KOH-Mediated Synthesis of Substituted Isothiazoles via Two-Component Annulation with Dithioate and Aryl Acetonitrile

We report a simple synthetic method for obtaining 3-hydroxy-4,5-disubstituted isothiazoles utilizing dithioester and aryl acetonitrile. The isothiazoles obtained in this method involve the formation of new C-C, C-O, and N-S bonds in one step using a simple base such as KOH under aerial conditions. The 3-hydroxy-4,5-disubstituted isothiazole was successfully employed for further functionalization. The strategy provides high selectivity for the synthesis of isothiazoles, which may have applications in pharmaceuticals, organic materials, and agrochemicals in both academic and industrial settings.

Anomeric Answer to Sulfenamide Stability and α-Nucleophilicity

The S-N bond remains a synthetically challenging motif for organic chemists to access. The problem arises from instability in many sulfenamide derivatives, which has led to fewer S-N bond surrogate molecules compared to their hydroxylamine (NH2OH) and hydrazine (NH2NH2) analogues. In turn, sulfenamides have often been omitted in studies regarding α-nucleophilicity. Herein, we provide factors responsible for the stability of the sulfenamide motif and provide new insights on the nucleophilic properties of sulfenamides as they relate to the α-effect.

The Synthesis and Biological Applications of the 1,2,3-Dithiazole Scaffold

The 1,2,3-dithiazole is an underappreciated scaffold in medicinal chemistry despite possessing a wide variety of nascent pharmacological activities. The scaffold has a potential wealth of opportunities within these activities and further afield. The 1,2,3-dithiazole scaffold has already been reported as an antifungal, herbicide, antibacterial, anticancer agent, antiviral, antifibrotic, and is a melanin and Arabidopsis gibberellin 2-oxidase inhibitor. These structure activity relationships are discussed in detail, along with insights and future directions. The review also highlights selected synthetic strategies developed towards the 1,2,3-dithiazole scaffold, how these are integrated to accessibility of chemical space, and to the prism of current and future biological activities.

Methyl 3-Bromo-5-carbamoylisothiazole-4-carboxylate

Reaction of methyl 3-bromo-5-cyanoisothiazole-4-carboxylate with conc. H2SO4 gave methyl 3-bromo-5-carbamoylisothiazole-4-carboxylate in 93% yield. The compound was fully characterized.

Synthesis of 3-Bromo-4-phenylisothiazole-5-carboxylic Acid and 3-Bromoisothiazole-5-carboxylic Acid

Reactions of 3-bromo-4-phenylisothiazole-5-carboxamide and 3-bromoisothiazole-5-carboxamide with NaNO2 (4 equiv.), in TFA, at ca. 0 °C gave the carboxylic acid products in 99% and 95% yields, respectively. The two compounds were fully characterized.

3-Chloro-4-(p-tolyl)isothiazole-5-carbonitrile

A reaction of 3-chloroisothiazole-5-carbonitrile with 1-iodo-4-methylbenzene (2 equiv.) produced 3-chloro-4-(p-tolyl)isothiazole-5-carbonitrile in a 60% yield. The compound was fully characterized.

(Z)-2-{[(4-Chloro-5H-1,2,3-dithiazol-5-ylidene)amino](methylthio)methylene}malononitrile

Reaction of 4,5-dichloro-1,2,3-dithiazolium chloride with 2-[amino(methylthio)methylene])malononitrile (1 equiv) in the presence of pyridine (2 equiv) gave (Z)-2-{[(4-chloro-5H-1,2,3-dithiazol-5-ylidene)amino](methylthio)methylene}malononitrile in 20% yield. The compound was fully characterized.

Reaction of 4,5-Dichloro-1,2,3-dithiazolium Chloride with 2-(Phenylsulfonyl)acetonitrile

The reaction of 4,5-dichloro-1,2,3-dithiazolium chloride with 2-(phenylsulfonyl)acetonitrile (1 equiv) in the presence of pyridine (2 equiv) gave S-(3-chloro-5-cyanoisothiazol-4-yl)benzenesulfonothioate and (Z)-2-(4-chloro-5H-1,2,3-dithiazol-5-ylidene)-2-(phenylsulfonyl)acetonitrile in 19% and 23% yield, respectively. The compounds were fully characterized and the mechanistic rationale is proposed for the formation of the benzensulfonate.

Synthesis of 2-Mercapto-(2-Oxoindolin-3-Ylidene)Acetonitriles from 3-(4-Chloro-5H-1,2,3-Dithiazol-5-Ylidene)Indolin-2-ones

Alkylidene oxindoles are important functional moieties and building blocks in pharmaceutical and synthetic chemistry. Our interest in biologically active compounds focused our studies on the synthesis of novel oxindoles, bearing on the exocyclic double bond at the C8, CN, and S groups. Extending the potential applications of Appel’s salt, we developed a new synthetic approach by investigating the reactions of C5-substituted 2-oxindoles with 4,5-dichloro-1,2,3-dithiazolium chloride (Appel’s salt) to give original (Z)-3-(4-chloro-5H-1,2,3-dithiazol-5-ylidene)indolin-2-one derivatives, and new 2-mercapto-(2-oxoindolin-3-ylidene)acetonitriles via a dithiazole ring-opening reaction. The work described in this article represents further applications of Appel’s salt in the conception of novel heterocyclic rings, in an effort to access original bioactive compounds. Fifteen new compounds were prepared and fully characterized.

The Conversion of 5,5'-Bi(1,2,3-dithiazolylidenes) into Isothiazolo[5,4-d]isothiazoles

Thermolysis of 4,4'-dichloro-, 4,4'-diaryl-, and 4,4'-di(thien-2-yl)-5,5'-bi(1,2,3-dithiazol-ylidenes) affords the respective 3,6-dichloro-, 3,6-diaryl- and 3,6-di(thien-2-yl)isothiazolo[5,4-d]-isothiazoles in low to high yields. The transformation of the 4,4'-diaryl- and 4,4'-di(thien-2-yl)-5,5'-bi(1,2,3-dithiazolylidenes) occurs at lower temperatures in the presence of the thiophiles triphenylphosphine or tetraethylammonium iodide. Optimized reaction conditions and a mechanistic rationale for the thiophile-mediated ring transformation are presented.

A Qualitative Comparison of the Reactivities of 3,4,4,5-Tetrachloro-4H-1,2,6-thiadiazine and 4,5-Dichloro-1,2,3-dithiazolium Chloride

The high yielding transformations of 3,4,4,5-tetrachloro-4H-1,2,6-thiadiazine into 3,5-dichloro-4H-1,2,6-thiadiazin-4-one (up to 85%) and 2-(3,5-dichloro-4H-1,2,6-thiadiazin-4-ylidene)malononitrile (up to 83%) have been investigated and compared to the analogous transformations of the closely-related 4,5-dichloro-1,2,3-dithiazolium chloride (Appel's salt) into 4-chloro-5H-1,2,3-dithiazol-5-one and 2-(4-chloro-5H-1,2,3-dithiazol-5-ylidene)malononitrile. Furthermore, cyclocondensation of 3,4,4,5-tetrachloro-4H-1,2,6-thiadiazine with 2-aminophenol and 1,2-benzenediamines gave fused 4H-1,2,6-thiadiazines in 68%-85% yields.