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

Abstract

The reactivity of ortho‐functionalized N‐heterocycle‐substituted iodoarenes (NHIAs) as organocatalysts in iodine(I/III)‐mediated oxidations was systematically investigated in the α‐tosyloxylation of ketones as the model reaction. During a systematic catalyst evolution, it was found that NH‐triazoles and benzoxazoles have the most significant positive influence on the reactivity of the central iodine atom. A further catalyst improvement which focused on the substitution pattern of the arene revealed a remarkable ortho‐effect. By introduction of an o‐OMe group we were able to generate a novel NHIA with a so far unseen catalytic efficiency. This new catalyst is not only easy to synthesize but also enabled the α‐tosyloxylation of carbonyl compounds at the lowest reported catalyst loading of only 1 mol%. Finally, the performance of this iodine(I) catalyst was successfully demonstrated in intramolecular oxidative couplings of biphenyls and oxidative rearrangements.

N‐Heterocyclic Iod(az)olium Salts – Potent Halogen‐Bond Donors in Organocatalysis

“…(Figure 2, a). 36,37 We also developed chiral Nheterocycle-substituted iodoarenes as chiral iodane precursors and applied them in a plethora of highly enantioselective couplings (Figure 2, b). 38,39 Very recently, we were able to introduce iodolopyrazolium salts as a unique class of N-heterocycle-based iodolium salts.…”

Ligand-free (Z)-selective transfer semihydrogenation of alkynes catalyzed by in situ generated oxidizable copper nanoparticles

“…The former 96 allows semihydrogenation in a biphasic system, while the lat-97 ter enables the reaction in emulsion. In mixtures of water with 98 DMF or MeCN, the reduction is slower (Table 1, entries [16][17]. 99 In the case of H2O + n-hexane, no products of semihydrogena-100 tion were detected (Table 1, entry 19).…”

Iodolopyrazolium Salts: Synthesis, Derivatizations, and Applications

“…Formation of 3b might be the reason why pyrazole 1b showed a very low performance in our recently investigated -tosyloxylation using NHIs. [55] Next, the alkyl side chain was varied.…”

“…[52][53][54] Our group is interested in the synthesis and reactivity of N-heterocyclic stabilized iodanes (NHIs) as well as their monovalent iodoarenes as pre-catalysts. [55][56][57][58][59] Recently, we investigated several hydroxy(tosyloxy) species as oxidants, including C-and Nbound pyrazole and indazole derivatives. [57,58] Herein, we want to report the synthesis of cyclic, pyrazole-substituted iodolium salts (benzo [4,5]iodolo [3,2-c]pyrazol-4-ium (bis)triflates) and their versatile utilization as intermediates for pyrazole functionalization strategies as well as their application as potent halogen bonding (XB) donors.…”