Visible-Light-Promoted Aerobic α-Thiocyanation of Carbonyl Compounds with Ammonium Thiocyanate

In the present study, we successfully developed an efficient thiocyanation of carbonyl compounds by using low-toxicity and inexpensive ammonium thiocyanate as the thiocyanate source under visible light in air (O2) at room temperature. This unified strategy is very facile for thiocyanation of various carbonyl compound derivatives (β-keto esters, β-keto amides, pyrazo-5-ones, isoxazol-5-ones, etc.). More importantly, the reaction proceeded smoothly without the addition of a photocatalyst and strong oxidant, ultimately minimizing the production of chemical waste. Furthermore, this green and sustainable synthetic chemistry can be used in the late-stage functionalization (LSF) of biorelevant compounds, which offers unique opportunities to achieve smooth and clean thiocyanation of drugs under mild reaction conditions.

I2-catalyzed one-pot oxidative condensation of thiourea, methyl ketones, and aryl thiols into 5-sulfenylated 2-amino-1,3-thiazoles by DMSO

A one-pot, efficient oxidative-condensation process for constructing both 4-alkyl and 4-aryl-5-(arylthio) thiazol-2-amines using DMSO/I2 is introduced. In this procedure, methyl ketones, thiourea, DMSO, and thiols are reacted together in the presence of molecular I2 at 80 °C simply to produce 4-alkyl or aryl-5-(arylthio)thiazol-2-amines due to formation of a C-S bond between thiourea and methyl carbon linked to carbonyl group and the another C-S bond formation between thiol and thiazol ring. Under reaction conditions, both aryl and alkyl methyl ketones including acetophenone and substituted acetophenones also, 2-alkanones such as acetone, 2-butanone, 2-pentanone, and 2-heptanone yield those products successfully.

Emerging developments in dye-sensitized metal oxide photocatalysis: exploring the design, mechanisms, and organic synthesis applications

In the present day, the incorporation of environmentally conscious practices in the realm of photocatalysis holds a prominent position within the domain of organic synthesis. The imperative to tackle environmental issues linked to catalysts that cannot be recycled, generation of waste, byproducts, and challenges in achieving reaction selectivity during organic synthesis are more crucial than ever. One potential solution involves the integration of recyclable nanomaterials with light as a catalyst, offering the possibility of achieving sustainable and atom-efficient transformations in organic synthesis. Metal oxide nanoparticles exhibit activation capabilities under UV light, constituting a small percentage (4-8%) of sunlight. However, this method lacks sufficient environmental friendliness, and the issue of electron-hole recombination poses a significant hurdle. To tackle these challenges, multiple approaches have been proposed. This comprehensive review article focuses on the efficacy of dyes in enhancing the capabilities of heterogeneous photocatalysts, offering a promising avenue to overcome the constraints associated with metal oxides in their role as photocatalysts. The article delves into the intricate design aspects of dye-sensitized photocatalysts and sheds light on their mechanisms in facilitating organic transformations.

Electrochemical thiocyanation of barbituric acids

The electrochemical thiocyanation of barbituric acids with NH₄SCN was disclosed in an undivided cell under constant current conditions. The electrosynthesis is the most efficient at a record high current density (j_anode ≈50-70 mA cm^-2). NH₄SCN has a dual role as the source of the SCN group and as the electrolyte. Electrochemical thiocyanation of barbituric acids starts with the generation of (SCN)₂ from the thiocyanate anion. The addition of thiocyanogen to the double bond of the enol tautomer of barbituric acid gives thiocyanated barbituric acid. A variety of thiocyanated barbituric acids bearing different functional groups were obtained in 18-95% yields and were shown to exhibit promising antifungal activity.

Recent advances in photochemical and electrochemically induced thiocyanation: a greener approach for SCN-containing compound formation

Techniques utilizing photo- and electrochemically induced reactions have been developed to accelerate organic processes. These techniques use light or electrical energy (electron transfer) as a direct energy source without using an initiator or reagent. Thiocyanates are found in biologically active and pharmacological compounds and can be converted into various functional groups. It is one of the most prominent organic scaffolds. Significant development in photo- and electro-chemically induced thiocyanation procedures has been made in recent years for the conception of carbon-sulfur bonds and synthesis of pharmaceutically important molecules. This review discusses different photo- and electro-chemically driven thiocyanation C(sp3)-SCN, C(sp2)-SCN, and C(sp)-SCN bond conception processes that may be useful to green organothiocyanate synthesis. We focus on the synthetic and mechanistic characteristics of organic photo- and electrochemically accelerated C-SCN bond formation thiocyanation reactions to highlight major advances in this novel green and sustainable research field.

Reduced graphene oxide–zinc sulfide (RGO–ZnS) nanocomposite: a new photocatalyst for oxidative cyclization of benzylamines to benzazoles under visible-light irradiation

A simple route for the preparation of a reduced graphene oxide–zinc sulfide (RGO–ZnS) nanocomposite via one-pot hydrothermal synthesis has been reported.

Hypervalent Iodine(III)-Promoted C3-H Regioselective Halogenation of 4-Quinolones under Mild Conditions

A simple and practical protocol for the C3-H regioselective halogenation of 4-quinolones by the action of potassium halide salt and PIFA/PIDA in good to excellent yields was developed. The current approach provides feasible access to the diversity of C3-halgenated 4-quinolones at room temperature with high regioselectivity and good functional group tolerance, from which bioactive compounds can be easily constructed. Moreover, the current method featured eco-friendly, operational convenience and is suitable for halogenation in a gram scale of 4-quinolones in water without sacrificing yields.

N-doped ZnO as an efficient photocatalyst for thiocyanation of indoles and phenols under visible-light

In this study, nitrogen-doped ZnO nanorods (N-ZnO NRs) were synthesized via a very simple hydrothermal process, fully characterized, and this photocatalyst was successfully exploited in thiocyanation reactions of indoles and phenols at room temperature under visible light irradiation. Two important classes of aromatic compounds indoles, and phenols using N-ZnO NRs as photocatalyst treated with ammonium thiocyanate as thiocyanation agent formed the corresponding thiocyano compounds in good yields. Nitrogen is one of the most appropriate p-type dopants that is nontoxic, similar to the atomic radius to oxygen, and lower electronegativity and ionization energy than the O atom. Therefore, the N doping converts ZnO into the p-type ZnO semiconductor structure. This potent, simple, and versatile protocol afforded thiocyanation reactions of indole and phenols under visible light. The reactions proceeded through a radical pathway by applying air molecular oxygen as a low cost and environmentally friendly terminal oxidant. The proposed mechanism based on control experiments was thoroughly described.

Visible-light-mediated phosphonylation reaction: formation of phosphonates from alkyl/arylhydrazines and trialkylphosphites using zinc phthalocyanine

In this work, we developed a ligand- and base-free visible-light-mediated protocol for the photoredox syntheses of arylphosphonates and, for the first time, alkyl phosphonates. Zinc phthalocyanine-photocatalyzed Csp2-P and Csp3-P bond formations were efficiently achieved by reacting aryl/alkylhydrazines with trialkylphosphites in the presence of air serving as an abundant oxidant. The reaction conditions tolerated a wide variety of functional groups.

NBS-assisted palladium-catalyzed bromination/cross-coupling reaction of 2-alkynyl arylazides with KSCN: an efficient method to synthesize 3-thiocyanindoles

An efficient NBS-assisted palladium-catalyzed bromination/cross-coupling synthesis of 3-thiocyanindoles from 2-alkynyl arylazides with KSCN has been described.

Boron-doped TiO2 (B-TiO2): visible-light photocatalytic difunctionalization of alkenes and alkynes

Boron-doped TiO₂ (B-TiO₂) was prepared, characterized, and applied as a reusable, inexpensive, and available heterogeneous nanophotocatalyst under visible light for the synthesis of phenacyl thiocyanates.

Mechanochemical Thiocyanation of Aryl Compounds via C-H Functionalization

Aryl thiocyanate compounds are important building blocks for the synthesis of bioactive compounds and intermediates for several functional groups. Reported thiocyanation reactions via C-H functionalization have limited substrate scope and low RME. The ball-milling method reported here uses ammonium persulfate and ammonium thiocyanate as reagents and silica as a grinding auxiliary. It afforded aryl thiocyanates with moderate to excellent yields for a wide variety of aryl compounds (36 examples, 8-96% yield), such as anilines, phenols, anisoles, thioanisole, and indole, thus tolerating substrates with sensitive functional groups. New products such as benzo[d][1,3]oxathiol-2-ones were obtained with C-4 substituted phenols. Thus, to our knowledge, we report, for the first time, aryl thiocyanation reaction by ball-milling at room temperature and solvent-free conditions, with short reaction times and no workup. Analysis of several mass-based green metrics indicates that it is an efficient greener method.

A Review on Thiocyanation of Indoles

BACKGROUND

The thiocyanation of indoles is a direct way for carbon-sulfur bond formation to access 3-thiocyanato-indoles. 3-thiocyanato-indoles exhibit potent biological and pharmacological activities and also serve as building blocks to synthesize many biologically active sulfur-containing indole derivatives.

OBJECTIVE

The aim of this review is to highlight different approaches for the thiocyanation of indoles focusing on its scope and mechanism.

CONCLUSION

In this review, we have summarized various methods for the thiocyanation of indoles. Selection of new methods for the preparation of 3-thiocyanato-indoles will be done. The mechanistic aspects and significance of the methods are also briefly discussed.

Black TiO2 nanoparticles with efficient photocatalytic activity under visible light at low temperature: regioselective C–N bond cleavage toward the synthesis of thioureas, sulfonamides, and propargylamines

Several different colored forms of TiO₂ were prepared through the easy treatment of white TiO₂ and NaBH₄ as a safe hydrogen source. Then, tertiary amines were harnessed toward the regioselective synthesis of three prominent scaffolds.

NCS-promoted thiocyanation and selenocyanation of pyrrolo[1,2-a]quinoxalines

An efficient NCS-promoted thiocyanation of pyrrolo[1,2-a]quinoxalines with NH₄SCN or KSCN was developed. Moreover, in the presence of KSeCN, the selenocyanation of pyrrolo[1,2-a]quinoxalines was also achieved.