tert-Butanesulfinimines: structure, synthesis and synthetic applications

Stereoselective Aminomethylation of β,β-Disubstituted Enesulfinamides: Asymmetric Construction of Less Accessible Acyclic α,α-Disubstituted α-Aminomethylated Ketimines

β,β-Disubstituted enesulfinamides undergo stereoselective nucleophilic addition to the formaldehyde imines, in situ formed from tosylmethylcarbamates, affording α-aminomethylated ketimines bearing a challenging acyclic quaternary stereocenter substituted by two sterically and electronically similar groups (e.g., Me and Et). The defined geometry of the C═C bond in the enesulfinamides, combined with the strong chiral induction offered by their chiral sulfinyl group, ensures precise stereocontrol during the formation of the new C-C bond.

Direct Asymmetric Synthesis of α-Aminoimines from 1,2-Bis-N-Sulfinylimines by Using Allyl Boronic Acids

A unique direct asymmetric synthesis of α-aminoimines is realized, through rapid and exclusive mono-allylation of chiral bis-N-sulfinylimines using allylboronic acids. The highly selective allylation was possible as electrophilic imine functional group in the product α-aminoimines remained unreactive towards allyl boronic acid nucleophiles. Notably, by varying the geometry and chiral auxiliary, all four isomers of the α-aminoimines were accessed from readily available precursors. A range of allyl nucleophiles, which are tricky to generate by other means possessing highly reactive functional groups also took part in this reaction, expanding the scope further. The applicability of the products α-aminoimines were further demonstrated by accessing a range of structurally diverse chiral cyclic and acyclic 1,2-diamines bearing adjacent stereocenters through addition of a second nucleophile or Prins-type cyclization by exploiting the nucleophilicity of the tethered alkene moiety. Moreover, the leaving group aptitude of sulfinyl auxiliary attached to imine, was exploited to access valuable chiral α-aminonitriles under thermal conditions without employing any reagents. Detailed DFT calculation revealed a chair-like transition state, arising from corresponding allylboroxine species, likely operating for the allylboration reaction across imine.

Synthetic pathways to create asymmetric center at C1 position of 1-substituted-tetrahydro-β-carbolines - a review

The 2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indoles or tetrahydro-β-carbolines (THβCs) are tricyclic compounds that are found in various natural sources that exhibit a wide range of important pharmacological activities. Chiral 1-substituted-THβCs, which have an asymmetric center at C1, have attained significant interest due to their possible Monoamine Oxidase (MAO) inhibitory activity, benzodiazepine receptor binding activity, and antimalarial effectiveness against chloroquine-resistant Plasmodium falciparum. This review highlights and summarizes various novel stereoselective approaches to introduce chirality at the C1 position of 1-substituted-THβCs in good yield and enantiomeric excess (ee) or diastereomeric excess (de). These methods include the Pictet-Spengler reaction, chiral auxiliary, Asymmetric Transfer Hydrogenation (ATH) with chiral catalysts, asymmetric addition reaction, and enzymatic catalysis. The syntheses of chiral THβCs are reviewed comprehensively, emphasizing their role in drug development from 1977 to 2024.

A Disconnection for Rapid Access to Heterocyclic Benzylic Amines with Fully Substituted α-Carbons

2- or 4-Pyridyl benzylic amines represent a privileged motif in drug discovery. However, the formation of heterocyclic benzylic amines with fully substituted α-carbons can require the execution of lengthy synthetic routes, which limit their application. Addition of various nucleophilic agents to Ellman's imines has been well established; however, there is no precedented literature reported for pyridyl-type nucleophiles, which are very important for medicinal chemistry. In this letter, we disclose the development of a one-step synthesis of heterocyclic benzylic amines with fully substituted α-carbons from heteroaryl halides and sulfinyl imines. Starting from 2,4-dibromopyridine, regioselective synthesis of 2- or 4-pyridyl benzylic amines could be achieved by choosing toluene or MTBE as a solvent.

Stereoselective Synthesis of Densely Substituted Pyrrolidines via a [3 + 2] Cycloaddition Reaction between Chiral N-tert-Butanesulfinylazadienes and Azomethine Ylides

The N-tert-butanesulfinylimine group behaves as a suitable electron-withdrawing group in 1-azadienes, allowing the diastereoselective synthesis of densely substituted pyrrolidines by 1,3-dipolar cycloadditions (1,3-DCs) with azomethylene ylides. The use of Ag2CO3 as catalyst has allowed one to obtain a wide variety of proline derivatives with high regio- and diastereoselectivities. Subsequent efficient transformations provide valuable proline derivatives, some of which can be used as organocatalysts. The influence of the N-tert-butanesulfinyl group on the diastereoselectivity was studied by computational methods.

Fluorinated Imines in Tandem and Cycloaddition Reactions

The chemistry of fluorinated compounds has experienced extraordinary growth in recent decades due to the many and varied properties which many of the compounds that contain fluorinated groups possess. Among all of them, fluorinated chiral imines, in particular the Ellman's imines, are of great importance since they are some of the most interesting building blocks for the synthesis of a large number of enantioenriched carbocycles and heterocycles with extraordinary biological and synthetic properties. This personal account covers the most significant results obtained in our research group in the last two decades concerning asymmetric tandem reactions, paying special attention to the intramolecular aza-Michael reaction (IMAMR), diversity oriented synthesis (DOS), asymmetric tandem reactions involving a p-tolylsulfinyl group as chiral inducer and cycloaddition processes, in particular, the Pauson-Khand reaction, [2+2+2]-cycloadditions and metathesis reactions, starting mainly from enyne compounds and through the use of fluorinated chiral N-sulfinyl imines and their derivatives as starting materials.

Stereoselective Synthesis of Less Accessible α-Tertiary Amino Ketimines via Electrophilic Amination of α-Branched N-tert-Butanesulfinyl Ketimines

A stereocontrolled electrophilic amination of α-branched N-tert-butanesulfinyl ketimines was developed to construct α-aminoketone derivatives containing less accessible α-tetrasubstituted stereocenters. Stereospecific α-deprotonation of ketimines with potassium tert-butoxide gave stereodefined metalloenamine intermediates that could act as nucleophiles to attack azodicarboxylic derivatives, affording α-aminated products in high yields with excellent stereoselectivities.

Stereoselective Synthesis of 1-Substituted Homotropanones, including Natural Alkaloid (-)-Adaline

The stereocontrolled synthesis of 1-substituted homotropanones, using chiral N-tert-butanesulfinyl imines as reaction intermediates, is described. The reaction of organolithium and Grignard reagents with hydroxy Weinreb amides, chemoselective N-tert-butanesulfinyl aldimine formation from keto aldehydes, decarboxylative Mannich reaction with β-keto acids of these aldimines, and organocatalyzed L-proline intramolecular Mannich cyclization are key steps of this methodology. The utility of the method was demonstrated with a synthesis of the natural product (-)-adaline, and its enantiomer, (+)-adaline.

Stereocontrolled α-Allylation of α-Branched N-tert-Butanesulfinyl Ketimines via a Michael-Wittig Cascade for the Construction of Acyclic Quaternary Stereocenters

A single-flask cascade of Michael addition and Wittig olefination was developed to allow the stereoselective α-allylic alkylation of α-branched N-tert-butanesulfinyl ketimines for the construction of acyclic quaternary stereocenters bearing two sterically and electronically similar substituents. In this process, tBuOK-promoted stereoselective α-deprotonation gives fully substituted aza-enolates with a stereodefined geometry, Michael addition with α,β-unsaturated phosphonates generates C-C bonds with exceptional stereocontrol, and finally paraformaldehyde trapping of the conjugate addition intermediate generates functionalized α-allylated imines.

Blue Light-Mediated, Photocatalyst-Free Decarboxylative Alkylation of Heteroaryl Sulfinimines

We report a diastereoselective, photocatalyst-free decarboxylative alkylation of (hetero)aryl sulfinimines using redox-active esters under blue light. High yields and diastereoselectivities can be achieved under mild conditions, and we demonstrate its utility as a synthetic method, especially for medicinal chemists.

Stereocontrolled Construction of Acyclic Quaternary Carbon Centers via α-Hydroxymethylation of α-Branched N-tert-Butanesulfinyl Ketimines

Hydroxymethylation of α-branched N-tert-butanesulfinyl ketimines with formaldehyde equivalents was developed to stereoselectively construct acyclic quaternary stereocenters bearing two sterically and electronically similar substituents. The stereoselective tBuOK-promoted α-deprotonation of acyclic ketimines allowed for the stereodefined formation of fully substituted aza-enolates, followed by facially selective C-C bond formation involving formaldehyde formed in situ, yielding α-hydroxymethylated products with precise stereocontrol.

Enantioselective Analysis of Mexiletine Using Chromatographic Techniques: A Review

Background:

Mexiletine belongs to the β-amino-aryl-ether group of pharmaceutical and applied in the diagnosis of antiarrhythmics, allodynia, and myotonic disorders. In its chemical structure, it possesses a chiral center and practiced in the form of the racemic mixture. The production and accessibility of mexiletine have accompanied with a meaningful development in awareness of its pharmacologic actions. But in clinical arrhythmias and binding experiments on cardiac sodium channels, the (R)-enantiomer of mexiletine is more potent than the (S)-enantiomer. Also, (S)-enantiomer is further active in the diagnosis of allodynia than the (R)-enantiomer.

Methods:

During the last two decades, chromatographic techniques such as HPLC, and GC coupled with mass spectrometry or field ionization detector was used for the stereoselective analysis of MEX enantiomers.

Results:

The direct enantioresolution deal with the use of chiral stationary phases (CSPs) with or no pre-derivatization which depend on a chromophoric entity in the racemates whereas indirect HPLC process involved the use of chiral derivatization reagents (CDR) for the synthesis of diastereomeric derivatives of racemates. Different techniques have their strengths and weaknesses.

Conclusion:

Regulation of enantiomeric purity and estimation of particular enantiomers of drug molecules stays an essential topic for therapeutic, diagnostic, and regulatory uses and to promote a precise assessment of the hazards to human health by false enantiomers. This review aims to offer a systematic survey of the analytical methods (chromatography based) used in the enantioselective analysis of MEX developed in the last two decades (the year 2000 onwards).

An expeditious route to sterically encumbered nonproteinogenic α-amino acid precursors using allylboronic acids

A diastereoselective allylation of N-tert-butane sulfinyl α-iminoesters using allylboronic acids is developed to obtain optically active non-proteinogenic α-amino acid precursors in good yields and diastereoselectivities. Gram-scale synthesis, broad tolerance of functional groups, excellent stereodivergence, post-synthetic modifications, and easy removal of the chiral auxiliary are some of the key highlights. The protocol is applicable to various amino acids and short peptides, resulting in the incorporation of these precursors at the N-terminal position.

A diastereoselective allylation of N-tert-butane sulfinyl α-iminoesters using allylboronic acids is developed to obtain optically active non-proteinogenic α-amino acid precursors in good yield and diastereoselectivities.

Stereoselective Synthesis of δ- and ε-Amino Ketone Derivatives from N-tert-Butanesulfinyl Aldimines and Functionalized Organolithium Compounds

The addition of functionalized organolithium compounds derived from 5-chloro-2-methoxy-1-pentene and 6-chloro-2-methoxy-1-hexene to N-tert-butanesulfinyl aldimines imines, and a subsequent hydrolysis of the enol ether moiety, yielded different δ- and ε-amino ketone derivatives, respectively, in moderate yields and diastereoselectivities. The application of these compounds in organic synthesis was demonstrated by the preparation of 2-substituted 6-methylpiperidines in a stereoselective manner, among them natural alkaloids (+)- and (−)-isosolenopsin A.

Four-Step Total Synthesis of (+)-Euphococcinine and (±)-Adaline

A four-step enantiospecific total synthesis of bicyclic homotropinone alkaloid euphococcinine and a racemic synthesis of adaline were reported. Key reactions in the synthesis are the diastereoselective addition of a Wittig phosphorene to the ketimines derived from Davis-Ellman sulfinamides, ring-closing metathesis, and intramolecular Michael reactions.

Syntheses and Transformations of Sulfinamides

Sulfinamides, especially enantiopure sulfinamides, are widely used in organic and medicinal synthesis. Syntheses and transformations of racemic and enantioenriched sulfinamides have achieved great progress. Especially sulfinamides demonstrate interesting and valuable reactivity, which deserves to be pertinent. This review summarizes the latest development in the synthesis and transformation of sulfinamides and will be helpful for future related research.

1 Introduction

2 Synthesis of Sulfinamides

2.1 Synthesis of Racemic Sulfinamides

2.2 Synthesis of Enantiomerically Pure Sulfinamides

2.3 Synthesis of Other Sulfinamides

3 Transformations of Sulfinamides

3.1 Condensation with Aldehydes and Ketones

3.2 Reaction with Alkynes

3.3 Reaction with Alkenes

3.4 Reaction with Aryl and Alkyl Halides

3.5 Reaction with Alcohols, Dibenzyl Ether, and Benzyl Mercaptan

3.6 Synthesis of tert-Butyldisulfanyl-Substituted Hetarenes

3.7 Synthesis of Asymmetric Sulfides

3.8 Synthesis of N-Phosphino-sulfinamide Ligands

3.9 Asymmetric Synthesis of γ-Amino Acids

3.10 Sulfonylation of Heterocyclic Compounds

4 Summary and Outlook

N-tert-Butanesulfinyl imines in the asymmetric synthesis of nitrogen-containing heterocycles

The synthesis of nitrogen-containing heterocycles, including natural alkaloids and other compounds presenting different types of biological activities have proved to be successful employing chiral sulfinyl imines derived from tert-butanesulfinamide. These imines are versatile chiral auxiliaries and have been extensively used as eletrophiles in a wide range of reactions. The electron-withdrawing sulfinyl group facilitates the nucleophilic addition of organometallic compounds to the iminic carbon with high diastereoisomeric excess and the free amines obtained after an easy removal of the tert-butanesulfinyl group can be transformed into enantioenriched nitrogen-containing heterocycles. The goal of this review is to the highlight enantioselective syntheses of heterocycles involving the use of chiral N-tert-butanesulfinyl imines as reaction intermediates, including the synthesis of several natural products. The synthesis of nitrogen-containing heterocycles in which the nitrogen atom is not provided by the chiral imine will not be considered in this review. The sections are organized according to the size of the heterocycles. The present work will comprehensively cover the most pertinent contributions to this research area from 2012 to 2020. We regret in advance that some contributions are excluded in order to maintain a concise format.

Mannich-Type Reaction of α-Sulfanyl N-tert-Butanesulfinylimidates: Diastereoselective Access to α-Mercapto-β-amino Acid Derivatives

A series of α-mercapto-β-amino acid derivatives were synthesized diastereoselectively in good yields through the aza-enolization of α-sulfanyl N-tert-butanesulfinylimidates, followed by their nucleophilic addition to N-tosyl imines via a Mannich-type reaction. The resulting derivatives bearing a β-sulfonylamino sulfide moiety participated in further inter- and intramolecular transformations involving episulfonium ion intermediates generated through neighboring-group participation.

Ru-Tethered (R,R)-TsDPEN with DMAB as an efficient catalytic system for high enantioselective one-pot synthesis of chiral β-aminol via asymmetric transfer hydrogenation

This work reflects Ru-tethered-TsDPEN as an active chiral catalyst for one pot selective synthesis of optically active α-substituted alcohols and its derivatives from α-bromo ketones in the presence of dimethylamine borane (DMAB) as the hydrogen source.

Asymmetric Total Synthesis and Assignment of Absolute Configuration of Arbornamine

The asymmetric total synthesis of arbornamine was accomplished in 13 steps, leading to the assignment of its absolute configuration. The key features of the strategy include construction of the C16 quaternary carbon center by a highly diastereoselective Grignard reagent addition to N-tert-butanesulfinylimine, sequential site-selective amidation and N-alkylation to form the C and E rings, and [Ni(COD)₂]-mediated Michael addition to close the D ring.

Addition of Lithium Anion of (Acetylmethylene)triphenylphosphorane to Nonracemic Sulfinimines: Total Synthesis of (+)-241D and Formal Total Synthesis of (+)-Preussin

The addition of lithium anion of (acetylmethylene)triphenylphosphorane to nonracemic sulfinimines was investigated. It was found that the addition proceeded with good diastereoselectivity and further reaction of the formed sulfinimidophosphorane with several aldehydes afforded the β-sulfinamido substituted enones in good yields. The resultant enones were elaborated to the synthesis of alkaloid (+)-241D, to the formal total synthesis of (+)-preussin, and to the synthesis of aminocyclopentenol.

Asymmetric Transfer Hydrogenation of N-Unprotected Indoles with Ammonia Borane

A metal-free asymmetric transfer hydrogenation of unprotected indoles was successfully realized using a catalyst derived from HB(C₆F₅)₂ and (S)-tert-butylsulfinamide with ammonia borane as a hydrogen source. A variety of indolines were achieved in 40-78% yields with up to 90% ee.

Asymmetric Induction with a Chiral Amine Catalyzed by a Ru-PNP Pincer Complex: Insight from Theoretical Investigation

In this paper, the mechanism of asymmetric amination of a racemic alcohol with Ellman's sulfinamide and the origin of diastereoselectivity catalyzed by a Ru-PNP pincer complex were studied using density functional theory (DFT). The mechanism involves dehydrogenation of the racemic alcohol, C-N coupling, and hydrogen transfer from the catalyst to the in situ formed imine. The calculated results indicate that both the alcohol dehydrogenation and imine hydrogenation are stepwise. The hydride transfer from a Ru hydride complex to the imine is shown to be the chirality-determining step in the whole catalytic cycle. It was found that the diastereoselectivity mainly stems from the hydrogen bonding interactions between the oxygen atom of the sulfinyl moiety and the hydrogen atom of the NH group of the ligand.

Modern Stereoselective Synthesis of Chiral Sulfinyl Compounds

Chiral sulfinyl compounds, sulfoxides, sulfoximines, sulfinamides, and other derivatives, play an important role in asymmetric synthesis as versatile auxiliaries, ligands, and catalysts. They are also recognized as pharmacophores found in already marketed and well-sold drugs (e.g., esomeprazole) and used in drug design. This review is devoted to the modern methods of preparation of sulfinyl derivatives in enantiopure or enantiomerically enriched form. Selected new approaches leading to racemic products for which the asymmetric variant can be developed in the future are mentioned as well.

One-Step Diastereoselective Pyrrolidine Synthesis Using a Sulfinamide Annulating Reagent

This communication highlights the use of chiral sulfinamides as nitrogen nucleophiles in intermolecular aza-Michael reactions. When chiral sulfinamides are coupled to a chloroethyl group, the corresponding novel annulating reagents can be used to streamline the stereoselective synthesis of complex pyrrolidine-containing molecules. As a result, it has enabled a medicinal chemistry campaign for the synthesis of biologically active RORγt inverse agonists.

Total Synthesis and Anti-Cancer Activity of All Known Communesin Alkaloids and Related Derivatives

A unified enantioselective total synthesis and anticancer evaluation of all known epoxide-containing communesin alkaloids and related derivatives is described. Our synthesis is predicated on the convergent and modular diazene-directed assembly of two complex fragments to secure the critical C3a-C3a' linkage followed by a guided biomimetic aminal reorganization to deliver the heptacyclic core of these alkaloids. Concise enantioselective syntheses of the fragments were devised, with highlights including the application of a rationally designed sulfinamide chiral auxiliary, an efficient calcium trifluoromethanesulfonate promoted intramolecular amination, and a diastereoselective epoxidation that simultaneously converts the new chiral auxiliary to a versatile amine protective group. The modularity of our convergent approach enabled the rapid synthesis of all epoxide-containing members of the communesin family from a single heterodimeric intermediate, including the first total synthesis of communesins C-E, and G-I, and facilitated our stereochemical revision of (-)-communesin I, the most recently isolated communesin alkaloid. Furthermore, the generality of our biogenetically inspired heterodimer rearrangement was demonstrated in a guided synthesis of a communesin derivative with an unnatural topology. Finally, we report the first comparative analysis of the anticancer activities of all naturally occurring communesin alkaloids A-I and eight complex derivatives against five human cancer cell lines. From these data, we have identified (-)-communesin B as the most potent natural communesin and discovered that derivatives with N8'-sulfonamide substitution exhibit up to a 10-fold increase in potency over the natural alkaloids.

Diastereoselective α-Amination of N- tert-Butanesulfinyl Imidates Using N-Aryl- N-diphenylphosphinyldiazenes

Diastereoselective α-amination of N- tert-butanesulfinyl imidates has been developed using N-aryl (or N- tert-butyl) N-diphenylphosphinyldiazenes as nitrogen sources. The chiral 1-azaenolates derived from imidates undergo nucleophilic addition with diazenes to give α-hydrazino imidates in good yields.

Asymmetric synthesis of 1-substituted 2-azaspiro[3.3]heptanes: important motifs for modern drug discovery

Highly diastereoselective addition of ethyl cyclobutanecarboxylate anions to Davis-Ellman's imines is reported. This methodology afforded the preparation of enantiomerically and diastereomerically pure 1-substituted 2-azaspiro[3.3]heptanes. This three-step procedure proceeded efficiently (yield up to 90%) and diastereoselectively (dr values up to 98 : 2). This methodology is applicable to the synthesis of 1-substituted 2-azaspiro[3.4]octane and 1-substituted 2-azaspiro[3.5]nonane.

Enantiodivergent Approach to the Synthesis of Cis-2,6-Disubstituted Piperidin-4-ones

Enantiopure β-amino ketone derivatives were synthesized by decarboxylative Mannich reaction of chiral N- tert-butanesulfinyl imines with β-keto acids and were subsequently transformed into cis-2,6-disubstituted piperidin-4-ones through an organocatalyzed condensation with aldehydes. Both enantiomers were accessible from the same precursors by inverting the order in the reaction sequence of the aldehydes involved in the imine formation and the intramolecular Mannich condensation. The synthesis of the piperidine alkaloids (+)-241D, (-)-epimyrtine, and (-)-lasubine II demonstrated the utility of this methodology.

K3PO4-promoted domino reactions: diastereoselective synthesis of trans-2,3-dihydrobenzofurans from salicyl N-tert-butanesulfinyl imines and sulfur ylides

An efficient domino annulation between sulfur ylides and salicyl N-tert-butylsulfinyl imines was developed. The reaction proceeds with a diastereodivergent process, the configuration of the sulfinyl group determining the stereochemical course of the reaction. The method allows the synthesis of a highly substituted trans-2,3-dihydrobenzofuran skeleton with high yield and good chemo- and diastereoselectivity.

Asymmetric Synthesis 1-Substituted 2,6-Diazaspiro[3.3]heptanes through Addition of 3-Azetidinecarboxylate Anions to Davis-Ellman Imines

Asymmetric synthesis of 1-substituted 2,6-diazaspiro[3.3]heptane is described. This methodology affords excellent yields (up to 89%) and high diastereomeric ratios ( dr up to 98:2) and delivers differentially protected amines within the products.

Enantioselective Synthesis of Nicotine via an Iodine-Mediated Hofmann-Löffler Reaction

An iodine-mediated Hofmann-Löffler reaction has been developed that enables the first enantioselective synthesis of nicotine based on this synthetic methodology. The effect of the free pyridine core on the involved electrophilic iodine reagents was explored in detail. The final synthesis proceeds under moderate reaction conditions that tolerate the free pyridine core. The same synthetic sequence is also applicable to a number of derivatives with higher substituted pyridine cores, including bipyridine derivatives.

Enantioselective Synthesis, DFT Calculations, and Preliminary Antineoplastic Activity of Dibenzo 1-Azaspiro[4.5]decanes on Drug-Resistant Leukemias

The addition of 2-bromobenzylmagnesium bromide to chiral N- tert-butanesulfinyl imines derived from tetralone-type ketones proceeds with high levels of diastereocontrol. The resulting sulfinamide derivatives were transformed into dibenzoazaspiro compounds after a palladium-catalyzed intramolecular N-arylation. DFT calculations have been performed to rationalize the stereochemical course of the reaction. Similar results have been obtained considering either diethyl ether or toluene as a solvent, in both cases in an excellent agreement with experimental findings. NCI topological calculations have also been used to evidence crucial noncovalent interactions. In addition, the azaspiro compounds reduced the viability of chronic myeloid leukemia cells in the micromolar range. Notably, both the halogen-substituted ( R)- and ( S)-8g and -8h as well as ( R)-8j were at least two times more effective on a multidrug-resistant derivative than on the parental cell line, exerting a collateral sensitivity effect.