Isoxazole group directed Rh(III)-catalyzed alkynylation using TIPS-EBX

A highly effective isoxazole directed ortho C-H alkynylation has been developed. Rhodium(III) catalyzed direct di-(and/or mono) alkynylation using a hypervalent iodine reagent (TIPS-EBX) is reported. The reaction proceeds with a wide substrate scope under benign conditions. Preliminary mechanistic studies support this chelation assisted C-H alkynylation.

Rhodium-catalysed ortho-alkynylation of nitroarenes

The ortho-alkynylation of nitro-(hetero)arenes takes place in the presence of a Rh(iii) catalyst to deliver a wide variety of alkynylated nitroarenes regioselectively. These interesting products could be further derivatized by selective reduction of the nitro group or palladium-catalysed couplings. Experimental and computational mechanistic studies demonstrate that the reaction proceeds via a turnover-limiting electrophilic C-H metalation ortho to the strongly electron-withdrawing nitro group.

Rhodium(III)-Catalyzed C-H Alkynylation of N-Methylsulfoximines

A rhodium(III)-catalyzed direct C-H alkynylation of a wide range of N-methylsulfoximines with (bromoethynyl)triisopropylsilane has been developed. This protocol is compatible with both (S,S)-diaryl sulfoximines and (S,S)-alkyl aryl sulfoximines, and shows mild conditions, and good functional group tolerance. The synthetic utility of this method has been demonstrated by subsequent various transformations of the products.

Broad-Scope Rh-Catalyzed Inverse-Sonogashira Reaction Directed by Weakly Coordinating Groups

We report the alkynylation of C(sp2)-H bonds with bromoalkynes (inverse-Sonogashira reaction) directed by synthetically useful ester, ketone, and ether groups under rhodium catalysis. Other less common directing groups such as amine, thioether, sulfoxide, sulfone, phenol ester, and carbamate are also suitable directing groups. Mechanistic studies indicate that the reaction proceeds by a turnover-limiting C-H activation step via an electrophilic-type substitution.

Rh(iii)-Catalyzedortho-C–H alkynylation ofN-phenoxyacetamides with hypervalent iodine-alkyne reagents at room temperature

Directing group ONHR preservedortho-alkynylation under mild conditions catalyzed by rhodium is reported.

Copper-catalyzed aminoalkynylation of alkenes with hypervalent iodine reagents

A copper-catalyzed aminoalkynylation of alkenes is achieved with ethynylbenziodoxolone (EBX) reagents under mild conditions with only 1 mol% copper catalyst. This transformation allows for rapid construction of diverse important azahetereocycles and installation of valuable alkyne groups in one step. The developed method features remarkable substrate scope for both terminal and internal alkenes as well as different alkynyl groups, presenting great potential for broad applications in synthesis, bioconjugation, and molecular imaging.

Ligand-Enabled Alkynylation of C(sp3 )-H Bonds with Palladium(II) Catalysts

The palladium(II)-catalyzed β- and γ-alkynylation of amide C(sp³ )-H bonds is enabled by pyridine-based ligands. This alkynylation reaction is compatible with substrates containing α-tertiary or α-quaternary carbon centers. The β-methylene C(sp³ )-H bonds of various carbocyclic rings were also successfully alkynylated.

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.

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.

Efficient access to alkynylated quinalizinones via the gold(i)-catalyzed aminoalkynylation of alkynes

The gold-catalyzed aminoalkynylation of alkynes for the synthesis of quinalizinones from pyridinoalkynes using 1-[(triisopropylsilyl)-ethynyl]-1,2-benziodoxol-3(1H)-one (TIPS-EBX) is reported.

Iridium- and rhodium-catalyzed C–H activation and formyl arylation of benzaldehydes under chelation-assistance

Mild and efficient synthesis of benzophenones via Ir(iii)- and Rh(iii)-catalyzed, directing group-assisted formyl C–H arylation of benzaldehydes has been achieved using diaryliodonium salts, in which Rh(iii) and Ir(iii) catalysts exhibited a complementary substrate scope.

Cobalt(iii)-catalyzed annulation of esters and alkynes: a facile route to indenones

An efficient protocol for the synthesis of indenones has been developed via the annulation of benzoic esters and internal alkynes by exploiting the cobalt catalyst.

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.

Cobalt-catalyzed synthesis of quinolines from the redox-neutral annulation of anilides and alkynes

A new method of cobalt-catalyzed annulation of anilides and internal alkynes for the efficient synthesis of quinoline scaffolds was developed.

Rhodium(iii)-catalyzed C–H activation and intermolecular annulation with terminal alkynes: from indoles to carbazoles

A new and mild Rh(iii)-catalyzed intermolecular annulation of indoles with terminal alkynes for the direct synthesis of carbazoles has been developed.

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.