Asymmetric Conjugate Addition of Benzofuran-2-ones to Alkyl 2-Phthalimidoacrylates: Modeling Structure-Stereoselectivity Relationships with Steric and Electronic Parameters

Synergistic Pd/Cu-Catalyzed 1,5-Double Chiral Inductions

Much attention has been focused on the catalytic asymmetric creation of single chiral centers or two adjacent stereocenters. However, the asymmetric construction of two nonadjacent stereocenters is of significant importance but is challenging because of the lack of remote chiral induction models. Herein, based on a C═C bond relay strategy, we report a synergistic Pd/Cu-catalyzed 1,5-double chiral induction model. All four stereoisomers of the target products bearing 1,5-nonadjacent stereocenters involving both allenyl axial and central chirality could be obtained divergently by simply changing the combination of two chiral catalysts with different configurations. Control experiments and DFT calculations reveal a novel mechanism involving 1,5-oxidative addition, contra-thermodynamic η3-allyl palladium shift, and conjugate nucleophilic substitution, which play crucial roles in the control of reactivity, regio-, enantio-, and diastereoselectivity. It is expected that this C═C bond relay strategy may provide a general protocol for the asymmetric synthesis of structural motifs bearing two distant stereocenters.

Construction of 1,3-Nonadjacent Stereogenic Centers Through Enantioselective Addition of α-Thioacetamides to α-Substituted Vinyl Sulfones Catalyzed by Chiral Strong Brønsted Base

An enantioselective addition reaction for the construction of 1,3-nonadjacent stereogenic centers is developed by means of a chiral strong Brønsted base catalyst. The chiral sodium ureate catalyst efficiently promoted the reaction of α-thioacetamides as less acidic pronucleophiles with vinyl sulfones having a variety of α-substituents including aryl, alkyl and halo groups, and α-phenylacrylates, accomplishing the construction of various 1,3-nonadjacent stereogenic centers in highly diastereo- and enantioselective manners. This is a rare example of the construction of 1,3-nonadjacent stereogenic centers with less acidic pronucleophiles. In addition, the application of Michael acceptors having various types of α-substituents in a single catalyst system is achieved for the first time, demonstrating the utility of the present catalyst system for the construction of 1,3-nonadjacent stereogenic centers.

Organocatalytic Synthesis of Triflones Bearing Two Non-Adjacent Stereogenic Centers

Trifluoromethylsulfones (triflones) are useful compounds for synthesis and beyond. Yet, methods to access chiral triflones are scarce. Here, we present a mild and efficient organocatalytic method for the stereoselective synthesis of chiral triflones using α-aryl vinyl triflones, building blocks previously unexplored in asymmetric synthesis. The peptide-catalyzed reaction gives rise to a broad range of γ-triflylaldehydes with two non-adjacent stereogenic centers in high yields and stereoselectivities. A catalyst-controlled stereoselective protonation following a C-C bond formation is key to control over the absolute and relative configuration. Straightforward derivatization of the products into, e.g., disubstituted δ-sultones, γ-lactones, and pyrrolidine heterocycles highlights the synthetic versatility of the products.

Harvesting the fragment-based nature of bifunctional organocatalysts to enhance their activity

Enhancing the activity of bifunctional organocatalysts: a fragment-based approach coupled with activity maps helps identifying better-performing catalytic motifs.

Tunable and Cooperative Catalysis for Enantioselective Pictet-Spengler Reaction with Varied Nitrogen-Containing Heterocyclic Carboxaldehydes

Herein we report an organocatalytic enantioselective functionalization of heterocyclic carboxaldehydes via the Pictet-Spengler reaction. Through careful pairing of novel squaramide and Brønsted acid catalysts, our method tolerates a breadth of heterocycles, enabling preparation of a series of heterocycle conjugated β-(tetrahydro)carbolines in good yield and enantioselectivity. Careful selection of carboxylic acid co-catalyst is essential for toleration of a variety of regioisomeric heterocycles. Utility is demonstrated via the three-step stereoselective preparation of pyridine-containing analogues of potent selective estrogen receptor downregulator and U.S. FDA approved drug Tadalafil.

Recent Advances on Benzofuranones: Synthesis and Transformation via C–H Functionalization

The benzofuranone structure is important in many fields, such as natural products, pharmaceuticals, building blocks, antioxidants, and dyes. The efficient synthesis and transformation of benzofuranones have attracted great attention in organic synthesis. They can be synthesized by the Friedel–Crafts reaction and intramolecular dehydration ring-closing and transition-metal-catalyzed reactions, among others. Their direct utilization in the preparation of other functional molecules further enhance their application. Due to their low pK a value and easy enolization, the transformation of benzofuranones via C(3)–H bond functionalization has been a hot issue since 2010. Herein, we highlight advances in the synthesis of benzofuranones and their transformation via C–H functionalization. Other transformations related to benzofuranones are also discussed.

1 Introduction

2 Synthesis of Benzofuranones

3 C–H Functionalization of Benzofuranones

4 Other Types of Reactions of Benzofuranones

5 Conclusion and Outlook

A Catalyst-Controlled Enantiodivergent Bromolactonization

A catalyst-controlled enantiodivergent bromolactonization of olefinic acids has been developed. Quinine-derived amino-amides bearing the same chiral core but different achiral aryl substituents were used as the catalysts. Switching the methoxy substituent in the aryl amide system from meta- to ortho-position results in a complete switch in asymmetric induction to afford the desired lactone in good enantioselectivity and yield. Mechanistic studies, including chemical experiments and density functional theory calculations, reveal that the differences in steric and electronic effects of the catalyst substituent alter the reaction mechanism.

1,3-Dipolar Cycloaddition between Dehydroalanines and C,N-Cyclic Azomethine Imines: Application to Late-Stage Peptide Modification

A non-catalytic, mild, and easy-to-handle protecting group switched 1,3-dipolar cycloaddition (1,3-DC) between bi- or mono-N-protected Dha and C,N-cyclic azomethine imines, which afford various quaternary amino acids with diverse scaffolds, is disclosed. Specifically, normal-electron-demand 1,3-DC reaction occurs between bi-N-protected Dha and C,N-cyclic azomethine imines, while inverse-electron-demand 1,3-DC reaction occurs between mono-N-protected Dha and C,N-cyclic azomethine imines. Above all, the reactions can be carried out between peptides with Dha residues at the position of interest and C,N-cyclic azomethine imines, both in homogeneous phase and on resins in SPPS. It provides a new toolkit for late-stage peptide modification, labeling, and peptide-drug conjugation. To shed light on the high regioselectivity of the reaction, DFT calculations were carried out, which were qualitatively consistent with the experimental observations.

Connecting and Analyzing Enantioselective Bifunctional Hydrogen Bond Donor Catalysis Using Data Science Tools

The generalization of related asymmetric processes in organocatalyzed reactions is an ongoing challenge due to subtle, noncovalent interactions that drive selectivity. The lack of transferability is often met with a largely empirical approach to optimizing catalyst structure and reaction conditions. This has led to the development of diverse structural catalyst motifs and inspired unique design principles in this field. Bifunctional hydrogen bond donor (HBD) catalysis exemplifies this in which a broad collection of enantioselective transformations has been successfully developed. Herein, we describe the use of data science methods to connect catalyst and substrate structural features of an array of reported enantioselective bifunctional HBD catalysis through an iterative statistical modeling process. The computational parameters used to build the correlations are mechanism-specific based on the proposed transition states, which allows for analysis into the noncovalent interactions responsible for asymmetric induction. The resulting statistical models also allow for extrapolation to out-of-sample examples to provide a prediction platform that can be used for future applications of bifunctional hydrogen bond donor catalysis. Finally, this multireaction workflow presents an opportunity to build statistical models unifying various modes of activation relevant to asymmetric organocatalysis.

Asymmetric Synthesis of Oxindole-Derived Vicinal Tetrasubstituted Acyclic Amino Acid Derivatives by the Mannich-Type Reaction

The catalytic asymmetric Mannich-type reaction of 3-hydroxy/3-aminooxindoles with 2-aminoacrylates to afford oxindole-derived acyclic amino acid derivatives bearing vicinal tetrasubstituted stereocenters is reported. (DHQ)₂PHAL (4g) and quinine-derived squaramide (4d) were identified as efficient catalysts. Transformations of the Mannich-type reaction products highlight the utility of this synthetic strategy.

Enantioselective synthesis of chiral α-alkynylated thiazolidones by tandem S-addition/acetalization of alkynyl imines

A SPINOL-derived chiral phosphoric acid catalyzed asymmetric formal [2 + 3]-annulation of in situ generated alkynyl imines and 1,4-dithiane-2,5-diol has been developed to afford enantiopure α-alkynylated thiazolidones with up to 72% yield and 98.5 : 1.5 er. This tandem annulation involved a tandem S-addition of alkynyl imines/intramolecular acetalization, followed by PDC-mediated oxidation. The α-alkynylated thiazolidones could facilely afford the corresponding chiral α-alkynylated or α-alkenylated cyclic sulfoxides via further elaboration.

Quantitative Structure-Selectivity Relationships in Enantioselective Catalysis: Past, Present, and Future

The dawn of the 21st century has brought with it a surge of research related to computer-guided approaches to catalyst design. In the past two decades, chemoinformatics, the application of informatics to solve problems in chemistry, has increasingly influenced prediction of activity and mechanistic investigations of organic reactions. The advent of advanced statistical and machine learning methods, as well as dramatic increases in computational speed and memory, has contributed to this emerging field of study. This review summarizes strategies to employ quantitative structure-selectivity relationships (QSSR) in asymmetric catalytic reactions. The coverage is structured by initially introducing the basic features of these methods. Subsequent topics are discussed according to increasing complexity of molecular representations. As the most applied subfield of QSSR in enantioselective catalysis, the application of local parametrization approaches and linear free energy relationships (LFERs) along with multivariate modeling techniques is described first. This section is followed by a description of global parametrization methods, the first of which is continuous chirality measures (CCM) because it is a single parameter derived from the global structure of a molecule. Chirality codes, global, multivariate descriptors, are then introduced followed by molecular interaction fields (MIFs), a global descriptor class that typically has the highest dimensionality. To highlight the current reach of QSSR in enantioselective transformations, a comprehensive collection of examples is presented. When combined with traditional experimental approaches, chemoinformatics holds great promise to predict new catalyst structures, rationalize mechanistic behavior, and profoundly change the way chemists discover and optimize reactions.

The effect of chiral N-substituents with methyl or trifluoromethyl groups on the catalytic performance of mono- and bifunctional thioureas

We evaluated thiourea organocatalysts that incorporate a chiral group which includes a trifluoromethyl moiety and contrasted their performance with non-fluorinated analogs. The comparison between such systems allows the direct study of the NH acidity of a thiourea bonded to an aliphatic substituent. In principle, -CF3 systems feature an enhanced hydrogen bond (HB) donor capacity that is undoubtedly beneficial for HB-catalysis applied to the Baylis-Hillman reaction. We found that the thiourea substituted on both nitrogens with this group accelerates this reaction like Schreiner's thiourea. On the other hand, we observed a different behavior in reactions promoted by bifunctional catalysts (thiourea-primary amine). In the Michael addition of isobutyraldehyde to methyl benzylidenepyruvate, the -CF3 containing catalysts were better than the -CH3 systems, whereas the conjugate addition to N-phenylmaleimide showed the opposite behavior. Theoretical calculations of the transition states indicated that the phenylethyl group in fluorinated and non-fluorinated compounds have different kinds of interactions with the electrophile. These interactions are responsible for a different arrangement of the electrophile and thereby the selectivity of the catalyst. Therefore, it cannot be generalized that in all cases NH acidity correlates with the performance of the catalyst, particularly, with aliphatic substituents that unlike the aromatic ones possess groups that are outside the plane of the thiourea.

Organocatalyzed asymmetric tandem conjugate addition–protonation of isocyanoacetates to 2-chloroacrylonitrile

Dihydroquinine-derived thiourea catalyzed asymmetric tandem conjugate addition–protonation of α-isocyanoacetates to 2-chloroacrylonitrile was developed.

A novel chiral DMAP–thiourea bifunctional catalyst catalyzed enantioselective Steglich and Black rearrangement reactions

A novel chiral DMAP–thiourea bifunctional catalyst has been prepared and applied in the highly enantioselective Steglich and Black rearrangement reactions.

Diastereoselective Rh-catalyzed decarboxylative allylation to form quaternary stereocenters using sulfinimine as the directing group

In this paper, we reported for the first time that the diastereoselective Rh-catalyzed decarboxylative allylation of chiral sulfinimines could be used to form quaternary stereocenters.

Access to α,γ-Diamino Diacid Derivatives via Organocatalytic Asymmetric 1,4-Addition of Azlactones and Dehydroalanines

A convenient and functional-group-tolerant organocatalytic asymmetric 1,4-addition of azlactones and dehydroalanine is disclosed. The reaction is used for the first synthesis of chiral α,γ-diamino diacid derivatives with nonadjacent stereogenic centers in moderate to high yields, with excellent diastereo- and enantioselectivities, under the catalysis of a chiral thiourea catalyst. In addition, the reaction could be conducted in gram-scale, and the products of the reaction could be readily converted to various α,γ-diamino diacid derivatives, α,γ-diamino dialcohols, and modified peptides with nonproteinogenic amino acid residues.

Combining traditional 2D and modern physical organic-derived descriptors to predict enhanced enantioselectivity for the key aza-Michael conjugate addition in the synthesis of Prevymis™ (letermovir)

Quantitative structure-activity relationships have an extensive history for optimizing drug candidates, yet they have only recently been applied in reaction development. In this report, the predictive power of multivariate parameterization has been explored toward the optimization of a catalyst promoting an aza-Michael conjugate addition for the asymmetric synthesis of letermovir. A hybrid approach combining 2D QSAR and modern 3D physical organic parameters performed better than either approach in isolation. Using these predictive models, a series of new catalysts were identified, which catalyzed the reaction to provide the desired product in improved enantioselectivity relative to the parent catalyst.

α-Alkylation of Chiral Sulfinimines for Constructing Quaternary Chiral Carbons by Introducing Removable Directing Groups

This study developed a facile and efficient synthetic strategy to construct quaternary chiral centers at the α-position of imines and ketones. High regioselectivity and diastereoselectivity were achieved through the synergetic effect of electron-withdrawing directing groups and N-tert-butyl sulfinamide as chiral auxiliaries. Either of them could be removed under the optimized conditions without any epimerization.

N-Heterocyclic carbene promoted enantioselective desymmetrization reaction of diarylalkane-bisphenols

An enantioselective NHC-catalyzed desymmetrization reaction of diarylalkane-bisphenols with aldehydes was reported under the guidance of linear free energy relationships (LFERs).

Catalytic asymmetric synthesis of pyrrolidine derivatives bearing heteroatom-substituted quaternary stereocenters

An enantioselective [3 + 2] cycloaddition of heteroatom-substituted alkenes with α-substituted isocyanoacetates has been developed. Excellent reactivity and enantioselectivity were obtained.

Multidimensional Correlations in Asymmetric Catalysis through Parameterization of Uncatalyzed Transition States

The study of the oxidative amination of tetrahydroisoquinolines under chiral-anion phase-transfer (CAPT) catalysis by multidimensional correlation analysis (MCA) is revisited. The parameterization of the transition states (TSs) for the uncatalyzed reaction, the introduction of conformational descriptors, and the use of computed interaction energies and distances as parameters allowed access to a considerably simplified mathematical correlation of substrate and catalyst structure to enantioselectivity. The equation obtained is suggestive of key interactions occurring at the TS. Specifically, the CAPT catalyst is proposed to coordinate the intermediate iminium cation by P=O⋅⋅⋅H-O hydrogen-bonding and N⋅⋅⋅H-C electrostatic interactions. The conformational freedom of the benzyl substituent of the substrate was also found to be important in providing an efficient mode of molecular recognition.

An enantioselective conjugate addition reaction of 3-substituted benzothiophen-2-ones and 2-phthalimidoacrylates

A highly enantioselective conjugate addition reaction of 3-substituted benzothiophen-2-ones to 2-phthalimidoacrylates has been developed using a bifunctional tertiary-amine thiourea catalyst.

Dynamic control over catalytic function using responsive bisthiourea catalysts

Responsive molecular motor-based bisthiourea organocatalysts were used in the enantioselective Henry reaction to achieve efficient dual stereocontrol in the presence of an external base.