Imidazoles are an important group of the azole family of heterocycles frequently found in pharmaceuticals, drug candidates, ligands for transition metal catalysts, and other molecular functional materials. Owing to their wide application in academia and industry, new methods and strategies for the generation of functionalized imidazole derivatives are in demand. We here describe a general and comprehensive approach for the synthesis of complex aryl imidazoles, where all three C–H bonds of the imidazole core can be arylated in a regioselective and sequential manner. We report new catalytic methods for selective C5- and C2-arylation of SEM-imidazoles and provide a mechanistic hypothesis for the observed positional selectivity based on electronic properties of C–H bonds and the heterocyclic ring. Importantly, aryl bromides and low-cost aryl chlorides can be used as arene donors under practical laboratory conditions. To circumvent the low reactivity of the C-4 position, we developed the SEM-switch that transfers the SEM-group from N-1 to N-3 nitrogen and thus enables preparation of 4-arylimidazoles and sequential C4–C5-arylation of the imidazole core. Furthermore, selective N3-alkylation followed by the SEM-group deprotection (trans-N-alkylation) allows for regioselective N-alkylation of complex imidazoles. The sequential C-arylation enabled by the SEM-switch allowed us to produce a variety of mono-, di-, and triarylimidazoles using diverse bromo- and chloroarenes. Using our approach, the synthesis of individual compounds or libraries of analogues can begin from either the parent imidazole or a substituted imidazole, providing rapid access to complex imidazole structures.

We report a new catalytic protocol for highly selective C–H arylation of pyridines containing common and synthetically versatile electron-withdrawing substituents (NO2, CN, F and Cl). The new protocol expands the scope of catalytic azine functionalization as the excellent regioselectivity at the 3- and 4-positions well complements the existing methods for C–H arylation, Ir-catalyzed borylation, as well as classical functionalization of pyridines. Another important feature of the new method is its flexibility to adapt to challenging substrates by a simple modification of the carboxylic acid ligand or the use of silver salts. The regioselectivity can be rationalized on the basis of the key electronic effects (repulsion between the nitrogen lone pair and polarized C–Pd bond at C2-/C6-positions and acidity of the C–H bond) in combination with steric effects (sensitivity to bulky substitutents).

Employing organic redox mediators (ORMs) for lithium−oxygen (Li−O 2 ) batteries has emerged as an important strategy to suppress charging overpotentials. Judicious molecular designs of ORMs can also tailor their redox potential and electrontransfer rate to optimize the catalytic efficiency. However, the stability of ORMs in Li−O 2 cells was scarcely studied. Here, the catalytic efficiency and stability of several important ORMs are assessed through in situ gas analysis and reactivity tests with singlet oxygen. Some well-known ORMs are detrimentally decomposed during the first cycle in Li−O 2 cells, whereas nitroxyl-radical-based ORMs bear the most stable and efficient response. Analogous nitroxyl-radical derivatives further increase round-trip energy efficiency and electron-transfer kinetics. This study underlines chemical stability aspects of ORMs, which are mandatory for the long-term cyclability in Li−O 2 cells. We emphasize that besides the importance of ORMs in these systems and their proper selection, an effective operation of Li−O 2 cells depends also strongly on the stability of the carbonaceous cathodes and the electrolyte solutions. The stability of all the components in these systems is inter-related.

We have developed inter- and intramolecular C-H alkenylation reactions of pyrazoles. The catalyst, derived from Pd(OAc)2 and pyridine, enabled the oxidative alkenylation of pyrazoles containing a variety of functional groups at the C4 position. Activated alkenes, including acrylate, acrylamide, and styrene derivatives, and enamides could be installed in this process. The sequential C-H alkenylation and cyclization reactions gave rise to fused bicyclic pyrazoles, providing a new strategy to annulate readily available pyrazole compounds.

The proposed structure of lasonolide A was synthesized employing radical cyclization reactions of beta-alkoxyacrylates for preparation of the tetrahydropyranyl units A and B, but the spectroscopic data did not match those of the natural product. Both enantiomers of a revised structure featuring 17E,25Z double bonds were synthesized, and the (-)-isomer was found to be the biologically active enantiomer.