Metal-Free Iodine(III)-Promoted Direct Intermolecular C–H Amination Reactions of Acetylenes

Metal free cross-dehydrogenative N-N coupling of primary amides with Lewis basic amines

Hydrazides, N-N containing structural motifs, are important due to their presence in a wide variety of biologically significant compounds. While the homo N-N coupling of two NH moieties to form the hydrazide N-N bond is well developed, the cross-dehydrogenative hetero N-N coupling remains very unevolved. Here we present an efficient intermolecular N-N cross-coupling of a series of primary benzamides with broad range of Lewis basic primary and secondary amines using PhI(OAc)2 as both a terminal oxidant and a cross-coupling mediator, without the need for metal catalysts, high temperatures, and inert atmospheres, and with substantial potential for use in the late-stage functionalization of drugs.

Metal-Free Selective Ortho-C-H Amidation of Hypervalent(III) Iodobezenes with N-Methoxy Amides under Mild Conditions

A metal-free selective ortho-C-H amidation of aryl iodines(III) with the use of N-methoxy amides as aminating reagents under mild conditions is described here. In the protocol, excellent chemoselectivity and high regioselectivity were obtained. Notably, the iodine substituent rendered the amidation product suitable to be used for further elaboration.

Metal-free synthesis of dihydrofuran derivatives as anti-vicinal amino alcohol isosteres

Dihydrofuran cores are commonly incorporated into synthetically and pharmacologically significant scaffolds in natural product and drug discovery chemistry. Herein, we report a concise and practical strategy to construct spiro-dihydrofuran and amino dihydrofuran scaffolds as anti-vicinal amino alcohol isosteres. Hypervalent iodine (PhI(OAc)(NTs₂))-mediated C-H activation of alkynes resulted in two-bond formations with one pi bond cleavage: (i) C(sp²)-N(sp³) and O(sp³)-C(sp²); (ii) C(sp²)-N(sp³) and C(sp³)-C(sp²). The metal-free 5-endo-dig oxidative cyclization provided versatile amino 2,3- and 2,5-dihydrofurans bearing the C₅ quaternary carbon. The non-toxicity of all synthesised dihydrofurans was verified via in vitro cell viability assay.

Electrochemically-initiated intramolecular 1,2-amino oxygenation of alkynes: facile access to formyl- and acyl-substituted indolizines

An environmentally benign electrooxidative approach to the intramolecular aminooxygenation of alkynes through an electrophilic cyclization reaction has been developed, providing an efficient approach toward diverse formyl- and acyl-substituted indolizines.

Atom-Economical Thiocyanation-Amination of Alkynes with N-Thiocyanato-Dibenzenesulfonimide

A highly regioselective protocol for intermolecular thiocyanation-amination of alkynes by N-thiocyano-dibenzenesulfonimide (NTSI) as the SCN and nitrogen sources has been developed. A C-S bond and C-N bond are simultaneously constructed in only one step. The reaction under simple mild conditions features a broad substrate scope, atom economy, high yields (up to 94%), and excellent functional group tolerance.

Ligand-Enabled Copper-Catalyzed N-Alkynylation of Sulfonamide with Alkynyl Benziodoxolone: Synthesis of Amino Acid-Derived Ynamide

Ynamides are versatile building blocks in organic synthesis. However, the synthesis of amino acid-derived ynamides is difficult but in high demand. Herein, we disclose the copper-catalyzed Csp-N coupling of sulfonamide, including amino acid and peptide derivatives, to give ynamides by using alkynyl benziodoxolones with broad functional group tolerance under mild reaction conditions. The electron-rich bipyridine as a ligand and ethanol as solvent were used for the success of this reaction. The usefulness of the obtained amino acid-derived ynamide as building block was showcased by further derivatization to unique amino acid derivatives. A control experiment to elucidate the mechanistic insight was also described.

Beyond osmium: progress in 1,2-amino oxygenation of alkenes, 1,3-dienes, alkynes, and allenes

Olefin 1,2-difunctionalization has emerged as a popular strategy within modern synthetic chemistry for the synthesis of vicinal amino alcohols and derivatives. The advantage of this approach is the single-step simplicity for rapid diversification, feedstock nature of the olefin starting materials, and the possible modularity of the components. Although there is a vast number of possible iterations of 1,2-olefin difunctionalization, 1,2-amino oxygenation is of particular interest due to the prevalence of both oxygen and nitrogen within pharmaceuticals, natural products, agrochemicals, and synthetic ligands. The Sharpless amino hydroxylation provided seminal results in this field and displayed the value in achieving methods of this nature. However, a vast number of new and novel methods have emerged in recent decades. This review provides a comprehensive review of modern advances in accomplishing 1,2-amino oxygenation of alkenes, 1,3-dienes, alkynes, and allenes that move beyond osmium to a range of other transition metals and more modern strategies such as electrochemical, photochemical, and biochemical reactivity.

Photo-mediated synthesis of halogenated spiro[4,5]trienones of N-aryl alkynamides with PhI(OCOCF3)2 and KBr/KCl

A novel and convenient photo-mediated halogenated spirocyclization of N-(p-methoxyaryl)propiolamides has been developed. The photolysis of phenyliodine bis(trifluoroacetate) (PIFA) as an iodination reagent led to iodinated ipso-cyclization under the irradiation of a xenon lamp, while brominated ipso-cyclization or chlorinated ipso-cyclization was achieved by irradiating a mixture of PIFA and KBr/KCl under a blue LED. The present protocol simply utilizes light as the safe and clean energy source and doesn't require any external photocatalyst providing various 3-halospiro[4,5]trienones in good to excellent yields (up to 93%).

Copper-Catalyzed Amination of C(sp3)-H bonds: From Anilides to Indolines

Copper-catalyzed oxidative intramolecular cyclization of o-alkylated anilines via cleavage of C(sp³)-H and N-H bonds for the production of indolines is described. This approach provides a straightforward strategy for the synthesis of nitrogen-containing heterocyclic compounds through the functionalization of unactivated C(sp³)-H bonds with high site selectivity. The present catalytic system shows high preference for functionalization of unactivated C(sp³)-H bonds over C(sp²)-H bonds, leading to C-N bond formation.

Directed B–H functionalization of the closo-dodecaborate cluster via concerted iodination–deprotonation: reaction mechanism and origins of regioselectivity

A concerted iodination–deprotonation process was discovered for the B–H bond iodination of closo-dodecaborate cluster, which is responsible for the regioselectivity of ortho-B–H functionalization.

tert-Butyl peroxide (TBHP)/KI-mediated dual C(sp2)-H bond amination of arylamines with α-diazo carbonyls toward 1,2,4-benzotriazines

A new radical-induced dehydrogenative heterocyclization of arylamines with α-diazo carbonyls has been established under metal-free oxidative conditions, enabling two-fold C(sp2)-H bond amination to access a wide range of functionalized 1,2,4-triazine derivatives with generally good yields by combining KI/tert-butyl peroxide (TBHP). The present protocol features wide substrate scope, commercial accessibility, and mild reaction conditions. Mechanistic details of this radical process are rendered by conducting systematic theoretical calculations.

Hypervalent iodine reactions utilized in carbon–carbon bond formations

This review covers recent developments of hypervalent iodine chemistry in dearomatizations, radicals, hypervalent iodine-guided electrophilic substitution, arylations, photoredox, and more.

Site-Selective C-H Functionalization of (Hetero)Arenes via Transient, Non-Symmetric Iodanes

A strategy for C-H functionalization of arenes and heteroarenes has been developed to allow site-selective incorporation of various anions, including Cl, Br, OMs, OTs, and OTf. This approach is enabled by in situ generation of reactive, non-symmetric iodanes by combining anions and bench-stable PhI(OAc)₂. The utility of this mechanism is demonstrated via para-selective chlorination of medicinally relevant arenes, as well as site-selective C-H chlorination of heteroarenes. Spectroscopic, computational, and competition experiments describe the unique nature, reactivity, and selectivity of these transient, unsymmetrical iodanes.

Iodide/H₂O₂ Catalyzed Intramolecular Oxidative Amination for the Synthesis of 3,2'-Pyrrolidinyl Spirooxindoles

An ammonium iodide/hydrogen peroxide-mediated intramolecular oxidative amination of 3-aminoalkyl-2-oxindoles was achieved, affording the corresponding 3,2'-pyrrolidinyl spirooxindoles and their 6- or 7-membered analogous in moderate to high yields. This metal-free procedure features very mild reaction conditions, non-toxicity and easily handled hydrogen peroxide as a clean oxidant.

Promoting Intermolecular C-N Bond Formation under the Auspices of Iodine(III)

The quest for the development of new protocols that provide general conditions for oxidative carbon-nitrogen bond formation has grown over recent years. Within this context, due to feasibility and benignity considerations in biochemical sciences, reactions that rely on main group oxidants as the only promoters have received particular interest. We have recently found that simple protonolysis events enable the incorporation of nitrogenated groups of the bissulfonimide family into the coordination sphere of common iodine(III) complexes such as diacetoxy iodobenzene. The products of the type ArI(OAc)(NTs₂) represent rare examples of iodine(III) compounds displaying reactive iodine-nitrogen single bonds. Further protonolysis furnishes the corresponding iodine(III) compounds ArI(NTs₂)₂ containing two defined iodine-nitrogen single bonds for unprecedented dual transfer of both nitrogenated groups. It is of great synthetic importance that these new compounds contain iodine-nitrogen entities, which upon dissociation in solution lead to electrophilic iodine centers and nucleophilic nitrogen groups. This has enabled the development of a body of conceptually new amination reactions, which do not rely on conventional electrophilic nitrogen reagents but rather employ iodine(III) as an electrophilic activator and bissulfonimides as the source of subsequent nucleophilic amination. Additional diversification arises from the ambident nature of bissulfonimines enabling oxygenation pathways. The exciting chemistry covered in this Account comprises structural features of the reagents (including X-ray analysis), scope and limitation in synthetic amination of different hydrocarbons (including sp-, sp²-, and sp³-hybridized centers as in acetylenes, alkenes, enols, butadienes, allenes, arenes, and alkylketones), and physical-organic and theoretical analysis of the underlying reaction mechanisms. The oxidative transformations with all their rich diversifications originate from the versatile redox chemistry of the iodine(III) and iodine(I) pair, which shares several aspects of transition metal high oxidation state chemistry. For the present aryliodine(III) reagents, steric and electronic fine-tuning is possible through accurate engineering of the arene substituent. In addition to the general reactivity of the I-N bond, chiral aryliodine(III) reagents with defined stereochemical information in the aryl backbone are conceptually compatible with this approach. Thus, the development of enantioselective amination reactions with up to 99% ee was also successful. Several of the active enantioselective reagents have been isolated and structurally characterized. Following this approach for the important class of chiral vicinal diamines, an unprecedented direct diamination of alkenes could be conducted in an enantioselective catalytic manner under full intermolecular reaction control. This latter reaction is based on the precise engineering of a chiral aryliodine(III) catalyst in combination with bismesylimide as nitrogen source. It is the consequence of the precise understanding of the reaction behavior of structurally defined bisimidoiodine(III) reagents.

Sulfoximidoyl-Containing Hypervalent Iodine(III) Reagents: 1-Sulfoximidoyl-1,2-benziodoxoles

Treatment of NH-sulfoximines with pseudocyclic benziodoxole triflate results in N-I bond formation leading to a new type of sulfoximidoyl-containing hypervalent iodine(III) reagents in high yields. Degradation studies revealed a pronounced stability in both the solid state and in solution.

C–H imidation: a distinct perspective of C–N bond formation

The direct imidation strategy proficiently constructs C–N bonds and creates the useful amine functional group in the molecular template.

Iodocyclization of N-Arylpropynamides Mediated by Hypervalent Iodine Reagent: Divergent Synthesis of Iodinated Quinolin-2-ones and Spiro[4,5]trienones

PhI(OCOCF₃)₂ acts as both a nonmetal oxidant and an iodination reagent to trigger iodocyclization of N-arylpropynamides while selectively affording iodinated quinolin-2-ones or the spiro[4,5]trienone skeleton, depending on the substituent pattern. In cases where the N-arylpropynamide bears a para-fluorine on the aniline ring, the spiro compound is formed via an exclusive defluorination process; otherwise, the product was quinolin-2-one.