Methanofullerene Synthesis via Photogenerated Fullerene Radical Anion Intermediates

This work describes the synthesis of PCBM ([6,6]-phenyl-C₆₁-butyric acid methyl ester) derivatives and other methanofullerene derivatives via generation of fullerene radical anions under photoirradiation and controlled by photoswitching, without preparation, a strong reducing agent, or precise control of the reaction conditions.

Transition metal-catalyzed alkene isomerization as an enabling technology in tandem, sequential and domino processes

One-pot reactions based on catalytic isomerization of alkenes not only offer the inherent advantages of atom-, step- and redox-economy but also enable the preparation of value-added products that would be difficult to access by conventional methods.

Unraveling the Mechanism of the IrIII -Catalyzed Regiospecific Synthesis of α-Chlorocarbonyl Compounds from Allylic Alcohols

We have used experimental studies and DFT calculations to investigate the IrIII -catalyzed isomerization of allylic alcohols into carbonyl compounds, and the regiospecific isomerization-chlorination of allylic alcohols into α-chlorinated carbonyl compounds. The mechanism involves a hydride elimination followed by a migratory insertion step that may take place at Cβ but also at Cα with a small energy-barrier difference of 1.8 kcal mol-1 . After a protonation step, calculations show that the final tautomerization can take place both at the Ir center and outside the catalytic cycle. For the isomerization-chlorination reaction, calculations show that the chlorination step takes place outside the cycle with an energy barrier much lower than that for the tautomerization to yield the saturated ketone. All the energies in the proposed mechanism are plausible, and the cycle accounts for the experimental observations.

Orthogonal Stability and Reactivity of Aryl Germanes Enables Rapid and Selective (Multi)Halogenations

While halogenation is of key importance in synthesis and radioimaging, the currently available repertoire is largely designed to introduce a single halogen per molecule. This report makes the selective introduction of several different halogens accessible. Showcased here is the privileged stability of nontoxic aryl germanes under harsh fluorination conditions (that allow selective fluorination in their presence), while displaying superior reactivity and functional-group tolerance in electrophilic iodinations and brominations, outcompeting silanes or boronic esters under rapid and additive-free conditions. Mechanistic experiments and computational studies suggest a concerted electrophilic aromatic substitution as the underlying mechanism.

An umpolung strategy to react catalytic enols with nucleophiles

The selective synthesis of α-functionalized ketones with two similar enolizable positions can be accomplished using allylic alcohols and iridium(III) catalysts. A formal 1,3-hydrogen shift on allylic alcohols generates catalytic iridium-enolates in a stereospecific manner, which are able to react with electrophiles to yield α-functionalized ketones as single constitutional isomers. However, the employment of nucleophiles to react with the nucleophilic catalytic enolates in this chemistry is still unknown. Herein, we report an umpolung strategy for the selective synthesis of α-alkoxy carbonyl compounds by the reaction of iridium enolates and alcohols promoted by an iodine(III) reagent. Moreover, the protocol also works in an intramolecular fashion to synthesize 3(2H)-furanones from γ-keto allylic alcohols. Experimental and computational investigations have been carried out, and mechanisms are proposed for both the inter- and intramolecular reactions, explaining the key role of the iodine(III) reagent in this umpolung approach.

Nucleophiles cannot be directly reacted with enolates due to polarity mismatching. Here, the authors developed an umpolung strategy for the selective synthesis of α-alkoxy carbonyl compounds by reaction of iridium enolates with nucleophilic alcohols promoted by an iodine(III) reagent.

Reductive Halogenation Reactions: Selective Synthesis of Unsymmetrical α-Haloketones

A method for the selective synthesis of unsymmetrical α-haloketones has been developed. The key transformation is a triphenylphosphine oxide catalyzed reductive halogenation of an α,β-unsaturated ketone in which trichlorosilane is the reducing reagent and an N-halosuccinimide is the electrophilic halogen source. This method allows for a halogen atom to be installed selectively at either of two very similarly substituted sites adjacent to a ketone group.

Au-Catalyzed tandem intermolecular hydroalkoxylation/Claisen rearrangement between allylic alcohols and chloroalkynes

An efficient protocol for the synthesis of γ,δ-unsaturated α-chloroketones has been developed via Au-catalyzed tandem intermolecular hydroalkoxylation/Claisen rearrangement.

Selective Synthesis of Unsymmetrical Aliphatic Acyloins through Oxidation of Iridium Enolates

The first method to access unsymmetrical aliphatic acyloins is presented. The method relies on a fast 1,3-hydride shift mediated by an Ir^III complex in allylic alcohols followed by oxidation with TEMPO⁺ . The direct conversion of allylic alcohols into acyloins is achieved in a one-pot procedure. Further functionalization of the Cα' of the α-amino-oxylated ketone products gives access to highly functionalized unsymmetrical aliphatic ketones, which further highlights the utility of this transformation.

2,2-Diiododimedone: a mild electrophilic iodinating agent for the selective synthesis of α-iodoketones from allylic alcohols

In combination with an iridium catalyst, a new electrophilic iodinating agent enables the synthesis of α-iodocarbonyls from allylic alcohols.

Base-Catalyzed Stereospecific Isomerization of Electron-Deficient Allylic Alcohols and Ethers through Ion-Pairing

A mild base-catalyzed strategy for the isomerization of allylic alcohols and allylic ethers has been developed. Experimental and computational investigations indicate that transition metal catalysts are not required when basic additives are present. As in the case of using transition metals under basic conditions, the isomerization catalyzed solely by base also follows a stereospecific pathway. The reaction is initiated by a rate-limiting deprotonation. Formation of an intimate ion pair between an allylic anion and the conjugate acid of the base results in efficient transfer of chirality. Through this mechanism, stereochemical information contained in the allylic alcohols is transferred to the ketone products. The stereospecific isomerization is also applicable for the first time to allylic ethers, yielding synthetically valuable enantioenriched (up to 97% ee) enol ethers.

General, Simple, and Chemoselective Catalysts for the Isomerization of Allylic Alcohols: The Importance of the Halide Ligand

Remarkably simple Ir^III catalysts enable the isomerization of primary and sec-allylic alcohols under very mild reaction conditions. X-ray absorption spectroscopy (XAS) and mass spectrometry (MS) studies indicate that the catalysts, with the general formula [Cp*Ir^III ], require a halide ligand for catalytic activity, but no additives or additional ligands are needed.

Iridium(i) hydroxides in catalysis: rearrangement of allylic alcohols to ketones

The iridium(i) hydroxide complex [Ir(OH)(COD)(IⁱPr)] has been shown to be a competent catalyst for the rearrangement of allylic alcohols to ketones.

Transition metal-catalyzed redox isomerization of codeine and morphine in water

A water-soluble rhodium complex formed from commercially available [Rh(COD)(CH₃CN)₂]BF₄ and 1,3,5-triaza-7-phosphaadamantane (PTA) catalyzes the isomerization of both codeine and morphine into hydrocodone and hydromorphone in water with very high efficiency.