Iodine-Catalyzed Claisen-Rearrangements of Allyl Aryl Ethers and Subsequent Iodocyclizations

Iodine-Catalyzed Carbonyl-Alkyne Metathesis Reactions

The reaction between aldehydes or ketones and alkynes-the carbonyl-alkyne metathesis-constitutes a very useful strategy for the synthesis of α,β-unsaturated carbonyls. We now demonstrate that iodine is a highly efficient catalyst for both the intra- and intermolecular metathesis reaction in very small concentrations (0.1-1 mol %). Our protocol outperforms other catalytic systems, is operationally very simple, cheap, metal-free, and tolerates a large variety of functional groups (e. g., -CN, -CO2Me, -Br, -OH) at very low catalyst loadings. We can furthermore show that iodine-catalyzed carbonyl-alkyne metatheses can be combined with other iodine-catalyzed reactions in one-pot procedures to afford larger and more complex molecular structures. Finally, our mechanistic studies indicate that the iodonium ion is the active catalyst under the reaction conditions.

Hypervalent Iodine-Catalyzed Fluorination of Diene-Containing Compounds: A Computational Study

Studies have shown that the incorporation of fluorine into materials can improve their properties, but C-F bonds are not readily formed in nature. Although some researchers have studied the reaction of fluorinating alkenes catalyzed by hypervalent iodine, far too little attention has been paid to its reaction mechanism. This study aimed to explore the mechanism of the hypervalent iodine-catalyzed 1,4-difluorination of dienes. We found that the catalyst is favorable for the activation of C1=C2 double bonds through halogen bonds, and then two HFs interact with one F atom in the catalyst via hydrogen bonds, resulting in the cleavage of I-F bonds and the formation of [F-H∙∙∙F]-. Subsequently, the catalyst interacts with C1, and the roaming [F-H···F]- attacks C4 from the opposite side of the catalyst. After the fluorination step is completed, the nucleophile F- substitutes the catalyst via the SN2 mechanism. Our calculations demonstrated that the interaction between HF and F- is favorable for the stabilization of the transition state within the fluorination process for which the presence of two HFs in the reaction is the best. We also observed that [F-H∙∙∙F]- attacking C4 from the opposite side of the catalyst is more advantageous than attacking from the same side. This study therefore offers a novel perspective on the mechanism of the hypervalent iodine-catalyzed fluoridation of dienes.

Tunable Regioselective Allylic Alkylation/Iodination of Imidazoheterocycles in Water

The switchable roles of allylic alcohol and molecular iodine as reagents and catalysts have been demonstrated in the regioselective allylic alkylation and iodination of imidazoheterocycles employing the mixture of allylic alcohol-I2. First, we have explored the catalytic activity of iodine for the allylation of imidazoheterocycles using allylic alcohol in an aqueous medium. The allylation of a library of imidazoheterocycles and other electron-rich heterocycles like indole, pyrazole, 4-hydroxy coumarin, and 6-amino uracil has been achieved by employing this methodology. The efficiency of the I2 catalyst for N-allylation of azoles has also been demonstrated. Next, we have shown that this mixture of allylic alcohol and I2 could be beneficial for the iodination of imidazoheterocycles under room temperature. Mechanistic studies indicate that the activation of allylic alcohol by molecular iodine took place probably through halogen bonding, and NMR studies show that the reaction did not proceed through allylic ether formation.

Allylation of C-, N-, and O-Nucleophiles via a Mechanochemically-Driven Tsuji-Trost Reaction Suitable for Late-Stage Modification of Bioactive Molecules

We present the first solvent-free, mechanochemical protocol for a palladium-catalyzed Tsuji-Trost allylation. This approach features exceptionally low catalyst loadings (0.5 mol %), short reaction times (<90 min), and a simple setup, eliminating the need for air or moisture precautions, making the process highly efficient and environmentally benign. We introduce solid, nontoxic, and easy-to-handle allyl trimethylammonium salts as valuable alternative to volatile or hazardous reagents. Our approach enables the allylation of various O-, N-, and C-nucleophiles in yields up to 99 % even for structurally complex bioactive compounds, owing to its mild conditions and exceptional functional group tolerance.

Allylation of C-, N-, and O-Nucleophiles via a Mechanochemically-Driven Tsuji-Trost Reaction Suitable for Late-Stage Modification of Bioactive Molecules

We present the first solvent-free, mechanochemical protocol for a palladium-catalyzed Tsuji-Trost allylation. This approach features exceptionally low catalyst loadings (0.5 mol %), short reaction times (<90 min), and a simple setup, eliminating the need for air or moisture precautions, making the process highly efficient and environmentally benign. We introduce solid, nontoxic, and easy-to-handle allyl trimethylammonium salts as valuable alternative to volatile or hazardous reagents. Our approach enables the allylation of various O-, N-, and C-nucleophiles in yields up to 99 % even for structurally complex bioactive compounds, owing to its mild conditions and exceptional functional group tolerance.