which the overall chirality originates exclusively from a stereogenic metal center (metal-centered chirality) with all coordinating ligands being achiral. The non-C2-symmetric chiral-at-metal complex contains two cyclometalated 7-methyl-1,7-phenanthrolinium heterocycles which can be described as two chelating pyridylidene remote N-heterocyclic carbene (rNHC) ligands. The octahedral coordination sphere is completed with one CO and one acetonitrile ligand. A monodentate chiral oxazoline ligand is used as a chiral auxiliary ligand to obtain enantiomerically pure chiral-at-osmium complexes (>99 : 1 e.r.). Finally, it is demonstrated that the developed chiral-at-osmium complex is suitable for ring-closing enantioselective C(sp3)-H aminations, including the first example of catalytic enantioselective cyclizations of azidoformates to chiral 2-oxazolidinones.