Stereoselective Synthesis of β-Alkoxy-β-amido Vinylbenziodoxoles via Iodo(III)etherification of Ynamides

Organohypervalent heterocycles

This review summarizes the structural and synthetic aspects of heterocyclic molecules incorporating an atom of a hypervalent main-group element. The term "hypervalent" has been suggested for derivatives of main-group elements with more than eight valence electrons, and the concept of hypervalency is commonly used despite some criticism from theoretical chemists. The significantly higher thermal stability of hypervalent heterocycles compared to their acyclic analogs adds special features to their chemistry, particularly for bromine and iodine. Heterocyclic compounds of elements with double bonds are not categorized as hypervalent molecules owing to the zwitterionic nature of these bonds, resulting in the conventional 8-electron species. This review is focused on hypervalent heterocyclic derivatives of nonmetal main-group elements, such as boron, silicon, nitrogen, carbon, phosphorus, sulfur, selenium, bromine, chlorine, iodine(III) and iodine(V).

Three-component N-alkenylation of azoles with alkynes and iodine(III) electrophile: synthesis of multisubstituted N-vinylazoles

A stereoselective N-alkenylation of azoles with alkynes and iodine(III) electrophile is reported. The reaction between various azoles and internal alkynes is mediated by benziodoxole triflate as the electrophile in a trans-fashion, affording azole-bearing vinylbenziodoxoles in moderate to good yields. The tolerable azole nuclei include pyrazole, indazole, 1,2,3-triazole, benzotriazole, and tetrazole. The iodanyl group in the product can be leveraged as a versatile synthetic handle, allowing for the preparation of hitherto inaccessible types of densely functionalized N-vinylazoles.

Structure-reactivity analysis of novel hypervalent iodine reagents in S-vinylation of thiols

The transition-metal free S-vinylation of thiophenols by vinylbenziodoxolones (VBX) constituted an important step forward in hypervalent iodine-mediated vinylations, highlighting the difference to vinyliodonium salts and that the reaction outcome was influenced by the substitution pattern of the benziodoxolone core. In this study, we report several new classes of hypervalent iodine vinylation reagents; vinylbenziodazolones, vinylbenziodoxolonimine and vinyliodoxathiole dioxides. Their synthesis, structural and electronic properties are described and correlated to the S-vinylation outcome, shedding light on some interesting facets of these reagents.

Carboiodanation of Arynes: Organoiodine(III) Compounds as Nucleophilic Organometalloids

Organic iodine(III) compounds represent the most widely used hypervalent halogen compounds in organic synthesis, where they typically perform the role of an electrophile or oxidant to functionalize electron-rich or -nucleophilic organic compounds. In contrast to this convention, we discovered their unique reactivity as organometallic-like nucleophiles toward arynes. Equipped with diverse transferable ligands and supported by a tethered spectator ligand, the organoiodine(III) compounds undergo addition across the electrophilic C-C triple bond of arynes while retaining the trivalency of the iodine center. This carboiodanation reaction can forge a variety of aryl-alkynyl, aryl-alkenyl, and aryl-(hetero)aryl bonds along with the concurrent formation of an aryl-iodine(III) bond under mild conditions. The newly formed aryl-iodine(III) bond serves as a versatile linchpin for downstream transformations, particularly as an electrophilic reaction site. The amphoteric nature of the iodine(III) group as a metalloid and a leaving group in this sequence enables the flexible and expedient synthesis of extended π-conjugated molecules and privileged biarylphosphine ligands, where all of the iodine(III)-containing compounds can be handled as air- and thermally stable materials.

Catalyst-Free Trans-Selective Oxyiodination and Oxychlorination of Alkynes Employing N-X (Halogen) Reagents

β-halogenated enol esters and ethers are versatile building blocks in organic synthesis, which has attracted increasing attention. In this study, we report the facile trans-oxyiodination and oxychlorination of alkynes, leading to the direct construction of versatile halogenated enol esters and ethers. This transformation features an easy operation, optimal atomic economy, a strong functional group tolerance, broad substrate scope, and excellent trans-selectivity. Employing highly electrophilic bifunctional N-X (halogen) reagents was the key to achieving broad reaction generality. To our knowledge, this transformation represents the first oxyhalogenation system employing N-X (halogen) reagents as both oxylation and halogenation sources.

Stereoselective Approach to Multisubstituted Enolates from Unactivated Alkynes: Oxyalkylidenation of Alkynyl Ketone Enolates with Aldehydes

The preparation of multisubstituted enolates with precise regio- and stereocontrol is a nontrivial task when conventional deprotonation methods are used on the corresponding carbonyl compounds. We describe herein an approach to preparing stereodefined enolates by leveraging the stereoselective oxyfunctionalization of unactivated alkynes, particularly in the context of the alkynylogous aldol reaction. trans-Iodo(III)acetoxylation of alkynes and subsequent Sonogashira coupling allow for the facile preparation of multisubstituted enynyl acetates, which can be deacetylated by MeLi into the corresponding enolates. The alkynyl enolates react with aldehydes to afford γ,δ-unsaturated β-diketones through a cascade of alkynylogous aldol addition, intramolecular Michael addition, and ring opening of the oxetene intermediate.

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

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.