OH-Directed Alkynylation of 2-Vinylphenols with Ethynyl Benziodoxolones: A Fast Access to Terminal 1,3-Enynes

Pd-Catalyzed, Ligand-Enabled Stereoselective 1,2-Iodine(III) Shift/1,1-Carboxyalkynylation of Alkynylbenziodoxoles

A Pd^II -catalyzed 2:1 coupling reaction of alkynylbenziodoxole with carboxylic acid to afford (alk-1-en-3-ynyl)benziodoxole, which is efficiently promoted by an octahydrophenazine ligand, is reported. The reaction involves a Pd-assisted 1,2-iodine(III) shift of the alkynylbenziodoxole followed by stereoselective introduction of carboxy and alkynyl groups (the latter originating from another molecule of the alkynylbenziodoxole) into the 1-position of the transient Pd-vinylidene species. The product of this 1,1-carboxyalkynylation reaction serves as a new functionalized enyne-type building block for further synthetic transformations.

New reactivity of ethynyl benziodoxolone: modulating iron-catalyzed dehydration of propargyl alcohols

This is the first example of using only a catalytic amount of silyl-EBX in a dehydration reaction since its discovery. Preliminary mechanistic studies ruled out the radical pathways and supported an E1 process.

Palladium-catalyzed direct ortho-alkynylation of arylalkylacid derivatives at γ and δ positions via an N,O-bidentate directing group

A new N,O-bidentate directing group: first example of the ortho-alkynylation of arylalkylacid derivatives at γ and δ positions.

Pd-Catalyzed Conversion of Alkynyl-λ(3)-iodanes to Alkenyl-λ(3)-iodanes via Stereoselective 1,2-Iodine(III) Shift/1,1-Hydrocarboxylation

Alkynyl-λ(3)-iodanes have been established as alkynyl cation equivalents for the alkynylation of carbon- and heteroatom-based nucleophiles. Herein, we report an unprecedented reaction mode of this compound class, which features a Pd(II)-assisted 1,2-I(III) shift of an alkynylbenziodoxole. A Pd(II) catalyst mediates this shift and the subsequent interception of the transient vinylidene species with carboxylic acid (1,1-hydrocarboxylation). The product of this stereoselective rearrangement-addition reaction, β-oxyalkenylbenziodoxole, represents a novel and useful building block for further synthetic transformations.

Ir(III)-catalyzed C-H alkynylation of arenes under chelation assistance

An efficient and mild Ir(III)-catalyzed, chelation assisted C-H alkynylation of arenes has been developed using hypervalent iodine alkynes as alkynylating reagents. A broad scope of N-phenyl-2-aminopyridines and 2-phenoxypyridines has been established as effective substrates for this C-H functionalization and the desired alkynylated products were isolated in moderate to high yields.

Advances in Synthetic Applications of Hypervalent Iodine Compounds

The preparation, structure, and chemistry of hypervalent iodine compounds are reviewed with emphasis on their synthetic application. Compounds of iodine possess reactivity similar to that of transition metals, but have the advantage of environmental sustainability and efficient utilization of natural resources. These compounds are widely used in organic synthesis as selective oxidants and environmentally friendly reagents. Synthetic uses of hypervalent iodine reagents in halogenation reactions, various oxidations, rearrangements, aminations, C-C bond-forming reactions, and transition metal-catalyzed reactions are summarized and discussed. Recent discovery of hypervalent catalytic systems and recyclable reagents, and the development of new enantioselective reactions using chiral hypervalent iodine compounds represent a particularly important achievement in the field of hypervalent iodine chemistry. One of the goals of this Review is to attract the attention of the scientific community as to the benefits of using hypervalent iodine compounds as an environmentally sustainable alternative to heavy metals.

A facile strategy for accessing 3-alkynylchromones through gold-catalyzed alkynylation/cyclization of o-hydroxyarylenaminones

A strategy based on tandem alkynylation ofo-hydroxyarylenaminones followed by intramolecular cyclization has been developed to generate a diverse array of 3-alkynyl chromones.

Metal-free carbonyl C(sp2)–H oxidative alkynylation of aldehydes using hypervalent iodine reagents leading to ynones

The metal-free and facile synthesis of ynones via carbonyl C(sp²)–H oxidative alkynylation of aldehydes with enynyl benziodoxolones is presented.

Alkynylation with Hypervalent Iodine Reagents

Alkynes are among the most versatile functional groups in organic synthesis. They are also frequently used in chemical biology and materials science. Whereas alkynes are traditionally added as nucleophiles into organic molecules, hypervalent iodine reagents offer a unique opportunity for the development of electrophilic alkyne synthons. Since 1985, alkynyliodonium salts have been intensively used for the alkynylation of nucleophiles, in particular soft carbon nucleophiles and heteroatoms. They have made an especially strong impact in the synthesis of highly useful ynamides. Nevertheless, their use has been limited by their instability. Since 2009, more stable ethynylbenziodoxol(on)e (EBX) reagents have been identified as superior electrophilic alkyne synthons in many transformations. They can be used for the alkynylation of acidic C-H bonds with bases or aromatic C-H bonds using transition metal catalysts. They were also highly successful for the functionalization of radicals or transition metal-catalyzed domino processes. Finally, they allowed the alkynylation of a further range of heteroatom nucleophiles, especially thiols, under exceptionally mild conditions. With these recent developments, hypervalent iodine reagents have definitively demonstrated their utility for the efficient synthesis of alkynes based on non-classical disconnections.