Synthesis of NOBIN Derivatives for Asymmetric Catalysis

Chiral Phosphoric Acid Catalyzed Asymmetric Hydrolysis of Biaryl Oxazepines for the Synthesis of Axially Chiral Biaryl Amino Phenol Derivatives

The development of catalytic asymmetric reaction with water as the reactant is challenging due to the reactivity- and stereoselectivity-control issues resulted from the low nucleophilicity and the small size of water. We disclose herein a chiral phosphoric acid (CPA) catalyzed atroposelective ring-opening reaction of biaryl oxazepines with water. A series of biaryl oxazepines undergo the CPA catalyzed asymmetric hydrolysis in a highly enantioselective manner. The key for the success of this reaction is the use of a new SPINOL-derived CPA catalyst and the high reactivity of biaryl oxazepine substrates towards water under acidic conditions. Density functional theory calculations suggest that the reaction proceeds via a dynamic kinetic resolution pathway and the CPA catalyzed addition of water to the imine group is both enantio- and rate-determining.

Axially chiral styrene-based organocatalysts and their application in asymmetric cascade Michael/cyclization reaction

An axially chiral styrene-based organocatalyst, featuring a combination of axially chiral styrene-based structure and a pyrrole ring, has been designed and synthesized. This catalyst demonstrates remarkable capabilities in producing a wide range of densely substituted spirooxindoles that feature an alkyne-substituted quaternary stereogenic center. These spirooxindoles are generated through mild cascade Michael/cyclization reactions, resulting in high conversion rates and exceptional enantioselectivity. Our catalytic model, based on experiments, X-ray structure analysis and DFT calculations suggests that chiral matched π-π interactions and multiple H-bonds between the organocatalyst and substrates play significant roles in controlling the stereoselectivity of the reaction.

Iridium(I)-Catalyzed Atroposelective Alkenylation of Heterobiaryls with Terminal Alkynes

Herein we report an iridium(I)-catalyzed atroposelective alkenylation of isoquinoline-derived heterobiaryls with terminal alkynes. In the presence of a cationic iridium(I) catalyst with (R)-SEGPHOS as the chiral ligand, this atom-economical alkenylation protocol allows the rapid construction of a series of axially chiral alkenylated heterobiaryls in moderate to good yields with good to high enantioselectivities.

Palladium-catalyzed interannular C-H amination of biaryl amines

A palladium-catalyzed interannular C-H amination of biaryl amines with O-benzoylhydroxylamines is reported. This reaction undergoes smoothly with operational practicality and good tolerance of functional groups, thereby providing a concise synthesis of 2,2'-diaminobiaryls. Moreover, the readily accessible scale-up synthesis and the ability to transform the products into structurally diverse N-containing heterocycles demonstrate the synthetic potential of this catalytic protocol.

Conformational enantiodiscrimination for asymmetric construction of atropisomers

Molecular conformations induced by the rotation about single bonds play a crucial role in chemical transformations. Revealing the relationship between the conformations of chiral catalysts and the enantiodiscrimination is a formidable challenge due to the great difficulty in isolating the conformers. Herein, we report a chiral catalytic system composed of an achiral catalytically active unit and an axially chiral 1,1'-bi-2-naphthol (BINOL) unit which are connected via a C-O single bond. The two conformers of the catalyst induced by the rotation about the C-O bond, are determined via single-crystal X-ray diffraction and found to respectively lead to the formation of highly important axially chiral 1,1'-binaphthyl-2,2'-diamine (BINAM) and 2-amino-2'-hydroxy-1,1'-binaphthyl (NOBIN) derivatives in high yields (up to 98%), with excellent enantioselectivities (up to 98:2 e.r.) and opposite absolute configurations. The results highlight the importance of conformational dynamics of chiral catalysts in asymmetric catalysis.

Enantioselective construction of ortho-sulfur- or nitrogen-substituted axially chiral biaryls and asymmetric synthesis of isoplagiochin D

Axially chiral biaryl motifs possessing ortho-heteroatom-substituted functionalities exist widely in the structures of natural products and have served as foundation for constructing prominent chiral organocatalysts, ligands, functional materials, and even bioactive molecules. However, a general and enantioselective synthesis of such chiral structures with high synthetic value is rare. Taking advantage of the BaryPhos-facilitated asymmetric Suzuki-Miyaura cross-coupling, we have established a general, efficient and enantioselective construction of the ortho sulfur- or nitrogen-substituted axially chiral biaryls. The protocol shows excellent compatibility to various functional groups and structural features, delivering chiral biaryl structures with ortho-sulfonyl groups or with ortho-nitro groups at a broad range of molecular diversity and complexity. The immobilization of BaryPhos on polyethylene glycol (PEG) support has enabled homogeneous enantioselective cross-coupling in aqueous media and the palladium catalyst recycling for multiple times. The method has enabled a concise 10-step asymmetric synthesis of isoplagiochin D as well as the construction of chiroptical molecules with circularly polarized luminescence (CPL) properties.

Ortho-heteroatom-substituted axially chiral biaryls are valuable structures in synthetic and medicinal chemistry. Here, the authors established an efficient synthesis of these chiral structures via asymmetric cross-coupling.

Organocatalytic atroposelective N-alkylation: divergent synthesis of axially chiral sulfonamides and biaryl amino phenols

Axial chirality exists ubiquitously in numerous natural products and has been extensively recognized for decades in pharmaceuticals and enantioselective transformations. The development of efficient methodologies to obtain enantiopure structures bearing...

Rational Design of Axially Chiral Styrene-Based Organocatalysts and Their Application in Catalytic Asymmetric (2+4) Cyclizations

A new class of axially chiral styrene-based thiourea tertiary amine catalysts, which have unique characteristics such as an efficient synthetic route, multiple chiral elements, and multiple activating groups, has been rationally designed. These new chiral catalysts have proven to be efficient organocatalysts, enabling the chemo-, diastereo-, and enantioselective (2+4) cyclization of 2-benzothiazolimines with homophthalic anhydrides in good yields (up to 96 %) with excellent stereoselectivities (all >95:5 dr, up to 98 % ee). More importantly, theoretical calculations elucidated the important role of an axially chiral styrene moiety in controlling both the reactivity and enantioselectivity. This work not only represents the first design of styrene-based chiral thiourea tertiary amine catalysts and the first catalytic asymmetric (2+4) cyclization of 2-benzothiazolimines, but also gives an in-depth understanding of axially chiral styrene-based organocatalysts.

Synthesis of non-C2 symmetrical NOBIN-type biaryls through a cascade N-arylation and [3,3]-sigmatropic rearrangement from O-arylhydroxylamines and diaryliodonium salts

We developed herein a regioselective construction of non-C₂ symmetrical NOBIN-type biaryls through a cascade N-arylation and [3,3]-sigmatropic rearrangement from O-arylhydroxylamines and diaryliodonium salts under mild conditions. The employment of copper salt could inhibit the further O-arylation of the newly formed biaryl products, otherwise, O-arylated NOBIN-type products were furnished in moderate to good isolated yields. The products of this protocol can be further converted into highly valuable functional molecules and heterocycles.

Copper-Catalyzed Synthesis of Axially Chiral Biaryls with Diaryliodonium Salts as Arylation Reagents

NOBIN and BINAM derivatives harboring biaryl frameworks are recognized as a class of important atropisomers with versatile applications. Here, we present an efficient synthetic route to access such compounds through copper-catalyzed domino arylation of N-arylhydroxylamines or N-arylhydrazines with diaryliodonium salts and [3,3]-sigmatropic rearrangement. This reaction features mild conditions, good substrate compatibility, and excellent efficiency. The practicality of this protocol was further extended by the synthesis of biaryl amino alcohols.

Enantioselective Synthesis of 3,3'-Disubstituted 2-Amino-2'-hydroxy-1,1'-binaphthyls by Copper-Catalyzed Aerobic Oxidative Cross-Coupling

A challenging direct asymmetric catalytic aerobic oxidative cross-coupling of 2-naphthylamine and 2-naphthol, using a novel Cu^I /SPDO system, has been successfully developed for the first time. Enantioenriched 3,3'-disubstituted NOBINs were achieved and could be readily derived to divergent chiral ligands and catalysts. This reaction features high enantioselectivities (up to 96 % ee) and good yields (up to 80 %). The DFT calculations suggest that the F-H interactions between CF₃ of L17 and H-1,8 of 2-naphthol, and the π-π stacking between the two coupling partners could play vital roles in the enantiocontrol of this cross-coupling reaction.

Recent Advances in Asymmetric Iron Catalysis

Asymmetric transition-metal catalysis represents a fascinating challenge in the field of organic chemistry research. Since seminal advances in the late 60s, which were finally recognized by the Nobel Prize to Noyori, Sharpless and Knowles in 2001, the scientific community explored several approaches to emulate nature in producing chiral organic molecules. In a scenario that has been for a long time dominated by the use of late-transition metals (TM) catalysts, the use of 3d-TMs and particularly iron has found, recently, a widespread application. Indeed, the low toxicity and the earth-abundancy of iron, along with its chemical versatility, allowed for the development of unprecedented and more sustainable catalytic transformations. While several competent reviews tried to provide a complete picture of the astounding advances achieved in this area, within this review we aimed to survey the latest achievements and new concepts brought in the field of enantioselective iron-catalyzed transformations.

Tandem approach to NOBIN analogues from arylhydroxylamines and diaryliodonium salts via [3,3]-sigmatropic rearrangement

Herein, we present a transition-metal free direct O-arylation of arylhydroxylamines employing diaryliodonium salts as arylation reagents to form transient N,O-diarylhydroxylamines that could subsequently undergo [3,3]-sigmatropic rearrangement and re-aromatization to afford structurally diverse NOBIN analogs in good to excellent yields under mild conditions.

Iron-Catalyzed Oxidative C-C Cross-Coupling Reaction of Tertiary Anilines with Hydroxyarenes by Using Air as Sole Oxidant

A mild procedure for the oxidative C-C cross-coupling of tertiary anilines with phenols is described which provides the products generally in high yields and with excellent selectivity. The reaction is catalyzed by the hexadecafluorinated iron-phthalocyanine complex FePcF16 in the presence of substoichiometric amounts of methanesulfonic acid and ambient air as sole oxidant.

Ir(iii)-Catalyzed direct C–H functionalization of N-phenylacetamide with α-diazo quinones: a novel strategy for producing 2-hydroxy-2′-amino-1,2′-biaryl scaffolds

A novel strategy is reported for the construction of 2-hydroxy-2′-amino-1,1′-biaryl scaffolds via Ir(iii)-catalyzed direct C–H bond activation under mild reaction conditions.

Atroposelective Synthesis of Biaryl Diamines and Amino Alcohols via Chiral Phosphoric Acid Catalyzed para-Aminations of Anilines and Phenols

A versatile method for atroposelective synthesis of chiral biaryl diamines and amino alcohols has been developed via para-amination of anilines and phenols with azodicarboxylates enabled by chiral phosphoric acid catalysis. Meanwhile, highly efficient kinetic resolution of the racemic biaryl anilines has also been realized through these reactions, giving selectivity factor up to 246. The gram-scale reaction and facile derivatizations of the chiral products well demonstrate the potential of these reactions in the development of novel chiral ligands and catalysts.

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Versatile methods for asymmetric synthesis of biaryl diamines and amino alcohols

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Atroposelective para-aminations of biaryl anilines and phenols

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Kinetic resolution of racemic biaryl anilines

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Facile transformations of chiral products

Chiral Phosphoric Acid-Catalyzed Enantioselective Direct Arylation of Iminoquinones: A Case Study of the Model Selectivity

Chiral phosphoric acid (CPA)-catalyzed enantioselective arylation reactions have attracted immense attention recently. However, the preferential activation model in the stereodetermining step is controversial, and hence, the origin of enantioselectivity is still far from being understood. Two stereochemical models are provided on the basis of the asymmetric arylations of iminoquinones with naphthylamines (reaction 1) or naphthols (reaction 2) catalyzed by (R/S)-TRIP to explain the high enantioselectivity and the effect of CPAs scaffolds. Unexpectedly, our calculations reveal that substrate naphthylamines or naphthols prefer enantioselective aminal formation model II or 1,4-addition model I, respectively, which is the reverse of Tan's and Xu's model. The different noncovalent and steric interactions between catalysts and substrates are responsible for the observed model preference. Moreover, the enantioselectivity arises from distortion (reaction 1) and noncovalent interactions (reaction 2) that discriminate between the diastereomeric transition states. We further investigated the effect of SPINOL-based CPAs on the enantioselectivity and found that the more rigid skeleton and a smaller binding pocket lead to lower enantioselectivity as compared with that of BINOL-based CPA. The new insights into the reaction activation model rationalize the stereoselectivity outcome of direct asymmetric arylation reactions, and our general model can be extended to related transformations.

Practical access to axially chiral sulfonamides and biaryl amino phenols via organocatalytic atroposelective N-alkylation

The importance of axial chirality in enantioselective synthesis has been widely recognized for decades. The practical access to certain structures such as biaryl amino phenols known as NOBINs in enantiopure form, however, still remains a challenge. In drug delivery, the incorporation of axially chiral molecules in systematic screening has also received a great deal of interest in recent years, which calls for innovation and practical synthesis of structurally different axially chiral entities. Herein we present an operationally simple catalytic N-alkylation of sulfonamides using commercially available chiral amine catalysts to deliver two important classes of axially chiral compounds: structurally diverse NOBIN analogs as well as axially chiral N-aryl sulfonamides in excellent enantiopurity. Structurally related chiral sulfonamide has shown great potential in drug molecules but enantioselective synthesis of them has never been accomplished before. The practical catalytic procedures of our methods also bode well for their wide application in enantioselective synthesis.

NHC-catalyzed atropoenantioselective synthesis of axially chiral biaryl amino alcohols via a cooperative strategy

Axially chiral biaryl amino-alcohols play a pivotal role in organic synthesis and drug discovery. However, only a very few enantioselective methods have been reported to synthesize chiral biaryl amino-alcohols. Therefore, the rapid enantioselective construction of optically active biaryl amino-alcohols still remains a formidable challenge. Here we report an N-heterocyclic carbene (NHC)-catalyzed atropoenantioselective acylation of biphenols triggered by a cooperative strategy consisting of desymmetrization followed by kinetic resolution. This protocol features broad substrate scope and good functional group tolerance, and allows for a rapid construction of axially chiral biaryl amino-alcohols in good to high yields and with excellent enantioselectivities. Furthermore, the structurally diverse axially chiral biaryl amino-alcohol derivatives provide multiple possibilities for chemists to develop catalysts or ligands for different chemical transformations.

Axially chiral biaryl amino-alcohols play a pivotal role in organic synthesis and drug discovery. Here, the authors report a cooperative strategy consisting of desymmetrization followed by kinetic resolution to deliver non-classical NOBIN derivatives in high yields and enantioselectivity via NHC catalysis.

Highly atroposelective synthesis of nonbiaryl naphthalene-1,2-diamine N-C atropisomers through direct enantioselective C-H amination

Nonbiaryl N-C atropisomer is an important structural scaffold, which is present in natural products, medicines and chiral ligands. However the direct enantioselective C-H amination to access optically pure N-C atropisomer is still difficult and rare. Here we report a π-π interaction and dual H-bond concerted control strategy to develop the chiral phosphoric acids (CPAs) catalyzed direct intermolecular enantioselective C-H amination of N-aryl-2-naphthylamines with azodicarboxylates as amino sources for the construction of atroposelective naphthalene-1,2-diamines. This type of N-C atropisomers is stabilized by intramolecular hydrogen bond and the method features a broad range of substrates, high yields and ee values, providing a strategy to chirality transfer via the modification of N-C atropisomers.

Switchable Smiles Rearrangement for Enantioselective O-Aryl Amination

Asymmetric assembly of atropisomeric anilines from abundant and readily available precursors is one of the most challenging but valuable processes in organic synthesis. The use of highly efficient Smiles rearrangement to accomplish switchable enantioselective amination reactions of O-arenes provides access to nonsymmetric 2'-amino[1,1'-binaphthalen]-2-ol (i.e., NOBIN-type) and [1,1'-binaphthalene]-2,2'-diamine (i.e., BINAM-type) derivatives. This transition metal-free strategy provides a powerful way to access a wide range of advanced highly functionalized enantioenriched anilines.

Isothiourea-Catalysed Regioselective Acylative Kinetic Resolution of Axially Chiral Biaryl Diols

An operationally simple isothiourea-catalysed acylative kinetic resolution of unprotected 1,1'-biaryl-2,2'-diol derivatives has been developed to allow access to axially chiral compounds in highly enantioenriched form (s values up to 190). Investigation of the reaction scope and limitations provided three key observations: i) the diol motif of the substrate was essential for good conversion and high s values; ii) the use of an α,α-disubstituted mixed anhydride (2,2-diphenylacetic pivalic anhydride) was critical to minimize diacylation and give high selectivity; iii) the presence of substituents in the 3,3'-positions of the diol hindered effective acylation. This final observation was exploited for the highly regioselective acylative kinetic resolution of unsymmetrical biaryl diol substrates bearing a single 3-substituent. Based on the key observations identified, acylation transition state models have been proposed to explain the atropselectivity of this kinetic resolution.

Construction of Axially Chiral Compounds via Asymmetric Organocatalysis

Axially chiral compounds have received much attention from chemists because of their widespread appearance in natural products, biologically active compounds, and useful chiral ligands in asymmetric catalysis. Because of the importance of this structural motif, the catalytic enantioselective construction of axially chiral scaffolds has been intensively investigated, and great progress has been accomplished. However, the majority of methodologies in this field focus on the use of metal catalysis, whereas approaches involving organocatalysis have started to emerge only recently. This Account describes certain advances in the organocatalytic asymmetric synthesis of axially chiral compounds involving the following strategies: kinetic resolution, desymmetrization, cyclization/addition, direct arylation, and so on. We began our investigation by developing a highly efficient strategy for the kinetic resolution of axially chiral BINAM derivatives involving a chiral Brønsted acid-catalyzed imine formation and transfer hydrogenation cascade process, thereby providing a convenient route to generate chiral BINAM derivatives in high yields with excellent enantioselectivities. The desymmetrization of 1-aryltriazodiones (ATADs) through an organocatalyzed tyrosine clicklike reaction wherein a nucleophile was added to the ATAD afforded an interesting type of axially chiral N-arylurazole in an excellent remote enantiocontrolled manner. We then focused on a direct construction strategy involving cyclization and the addition strategy given the inherent limitations of the kinetic resolution in terms of the chemical yield and the desymmetrization in terms of the substrate scope. By utilizing the catalytic enantioselective Paal-Knorr reaction, we disclosed a general and efficient cyclization method to access enantiomerically pure arylpyrroles. The direct heterocycle formation and the stepwise method, which was executed in a one-pot fashion containing enantioselective cyclization and subsequent aromatization, were successfully applied for the construction of diverse axially chiral arylquinazolinones catalyzed by chiral Brønsted acids. We discovered the asymmetric organocatalytic approach to construct axially chiral styrenes through the 1,4-addition of arylalkynals in good chemical yields and enantioselectivities. Such structural motifs are important precursors for further transformations into biologically active compounds and useful synthetic intermediates and may have potential applications in asymmetric syntheses as olefin ligands or organocatalysts. To further tackle this challenge, we accomplished the phosphoric acid-catalyzed enantioselective direct arylative reactions of 2-naphthol and 2-naphthamine with quinone derivatives to deliver efficient access to a class of axially chiral BINOL and NOBIN derivatives in good yields with excellent enantioselectivities under mild reaction conditions. Most importantly, we discovered that the azo group can effectively perform as a directing and activating group for organocatalytic formal aryl C-H functionalization via formal nucleophilic aromatic substitution of azobenzene derivatives. Thus, a wide range of axially chiral arylindoles were synthesized in good yields with excellent enantioselectivities. We anticipate that this strategy will foster the development of many other transformations and motivate a new enthusiasm for organocatalytic enantioselective aryl functionalization. Moreover, SPINOLs are fundamental synthetic precursors in the construction of other chiral organocatalysts and ligands. We have successfully developed a phosphoric acid-catalyzed enantioselective approach for SPINOLs. This approach is highly convergent and functional-group-tolerant for the efficient generation of SPINOLs with good results, thus delivering practical access to this privileged structure.

Organocatalytic Atroposelective Arylation of 2-Naphthylamines as a Practical Approach to Axially Chiral Biaryl Amino Alcohols

The first phosphoric acid catalyzed direct arylation of 2-naphthylamines with iminoquinones for the atroposelective synthesis of axially chiral biaryl amino alcohols has been developed. This reaction constitutes a highly functional-group-tolerant route for the rapid construction of enantioenriched axially chiral biaryl amino alcohols, and is a rare example of 2-naphthylamines acting as nucleophiles in an organocatalytic enantioselective transformation. Furthermore, the products, which feature various halogen atoms, provide access to structurally diverse axially chiral amino alcohols through further transformations.