The Fluoride Anion-Catalyzed Sulfurization of Thioketones with Elemental Sulfur Leading to Sulfur-Rich Heterocycles: First Sulfurization of Thiochalcones

Fluoride anion was demonstrated as a superior activator of elemental sulfur (S8) to perform sulfurization of thioketones leading to diverse sulfur-rich heterocycles. Due to solubility problems, reactions must be carried out either in THF using tetrabutylammonium fluoride (TBAF) or in DMF using cesium fluoride (CsF), respectively. The reactive sulfurizing reagents are in situ generated, nucleophilic fluoropolysulfide anions FS(8−x)−, which react with the C=S bond according to the carbophilic addition mode. Dithiiranes formed thereby, existing in an equilibrium with the ring-opened form (diradicals/zwitterions) are key-intermediates, which undergo either a step-wise dimerization to afford 1,2,4,5-tetrathianes or an intramolecular insertion, leading in the case of thioxo derivatives of 2,2,4,4-tetramethylcyclobutane-1,3-dione to ring enlarged products. In reactions catalyzed by TBAF, water bounded to fluoride anion via H-bridges and forming thereby its stable hydrates is involved in secondary reactions leading, e.g., in the case of 2,2,4,4-tetramethyl-3-thioxocyclobutanone to the formation of some unexpected products such as the ring enlarged dithiolactone and ring-opened dithiocarboxylate. In contrast to thioketones, the fluoride anion catalyzed sulfurization of their α,β-unsaturated analogues, i.e., thiochalcones is slow and inefficient. However, an alternative protocol with triphenylphosphine (PPh3) applied as a catalyst, offers an attractive approach to the synthesis of 3H-1,2-dithioles via 1,5-dipolar electrocyclization of the in situ-generated α,β-unsaturated thiocabonyl S-sulfides. All reactions occur under mild conditions and can be considered as attractive methods for the preparation of sulfur rich heterocycles with diverse ring-size.

Fluorescence Fluoride Ion Sensor Utilizing Desilylation of N-Silylated 9- Aminoanthracene

N,N-Bis(trimethylsilyl)-9-aminoanthracene (Si9AA) was synthesized by deprotonation of 9-aminoanthracne (9AA) with n-BuLi followed by the addition of trimethylsilyl chloride (TMSCl). Under ultraviolet, Si9AA showed blue fluorescence originated from the anthracene skeleton due to orthogonal relation between anthracene skeleton and bis(trimethylsilyl)amino group, which was determined by X-ray crystallographic analysis, while 9AA, in which conjugation exists between the anthracene and the amino group, showed green fluorescence. In a THF solution, Si9AA was converted to 9AA by desilylation of bis(trimethylsilyl)amino group with fluoride ion, which was contained in tetrabutylammonium fluoride (TBAF) or KF-18-crown-6 complex, resulting in fluorescence color change from blue to green. Si9AA was found to utilize as a sensor to detect fluoride ion in THF solution or on a thin layer chromatography (TLC) via the fluorescence color change without any metals, regarding a metal free fluorescence fluoride sensor in green chemistry.

Tetrabutylphosphonium 4-ethoxyvalerate as a biomass-originated media for homogeneous palladium-catalyzed Hiyama coupling reactions

The introduction of a biomass-derived ionic liquid into the Hiyama coupling reactions, which has been considered as a powerful tool for the synthesis of symmetrically and non-symmetrically substituted biaryl structures, could further control or even reduce the environmental impact of this transformation. It was shown that tetrabutylphosphonium 4-ethoxyvalerate, a γ-valerolactone-based ionic liquid, can be utilized as an alternative solvent to create carbon–carbon bonds between aryl iodides and functionalized organosilanes in the presence of 1 mol% Pd under typical Hiyama conditions (130 °C, 24 h, tetrabutylammonium fluoride activator). A comparison of different ionic liquids was performed, and the effects of the catalyst precursor and the moisture content of the reaction mixture on the activity of the catalyst system were investigated. The functional group tolerance was also studied, resulting in 15 cross-coupling products (3a–o) with isolated yields of 45–72% and excellent purity (> 98%).

A Two-Step Synthesis of a Novel 7,8-Dihydro-5,8-ethanoindolizine-6,9(5H)-dione

A two-step synthesis of the novel 5,8-dimethyl-7,8-dihydro-5,8-ethanoindolizine-6,9(5H)-dione from 2,3-dimethyl-1,4-benzoquinone is described. The key step of the synthesis of this unusual fused tricyclic system is the intramolecular regiospecific aza-Michael addition of a pyrrole to an activated double bond by reaction with tetrabutylammonium fluoride under mechanochemical conditions.

Dependence of deposition method on the molecular structure and stability of organosilanes revealed from degrafting by tetrabutylammonium fluoride

We probe the structure of self-assembled monolayers comprising organosilanes on flat silica-based surfaces prepared by liquid and vapor deposition by removing the organosilane molecules gradually from the substrate via tetrabutylammonium fluoride.

An Efficient Deprotection of 2,6-Bis(trifluoromethyl)phenylboronic Esters via Catalytic Protodeboronation Using Tetrabutyl­ammonium Fluoride

We herein describe an efficient deprotection of 2,6-bis(trifluoromethyl)phenylboronic esters, which serve as effective protective groups for 1,2- or 1,3-diols in various organic transformations, via protodeboronation by using a catalytic amount of tetrabutylammonium fluoride (TBAF).