Development of a Novel, Highly Efficient Halide-Catalyzed Sulfenylation of Indoles

t-BuOLi promoted regioselective N-thiolation of indoles with N-arylthio phthalimide

The selective N-thiolation of indole substrates poses a challenge due to their diminished nucleophilicity at nitrogen. Herein, we present a novel method for the thiolation of the NH group in indole derivatives by using N-arylthio phthalimide as the sulfur source, t-BuOLi as the base and MeCN as the solvent. The process was successfully conducted under transition metal catalyst-free and room temperature conditions with a high product yield and a short reaction time. The developed protocol exhibited excellent regioselectivity and broad substrate tolerance in the preparation of N-thioindoles with diverse functional groups.

Me3SiBr-promoted cascade electrophilic thiocyanation/cyclization of ortho-alkynylanilines to synthesize indole derivatives

A Lewis acid-promoted electrophilic thiocyanation/cyclization of ortho-alkynylanilines for the synthesis of indole derivatives has been developed. The reaction utilizes Me3SiBr as the Lewis acid and N-thiocyanatosuccinimide as the thiocyanation reagent. A series of 2-aryl-3-thiocyanato indoles were prepared in moderate to high yields under mild conditions without metals and oxidants. It provides an efficient protocol for the construction of the indole skeleton and C-SCN and C-N bonds in one step as well.

Palladium-Catalyzed C3-Carbaldehyde Directed Regioselective C2-Thioarylation of Indoles

Palladium-catalyzed thioarylation of indoles by diaryl disulfides in the presence of phenyliododiacetate is reported. The directing potential of weakly coordinating aldehyde group present at 3-position of indole was exploited for regioselective C2-H thioarylation over the possible C4-H functionalization. Mechanistic studies reveal that the process involves initial generation of thioaryl radical followed by sequential C-H activation, thiolate transfer, and reductive elimination.

A Method for the Synthesis of Thioindoles through Copper-Catalyzed C-S Bond Coupling Reaction

We herein report the copper-catalyzed C-S bond coupling reaction of indoles with N-thiosuccinimides, resulting in moderate to excellent yields of mono- and bis-sulfenylated compounds such as arylthioindoles, alkylthioindoles, selenylated indoles, and cysteine-substituted indoles. Thioarylation and thioglycosylation at the C2 position of indole alkaloids in the Radix Isatidis were achieved via structural modification. The first total syntheses of isatindigotindolosides III and IV have been successfully carried out. The electrophilic sulfenyl bromides generated in situ can play an important role in the catalytic cycle.

N-Sulfenylsuccinimide/phthalimide: an alternative sulfenylating reagent in organic transformations

In the field of organosulfur chemistry, sulfenylating agents are an important key in C-S bond formation strategies. Among various organosulfur precursors, N-sulfenylsuccinimide/phthalimide derivatives have shown highly electrophilic reactivity for the asymmetric synthesis of many organic compounds. Hence, in this review article, we focus on the application of these alternative sulfenylating reagents in organic transformations.

Base-mediated chalcogenoaminative annulation of 2-alkynylanilines for direct access to 3-sulfenyl/selenyl-1H-indoles

An efficient and transition metal-free synthesis of 3-sulfenyl/selenyl-1H-indoles via a base-assisted chalcogenoaminative annulation of 2-alkynyl aniline with disulfides/diselenides is described. A series of 2-alkynylanilines were found compatible with dichalcogenides in this transformation providing 3-sulfenyl/selenyl-1H-indoles in good to excellent yields. The presented methodology has the advantages of easily available raw materials, functional group tolerance, and a wide range of substrates that provide access to 3-sulfenylindoles and 3-selenylindoles.

Efficient Synthesis of 3-Mercaptoindoles via HI-Promoted Sulfenylation of Indoles with Sodium Sulfinates

A new direct sulfenylation method of indoles by sodium sulfinates and hydroiodic acid was developed giving variety of 3-sulfenylindoles in high yields under mild conditions without using any catalysts or other additives. In situ-generated RS-I species are supposed to be mainly responsible for the key electrophilic alkyl- or aryl-thiolation process.

DBU-Catalyzed Aerobic CDC Reaction of Thiophenols

A convenient method was developed for the preparation of thiolated compounds via a DBU-catalyzed aerobic cross-dehydrogenative coupling (CDC) reaction. The established protocol is environmentally friendly and operationally simple. Substrates like (hetero)aryl acetates, (hetero)aryl ketones, and indoles could be transformed into the corresponding thiolated products in moderate to high yields and further applied in the preparation of bioactive compounds in a prefunctionalization-free manner.

Radical and ionic meta -C–H functionalization of pyridines, quinolines, and isoquinolines

Carbon-hydrogen (C−H) functionalization of pyridines is a powerful tool for the rapid construction and derivatization of many agrochemicals, pharmaceuticals, and materials. Because of the inherent electronic properties of pyridines, selective meta -C−H functionalization is challenging. Here, we present a protocol for highly regioselective meta -C−H trifluoromethylation, perfluoroalkylation, chlorination, bromination, iodination, nitration, sulfanylation, and selenylation of pyridines through a redox-neutral dearomatization-rearomatization process. The introduced dearomative activation mode provides a diversification platform for meta-selective reactions on pyridines and other azaarenes through radical as well as ionic pathways. The broad scope and high selectivity of these catalyst-free reactions render these processes applicable for late-stage functionalization of drugs.

Visible-Light-Induced, Graphene Oxide-Promoted C3-Chalcogenylation of Indoles Strategy under Transition-Metal-Free Conditions

An efficient and general method for the synthesis of 3-sulfenylindoles and 3-selenylindoles employing visible-light irradiation with graphene oxide as a promoter at room temperature has been achieved. The reaction features are high yields, simple operation, metal-free and iodine-free conditions, an easy-to-handle oxidant, and gram-scalable synthesis. This simple protocol allows one to access a wide range of 3-arylthioindoles, 3-arylselenylindoles, and even 3-thiocyanatoindoles with good to excellent yields.

Recent advances in thiolation via sulfur electrophiles

This review systematically summarizes the recent developments for constructing sulfur compounds from sulfur electrophiles, and the mechanism mainly involved thirranium ions, sulfur ylides, C–S cross coupling and electrophilic substitution.

Transition-Metal-Free HFIP-Mediated Organo Chalcogenylation of Arenes/Indoles with Thio-/Selenocyanates

We have developed a protocol for the synthesis of diaryl thio-/selenoethers by the reaction of aryl chalcogenocyanates with electron rich arenes/hetero arenes via HFIP promoted C-H activation. The reaction produces chalcogenides in good to excellent yields under mild conditions without the need of a transition metal as a catalyst. The HFIP-mediated reactions tolerated a wide range of functional groups and set the stage for the synthesis of diversely decorated chalcogenides. A mechanism involving activation of the C-H bond through hydrogen bonding is proposed.

Straightforward Functionalization of Sulfur-Containing Peptides via 5- and 6-endo-dig Cyclization Reactions

We present a simple and convenient method for the generation of sulfenyl electrophiles from peptides containing S–S or S–H bonds by employing N-chlorosuccinimide. The corresponding sulfenyl electrophiles are further utilized in 5- and 6-endo-dig cyclization reactions yielding indolizinium salts, indoles, benzo[b]furans, polyaromatic hydrocarbons (PAHs) and isocoumarins, as well as quinolinones bearing a glutathione moiety. PAH derivatives can be used as selective fluorescent dyes for the visualization of lipid droplets in living cells.

Enantioselective synthesis of indole derivatives by Rh/Pd relay catalysis and their anti-inflammatory evaluation

An efficient Rh/Pd relay catalyzed intermolecular and cascade intramolecular hydroamination for the synthesis of exclusive trans 1-indolyl dihydronaphthalenols (up to 88% yield, 99% ee) is described under mild conditions. Moreover, the in silico and in vitro screening showed that the novel 1-indolyl dihydronaphthalenol products are potent lead compounds for treating inflammation disease.

Iodine-catalyzed thioallylation of indoles using Bunte salts prepared from Baylis-Hillman bromides

Metal-free iodine-catalyzed regioselective thioallylation of indoles has been accomplished at room temperature using Bunte salts prepared from Baylis-Hillman bromides. The resulting multi-functional C3 thioallylated indoles exhibit ample structural diversity and good functional group tolerance.

Convenient and Efficient Synthesis of Functionalized 2-Sulfenylindoles

A simple, efficient, and practical sulfenylation at the C2 position of N-tosylindoles under mild conditions was developed. The designed transformation is based on the reaction of N-tosylindoles with BuLi and S-alkyl, and S-aryl phosphorodithioates or thiotosylates to produce 2-sulfenylindoles in moderate to high yields. The presence of additional hydroxy, carboxy, or amino functionalities did not disturb the formation of products.

Review of the Syntheses and Activities of Some Sulfur-Containing Drugs

Background:

Sulfur-containing compounds represent an important class of chemical compounds due to their wide range of biological and pharmaceutical properties. Moreover, sulfur-containing compounds may be applied in other fields, such as biological, organic, and materials chemistry. Several studies on the activities of sulfur compounds have already proven their anti-inflammatory properties and use to treat diseases, such as Alzheimer’s, Parkinson’s, and HIV. Moreover, examples of sulfur-containing compounds include dapsone, quetiapine, penicillin, probucol, and nelfinavir, which are important drugs with known activities.

Objective:

This review will focus on the synthesis and application of some sulfur-containing compounds used to treat several diseases, as well as promising new drug candidates.

Results:

Due to the variety of compounds containing C-S bonds, we have reviewed the different synthetic routes used toward the synthesis of sulfur-containing drugs and other compounds.

C-H Sulfonylation via 1,3-Rearrangement of Sulfonyl Group in N-Protected 3-Bis-sulfonimidoindole Derivatives Using Fluorine Reagent

A C-H sulfonylation of N-protected 3-bis-sulfonimidoindole derivatives via a 1,3-rearrangement of a sulfonyl group on a bis-sulfonimide moiety using tetra-n-butylammonium fluoride (TBAF) was developed to provide 2-sulfonyl-3-sulfonamidoindole derivatives in high yields as a novel C_sp2-H functionalization of heterocycles. The rearrangement of the sulfonyl group proceeded through an intermolecular addition of the desorbed sulfinyl ion from the bis-sulfonimide moiety in the substrate.

Iodine-Catalyzed Synthesis of 3-Arylthioindoles Employing a 1-Aryltriazene/CS2 Combination as a New Sulfenylation Source

A practical approach for the regioselective synthesis of 3-arylthioindoles has been accomplished using a combination of 1-aryltriazene/CS₂ as a new sulfenylation source. The methodology employs molecular iodine as a catalyst and is compatible with a variety of structurally diverse reactants.

The direct C3 chalcogenylation of indolines using a graphene-oxide-promoted and visible-light-induced synergistic effect

A green methodology for the construction of carbon–chalcogen (S and Se) bonds via a GO-promoted and metal-free light-induced synergistic effect is demonstrated.

Recent developments in palladium-catalyzed C–S bond formation

This review summarized the recent developments in palladium-catalyzed C–S bond formation involving sulfenylation and sulfonylation reactions.

Newly synthesized 3-sulfenylindole derivatives from 4-hydroxydithiocoumarin using an oxidative cross dehydrogenative coupling reaction (OCDCR): potential lead molecules for antiproliferative activity

Synthesis of 3-sulfenyl indole derivatives is achieved through oxidative cross-dehydrogenative coupling reaction. A few such newly synthesized compounds have also exhibited anti-proliferative activityviareactive oxygen species mediated cell damage.

Ditocopheryl Sulfides and Disulfides: Synthesis and Antioxidant Profile

Symmetrical ditocopheryl disulfides (Toc)₂ S₂ and symmetrical and unsymmetrical ditocopheryl sulfides (Toc)₂ S were simply prepared under remarkably mild conditions with complete control of the regiochemistry by using δ-, γ-, and β-tocopheryl-N-thiophthalimides (Toc-NSPht) as common starting materials. The roles of sulfur atom(s), H-bond and aryl ring substitution pattern on the antioxidant profile of these new compounds, which were assembled by linking together two tocopheryl units, are also discussed.

An efficient t-BuOK promoted C3-chalcogenylation of indoles with dichalcogenides

A versatile and efficient method for the synthesis of 3-chalcogenyl-indoles from indoles and dichalcogenides employing t-BuOK as a promoter at room temperature has been achieved. The present protocol exhibited a broad functional group tolerance. Diverse 3-sulfenyl- and 3-selenyl-indoles were rapidly obtained in good to excellent yields with high regioselectivities. It is noteworthy that this transformation was applicable to N-protected and N-unprotected indoles, allowing N-deprotection and C3-chalcogenylation of indoles in one step.

T3P® mediated domino C(sp2)–H sulfenylation/annulation of enaminones and methylsulfinyls for the synthesis of chromone thioether derivatives

Regio-selective preparation of 3-sulfenylated chromone using T3P® has been described for the first time.

Two-Step Synthesis of Unsymmetrical Diaryl Sulfides by Electrophilic Thiolation of Non-functionalized (Hetero)arenes

This article reports the efficient preparation of a series of unsymmetrically substituted thioethers through a two-step procedure consisting of an initial metal-free C-H sulfenylation of electron-rich (hetero)arenes with newly prepared succinylthioimidazolium salts. Subsequent reaction of the arylthioimidazolium intermediates with Grignard reagents afford the desired thioethers. The synthetic protocol described is modular, scalable, and high yielding, and provides access to sulfides that are not easy to obtain through the existing methodologies. Importantly, no prefunctionalization of the initial (hetero)arene is required.

Cu-Catalysed Direct Bis-Thiolation of Benzoheterocycles with Arylsulfonyl Hydrazides

A series of bis-arylsulfenylated indoles (10), benzofurans (3), and benzothiophenes (3) and of monosulfenylated indoles (5), 12 of which are novel, were prepared in good yields via a Cu-catalysed direct sulfenylation of benzoheterocycles with arylsulfonyl hydrazides. Sulfonothioates are probably the major thiolated intermediates in this transformation.

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.