Fine-tuned organic photoredox catalysts are introduced for the metal-free alkynylation of alkylnitrile radicals generated via oxidative ring opening of cyclic alkylketone oxime ethers. The redox properties of the dyes were determined by both cyclic voltammetry and computation and covered an existing gap in the oxidation potential of photoredox organocatalysts.

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Fine-tuned organic photoredox catalysts for fragmentation-alkynylation cascades of cyclic oxime ethers

This minireview aims to cover the developments over the past two decades in the chemistry of sulfonium salts. Specifically, insight is provided into the synthetic strategies available for the preparation of these compounds, the different reactivity patterns that are expected depending on their structural features or the reaction conditions applied, and the diversity of organic scaffolds that can thereby be synthesized. Additionally, the pros and cons derived from the use of sulfonium salts are presented and critically compared, when possible, in relation to reagents not based on sulfur but depicting similar reactivity.

https://chemistry-europe.onlinelibrary.wiley.com/doi/pdf/10.1002/ejic.202000249

Synthetic Applications of Sulfonium Salts

“Doubly Orthogonal” Labeling of Peptides and Proteins

In contrast to iodine(I)-based halogen bond donors, iodine(III)-derived ones have only been used as Lewis acidic organocatalysts in a handful of examples, and in all cases they acted in a monodentate fashion. Herein, we report the first application of a bidentate bis(iodolium) salt as organocatalyst in a Michael and a nitro-Michael addition reaction as well as in a Diels-Alder reaction that had not been activated by noncovalent organocatalysts before. In all cases, the performance of this bidentate XB donor distinctly surpassed the one of arguably the currently strongest iodine(I)-based organocatalyst. Bidentate coordination to the substrate was corroborated by a structural analysis and by DFT calculations of the transition states. Overall, the catalytic activity of the bis(iodolium) system approaches that of strong Lewis acids like BF 3 .

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/anie.202013172

A bidentate iodine(III)‐based halogen‐bond donor as a powerful organocatalyst

A widely applicable triazole-substituted chiral aryl iodide is described as catalyst for enantioselective oxidation reactions. The introduction of a substituent in ortho-position to the iodide is key for its high reactivity and selectivity. Besides a robust and modular synthesis, the main advantage of this catalyst is the excellent performance in a plethora of mechanistically diverse enantioselective transformations, such as spirocyclizations, phenol dearomatizations, α-oxygenations, and oxidative rearrangements. DFT-calculations of in situ generated [hydroxy(tosyloxy)iodo]arene isomers give an initial rational for the observed reactivity.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/anie.201912023

A Triazole-Substituted Aryl Iodide with Omnipotent Reactivity in Enantioselective Oxidations.

Hypervalent iodine compounds, in particular aryl-λ3-iodanes, have been used extensively as electrophilic group-transfer reagents. Even though these compounds are superior substrates in terms of reactivity and stability, their utilization is accompanied by stoichiometric amounts of an aryl iodide as waste. This highly nonpolar side product can be tedious to separate from the desired target molecules and significantly reduces the overall atom efficiency of these transformations. In this short review, we want to give a brief summary of recently developed methods, in which this arising former waste is used as an additional reagent in cascade transformations to generate multiple substituted products in one step and with high atom efficiency.

https://www.beilstein-journals.org/bjoc/content/pdf/1860-5397-14-108.pdf

Atom-economical group-transfer reactions with hypervalent iodine compounds.

NH2-Directed C–H Alkenylation of 2-Vinylanilines with Vinylbenziodoxolones

Pseudocyclic aryl-λ3 -iodanes are superior reagents for a variety of oxidative transformations due to a well-balanced relation between stability, solubility and reactivity. Their properties are substantially influenced by a dative interaction between a Lewis base, in general the oxygen atom of a carboxylic acid or an amide, and the central hypervalent iodine atom. This work presents the first systematic investigation of pseudocyclic N-heterocycle-stabilized iodanes (NHIs). The synthesis of these throughout shelf-stable solids is robust and can be achieved on a large scale. Their reactivity is highly tunable, depending on the stabilizing heterocycle. Solid state structures of selected derivatives are reported and their reactivity in a model oxygen transfer reaction is compared. Further derivatization reactions to N-heterocycle-stabilized pseudocyclic diaryliodonium salts and cyclic iodoso species are presented as well.

N-Heterocycle-Stabilized Iodanes: From Structure to Reactivity.

Iodolopyrazolium Salts: Synthesis, Derivatizations, and Applications

We herein describe the development of N-heterocycle-stabilized iodoarenes (NHAIs) as oxidation catalysts for oxidative C-X-bond forming reactions. Modification of the N-heterocycle as stabilizing donor in combination with an additional ortho-methoxylation of the iodoarene finally gives organocatalysts that can be applied in the alpha-oxytosylation of ketones even with catalyst loadings as low as 1 mol%.

https://onlinelibrary.wiley.com/doi/epdf/10.1002/adsc.201901356

Andreas Boelke

Papers

Atom-economical group-transfer reactions with hypervalent iodine compounds.

NH2-Directed C–H Alkenylation of 2-Vinylanilines with Vinylbenziodoxolones

N-Heterocycle-Stabilized Iodanes: From Structure to Reactivity.

Iodolopyrazolium Salts: Synthesis, Derivatizations, and Applications

Evolution of N-Heterocycle-Substituted Iodoarenes (NHIAs) to Efficient Organocatalysts in Iodine(I/III)-Mediated Oxidative Transformations