Peptide-Catalyzed Fragment Couplings that Form Axially Chiral Non-C2 -Symmetric Biaryls

Asymmetric synthesis of atropisomeric arylpyrazoles via direct arylation of 5-aminopyrazoles with naphthoquinones

Construction of axially chiral arylpyrazoles represents an attractive challenge due to the relatively low rotational barrier of biaryl structures containing five-membered heterocycles. This work describes the catalytic asymmetric construction of axially chiral arylpyrazoles using 5-aminopyrazoles and naphthoquinone derivatives. The chiral axis could be formed through a central-to-axial chirality relay step of the chiral phosphoric acid-catalyzed arylation reaction, which features excellent yields and enantioselectivities with a broad substrate scope under mild reaction conditions.

La(OTf)3-Catalyzed [3+2] Cycloaddition Reactions for the Synthesis of Benzo[d]oxazoles/Benzofurans

The La(OTf)3-catalyzed [3+2] cycloaddition reactions for the synthesis of benzo[d]oxazoles/benzofurans via quinones and 1,2-di-tert-butyl-3-(cyanimino)diaziridine (1,3-di-tert-butyl-2-cyanoguanidine)/vinyl azides have been explored. A series of 5-hydroxybenzofuran-4-carboxylic acid derivatives and 5-hydroxybenzo[d]oxazole-4-carboxylic acid derivatives were conveniently obtained with high yields and good stereoselectivities, which could be used for further transformations to valuable compounds.

Diversity-Oriented Catalytic Asymmetric Dearomatization of Indoles with o-Quinone Diimides

Herein, the first diversity-oriented catalytic asymmetric dearomatization of indoles with o-quinone diimides (o-QDIs) is reported. The catalytic asymmetric dearomatization (CADA) of indoles is one of the research focuses in terms of the structural and biological importance of dearomatized indole derivatives. Although great achievements have been made in target-oriented CADA reactions, diversity-oriented CADA reactions are regarded as more challenging and remain elusive due to the lack of synthons featuring multiple reaction sites and the difficulty in precise control of chemo-, regio-, and enantio-selectivity. In this work, o-QDIs are employed as a versatile building block, enabling the chemo-divergent dearomative arylation and [4 + 2] cycloaddition reactions of indoles. Under the catalysis of chiral phosphoric acid and mild conditions, various indolenines, furoindolines/pyrroloindolines, and six-membered-ring fused indolines are collectively prepared in good yields with excellent enantioselectivities. This diversity-oriented synthesis protocol enriches the o-quinone chemistry and offers new opportunities for CADA reactions.

Chiral Phosphoric Acid-Catalyzed Enantioselective Synthesis of Axially Chiral Compounds Involving Indole Derivatives

Indoles are one of the most ubiquitous subclass of N-heterocycles and are increasingly incorporated to design new axially chiral scaffolds. The rich profile of reactivity and N-H functionality allow chemical derivatization for enhanced medicinal, material and catalytic properties. Although asymmetric C-C coupling of two arenes gives the most direct access of axially chiral biaryl scaffolds, this chemistry has been the remit of metal catalysis and works efficiently on limited substrates. Our group has devoted special interest in devising novel organocatalytic arylation reactions to fabricate biaryl atropisomers. In this realm, indoles and derivatives have been reliably used as the arylation partners in combination with azoarenes, nitrosonapthalenes and quinone derivatives. Their efficient interaction with chiral phosphoric acid catalyst as well as the tunability of electronics and sterics have enabled excellent control of stereo-, chemo- and regioselectivity to furnish diverse scaffolds. In addition, indoles could act as nucleophiles in desymmetrization of 1,2,4-triazole-3,5-diones. This account provides a succinct illustration of these developments.

Asymmetric Synthesis of Axially Chiral Arylpyrazole via an Organocatalytic Arylation Reaction

Herein, a highly enantioselective arylation reaction of 3-aryl-5-aminopyrazoles and quinone derivatives was realized using a chiral phosphoric acid catalyst under mild conditions. The reaction has a broad scope with respect to both arylation reaction partners and hence offers rapid access to an array of axially chiral arylpyrazoles with pretty outcomes (up to 95% yield and 99% ee). Notably, the reaction is very efficient, as the catalyst loadings for the model reaction can be reduced to 1 mol % and the enantioselectivity is still maintained. Besides, the synthetic utility of the protocol was proven by a gram-scale reaction and the transformation of the product.

Asymmetric Formal Coupling of β-Ketoesters with Quinones Promoted by a Chiral Bifunctional N-Heterocyclic Olefin

A highly enantioselective formal coupling of β-ketoesters with quinones was accomplished by a chiral bifunctional N-heterocyclic olefin organocatalyst. With as low as 1 mol % catalyst loading, a number of enantioenriched quinone derivatives were afforded in good yields with high enantioselectivities and regioselectivities (up to 96% yield, 98% ee, and 19:1 rr). Gram-scale synthesis and the high inhibitory effect of several products on the viability of cancer cells demonstrate the potential utility of the current method.

Role of Cinchona Alkaloids in the Enantio- and Diastereoselective Synthesis of Axially Chiral Compounds

Asymmetric synthesis using organic catalysts has evolved since it was first realized and defined. Nowadays, it can be considered a valid alternative to transition metal catalysis for synthesizing chiral molecules. According to the literature, the number of asymmetric organocatalytic processes associated with atropisomer synthesis has rapidly increased over the past 10 years because organocatalysis addresses the challenges posed by the most widespread strategies used for preparing axially chiral molecules with satisfactory results.These strategies, useful to prepare a wide range of C-C, C-heteroatom, and N-N atropisomers, vary from kinetic resolution to direct arylation, desymmetrization, and central-to-axial chirality conversion. In this field, our contribution focuses on determining novel methods for synthesizing atropisomers, during which, in most cases, the construction of one or more stereogenic centers other than the stereogenic axis occurred. To efficiently address this challenge, we exploited the ability of catalysts based on a cinchona alkaloid scaffold to realize enantioselective organic transformations. Desymmetrization of N-(2-tert-butylphenyl) maleimides was one of the first strategies that we pursued for preparing C-N atropisomers. The main principle is based on the presence of a rotationally hindered C-N single bond owing to the presence of a large tert-butyl group. Following the peculiar reactivity of this type of substrate as a powerful electrophile and dienophile, we realized several transformations.First, we investigated the vinylogous Michael addition of 3-substituted cyclohexenones, where a stereogenic axis and two contiguous stereocenters were concomitantly and remotely formed and stereocontrolled using a primary amine catalyst. Subsequently, we realized desymmetrization via an organocatalytic Diels-Alder reaction of activated unsaturated ketones that enabled highly atropselective transformation with efficient diastereoselectivity, thereby simultaneously controlling four stereogenic elements. Employing chiral organic bases allowed us to realize efficient desymmetrizations using carbon nucleophiles, such as 1,3-dicarbonyl compounds, cyanoacetates, and oxindoles. These reactions, performed with different types of catalysts, highlighted the versatility of organocatalysis as a powerful strategy for atropselective desymmetrization of pro-axially chiral maleimides.Hereafter, we studied the Friedel-Crafts alkylation of naphthols with indenones, a powerful method for enantioselective synthesis of conformationally restricted diastereoisomeric indanones. We realized the first axially chiral selective Knoevenagel condensation using cinchona alkaloid primary amine as the catalyst. This reaction provided a powerful method to access enantioenriched olefins containing the oxindole core. Subsequently, we initiated an intense program for the computational investigation of the reaction mechanism of our atropselective processes. An understanding of the catalytic activity for vinylogous atropselective desymmetrization as well as of the role played by the acidic cocatalyst used for the experimental work was achieved.Recently, we have garnered interest in the novel frontiers of atropselective synthesis. As observed in recent publications, there is considerable interest in the development of methods for preparing N-N atropisomers, an emerging topic in the field of atropselective synthesis. We focused on the synthesis of hydrazide atropisomers by developing a one-pot sequential catalysis protocol based on two sequential organocatalytic reactions that provided high stereocontrol of two contiguous stereogenic elements.

Organocatalytic Enantioselective Synthesis of Axially Chiral Molecules: Development of Strategies and Skeletons

The growing importance of axially chiral architectures in different scientific domains has unveiled shortcomings in terms of efficient synthetic access and skeletal variety. This account describes our strategies in answering these challenges within the organocatalytic context where the emergence of bifunctional catalysts such as chiral phosphoric acids (CPAs) has proven invaluable in controlling the sense of axial chirality. The wide occurrence of bi(hetero)aryl skeletons in privileged structures constitutes a strong motivation to devise more effective arylation methods. Our design revolves around modulating the intrinsic nucleophilicity of aromatic amines and alcohols. The first approach involves the design of an electron-withdrawing activating group which could associate with the catalyst for reactivity enhancement and selectivity control. The resonance of arenes offers the unique mechanistic possibility to select between activating sites. C2-Azo- and nitroso-substituted naphthalenes undergo atroposelective ortho C- or N-arylation with (hetero)aromatic nucleophiles. For monocyclic benzenes, programmable charge localization leads to regioselective activation by catalytic control alone or aided by substrate design. For instance, selective addition to nitroso nitrogen enables successive annulation initiated by the amine to yield axially chiral N-arylbenzimidazoles. In a biomimetic manner, a finely tuned catalyst could direct a para-selective nucleophilic approach in the atroposelective arylation of azobenzenes. The second strategy employs electrophilic arene precursors for arylation which occurs via rearomatization with central-to-axial chirality transfer. This enabled the arylation of (imino)quinones with indoles to access phenylindole atropisomers. By adapting this chemistry with an additional oxidation event to liberate the carbonyl functionalities, aryl-o-naphthoquinone and aryl-p-quinone atropisomers were attained. Along with the development of new arylation strategies, deriving new axially chiral structures has been another consistent theme of our research program. The atroposelective functionalization of alkynes provides broad entry to atropisomeric alkenes. The monofunctionalization of alkynes through the interception of an electrophilic vinylidene-quinone-methide (VQM) intermediate with 2-naphthols yielded the new EBINOL scaffolds. By designing an internal directing group, the atroposelective dihalogenation of alkynes was realized using abundant alkali halides despite their weak nucleophilicities and poor solubilities. The atroposelective N-alkylation of alkenes was pursued to prepare multifunctionalized alkene atropisomers that could be converted into 2-arylpyrroles with chirality transfer. The synthesis of B-aryl-1,2-azaborines containing a C-B chiral axis was accomplished where the CPA catalyst effects the desymmetrization and defines the configuration of the distal C-B bond. Inspired by the axially chiral scaffold of allenes, we leveraged the developed arene activation strategy to achieve para-addition and dearomatization of judiciously designed azobenzenes, which led to structurally novel cyclohexadienylidene-based hydrazones. To complement these structures, axially chiral cyclohexadienyl oxime ethers were also attained through CPA-catalyzed condensation between hydroxylamines and spiro[4.5]trienones.

Palladium/Amino Acid Co-catalyzed Atroposelective C-H Olefination to Access Tetra-Ortho-Substituted Atropisomers Featuring 2,2'-Difluoro-1-biaryl Scaffolds

Despite the great advancement in atroposelective synthesis in the past decades, the enantioselective synthesis of 2,2'-difluoro-1-biaryls is unprecedented. Herein, a palladium and chiral amino acid catalyzed atroposelective C-H olefination to construct the axially chiral 2,2'-difluoro-1-biaryls is reported. A variety of polyfluoro-substituted biaryls were forged under mild conditions in good yields with excellent enantioselectivity (up to 99% ee). The potential application was demonstrated by a gram-scale synthesis and synthetic transformations.

Catalytic Atroposelective Electrophilic Amination of Indoles

Reported here is the first catalytic atroposelective electrophilic amination of indoles, which delivers functionalized atropochiral N-sulfonyl-3-arylaminoindoles with excellent optical purity. This reaction was furnished by 1,6-nucleophilic addition to p-quinone diimines. Control experiments suggest an ionic mechanism that differs from the radical addition pathway commonly proposed for 1,6-addition to quinones. The origin of 1,6-addition selectivity was investigated through computational studies. Preliminary studies show that the obtained 3-aminoindoles atropisomers exhibit anticancer activities. This method is valuable with respect to enlarging the toolbox for atropochiral amine derivatives.

Optimizing the Local Chemical Environment on a Bifunctional Helical Peptide Scaffold Enables Enhanced Enantioselectivity and Cooperative Catalysis

We describe a proof-of-concept study in which peptide-bound enamine and thiourea catalysts are used to facilitate the conjugate addition of cyclohexanone to nitroolefins. Our bifunctional peptide scaffold is modified to optimize the local environment around both catalysts to enhance both reactivity and enantioselectivity, affording selectivities of ≤95% ee. Circular dichroism, nuclear magnetic resonance nuclear Overhauser effect studies, and molecular dynamics simulations verify the helical structure of our catalyst in solution and the importance of the secondary structure in catalysis.

Organocatalytic enantioselective construction of axially chiral (1H)-isochromen-1-imines

Heterocycloalkenyl atropisomers, derived from biaryl atropisomers and axially chiral styrenes, have emerged as a new class of nonbiaryl C-C atropisomers due to the benefit in improving the pharmacological activity and structural diversity. This paper proposes an intramolecular annulation strategy for constructing the heterocycloalkenyl atropisomers (1H)-isochromen-1-imines by organocatalysis. Various heterocycloalkenyl atropisomers (1H)-isochromen-1-imines were prepared in good to excellent yields with excellent enantioselectivity (up to 98% ee), and could be easily converted to atropisomeric lactones isocoumarins.

Organocatalytic Enantioselective Construction of Spiroketal Lactones Bearing Axial and Central Chirality via an Asymmetric Domino Reaction

The catalytic asymmetric synthesis of chiral compounds with multiple stereogenic elements via a single catalytic process is challenging. This paper proposes a domino asymmetric electrophilic halocyclization strategy for constructing heterocycloalkenyl atropisomeric spiroketal lactones. A single catalyst was utilized to realize two independent stereodetermining steps. Various spiroketal lactones containing both chiral axes and chiral centers were prepared in excellent yields with excellent enantioselectivity and diastereoselective (up to 99% ee and >20:1 dr).

Chiral Phosphoric Acid-Catalyzed Asymmetric Arylation of Indolizines: Atroposelective Access to Axially Chiral 3-Arylindolizines

We report herein a highly straightforward strategy for the synthesis of a new axially chiral 3-arylindolizine scaffold via organocatalytic asymmetric arylation reactions of indolizines and p-quinone esters. Using the chiral phosphoric acid catalyst, a series of axially chiral 3-arylindolizines were accessed in good to excellent yields and atropo-enantioselectivities. This approach features a broad substrate scope, mild reaction conditions, good scalability, and facile derivatization. Moreover, preliminary investigations based on nonlinear effects and a thermal racemization study demonstrated the intrinsic pathway for the formation of axial chirality and its potential utility.

Catalytic asymmetric synthesis of 3,4'-indole-pyrazole derivatives featuring axially chiral bis-pentatomic heteroaryls

The atroposelective synthesis of bis-pentatomic heteroaryl systems is challenging due to the low rotation barrier and configurational instability of the 5,5-ring system. 3,4'-Indole-pyrazole is a bis-pentatomic heteroaryl scaffold existing in...

Recent advances in catalytic oxidative reactions of phenols and naphthalenols

This critical review aims to provide an overview of oxidative phenol and naphthalenol transformations in nature and synthetic chemistry.

Organocatalytic cycloaddition-elimination cascade for atroposelective construction of heterobiaryls

The first chiral phosphoric acid (CPA) catalyzed cycloaddition–elimination cascade reaction of 2-naphthol- and phenol-derived enecarbamates with azonaphthalenes has been established, providing a highly atroposelective route to an array of axially chiral aryl-C3-benzoindoles in excellent yields with excellent enantioselectivities. The success of this strategy derives from the stepwise process involving CPA-catalyzed asymmetric formal [3 + 2] cycloaddition and subsequent central-to-axial chirality conversion by elimination of a carbamate. In addition, the practicality of this reaction had been verified by varieties of transformations towards functionalized atropisomers.

An organocatalytic asymmetric cycloaddition–elimination cascade reaction of aryl enecarbamates with azonaphthalenes has been developed to access axially chiral heterobiaryls in excellent yields and enantioselectivities.

Organocatalytic Asymmetric Arylation of p-Quinone Phosphonates: A Green Access to Biaryl Monophosphorus Ligands

Herein, we report a highly efficient organocatalytic asymmetric synthesis of axially chiral biaryl phosphonates with p-quinone phosphonates and 2-naphthols via CPA-catalyzed asymmetric arylations. A series of chiral biaryl monophosphonates were obtained in excellent yields and enantioselectivities (up to 99% yield and 95% ee). This reaction could be operated at a gram scale with a low catalyst loading (0.5 mol %). Remarkably, our approach provides a green and ready access to chiral biaryl monophosphorus ligands. Compound 4ca was successfully converted to novel chiral biaryl monophosphorus ligands 7a, 7b, and 8 with high enantioselectivities in three steps.

Enantioselectivity switch in asymmetric Michael addition reactions using phosphonium salts

Efficient access to two enantiomers of one chiral compound is critical for the discovery of drugs. However, it is still a challenging problem owing to the difficulty in obtaining two enantiomers of one chiral catalyst. Here, we report a general method to obtain both enantiomeric products via fine tuning the hydrogen-bonding interactions of phosphonium salts. Amino acid derived phosphonium salts and dipeptide derived phosphonium salts exhibited different properties for controlling the transition state, which could efficiently promote the Michael addition reaction to give opposite configurations of products with high yields and enantioselectivities. Preliminary investigations on the mechanism of the reaction and applications of the products were also performed.

Enantioselective Synthesis of Axially Chiral Benzothiophene/Benzofuran-Fused Biaryls by N-Heterocyclic Carbene Catalyzed Arene Formation

Axially chiral biaryl scaffolds are prevalent in natural products, chiral ligands, and organocatalysts. However, N-heterocyclic carbene (NHC) catalyzed de novo construction of an aromatic ring with concomitant axial chirality induction for the synthesis of biaryl atropisomers is far less developed, and the efficient synthesis of axially chiral tetra-ortho-substituted biaryls remains an unsolved problem under NHC catalysis. Reported here is an NHC-catalyzed de novo synthesis of axially chiral benzothiophene/benzofuran-fused biaryls from enals and 2-benzyl-benzothiophene/benzofuran-3-carbaldehydes through a [2+4] annulation, decarboxylation, and oxidative aromatization cascade with central-to-axial chirality conversion. The developed method provides efficient and general access to novel axially chiral benzothiophene/benzofuran-fused biaryls in high enantioselectivities and works well for the synthesis of tetra-ortho-substituted biaryls.

Enantioselective Aromatic Amination?

The atroposelective formation of C-N bonds has recently emerged within the field of amination reactions. On first sight, it may seem quite surprising that such an ancient class of organic coupling reactions (Gabriel, Ullmann, Goldberg, Buchwald, Hartwig and many others) has so few enantioselective solutions, and this in spite of asymmetric synthesis being now a mature concept and field. Why should enantioselective C-N bond formation be so difficult? This question and some of the first examples that promise an imminent change of paradigm are herein discussed.

Sc(OTf)3-Catalyzed Formal [3 + 3] Cycloaddition Reaction of Diaziridines and Quinones for the Synthesis of Benzo[e][1,3,4]oxadiazines

A formal [3 + 3] cyclization reaction of diaziridines and quinones has been developed offering 1,3,4-oxadiazinanes in generally high yields (up to 96%). The reaction was catalyzed by Sc(OTf)₃ with a large substrate scope for both diaziridines and quinones. The synergistic activation of 1,3-dipolar diaziridines and the dipolar quinones was found to be essential to enable this reaction.

Recent Advances in Catalytic Asymmetric Construction of Atropisomers

Atropisomerism is a stereochemical behavior portrayed by three-dimensional molecules that bear rotationally restricted σ bond. Akin to the well-represented point-chiral molecules, atropisomerically chiral compounds are finding increasing utilities in many disciplines where molecular asymmetry is influential. This provides steady demand on atroposelective synthesis, where numerous synthetic pursuits have been rewarded with conceptually novel and streamlined methods while expanding the structural diversity of atropisomers. This review summarizes key achievements in stereoselective preparation of biaryl, heterobiaryl, and nonbiaryl atropisomers documented between 2015 and 2020. Emphasis is placed on the synthetic strategies for each structural class, while examples are cited to illustrate the potential applications of the accessed atropochiral targets.

N-Primary-amine tetrapeptide-catalyzed highly asymmetric Michael addition of aliphatic aldehydes to maleimides

The highly asymmetric Michael addition reaction between maleimides and aliphatic aldehydes catalyzed by low-loading β-turn tetrapeptides with excellent yields and enantioselectivities at room temperature was reported. α-Branched and α-unbranched aldehydes both are suitable nucleophiles. N-Aryl, alkyl and hydrogen maleimides all are well tolerated and led to high yields and enantioselectivities. The transformation can be enlarged to the gram scale without decrease in the yield and enantioselectivity. Furthermore, the succinimides were converted into γ-lactams and γ-lactones, showing good practicality of this work. Some reaction intermediates in the proposed reaction mechanism can be captured with the HR-MS method.

Catalytic Dynamic Kinetic Resolutions in Tandem to Construct Two-Axis Terphenyl Atropisomers

The defined structure of molecules bearing multiple stereogenic axes is of increasing relevance to materials science, pharmaceuticals, and catalysis. However, catalytic enantioselective approaches to control multiple stereogenic axes remain synthetically challenging. We report the catalytic synthesis of two-axis terphenyl atropisomers, with complementary strategies to both chlorinated and brominated variants, formed with high diastereo- and enantioselectivity. The chemistry proceeds through a sequence of two distinct dynamic kinetic resolutions: first, an atroposelective ring opening of Bringmann-type lactones produces a product with one established axis of chirality, and second, a stereoselective arene halogenation delivers the product with the second axis of chirality established. In order to achieve these results, a class of Brønsted basic guanidinylated peptides, which catalyze an efficient atroposelective chlorination, is reported for the first time. In addition, a complementary bromination is reported, which also establishes the second stereogenic axis. These bromo-terphenyls are accessible following the discovery that chiral anion phase transfer catalysis by C₂-symmetric phosphoric acids allows catalyst control in the second stereochemistry-determining event. Accordingly, we established the fully catalyst-controlled stereodivergent synthesis of all possible chlorinated stereoisomers while also demonstrating diastereodivergence in the brominated variants, with significant levels of enantioselectivity in all cases.

Formal oxo- and aza-[3 + 2] reactions of α-enaminones and quinones: a double divergent process and the roles of chiral phosphoric acid and molecular sieves

A double divergent process has been developed for the reaction of α-enaminones with quinones through facile manipulation of catalyst and additive, leading to structurally completely different products. The two divergent processes, which involve formal aza- and oxo-[3 + 2] cycloaddition reactions, are mediated by chiral phosphoric acid and molecular sieves, respectively. While inclusion of phosphoric acid in the reaction switched the reaction pathway to favor the efficient formation of a wide range of N-substituted indoles, addition of 4 Å molecular sieves to the reaction switched the reaction pathway again, leading to enantioselective synthesis of 2,3-dihydrobenzofurans in excellent yields and enantioselectivities under mild conditions. Studies in this work suggest that the chiral phosphoric acid acts to lower the transition state energy and promote the formation of amide intermediate for the formal aza-[3 + 2] cycloaddition and the molecular sieves serve to facilitate proton transfer for oxo-[3 + 2] cycloaddition. The reactivity of α-enaminones is also disclosed in this work.

Peptide-Catalyzed Highly Asymmetric Cross-Aldol Reaction of Aldehydes to Biomimetically Synthesize 1,4-Dicarbonyls

β-Turn tetrapeptides were demonstrated to catalyze asymmetric aldol reaction of α-branched aldehydes and α-carbonyl aldehydes, i.e. glyoxylates and α-ketoaldehydes, to biomimetically synthesize acyclic all-carbon quaternary center-bearing 1,4-dicarbonyls in high yield and excellent enantioselectivity under mild conditions. The spatially restricted environment of the tetrapeptide warrants high enantioselectivity and yield with broad substrates. Using this protocol, (R)-pantolactone, the key intermediate of vitamin B5, was readily accessed in a practical, efficient, and environmentally benign process from inexpensive starting materials.

Catalytic Atroposelective Synthesis of N-Aryl Quinoid Compounds

Diarylamines and related scaffolds are among the most common chemotypes in modern drug discovery. While they can potentially possess two chiral axes, there are no studies on their enantioselective synthesis, as these axes typically possess lower stereochemical stabilities. Herein, we report a chiral phosphoric acid catalyzed atroposelective electrophilic halogenation of N-aryl quinoids, a class of compounds that are analogous to diarylamines. This chemistry yields a large range of stereochemically stable N-aryl quinoids in excellent yields and atroposelectivity. This work represents the first example of the atroposelective synthesis of a diarylamine-like scaffold and will serve as a gateway to fundamental and applied studies on the scarcely studied chirality of these ubiquitous chiral scaffolds.