This article describes the application of N-heterocyclic iod(az)olium salts (NHISs) as highly reactive organocatalysts. A variety of mono-and dicationic NHISs are described and utilized as potent XB-donors in halogen-bond catalysis. They were benchmarked in seven diverse test reactions in which the activation of carbon-and metal-chloride bonds as well as carbonyl and nitro groups was achieved. N-Methylated dicationic NHISs rendered the highest reactivity in all investigated catalytic applications with reactivities even higher than all previously described monodentate XB-donors based on iodine(I) and (III) and the strong Lewis acid BF3.
The synthesis of iodolopyrazolium salts via an oxidative cyclization of 3-(2-iodophenyl)-1H-pyrazoles is described. The reaction is characterized by a broad substrate scope and various applications of these novel cyclic iodolium salts acting as useful synthetic intermediates are demonstrated, in particular in site-selective ring-openings. This was finally applied to generate derivatives of the anti-inflammatory drug celecoxib. Their application as highly active halogen bonding donors is shown as well.
A fast and reliable synthesis of pyrazole-substituted iodolium triflates is described. Their versatile application as useful synthetic intermediates for straight-forward modifications of pharmaceuticals is demonstrated using Celecoxib as model substrate. Finally, their application as potent halogen-bond donors in a Ritter-type reaction is shown.<br>
The synthesis of a series of 2,2′-bis(trimethyltetrel) azobenzenes is reported, evaluating the different synthetic approaches that different group 14 element substituents individually require. The synthetic access to the carbon substituted congener is very different from the heavier tetrels, in that the key step is the formation of the N=N bond in azobenzene, rather than the azobenzene-C bond. Sn could be introduced with a cross-coupling route, whereas the Si and Ge congeners were prepared by a stannylation-lithiation-electrophilic quenching sequence. Iodo-lithium exchange was also a possible route to obtain the dilithiated species, which can be attributed to the chelating effect of the nitrogen atoms. However, the organo-lead species could not be obtained via these routes. The resulting structures were fully characterized (NMR, FTIR, HRMS and XRD). Furthermore, their thermal properties (TGA and DSC) and their photoswitching behavior in solution (UV-VIS & NMR experiments) were investigated and compared for the different tetrels (C, Si, Ge, Sn).
Diaryliodonium salts are electrophilic arylation reagents in transition metal‐catalyzed and transition metal‐free reaction methods. Herein we present the application of azole‐stabilized diaryliodonium salts with additional thiophene‐2‐yl‐ligands as substrates for metal‐free nucleophilic arylations. Besides their synthesis, we demonstrate their application in chemoselective nitrations, oxygenations, aminations as well as thiolations under umpolung conditions. Convenient one‐pot procedures based on their in situ formation are also discussed.
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