Enantioselective Sulfonimidamide Acylation via a Cinchona Alkaloid-Catalyzed Desymmetrization: Scope, Data Science, and Mechanistic Investigation

Revealing Transition State Stabilization in Organocatalytic Ring-Opening Polymerization Using Data Science

In nature, enzymes leverage constituent amino acid residues to create catalytically active sites to effect high reactivity and selectivity. Multicomponent host-guest assemblies have been exploited to mimic enzymatic microenvironments by pre-organizing a network of noncovalent interactions. While organocatalysts such as thioureas have gained widespread success in organic transformation and controlled polymerization, evaluation of the participating structural features in the transition state (TS) remains challenging. Herein, we report the use of data science tools, i.e., a decision-tree-based machine-learning algorithm and Shapley additive explanations (SHAP) analysis, to model reactivity and regioselectivity in a thiourea-catalyzed ring-opening polymerization of 1,2-dithiolanes. Variation of aryl substituent position and electronic characteristics reveals key catalyst features involved in the TS. The analysis of feature importance helps explain the reason behind the optimal performance of (pseudo)halogen-substituted catalysts. Furthermore, the structural basis for the unveiled reactivity-regioselectivity trade-off in the catalysis are established.

Pyridine-N-oxide catalyzed asymmetric N-acylative desymmetrization of sulfonimidamides

A highly efficient enantioselective N-acylative desymmetrization of sulfonimidamides with chloroformates was reported using chiral 4-arylpyridine-N-oxide as the catalyst, affording N-acylative sulfonimidamides with sulfur(vi)-stereocenters in high yields and excellent enantioselectivities. Experiments and DFT calculations support an acyl transfer mechanism, and the nucleophilic substitution of sulfonimidamide by the O-acyloxypyridinium cation intermediate is the enantio-determining step of the reaction. The reaction features variability for acyloxy groups and compatibility with moisture.

Asymmetric Synthesis of S(IV)-Stereogenic Sulfinimidate Esters by Sulfinamide Activation

Catalyst-controlled approaches for the synthesis of S-stereogenic compounds have propelled significant advancements in asymmetric synthetic chemistry. In contrast, control over S-heteroatom (e.g., O) bond formation to access sulfinimidate esters remains an underexplored area. Drawing inspiration from recent progress in electrophilic amide activation, herein, we present a sulfinamide activation strategy for the enantioselective synthesis of S-chiral sulfinimidate esters. This method involves the activation of racemic sulfinamides by sulfonyl chloride, yielding a reactive aza-sulfinyl mixed anhydride intermediate. Employing a naturally occurring cinchonidine catalyst, the process achieves excellent enantiocontrol in the subsequent formation of S─O bonds with alcohols involving a dynamic kinetic resolution (DKR) process, resulting in sulfinimidate esters with excellent enantioselectivity. The catalytically obtained enantioenriched sulfinimidate esters offer a versatile platform for the construction of S-stereogenic frameworks, including sulfilimines and sulfoximines, with promising applications in asymmetric synthesis and drug discovery.

Control over S(VI)-Stereogenic Center: NHC-Catalyzed Enantioselective Synthesis of N-Acyl Cyclic Sulfonimidamides

The catalytic enantioselective synthesis of aza-sulfur(VI) compounds holds significant potential in pharmaceuticals owing to their broad spectrum of biological properties. Herein, we report the first N-heterocyclic carbene (NHC)-catalyzed enantioselective synthesis of cyclic sulfonimidamides (SIAs). The free N-H containing SIAs often exhibit configurational lability through tautomerization. We investigated this by demonstrating their nonsymmetric nature in both solid state and solution. The in situ generated chiral acylazolium intermediates from easily accessible aldehydes in the presence of NHC and oxidant were trapped with the prochiral cyclic SIA anions, allowing the enantioselective synthesis of configurationally stable N-acyl cyclic SIAs. Mechanistic studies reveal that the present strategy proceeds via the desymmetrization of the prochiral SIA anions. Moreover, the derivatization of the synthesized N-acyl SIAs highlights the practical utility of the present methodology.

Stereodivergent Synthesis of Complex N-Sulfonimidoyl Lactams via the Castagnoli-Cushman Reaction

The reactivity between sulfonimidamide-derived imines and cyclic anhydrides has been investigated. Sulfonimidamide imines readily react with homophthalic anhydride under mild conditions in the presence of non-nucleophilic bases to yield complex lactam products with high diastereoselectivity. Furthermore, it was discovered that sulfonimidamide imines react with homophthalic anhydride in the absence of a base to yield distinct diastereomer products with high diastereoselectivity. Density functional theory calculations suggest the existence of an open transition state pathway in the presence of base and a novel cyclic eight-membered transition state in the absence of base.

Enantioselective Synthesis of Chiral Sulfonimidoyl Fluorides Facilitates Stereospecific SuFEx Click Chemistry

Sulfur-centered electrophilic 'warheads' have emerged as key components for chemical proteomic probes through sulfur-exchange chemistry (SuFEx) with protein nucleophiles. Among these functional groups, sulfonimidoyl fluorides (SIFs) stand out for their modifiable sites, tunable electrophilicities, and chiral sulfur-center, presenting exciting possibilities for new covalent chemical probes. However, the synthetic access to chiral SIFs has been a challenge, limiting their exploration and applications. In this study, we describe a convenient route to obtain chiral SIFs from readily available sulfenamides via a series of one-pot tandem reactions with high enantiomeric excess (ees). The resulting chiral SIFs were further converted into a diverse array of chiral S(VI) derivatives under mild conditions or in buffer solutions. Most significantly, the specificity of the chiral SIFs in protein ligation experiments underscored the critical role of sulfur-center chirality in the design and screening of more-selective covalent probes and therapeutics.

Applying statistical modeling strategies to sparse datasets in synthetic chemistry

The application of statistical modeling in organic chemistry is emerging as a standard practice for probing structure-activity relationships and as a predictive tool for many optimization objectives. This review is aimed as a tutorial for those entering the area of statistical modeling in chemistry. We provide case studies to highlight the considerations and approaches that can be used to successfully analyze datasets in low data regimes, a common situation encountered given the experimental demands of organic chemistry. Statistical modeling hinges on the data (what is being modeled), descriptors (how data are represented), and algorithms (how data are modeled). Herein, we focus on how various reaction outputs (e.g., yield, rate, selectivity, solubility, stability, and turnover number) and data structures (e.g., binned, heavily skewed, and distributed) influence the choice of algorithm used for constructing predictive and chemically insightful statistical models.

Carbene-catalyzed chirality-controlled site-selective acylation of saccharides

Acylation stands as a fundamental process in both biological pathways and synthetic chemical reactions, with acylated saccharides and their derivatives holding diverse applications ranging from bioactive agents to synthetic building blocks. A longstanding objective in organic synthesis has been the site-selective acylation of saccharides without extensive pre-protection of alcohol units. In this study, we demonstrate that by simply altering the chirality of N-heterocyclic carbene (NHC) organic catalysts, the site-selectivity of saccharide acylation reactions can be effectively modulated. Our investigation reveals that this intriguing selectivity shift stems from a combination of factors, including chirality match/mismatch and inter- / intramolecular hydrogen bonding between the NHC catalyst and saccharide substrates. These findings provide valuable insights into catalyst design and reaction engineering, highlighting potential applications in glycoside analysis, such as fluorescent labelling, α/β identification, orthogonal reactions, and selective late-stage modifications.

Data Science Guiding Analysis of Organic Reaction Mechanism and Prediction

Advancements in synthetic organic chemistry are closely related to understanding substrate and catalyst reactivities through detailed mechanistic studies. Traditional mechanistic investigations are labor-intensive and rely on experimental kinetic, thermodynamic, and spectroscopic data. Linear free energy relationships (LFERs), exemplified by Hammett relationships, have long facilitated reactivity prediction despite their inherent limitations when using experimental constants or incorporating comprehensive experimental data. Data-driven modeling, which integrates cheminformatics with machine learning, offers powerful tools for predicting and interpreting mechanisms and effectively handling complex reactivities through multiparameter strategies. This review explores selected examples of data-driven strategies for investigating organic reaction mechanisms. It highlights the evolution and application of computational descriptors for mechanistic inference.

Synthesis of chiral sulfilimines by organocatalytic enantioselective sulfur alkylation of sulfenamides

Sulfilimines are versatile synthetic intermediates and important moieties in bioactive molecules. However, their applications in drug discovery are underexplored, and efficient asymmetric synthetic methods are highly desirable. Here, we report a transition metal-free pentanidium-catalyzed sulfur alkylation of sulfenamides with exclusive chemoselectivity over nitrogen and high enantioselectivity. The reaction conditions were mild, and a wide range of enantioenriched aryl and alkyl sulfilimines were obtained. The synthetic utility and practicability of this robust protocol were further demonstrated through gram-scale reactions and late-stage functionalization of drugs.

Desymmetrization of Cyclic Sulfonimidamides by Asymmetric Allylation

Herein we report the first transition metal-catalyzed approach to the enantioenriched synthesis of cyclic sulfonimidamides relying on commercially available palladium catalysts and ligands. High-throughput experimentation (HTE) was employed to identify the optimal catalyst system and solvent. The method is applied to a variety of saturated and unsaturated rings and exhibits the highest selectivity for 2-substituted allyl electrophiles. The products are further elaborated to complex, tricyclic scaffolds. DFT experiments presented herein highlight the key ligand substrate interactions leading to the high levels of enantioselectivity.