Oxidative Desulfurization of Azole-2-thiones with Benzoyl Peroxide: Syntheses of Ionic Liquids and Other Azolium Salts

Synthesis of Sterically Encumbered Thiourea S-Oxides through Direct Thiourea Oxidation

Thiourea S-oxides can be viewed as formal analogs of the currently unknown diamino-substituted Criegee intermediates (urea O-oxides). However, the preparation of such S-oxides is rather challenging, and the direct oxidation of thioureas typically only leads to formation of desulfurized products. Employing the accurate revDSD-PBEP86-D4 double hybrid density functional, it was found that the peracid mediated oxidation of thiourea S-oxides exhibits a lower reaction barrier than the oxidation of the corresponding thiourea itself in contrast to most other ordinary thioketones. The undesired overoxidation reactivity, which is associated with strong π-donation from the thiourea's nitrogen atoms, can be partially suppressed by introduction of bulky substituents and the utilization of protic solvents. In this regard, we managed to prepare two sterically encumbered thiourea S-oxides in isolated yields of 35-40 %. The S-oxides are stable in the solid state and in alcoholic solutions at room temperature for extended periods of time, but swiftly decompose in aprotic solvents by disproportionation. A dimesityl-substituted thiourea S-oxide complexed with residual mCBA could be characterized by means of X-ray crystallography, confirming the importance of hydrogen bonding in the stabilization of the amino-substituted C=S⁺ -O^- moiety.

A greener approach towards the synthesis of N-heterocyclic thiones and selones using the mechanochemical technique

This manuscript describes the synthesis of N-heterocyclic thiones and selones of a variety of imidazolium salts involving an eco-friendly and solventless ball-milling technique. The products have been isolated in almost quantitative yield, involving a minimum quantity of solvents only for the isolation of products by column chromatography, and in some cases for purification purposes. Both mono- and bisimidazolium salts afforded N-heterocyclic thiones and selones. The methodology is found to be superior in terms of reaction time, yield and energy efficiency as compared to conventional solution-state reactions.

Photoredox Cross-Dehydrogenative Coupling of N-Aryl Glycines Mediated by Mesoporous Graphitic Carbon Nitride: An Environmentally Friendly Approach to the Synthesis of Non-Proteinogenic α-Amino Acids (NPAAs) Decorated with Indoles

Indole-decorated glycine derivatives are prepared through an environmentally benign cross-dehydrogenative coupling between N-aryl glycine analogues and indoles (yield of ≤81%). Merging heterogeneous organocatalysis and photocatalysis, C–H functionalization has been achieved by selective C-2 oxidation of N-aryl glycines to afford the electrophilic imine followed by Friedel–Crafts alkylation with indole. The sustainability of the process has been taken into account in the reaction design through the implementation of a metal-free recyclable heterogeneous photocatalyst and a green reaction medium. Scale-up of the benchmark reaction (gram scale, yield of 69%) and recycling experiments (over seven runs without a loss of efficiency) have been performed to prove the robustness of the protocol. Finally, mechanistic studies were conducted employing electron paramagnetic resonance spectroscopy to unveil the roles of the photocatalyst and oxygen in the formation of odd-electron species.

Fine-tuning of the pharmacological potential of novel thiazolium ionic liquids by anion alteration

A novel series of thiazolium ionic liquids (TILs) bound to chloride (2a–c), tetrafluoroborate (BF₄) (3a–c), and bis-(trifluoromethanesulfonimide) (Tf₂N) anions (4a–c) was synthesized and their physicochemical characteristics were investigated using various microanalytical techniques. The pharmacological potential of the new TILs was assessed as chemotherapeutic agents for bacterial infections and ovarian cancer (SKOV-3). Notably, ILs with the same cations become more bactericidal upon their binding with the strongest chaotropic anion (TN₂f). The in vitro toxicity of the TILs toward ovarian carcinoma cell lines (SKOV-3) and normal human skin fibroblast cells (HSF) revealed that all tested TILs have the capacity to induce a dose- and time-dependent decline in SKOV-3 cell viability, with Tf₂N-linked TILs (4a–c) having a preferable efficacy. In addition, the new compounds showed excellent selectivity for cancer cells (SKOV-3) over healthy cells (HSF). [ⁱPBzTh][Tf₂N] (4b) is the most cytotoxic and specific one and may act as a promising anti-ovarian cancer agent.

A novel series of thiazolium ionic liquids (TILs) bound to chloride (2a–c), tetrafluoroborate (BF₄) (3a–c), and bis-(trifluoromethanesulfonimide) (Tf₂N) anions (4a–c) was synthesized and their physicochemical characteristics were investigated.

Ionic liquid-stabilized vanadium oxo-clusters catalyzing alkane oxidation by regulating oligovanadates

The specific ionic liquid [TBA][Pic]-stabilized vanadium oxo-clusters exist in the form of a trimer and a dimer and are highly active for catalyzing C–H bond oxidation with H₂O₂ as an oxidant.

Synthesis and reactions of C-phosphanylated thiazol-2-thiones

Regioselective synthesis of the P(iii) substituted thiazole-2-thione I is presented. Oxidation of I resulted in P(V) chalcogenide thiazole-2-thiones (E = O, S, Se). Desulfurization of I (E = O) using hydrogenperoxide led to the first C-phosphanoyl thiazolium salt II. Deprotonation of II and reaction with cyclooctadiene rhodium(i) chloride dimer yielded thiazole-2-ylidene rhodium(i) complex III.

Efficient routes towards a series of 5,5′-bithiazolidinylidenes as π-electron acceptors

Among different approaches, the thermal treatment of the fused bicycle involving a dithiole-2-one ring is the most efficient one and opens access to a variety of π-conjugated electron acceptors.

From bis(imidazole-2-thion-4-yl)phosphane to a flexible P-bridged bis(NHC) ligand and its silver complex

Synthesis of the first P(v)-bridged bis(NHC) ligand 7 was achieved via deprotonation of P(v)-functionalized bis(imidazolium) salt 6, which was obtained via oxidative desulfurization of bis(imidazole-2-thion-4-yl)phosphane 2.