We herein report the oxidative α-azidation of carbonyl compounds by using NaN 3 in the presence of dibenzoyl peroxide catalyzed by tetrabutylammonium iodide (TBAI). By utilizing these readily ...available bulk chemicals a variety of cyclic β-ketocarbonyl derivatives can be efficiently α-azidated under operationally simple conditions. Control experiments support a mechanistic scenario involving in situ formation of an ammonium hypoiodite species which first facilitates the α-iodination of the pronucleophile, followed by a phase-transfer-catalyzed nucleophilic substitution by the azide. Furthermore, we also show that an analogous α-nitration by using NaNO 2 under otherwise identical conditions is possible as well.
Dibenzoylperoxide emerged as a versatile oxidant for quaternary ammonium iodide or bromide‐catalyzed reactions of phenol derivatives with NaN3. While the use of iodides allowed for efficient benzylic ...azidations under these oxidative conditions, the use of bromides allowed for dearomative azidations instead. Both approaches have been successfully applied to different phenol derivatives and a first proof‐of‐concept for an enantioselective variant using chiral quat. ammonium bromides has been obtained as well.
We herein report two strategies for the quaternary ammonium hypoiodite‐mediated oxidative benzylic functionalization of p‐alkyl phenol derivatives. By using either dibenzoylperoxide or H2O2 in ...hexafluoroisopropanol in the presence of tetrabutyl ammonium iodide gives access to activated intermediates which can then be coupled with electron‐rich aromatic compounds. Overall, this sequential two‐step one‐pot procedure gives access to diversely decorated diarylmethane derivatives straightforwardly. Furthermore, the suitability of these products to undergo further oxidation reactions was successfully demonstrated.
The synergistic use of chiral bifunctional ammonium iodide catalysts in combination with simple catalytically relevant aldimines allows for an unprecedented asymmetric α-hydroxylation reaction of ...β-ketoesters using H2O2. The reaction proceeds via in situ formation of a hypervalent iodine species, which then reacts with the used aldimine to generate an activated electrophilic oxygen transfer reagent.
(Thio)‐urea‐containing bifunctional quaternary ammonium salts emerged as powerful non‐covalently interacting organocatalysts over the course of the last decade. The most commonly employed catalysts ...in this field are either based on Cinchona alkaloids, α‐amino acids, or trans‐cyclohexane‐1,2‐diamine. Our group has been heavily engaged in the design and use of such catalysts, i. e. trans‐cyclohexane‐1,2‐diamine‐based ones for around 10 years now, and it is therefore the intention of this short personal account to provide an overview of the, at least in our opinion, most significant and pioneering achievements in this field by looking on catalyst design and asymmetric method development, with a special focus on our own contributions.
(Thio)‐urea‐containing bifunctional quaternary ammonium salt catalysts have been well‐established nowadays and our group has been heavily engaged in the design and use of such catalysts over the last decade. We herein wish to present the most significant results and achievements in this field, with a special focus on our own contributions.
The Front Cover illustrates the α‐selenocyanation and α‐thiocyanation of various pronucleophiles (β‐ketoesters, oxindoles and β‐ketoacids) with NaSCN or KSeCN as easily accessible inorganic S(e)CN ...sources under oxidative conditions. Dibenzoylperoxide facilitates the coupling of two inherently nucleophilic species by generating electrophilic S(e)CN‐transfer reagents upon oxidation in situ. More information can be found in the Research Article by M. Waser et al.
We herein report an unprecedented strategy for the asymmetric α‐chlorination of β‐keto esters with hypervalent iodine‐based Cl‐transfer reagents using simple Cinchona alkaloid catalysts. Our ...investigations support an α‐chlorination mechanism where the Cinchona species serves as a nucleophilic catalyst by reacting with the chlorinating agent to generate a chiral electrophilic Cl‐transfer reagent in situ. Using at least 20 mol‐% of the alkaloid catalyst allows for good yields and enantioselectivities for a variety of different β‐keto esters under operationally simple conditions.
Simple Cinchona alkaloids serve as nucleophilic organocatalysts to facilitate the enantioselective α‐chlorination of β‐keto esters by using hypervalent iodine‐based Cl‐transfer reagents
We herein report the deoxyfluorination of cyclic α-hydroxy-β-ketoesters using diethylaminosulfur trifluoride (DAST). The reaction proceeds with excellent levels of stereospecificity, giving the ...configurationally inverted α-fluoro-β-ketoesters in high yields under operationally simple conditions.
Cyclic α-hydroxy-β-ketoesters were converted in the corresponding α-F-derivatives with high levels of enantiospecificity using DAST under operationally simple conditions.
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