Benzisothiazol-3-ones through a Metal-Free Intramolecular N-S Bond Formation

Selective Oxidation of Benzo[d]isothiazol-3(2H)-Ones Enabled by Selectfluor

A metal-free and Selectfluor-mediated selective oxidation reaction of benzo[d]isothiazol-3(2H)-ones in aqueous media is presented. This novel strategy provides a facile, green, and efficient approach to access important benzo[d]isothiazol-3(2H)-one-1-oxides with excellent yields and high tolerance to various functional groups. Furthermore, the purification of benzoisothiazol-3-one-1-oxides does not rely on column chromatography. Moreover, the preparation of saccharine derivatives has been achieved through sequential, double oxidation reactions in a one-pot aqueous media.

Synthesis of gem-Difluorinated Keto-Sulfoxides from Sulfoxonium Ylides

Organic molecules containing fluorine and sulfur atoms represent a large percentage of approved pharmaceuticals. Those with combination of both S and F atoms in their structure such as Xtandi, approved in 2012 for prostate cancer, indicates the importance of synthetic methods that accommodates both atoms in an organic moiety. In this study, a novel aspect of sulfoxonium ylide reactivity was explored, unveiling a streamlined and mild synthesis method for gem-difluorinated keto-sulfoxides. Our protocol offers a direct and practical approach to prepare these compounds in 14-80 % chemical yields, that were represented by 21 examples. NMR studies and Hammett correlations gave strong evidence about the mechanism of this transformation.

Selective C(sp3)-S Bond Cleavage of Thioethers to Build Up Unsymmetrical Disulfides

The selective C(sp3)-S bond cleavage of thioethers was first developed to prepare unsymmetrical disulfides by using electrophilic halogenation reagents. In this strategy, NBS (N-bromosuccinimide) achieves selective furfuryl C(sp3)-S bond cleavage of furfuryl alkylthioethers at room temperature. Meanwhile, NFSI (N-fluorobenzenesulfonimide) enables selective methyl C(sp3)-S bond cleavage of aryl and alkyl methylthioethers at an elevated temperature. Notably, the substrate scope investigation indicates that the order of selectivity of the C-S bond cleavage is furfuryl C(sp3)-S > benzyl C(sp3)-S > alkyl C(sp3)-S > C(sp2)-S bond. Moreover, this practical and operationally simple strategy also provides an important complementary way to access various unsymmetrical disulfides with excellent functional group tolerances and moderate to good yields.

Total Synthesis of (-)-Levesquamide

The total synthesis of levesquamide, a natural product with an unprecedented pentasubstituted pyridine-isothiazolinone skeleton, has been accomplished from kojic acid for the first time. The key features of the synthesis include a Suzuki coupling reaction between bromopyranone and oxazolyl borate fragments, a copper-mediated introduction of a thioether, a mild hydrolysis of a pyridine 2-N-methoxyamide, and a Pummerer-type cyclization of a tert-butyl sulfoxide to form the key pyridine-isothiazolinone unit of the natural product.

Recent Strategies in Nickel-Catalyzed C–H Bond Functionalization for Nitrogen-Containing Heterocycles

N-heterocycles are ubiquitous in natural products, pharmaceuticals, organic materials, and numerous functional molecules. Among the current synthetic approaches, transition metal-catalyzed C–H functionalization has gained considerable attention in recent years due to its advantages of simplicity, high atomic economy, and the ready availability of starting materials. In the field of N-heterocycle synthesis via C–H functionalization, nickel has been recognized as one of the most important catalysts. In this review, we will introduce nickel-catalyzed intramolecular and intermolecular pathways for N-heterocycle synthesis from 2008 to 2021.

Metal-free and Selectfluor-mediated diverse transformations of 2-alkylthiobenzamides to access 2,3-dihydrobenzothiazin-4-ones, benzoisothiazol-3-ones and 2-alkylthiobenzonitriles

Diverse transformations of 2-alkylthiobenzamides have been established to synthesize 2,3-dihydrobenzothiazin-4-ones, benzoisothiazol-3-ones and 2-alkylthiobenzonitriles in the presence of Selectfluor.

Switchable Synthesis of Sulfoxides and α-Alkoxy-β-ketothioethers Regulated by Temperature in a Selectfluor-Methanol System

A switchable and benign protocol for chemoselective synthesis of sulfoxides and α-alkoxy-β-ketothioethers has been developed. It was determined that various thiophenols and alkenes/alkynes are compatible to realize the target compounds from a medium to a high yield by regulating the reaction temperature. In particular, methanol not only served as a solvent but also participated in the reaction process as a hydrogen donor. In this study, Selectfluor has been proved to be an efficient multifunctional reagent in the reaction system.

Selectfluor-Promoted Intramolecular N-S Bond Formation of α-Carbamoyl Ketene Dithioacetals in the Presence of Water: Synthesis of Multifunctionalized Isothiazolones

A practical and efficient protocol toward fully substituted isothiazolones through Selectfluor-mediated intramolecular oxidative annulation of α-carbamoyl ketene dithioacetals has been developed in the presence of H₂O and metal-free conditions. Notably, the experimental results reveal that H₂O was crucial to the formation of new N-S bonds and the elimination of alkyl group from the sulfur atom. This protocol provides readily prepared substrates and possesses good functional group tolerance, mild reaction conditions, and operational simplicity, which provides potential access to applications in the pharmaceutical chemistry.

Amide-assisted α-C(sp3)–H acyloxyation of organic sulfides to access α-acyloxy sulfides

The direct acyloxyation of 2-(alkylthio)benzamide has been established via an amide-assisted α-C(sp3)–H functionalization in the presence of Selectfluor by using simple carboxylic acid and its corresponding salt as acyloxy sources.

Recent Advances in the Application of Selectfluor as a "Fluorine-free" Functional Reagent in Organic Synthesis

Selectfluor, [1-chloromethyl-4-fluoro-1,4-diazoniabicyclo-[2.2.2]octane bis(tetrafluoroborate)], is not only an important electrophilic fluorinating agent but also a facile and efficient "fluorine-free" functional reagent in other organic reactions. In this Minireview, we will present a brief history of Selectfluor as a transition metal oxidant, fluorine cation and radical initiator in "fluorine-free" functionalizations over the last five years.

Isothiazolinone Biocides: Chemistry, Biological, and Toxicity Profiles

The importance of isothiazole and of compounds containing the isothiazole nucleus has been growing over the last few years. Isothiazolinones are used in cosmetic and as chemical additives for occupational and industrial usage due to their bacteriostatic and fungiostatic activity. Despite their effectiveness as biocides, isothiazolinones are strong sensitizers, producing skin irritations and allergies and may pose ecotoxicological hazards. Therefore, their use is restricted by EU legislation. Considering the relevance and importance of isothiazolinone biocides, the present review describes the state-of-the-art knowledge regarding their synthesis, antibacterial components, toxicity (including structure–activity–toxicity relationships) outlines, and (photo)chemical stability. Due to the increasing prevalence and impact of isothiazolinones in consumer’s health, analytical methods for the identification and determination of this type of biocides were also discussed.

Silver-Promoted Site-Selective Intramolecular Cyclization of 2-Methylthiobenzamide Through α-C(sp3)-H Functionalization

Silver-mediated intramolecular α-C(sp³)-H bond functionalization of the methylthio group has been established in the presence of Selectfluor as an additive. This novel strategy provides efficient access to various diverse sulfur-based heterocycles with good yields and functional group compatibility. It is noteworthy that the completely novel benzooxathiin-4-imine skeletons were reported for the first time in this study.

Synthesis and crystal structure of trifluoromethyl-containing bendamustine hydrochloride

A simple strategy to afford trifluoromethyl-containing bendamustine hydrochloride in 34% overall via nine simple steps including substitution, selective reduction, N-acylation, cyclization, esterification, nitro-reduction, N-dihydroxyethylation, chlorination, and acid-catalyzed hydrolysis from commercially available 2,4-dinitrochlorobenzene is described. The structures of the intermediates and target product are established on the basis of infrared, nuclear magnetic resonance, and high resolution mass spectrometer. Moreover, the structure of target product is also confirmed by X-ray crystal analysis, and further studies indicate that the existence of intermolecular O–H···Cl and N–H···Cl hydrogen bonds are effective in stabilization of the crystal structure.

Fluorium-Initiated Dealkylative Cyanation of Thioethers to Thiocyanates

Thioethers are converted to thiocyanates via fluorium-initiated dealkylative cyanation. Selectfluor is used as the oxidant, and trimethylsilyl cyanide is used as the cyanation reagent. The well-streamlined procedure is user-friendly, operationally simple, and step-economical. The current mechanistic studies show that the sulfur radical cation and cyano radical are both involved. They combine to deliver cyanosulfonium, an intermediate toward thiocyanate after dealkylation. Alternatively, a nucleophilic mechanism is also possible. Our dealkyaltive cyanation is also efficient in synthesizing thiocyanates with strongly electrophilic functionalities.