Chiral Diene Ligands Research Articles

Ligand-controlled regiodivergent arylation of aryl(alkyl)alkynes and asymmetric synthesis of axially chiral 9-alkylidene-9,10-dihydroanthracenes

Transition metal-catalyzed addition of organometallics to aryl(alkyl)alkynes has been well known to proceed with the regioselectivity in forming a carbon–carbon bond at the alkyl-substituted carbon (β-addition). Herein, the reverse regiochemistry with high selectivity in giving 1,1-diarylalkenes (α-addition) was realized in the reaction of arylboronic acids with aryl(alkyl)alkynes by use of a rhodium catalyst coordinated with a chiral diene ligand, whereas the arylation of the same alkynes proceeded with the usual regioselectivity (β-addition) in the presence of a rhodium/DM-BINAP catalyst. The regioselectivity can be switched by the choice of ligands on the rhodium catalysts. This reverse regioselectivity also enabled the catalytic asymmetric synthesis of phoenix-like axially chiral alkylidene dihydroanthracenes with high enantioselectivity through an α-addition/1,4-migration/cyclization sequence.

Chiral Ligand-Decorated Rhodium Nanoparticles Incorporated in Covalent Organic Framework for Asymmetric Catalysis.

While metal nanoparticles (NPs) have demonstrated their great potential in catalysis, introducing chiral microenvironment around metal NPs to achieve efficient conversion and high enantioselectivity remains a long-standing challenge. In this work, tiny Rh NPs, modified by chiral diene ligands (Lx) bearing diverse functional groups, are incorporated into a covalent organic framework (COF) for the asymmetric 1,4-addition reactions between arylboronic acids and nitroalkenes. Though Rh NPs hosted in the COF are inactive, decorating Rh NPs with Lx creates the active Rh-Lx interface and induces high activity. Moreover, chiral microenvironment modulation around Rh NPs by altering the groups on chiral diene ligands greatly optimizes the enantioselectivity (up to 95.6 % ee). Mechanistic investigations indicate that the formation of hydrogen-bonding interaction between Lx and nitroalkenes plays critical roles in the resulting enantioselectivity. This work highlights the significance of chiral microenvironment modulation around metal NPs by chiral ligand decoration for heterogeneous asymmetric catalysis.

Chiral Ligand‐Decorated Rhodium Nanoparticles Incorporated in Covalent Organic Framework for Asymmetric Catalysis

AbstractWhile metal nanoparticles (NPs) have demonstrated their great potential in catalysis, introducing chiral microenvironment around metal NPs to achieve efficient conversion and high enantioselectivity remains a long‐standing challenge. In this work, tiny Rh NPs, modified by chiral diene ligands (Lx) bearing diverse functional groups, are incorporated into a covalent organic framework (COF) for the asymmetric 1,4‐addition reactions between arylboronic acids and nitroalkenes. Though Rh NPs hosted in the COF are inactive, decorating Rh NPs with Lx creates the active Rh−Lx interface and induces high activity. Moreover, chiral microenvironment modulation around Rh NPs by altering the groups on chiral diene ligands greatly optimizes the enantioselectivity (up to 95.6 % ee). Mechanistic investigations indicate that the formation of hydrogen‐bonding interaction between Lx and nitroalkenes plays critical roles in the resulting enantioselectivity. This work highlights the significance of chiral microenvironment modulation around metal NPs by chiral ligand decoration for heterogeneous asymmetric catalysis.

Enantioselective Synthesis of Axially and Centrally Chiral Styrenes via Nickel-Catalyzed Desymmetric Hydrocyanation of Biaryl Dienes.

Herein, a highly regio-, enantio-, and diastereoselective nickel-catalyzed desymmetric hydrocyanation of biaryl dienes for the simultaneous construction of axial and central chiralities is presented, which offers a convenient approach to a variety of tirenes containing the union of an axially chiral biaryl and a centrally α-chiral nitrile under mild conditions using a commercially available catalyst. The synthetic utility is highlighted by the development of a novel axially chiral phosphine ligand and biphenyl-based chiral diene ligand and their potential applications in the field of asymmetric catalytic reactions.

Synthesis of chiral boranes via asymmetric insertion of carbenes into B-H bonds catalyzed by the rhodium(I) diene complex.

Molecules with chiral boron atoms have been scarcely studied due to limited synthetic access. Herein, we report a new method for their synthesis via asymmetric insertion of arydiazoacetates into the B-H bonds of prochiral carbene-boranes NHC-BH2R. The reaction is catalyzed by the rhodium(I) complex with the chiral diene ligand tBu2-TFB, which can be conveniently prepared by diastereoselective coordination of the racemic diene with (S-Salox)Rh(CO)2. The target boranes were typically obtained in 75-90% yields with 90-95% ee.

A Scalable Synthesis of Chiral Himbert Diene Ligands for Asymmetric Catalysis

AbstractChiral dienes are important ligands in asymmetric catalysis but they are less accessible than other commonly used ligands such as chiral bisphosphines. Here, we show that intramolecular [4+2] cycloaddition of a simply attained chiral allenecarboxanilide readily affords pseudoenantiomeric bicyclo[2.2.2]octa‐2,5‐dienes containing an alkenyl bromide, which can be readily functionalized to give diverse chiral diene ligands. The synthesis is straightforward and easily conducted on multigram scales. These ligands exhibit high performance in nine types of enantioselective Rh(I)‐catalyzed 1,4‐addition or 1,2‐addition reactions.magnified image

Low Coordination State RhI‐Complex as High Performance Catalyst for Asymmetric Intramolecular Cyclopropanation: Construction of penta‐Substituted Cyclopropanes

AbstractA simple, broad‐scope rhodium(I)/chiral diene catalytic system for challenging asymmetric intramolecular cyclopropanation of various tri‐substituted allylic diazoacetates was successfully developed. The low coordination state RhI‐complex exhibits an extraordinarily high degree of tolerance to the variation in the extent of substitution of the allyl double bond, thus allowing the efficient construction of a wide range of penta‐substituted, fused‐ring cyclopropanes bearing three contiguous stereogenic centers, including two quaternary carbon stereocenters, in a highly enantioselective manner with ease at catalyst loading as low as 0.1 mol %. The stereoinduction mode of this RhI‐carbene‐directed asymmetric intramolecular cyclopropanation was investigated by DFT calculations, indicating that π‐π stacking interactions between the aromatic rings of chiral diene ligand and diazo substrate play a key role in the control of the reaction enantioselectivity.

Low Coordination State Rh(I)-Complex as High Performance Catalyst for Asymmetric Intramolecular Cyclopropanation: Construction of penta-Substituted Cyclopropanes.

A simple, broad-scope rhodium(I)/chiral diene catalytic system for challenging asymmetric intramolecular cyclopropanation of various tri-substituted allylic diazoacetates was successfully developed. The low coordination state Rh(I)-complex exhibits an extraordinarily high degree of tolerance to the variation in the extent of substitution of the allyl double bond, thus allowing the efficient construction of a wide range of penta-substituted, fused-ring cyclopropanes bearing three contiguous stereogenic centers, including two quaternary carbon stereocenters, in a highly enantioselective manner with ease at catalyst loading as low as 0.1 mol%. The stereoinduction mode of this Rh(I)-carbene-directed asymmetric intramolecular cyclopropanation was investigated by DFT calculations, indicating that π-π stacking interactions between the aromatic rings of chiral diene ligand and diazo substrate play a key role in the control of the reaction enantioselectivity.

Preparation of new chiral diene ligands and their use in the rhodium catalyzed asymmetric annulation of 2-formylarylboronic acid with dialkylalkynes.

Herein, we report the rhodium-catalyzed domino arylation/cyclization reaction of unactivated internal alkynes to afford the optically active indenols in excellent yields (up to 92%) and extremely high enantioselectivities (up to 99% ee) in the presence of new amide substituted chiral diene ligands. Notably, a total of 21 new chiral diene ligands are synthesized, which are potential choices for other asymmetric reactions.

Rhodium-Catalyzed Highly Enantio- and Diastereoselective Alkenylation of β,γ-Unsaturated Butenolides via Dynamic Kinetic Resolution.

A rhodium-catalyzed highly enantio- and diastereoselective alkenylation of β,γ-unsaturated butenolides is reported. The use of a chiral diene ligand, (S,S)-Ph-bod, enables the facile synthesis of chiral butyrolactones in high yields with extremely high enantioselectivities (>99% ee in all cases) and high diastereoselectivities (up to >20:1 dr). The key process of the reaction involves the isomerization of β,γ-unsaturated butenolides to racemic α,β-unsaturated butenolides and the subsequent dynamic kinetic resolution through ligand-controlled, enantioselective alkenylation with an alkenylrhodium species that is generated in situ via 1,4-rhodium migration.

Rhodium-Catalyzed Asymmetric 1,4-Addition of α/β-(N-Indolyl) Acrylates.

A rhodium-catalyzed asymmetric 1,4-addition of α/β-(N-indolyl) acrylates to access highly enantioenriched chiral N-alkylindoles promoted by chiral diene or sulfur-olefin ligands under mild reaction conditions has been developed, which provides an efficient and practical approach for constructing carbon stereocenters adjacent to the indole nitrogen. The reaction can be applied to various N-indolyl-substituted α,β-unstaturated esters and arylboron reagents, providing access to a wide range of α- and β-(N-indolyl) propionate derivatives in high yields with excellent enantioselectivities (≤99% ee).

Chiral Diene Ligands in Asymmetric Catalysis.

Asymmetric catalysis has emerged as a general and powerful approach for constructing chiral compounds in an enantioselective manner. Hence, developing novel chiral ligands and catalysts that can effectively induce asymmetry in reactions is crucial in modern chemical synthesis. Among such chiral ligands and catalysts, chiral dienes and their metal complexes have received increased attention, and a great progress has been made over the past two decades. This review provides comprehensive and critical information on the essential aspects of chiral diene ligands and their importance in asymmetric catalysis. The literature covered ranges from August 2003 (when the first effective chiral diene ligand for asymmetric catalysis was reported) to October 2021. This review is divided into two parts. In the first part, the chiral diene ligands are categorized according to their structures, and their preparation methods are summarized. In the second part, their applications in asymmetric transformations are presented according to the reaction types.

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Olefins are easily accessible and have diverse reacitivities. Meanwhile, they also can act as ligands in asymmetric catalysis. Acyclic chiral diene ligands as well as hybrid olefin ligands were developed for transition metal catalyzed asymmetric reactions. Chiral dienes can further be applied for acquiring chiral FLP catalysts via the in situ hydroboration. These FLP catalysts proved to be highly effective for asymmetric metal‐free hydrogenations and hydrosilylations.. More details are given in the article by Du et al. on page 1109—1116.image

Dearomative Synthesis of Chiral Dienes Enables Improved Late-Stage Ligand Diversification.

An efficient synthesis of chiral nonracemic diene ligands is facilitated by an enantioselective dearomative intermolecular arene cyclopropanation of anisole. The functionality of the resulting cycloheptatriene engenders distinct chemical environments in a downstream tricyclic bis(enol) triflate that permits selective late-stage functionalization. The synthesis of diverse C1- and pseudo-C2-symmetric dienes is therefore viable by iterative palladium-catalyzed cross-coupling reactions. The ligands provide moderate to high selectivities in known Rh(I)-mediated asymmetric transformations.

Chiral Dienes: From Ligands to FLP Catalysts

Comprehensive SummaryOlefins are very easily accessible compounds which are both popular substrates in synthetic chemistry and good ligands in the organometallic complexes. This dual character makes olefins a rich source of chiral ligands and catalysts for asymmetric catalysis. Herein, we will briefly summarize our studies on the development of chiral diene ligands for transition‐metal catalyzed asymmetric reactions and chiral FLP catalysts for asymmetric metal‐free hydrogenations and hydrosilylations. Several acyclic chiral diene ligands as well as P/olefin and S/olefin hybrid ligands were developed for Rh or Pd‐catalyzed asymmetric reactions. With these ligands in hand, we further put forward a novel strategy for acquiring chiral FLP catalysts via the in situ hydroboration of chiral dienes with Piers’ borane. These catalysts proved to be highly effective for asymmetric metal‐free hydrogenations and hydrosilylations of imines, silyl enol ethers, ketones, and aromatic N‐heterocycles. What is the most favorite and original chemistry developed in your research group?The development of acyclic dienes both as chiral ligands and as precursors of chiral FLP catalysts.How do you get into this specific field? Could you please share some experiences with our readers?When I started my independent research in 2008, chiral olefins belong to one novel ligand type. We got into the field with the thought of the simpler the better. This experience further led us to step into FLP catalysis.What is the most important personality for scientific research?Courage and persistence of doing something unique.What are your hobbies?Walking and playing cards.How do you keep balance between research and family?Life is not only research, but also family. You believe it, the balance is there.What is your favorite journal(s)?My favorite journal is Organic Letters, in which authors can publish their work rapidly and readers can browse the progress of organic chemistry comprehensively.

Rhodium‐Catalyzed Tandem Addition–Cyclization of 1,5‐Enynes with Organoboronic Acids for the Synthesis of Alkylidene‐Cyclobutanes

AbstractDescribed here is the rhodium(I)‐catalyzed tandem addition–cyclization of 1,5‐enynes with aryl‐ and alkenylboronic acids. In the presence of triethylamine and catalytic [Rh(OH)(COD)]2 in methanol, both the terminal and internal alkyne substrates possessing an electron‐deficient alkene undergo inter‐ and intramolecular C−C bond formations to yield alkylidene–cyclobutane products. The reaction proceeds through a series of processes involving generation of an aryl or alkenyl rhodium from the organoboronic acid, 1,2‐syn‐carbometalation of the alkyne and 4‐exo‐type‐cyclization of the resulting alkenyl rhodium intermediate with the tethered, carbonyl‐conjugated alkene. Thus, the reaction enables a net R,H‐addition across the 1,5‐enyne π‐system – hydroarylation and hydroalkenylation – under mild rhodium catalysis while achieving 4‐membered ring formation. Preliminary studies show that the reaction can also be rendered enantioselective by employing a chiral diene ligand for the rhodium catalyst.

Machine learnt patterns in rhodium-catalysed asymmetric Michael addition using chiral diene ligands

Interpretable featurisation allows Quantitative Structure-Property Relationships (QSPR) between chiral diene ligand structures and product stereoselectivities in rhodium-catalysed asymmetric Michael additions (RhCASA). The machine learning approach developed herein is simple to implement yet provides instructive insights and useful predictions (q2/R2 0.7–0.8). These simple interpretable features are found to give comparable predictive ability to both commercial (Dragon) and molecular signature descriptor library approaches. Strong insights into the specific areas of the chiral diene ligand that engender improved RhCASA process enantioselectivity are achieved. These were more interpretable, to synthetic chemists, than existing ML approaches, greatly facilitating design of new chiral diene-ligands.

Asymmetric Synthesis of Chiral Bicyclo[2.2.1]hepta-2,5-diene Ligands through Rhodium-Catalyzed Asymmetric Arylative Bis-cyclization of a 1,6-Enyne.

A series of novel chiral diene ligands (1R,4S)-L1, which are based on the bicyclo[2.2.1]heptadiene skeleton and are substituted with methyl and an ester group at the bridgehead carbons, were synthesized through rhodium-catalyzed asymmetric arylative bis-cyclization of 1,6-enyne 1 as a key step. The rhodium catalyst with one of the (1R,4S)-L1 ligands was used for the asymmetric bis-cyclization of 1 giving bicyclic product (1S,4R)-2 of 99% ee, which is a synthetic precursor of (1S,4R)-L1 ligands.

Synthesis of Rhodium Complexes with Chiral Diene Ligands via Diastereoselective Coordination and Their Application in the Asymmetric Insertion of Diazo Compounds into E−H Bonds

AbstractA new method for the synthesis of chiral diene rhodium catalysts is introduced. The readily available racemic tetrafluorobenzobarrelene complexes [(R2‐TFB)RhCl]2 were separated into two enantiomers via selective coordination of one of them with the auxiliary S‐salicyl‐oxazoline ligand. One of the resulting chiral complexes with an exceptionally bulky diene ligand [(R,R‐iPr2‐TFB)RhCl]2 was an efficient catalyst for the asymmetric insertion of diazoesters into B−H and Si−H bonds giving the functionalized organoboranes and silanes with high yields (79–97 %) and enantiomeric purity (87–98 % ee). The stereoselectivity of separation via auxiliary ligand and that of the catalytic reaction was predicted by DFT calculations.

Synthesis of Rhodium Complexes with Chiral Diene Ligands via Diastereoselective Coordination and Their Application in the Asymmetric Insertion of Diazo Compounds into E-H Bonds.

A new method for the synthesis of chiral diene rhodium catalysts is introduced. The readily available racemic tetrafluorobenzobarrelene complexes [(R2 -TFB)RhCl]2 were separated into two enantiomers via selective coordination of one of them with the auxiliary S-salicyl-oxazoline ligand. One of the resulting chiral complexes with an exceptionally bulky diene ligand [(R,R-iPr2 -TFB)RhCl]2 was an efficient catalyst for the asymmetric insertion of diazoesters into B-H and Si-H bonds giving the functionalized organoboranes and silanes with high yields (79-97 %) and enantiomeric purity (87-98 % ee). The stereoselectivity of separation via auxiliary ligand and that of the catalytic reaction was predicted by DFT calculations.