Combination of Lewis Basic Selenium Catalysis and Redox Selenium Chemistry: Synthesis of Trifluoromethylthiolated Tertiary Alcohols with Alkenes

Efficient synthesis of SCF3-containing 3-alkenylquinoxalinones via three-component radical cascade reaction

An efficient and practical method for the synthesis of 3-alkenylquinoxalinones containing the SCF3 group has been readily developed through a three-component radical cascade reaction involving quinoxalinones, alkynes and AgSCF3. The reaction was found to be compatible with a variety of substrates and exhibited a high functional group tolerance and complete E-selectivity. The preliminary study suggests the involvement of a SCF3 radical in the transformation.

Trifluoromethylthiolation of Arenes Using Lewis Acid and Lewis Base Dual Catalysis

Incorporation of the highly lipophilic trifluoromethanesulfenyl group into bioactive molecules facilitates transport through lipid membranes, and thus, CF3S-containing compounds are important for drug discovery. Although reagents and procedures have been reported for arene trifluoromethylthiolation, methods are still required that are applicable to a diverse substrate scope and can be performed under mild conditions. Here, we describe a rapid and efficient approach for the trifluoromethylthiolation of arenes by catalytic activation of N-trifluoromethylthiosaccharin using a combination of iron(III) chloride and diphenyl selenide. This dual catalytic process allowed regioselective functionalization of a wide range of arenes and N-heterocycles under mild conditions and was used for the trifluoromethylthiolation of bioactive compounds such as tyrosine and estradiol.

A Toolbox of Reagents for Trifluoromethylthiolation: From Serendipitous Findings to Rational Design

Two types of electrophilic trifluoromethylthiolating reagents were developed in the past 10 years in our laboratory. The development of the first type of reagent, trifluoromethanesulfenate I, which is highly reactive toward a variety of nucleophiles, was based on an unexpected discovery in the initial design for the development of an electrophilic trifluoromethylthiolating reagent with a hypervalent iodine skeleton. A structure-activity study disclosed that α-cumyl trifluoromethanesulfenate (reagent II) without the iodo substituent is equally effective. Subsequent derivatization let us develop an α-cumyl bromodifluoromethanesulfenate III that could be used for the preparation of [¹⁸F]ArSCF₃. To remediate the low reactivity of the type I electrophilic trifluoromethylthiolating reagent for Friedel-Crafts trifluoromethylthiolation of electron-rich (hetero)arenes, we designed and prepared N-trifluoromethylthiosaccharin IV, which exhibits broad reactivity toward various nucleophiles, including electron-rich arenes. A comparison of the structure of N-trifluoromethylthiosaccharin IV with that of N-trifluoromethylthiophthalimide showed that the replacement of one carbonyl group in N-trifluoromethylthiophthalimide with a sulfonyl group made N-trifluoromethylthiosaccharin IV much more electrophilic. Thus, the replacement of both carbonyls with two sulfonyl groups would further increase the electrophilicity. Such a rationale prompted us to design and develop the current most electrophilic trifluoromethylthiolating reagent, N-trifluoromethylthiodibenzenesulfonimide V, and its reactivity was much higher than that of N-trifluoromethylthiosaccharin IV. We further developed an optically pure electrophilic trifluoromethylthiolating reagent, (1S)-(-)-N-trifluoromethylthio-2,10-camphorsultam VI, for the preparation of optically active trifluoromethylthio-substituted carbon stereogenic centers. Reagents I-VI now constitute a powerful toolbox for the introduction of the trifluoromethylthio group into the target molecules.

Indane-Based Chiral Aryl Chalcogenide Catalysts: Development and Applications in Asymmetric Electrophilic Reactions

Asymmetric electrophilic reactions provide an ideal method for the construction of chiral molecules by incorporating one or more functional groups into the parent substrates under mild conditions. However, due to the issues of the reactivities of electrophilic species and the possible racemization of chiral intermediates as well as the restriction of the chiral scaffolds of chiral catalysts, many limitations remain in this field, such as the narrow scopes of substrates and electrophiles as well as the limited types of nucleophiles and reactions. To overcome the limitations in the synthesis of diversified chiral molecules, we developed a series of indane-based chiral amino aryl chalcogenide catalysts. These catalysts are easily prepared based on the privileged chiral indane scaffold. They can provide an appropriate H-bonding effect by varying the amino protecting groups as well as offer a proper Lewis basicity and steric hindrance by adjusting different substituents on the aryl chalcogenide motifs. These features allow for them to meet the requirements of reactivity and the chiral environment of the reactions. Notably, they have been successfully applied to various asymmetric electrophilic reactions of alkenes, alkynes, and arenes, expanding the field of electrophilic reactions.Using these catalysts, we realized the enantioselective CF₃S-lactonization of olefinic carboxylic acids, enantioselective CF₃S-aminocyclization of olefinic sulfonamides, desymmetrizing enantioselective CF₃S-carbocyclization of gem-diaryl-tethered alkenes, enantioselective CF₃S-oxycyclization of N-allylamides, enantioselective intermolecular trifluoromethylthiolating difunctionalization and allylic C-H trifluoromethylthiolation of trisubstituted alkenes, formally the intermolecular CF₃S-oxyfunctionalization of aliphatic internal alkenes, intermolecular azidothiolation, oxythiolation, thioarylation of N-allyl sulfonamides, desymmetrizing enantioselective chlorocarbocyclization of aryl-tethered diolefins, enantioselective Friedel-Crafts-type electrophilic chlorination of N-allyl anilides, and enantioselective chlorocarbocyclization and dearomatization of N-allyl 1-naphthanilides. Additionally, the enantioselective electrophilic carbothiolation of alkynes to construct enantiopure carbon chirality center-containing molecules and axially chiral amino sulfide vinyl arenes and the electrophilic aromatic halogenation to produce P-chirogenic compounds can be accomplished. In these reactions, a bifunctional binding mode is proposed in the catalytic cycles, in which an acid-derived anion-binding interaction might exist and account for the high enantioselectivities of the reactions.In this Account, we demonstrate our achievements in asymmetric electrophilic reactions and share our thoughts on catalyst design, our understanding of asymmetric electrophilic reactions, and our perspectives in the field of chiral chalcogenide-catalyzed asymmetric electrophilic reactions. We hope that the experience we share will promote the design and development of other novel organocatalysts and new challenging reactions.

Synthesis of 2,5-disubstituted selenophenes via a copper-catalyzed regioselective [2+2+1] cyclization of terminal alkynes and selenium

Herein, a straightforward method for the synthesis of 2,5-disubstituted selenophenes via [2+2+1] cyclization of easily accessible terminal alkynes and elemental selenium has been developed. This reaction features high atom- and step-economy, excellent regioselectivity, good functional group tolerance and the use of stable and non-toxic selenium as a selenium source. A series of control experiments suggests that the reaction might undergo Glaser coupling reaction of two molecules of alkynes, followed by insertion of H₂Se and subsequent cyclization. Moreover, the newly formed products can be further converted to diverse conjugated selenophene-based derivatives, demonstrating their potential applications in organic synthesis and materials science.

Recent Advances in Organoselenium Catalysis

Abstract:

: Organoselenium chemistry has developed as an important tool in the field of synthetic and medicinal chemistry. Various organoselenium reagents have been developed and used successfully to achieve different organic transformations such as the selenocyclizations, oxyselenenylations and selenoxide eliminations etc. Additionally, the potential of organoselenium reagents is not limited their use as stoichiometric reagents but they have successfully used as organocatalyst in number of synthetic transformations. Various organic and inorganic oxidants have been identified as terminal oxidants to regenerate the active catalytic specie. In this review article, the recent progress of organoselenium reagents in catalysis is being highlighted along with their asymmetric variants.

Metal-Free Direct Trifluoromethylthiolation of Aromatic Compounds Using Triptycenyl Sulfide Catalyst

Herein we report an efficient synthetic method for the electrophilic trifluoromethylthiolation of aromatic compounds. The key is to use triptycenyl sulfide (Trip-SMe) and TfOH to enhance the electrophilicity of SCF₃ fragment through the formation of sulfonium intermediates. This method enables direct installation of an SCF₃ group onto unactivated aromatics at room temperature, adopting a commercially available saccharin-based reagent. Preliminary DFT calculation was carried out to investigate the substitution effect on the catalytic activity.

Metal-free visible-light-enabled vicinal trifluoromethyl dithiolation of unactivated alkenes

The difunctionalization of alkenes involving a trifluoromethylthio group (SCF3) for the conversion of versatile and readily available olefins into structurally more complex molecules has been successfully studied. However, the disproportionate dithiolation of alkenes is unknown. Herein, a transition-metal-free protocol is presented for the vicinal trifluoromethylthio-thiolation of unactivated alkenes via a radical process under mild conditions with a broad substrate scope and excellent tolerance.

Recent advances in intermolecular 1,2-difunctionalization of alkenes involving trifluoromethylthiolation

Trifluoromethylthiolative difunctionalization of alkenes, a cheap and abundant feedstock, which installs a trifluoromethylthiol (SCF₃) group and another unique functional group across the carbon–carbon double bonds, provides an ideal strategy for the preparation of β-functionalized alkyl trifluoromethyl sulfides and has become a hot topic recently.

Practical and regioselective halo-trifluoromethylthiolation of sulfur ylides

A H2O mediated practical and highly regioselective chloro- and bromo-trifluoromethylthiolation of sulfur ylides is reported using a difunctionalization strategy. In the reaction sequence, sulfur ylides presumably react with an electrophilic trifluoromethylthiolating reagent to generate an α-SCF3 substituted sulfonium salt intermediate, which then undergoes a substitution with nucleophilic halogens.

Organoselenium and organotellurium compounds containing chalcogen-oxygen bonds in organic synthesis or related processes

This chapter emphasizes aspects related to the role of organochalcogen (Se, Te) compounds with single E‒O and/or double E=O (E=Se, Te) bonds in organic synthesis, as reagents, intermediates, or catalysts, and it gives a larger extent mainly to data reported in the field during the last ten years. For each of these two heavier chalcogens the material is structured according to the oxidation state of the chalcogen and, for the same oxidation state, in sections dedicated to a particular type of compounds. Functionalization or cyclization reactions in which the organochalcogen compounds take part as nucleophiles, electrophiles or radicals, employed in various synthetic transformations, are discussed and, where available, the mechanistic aspects are outlined. New chiral species and new strategies were developed during last years in order to increase the yield, the reaction rate and the stereoselectivity in specific organic transformations, i.e. addition, oxidation, elimination, cyclization or rearrangement reactions. A notably attention was devoted to easily accessible and environmental friendly catalysts, re-usable and “green” solvents, as well as waste-free procedures.

Synthesis, structural characterisation, and synthetic application of stable seleniranium ions

Stable seleniranium ions were prepared from easily available stable bromiranium ions and diselenides. The solid state structure of the obtained seleniranium ions was determined by X-ray crystallographic analysis and their alkene-to-alkene transfer was investigated by NMR techniques. The rapid alkene-to-alkene transfer of the selenium group enabled the application of the seleniranium ion salts as selenenylating agents, which led to very efficient and highly diastereoselective, selenium-induced polyene-type cyclisations of terpene analogues.

Recent progress in selenium-catalyzed organic reactions

Selenium-based catalysts, including organo- and inorganoselenium ones, in organic synthesis in the recent decade are reviewed.

Organoselenium small molecules as catalysts for the oxidative functionalization of organic molecules

This perspective highlights the critical analysis of the challenges, in the past decade, which led to the development of organoselenium compounds and their use as versatile catalysts in organic synthesis towards the oxidation of olefins and C–H bonds. Furthermore, the emphasis here differs from previous reviews of the field by classifying the various types of catalyses and the diverse strategies.

Selenium reagents as catalysts

Organoselenium chemistry has become an important tool in synthetic and medicinal chemistry.

Trifluoromethylthiolative 1,2-difunctionalization of alkenes with diselenides and AgSCF3

An efficient regioselective difunctionalization of alkenes via trifluoromethylthiolation has been accomplished employing diaryl diselenide and AgSCF₃ in the presence of BF₃·OEt₂.

FeCl3-Catalyzed Regio-Divergent Carbosulfenylation of Unactivated Alkenes: Construction of a Medium-Sized Ring

A FeCl₃-catalyzed regio-divergent carbosulfenylation of unactivated alkenes with electrophilic N-sulfenophthalimides has been developed. This protocol provides a straightforward and efficient access to various medium-sized rings, especially strained 7- and 8-membered carborings with a sulfur atom attached. The endo/exo selectivity in the reaction depends on the atom number of the chain between arene and alkene. Broad substrate scope, high yields, and gram-scale synthesis exemplified the utility and practicability of this protocol. In addition, this methodology can be extended to the carboselenylation of isolated alkenes.

Lewis Base/Bronsted Acid Dual-Catalytic C-H Sulfenylation of Aromatics

A Lewis base/Bronsted acid catalyzed aromatic sulfenylation is reported. These studies demonstrated that the incorporation of electron-rich sulfenyl groups proceeded in the absence of a Lewis base, with kinetic studies indicating an autocatalytic mechanism. The incorporation of electron-poor sulfenyl groups demonstrated little autocatalysis necessitating the use of a Lewis base. This method proved amenable to diverse arenes and heterocycles and was effective in the context of the late-stage functionalization of biologically active small molecules.

Enantioselective addition of selenosulfonates to α,β-unsaturated ketones

An organo-catalyzed enantioselective addition of selenosulfonates to α,β-unsaturated ketones was developed for the first time. With a chiral squaramide as an efficient catalyst, the desired α-selenylated ketones were obtained in a good yields with high enantioselectivity up to 89% ee, and good results could be obtained on a gram scale. The products could also be efficiently transformed into useful building blocks with a propenylic stereocenter; the strategy presented in this study may find further applications in organic synthesis.