Multifunctional Crown-5-calix[4]arene-based Phase-Transfer Catalysts for Aromatic 18F-Fluorination

Direct 18F-Fluorosulfurylation of Phenols and Amines Using an [18F]FSO2+ Transfer Agent Generated In Situ

We report the direct radiofluorosulfurylation method for the synthesis of ¹⁸F-labeled fluorosulfuryl derivatives from phenols and amines using an [¹⁸F]FSO₂⁺ transfer agent generated in situ. Nucleophilic radiofluorination is achieved even in a hydrous organic medium, obviating the need for azeotropic drying and the use of cryptands. This unprecedented, operationally simple isotopic functionalization facilitates the reliable production of potential radiotracers for positron emission tomography, rendering facile access to SuFEx radiochemistry.

Ionic Liquids as Organocatalysts for Nucleophilic Fluorination: Concepts and Perspectives

Besides their extremely useful properties as solvent, ionic liquids (ILs) are now considered to be highly instructive tools for enhancing the rates of chemical reactions. The ionic nature of the IL anion and cation seems to be the origin of this fascinating function of ILs as organocatalyst/promoter through their strong Coulombic forces on other ionic species in the reaction and also through the formation of hydrogen bonds with various functional groups in substrates. It is now possible to tailor-make ILs for specific purposes as solvent/promoters in a variety of situations by carefully monitoring these interactions. Despite the enormous potentiality, it seems that the application of ILs as organocatalysts/promoters for chemical reactions have not been fully achieved so far. Herein, we review recent developments of ILs for promoting the nucleophilic reactions, focusing on fluorination. Various aspects of the processes, such as organocatalytic capability, reaction mechanisms and salt effects, are discussed.

A Mild Silica Gel Promoted Synthesis and Initial Functional Study of Tetrapyridyl Tetrahydropyrrolopyrrolones

A one-pot strategy with yields up to 82% was reported to generate 2-(pyridin-2-yl)-2-(3,3a,6-tris(5-pyridin-2-yl)-5-oxohexahydropyrrolo[3,2-b] pyrrol-2(1H)-ylidene)acetonitrile 1a and its derivatives 1b-d. Silica gel promoted quantitative conversion from stable intermediate to 1a within 30 min at room temperature. Finally, four chemical σ bonds and two chiral carbons with high diastereoselectivity were achieved. Compound 1a can act as a novel high selective UV-vis and fluorescence "turn-on" probe for Zn²⁺ and Cd²⁺, respond to proton, and show dual-state emission (DSE) characteristics.

Coupling of Thiols and Aryl Halides Mediated by Dicyclohexano-18-Crown-6 and Potassium Carbonate

AIMS

A simple, transition-metal-free C-S coupling protocol for the synthesis of aryl thioethers is reported Background: Sulfur-containing moieties are ubiquitous in pharmaceutical drugs and materials and therefore methods for their construction are of great importance. One approach entails the catalytic coupling of an aryl halohydrocarbon with a thiol, but the transition metal catalysts usually used are prone to poisoning by participating sulfur species and efficient catalysis is usually only achieved after complex ligand optimization.

OBJECTIVE

New transition-metal-free approaches to the synthesis of C-S bonds are urgently need Method: We screened the reaction conditions such as alkali, crown ether, solvent, temperature, etc., tested the compatibility of the reaction substrate, and analyzed the mechanism process.

RESULT

the optimized reaction conditions were determined to be 1.0 equiv of aryl halides and 1.2 equiv of thiols at 110 ℃ in toluene with K2CO3 (1.5 equiv) as a base, promoted by 10 mol% dicyclohexano-18-crown-6. Up to 33 examples of thioethers were synthesized under transition-metal-free conditions in good to excellent yields.

CONCLUSION

we have developed a simple and efficient method for the C-S cross-coupling of a wide variety of (hetero)aryl halides and thiols mediated by dicyclohexano-18-crown-6 and without the need for transition-metal catalyst. In addition, the preparation and gram-scale experiments of a variety of drug molecules further verify the practicability of our developed method.