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1. Sustainable Methods in Hypervalent Iodine Chemistry

   Frey, B.; Maity, A.; Tan, H.; Roychowdhury, P.; Powers, D. C. (January 2022, Organic synthesis)

   Muniz, K.; Ishihara, K. (Ed.)

   Hypervalent iodine compounds are a widely used class of metal-free oxidants that find application in organic synthesis. Due to the homology between the reactivity of hypervalent iodine and many transition metals ¾ oxidative addition, ligand exchange, and reductive elimination can be facile for both ¾ hypervalent iodine species find application in a variety of synthetically important organic transformations. Major limitations of these reagents include the frequent need for (super)stoichiometric loading and the intrinsically poor atom economy that results from the generation of stoichiometric quantities of iodoarene byproducts. In addition, hypervalent iodine reagents are often synthesized using metal-based terminal oxidants, which compound the resulting waste stream. Recently, substantial progress has been made to address these limitations. Here, we discuss progress towards sustainable synthetic methods for the preparation of hypervalent iodine compounds and application of those methods in the context of hypervalent iodine catalysis. The discussion is organized according to the active oxygen content, and thus atom economy, of the terminal oxidant employed. Hypervalent iodine electrochemistry and the development of recyclable iodoarenes are also discussed. 

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2. Recent Progress in Synthetic Applications of Cyclic Hypervalent Iodine(III) Reagents

   https://doi.org/10.1002/adsc.202300275  

   Yoshimura, Akira; Saito, Akio; Zhdankin, Viktor_V (May 2023, Advanced Synthesis & Catalysis)

   Abstract Hypervalent iodine compounds have found broad application in modern organic chemistry as reagents and catalysts. Cyclic hypervalent iodine reagents based on the benziodoxole heterocyclic system have higher stability compared to their acyclic analogues, which makes possible the preparation and safe handling of the reagents with special ligands such as azido, cyano, and trifluoromethyl groups. Numerous iodine‐substituted benziodoxole derivatives have been prepared and utilized as reagents for transfer of the substituent on hypervalent iodine to organic substrate. Reactions of these reagents with organic substrates can be performed under metal‐free conditions, in the presence of transition metal catalysts, or using photocatalysts under photoirradiation conditions. In this review, we focus on the most recent synthetic applications of cyclic hypervalent iodine(III) reagents with the following ligands: N₃, NHR, CN, CF₃, SCF₃, OR, OAc, ONO₂, and C(=N₂)CO₂R. The review covers literature published mainly in the last 5 years. 

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3. Benziodoxole-Derived Organosulfonates: The Strongest Hypervalent Iodine Electrophiles and Oxidants

   https://doi.org/10.1055/s-0039-1690761  

   Yusubov, Mekhman S.; Postnikov, Pavel; Yoshimura, Akira; Zhdankin, Viktor V. (February 2020, Synlett)

   This account describes the development of organosulfonyloxy-substituted iodine(III) and iodine(V) benziodoxole derived reagents, which are thermally stable compounds with useful reactivity patterns. Iodine(III) benziodoxoles and pseudobenziodoxoles are powerful electrophiles and mild oxidants toward various unsaturated compounds. In particular, pseudocyclic benziodoxole-derived triflate (IBA-OTf) is an efficient reagent for oxidative heteroannulation reactions. Aldoximes react with nitriles in the presence of IBA-OTf at room temperature to give 1,2,4-oxadiazoles in high yields. Moreover, IBA-triflate is used as a catalyst in oxidative heteroannulations with m-chloroperoxybenzoic acid as the terminal oxidant. The iodine(V) benziodoxole derived tosylates, DMP-tosylate and IBX-tosylate, are superior oxidants for the oxidation of structurally diverse, synthetically useful alcohols, utilized as key precursors in the total syntheses of polyketide antibiotics and terpenes. And finally, the most powerful hypervalent iodine(V) oxidant, 2-iodoxybenzoic acid ditriflate (IBX·2HOTf), is prepared by treatment of IBX with trifluoromethanesulfonic acid. According to the X-ray data, the I–OTf bonds in IBX-ditriflate have ionic character, leading to the high reactivity of this reagent in various oxidations. In particular, IBX-ditriflate can oxidize polyfluorinated primary alcohols, which are generally extremely resistant to oxidation. 1 Introduction 2 Iodine(III) Benziodoxole Based Organosulfonates 3 Pseudocyclic Iodine(III) Benziodoxole Triflate (IBA-triflate) 4 Pseudocyclic Iodine(III) Benziodoxole Tosylates 5 Iodine(V) Benziodoxole Derived Tosylates 6 Iodine(V) Benziodoxole Derived Triflate (IBX-ditriflate) 7 Conclusions 

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4. Aryl-, Akynyl-, and Alkenylbenziodoxoles: Synthesis and Synthetic Applications

   https://doi.org/10.3390/molecules28052136  

   Mironova, Irina A.; Noskov, Dmitrii M.; Yoshimura, Akira; Yusubov, Mekhman S.; Zhdankin, Viktor V. (March 2023, Molecules)

   Hypervalent iodine reagents are in high current demand due to their exceptional reactivity in oxidative transformations, as well as in diverse umpolung functionalization reactions. Cyclic hypervalent iodine compounds, known under the general name of benziodoxoles, possess improved thermal stability and synthetic versatility in comparison with their acyclic analogs. Aryl-, alkenyl-, and alkynylbenziodoxoles have recently received wide synthetic applications as efficient reagents for direct arylation, alkenylation, and alkynylation under mild reaction conditions, including transition metal-free conditions as well as photoredox and transition metal catalysis. Using these reagents, a plethora of valuable, hard-to-reach, and structurally diverse complex products can be synthesized by convenient procedures. The review covers the main aspects of the chemistry of benziodoxole-based aryl-, alkynyl-, and alkenyl- transfer reagents, including preparation and synthetic applications. 

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5. Recyclable Catalysts for Alkyne Functionalization

   https://doi.org/10.3390/molecules26123525  

   Trigoura, Leslie; Xing, Yalan; Chauhan, Bhanu P. (June 2021, Molecules)

   In this review, we present an assessment of recent advances in alkyne functionalization reactions, classified according to different classes of recyclable catalysts. In this work, we have incorporated and reviewed the activity and selectivity of recyclable catalytic systems such as polysiloxane-encapsulated novel metal nanoparticle-based catalysts, silica–copper-supported nanocatalysts, graphitic carbon-supported nanocatalysts, metal organic framework (MOF) catalysts, porous organic framework (POP) catalysts, bio-material-supported catalysts, and metal/solvent free recyclable catalysts. In addition, several alkyne functionalization reactions have been elucidated to demonstrate the success and efficiency of recyclable catalysts. In addition, this review also provides the fundamental knowledge required for utilization of green catalysts, which can combine the advantageous features of both homogeneous (catalyst modulation) and heterogeneous (catalyst recycling) catalysis. 

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