Rhodium-Catalyzed Direct ortho C–N Bond Formation of Aromatic Azo Compounds with Azides

Carbonyl-Assisted Iridium-Catalyzed C-H Amination Using 2,2,2-Trichloroethoxycarbonyl Azide

The carbonyl-directed, mono C-H amination of arenes has been achieved using [Cp*Ir(III)Cl₂]₂ as the catalyst and 2,2,2-trichloroethoxycarbonyl (Troc) azide as an aminating reagent. The amination proceeds smoothly with a variety of arylcarbonyl compounds, including alkyl and vinyl arylketones, secondary and tertiary aryl amides, and acetyl indoles. The resulting ortho-TrocNH arylcarbonyl compounds are easily transformed to the corresponding free arylamines, aryl carbamates, or aryl ureas. Taking advantage of the electrophilic nature of both Troc and carbonyl groups in ortho-TrocNH arylcarbonyl compounds, the subsequent cyclization with dinucleophilic reagents has also been demonstrated. This provides an efficient strategy for the construction of aryl-fused N-heterocycles.

Transition Metal Catalyzed Azidation Reactions

A wide range of methodologies for the preparation of organic azides has been reported in the literature for many decades, due to their interest as building blocks for different transformations and their applications in biology as well as in materials science. More recently, with the spread of the use of transition metal-catalyzed reactions, new perspectives have also materialized in azidation processes, especially concerning the azidation of C–H bonds and direct difunctionalization of multiple carbon-carbon bonds. In this review, special emphasis will be placed on reactions involving substrates bearing a leaving group, hydroazidation reactions and azidation reactions that proceed with the formation of more than one bond. Further reactions for the preparation of allyl and vinyl azides as well as for azidations involving the opening of a ring complete the classification of the material.

Direct sulfonamidation of (hetero)aromatic C-H bonds with sulfonyl azides: a novel and efficient route to N-(hetero)aryl sulfonamides

N-Aryl sulfonamides belong to a highly important class of organosulfur compounds which are found in a number of FDA-approved drugs such as dofetilide, dronedarone, ibutilide, sotalol, sulfadiazine, sulfamethizole, vemurafenib, and many more. There is therefore continuing interest in the development of novel and convenient protocols for the preparation of these pharmaceutically important compounds. Recently, direct sulfonamidation of (hetero)aromatic C–H bonds with easily available sulfonyl azides has emerged as an attractive and powerful strategy to access N-(hetero)aryl sulfonamides where non-toxic nitrogen gas forms as the sole by-product. This review highlights recent advances and developments (2012–2020) in this fast growing research area with emphasis on the mechanistic features of the reactions.

N-Aryl sulfonamides belong to a highly important class of organosulfur compounds which are found in a number of FDA-approved drugs such as dofetilide, dronedarone, ibutilide, sotalol, sulfadiazine, sulfamethizole, vemurafenib, and many more.

Metal-free cascade reactions of aziridines with arylalkynes and aryldiazoniums: facile access to arylazopyrrolines

A novel and facile approach to synthesize arylazopyrroline scaffolds via metal-free cascade reactions of aziridines with arylalkynes and aryldiazoniums has been developed, providing access to a variety of 4-arylazo-2-pyrrolines in a highly concise fashion. This efficient process, which can be performed at the gram scale, enjoys operational simplicity and mild and metal-free conditions.

Iridium-Catalyzed C-H Amination/Cyclization for Medium to Large N-Heterocycle-Fused Dihydroquinazolinones

A practical iridium-catalyzed cascade/stepwise synthesis of dihydroquinazolinones (DHQs) and bis-DHQs fused to medium to large N-heterocyclic rings is developed. The reaction undergoes benzamide-directed intermolecular C-H amination with an aldehyde-tethered alkyl azide, and then the newly installed amino group undergoes intramolecular cyclization with a remote aldehyde group present in azide and amidyl group of benzamide either intrinsically or catalyzed by phosphoric acid, facilitating the formation of bicyclic and/or tricyclic rings in a very efficient manner.

Rhodium(iii)-catalyzed tandem reaction: efficient synthesis of dihydrobenzo thiadiazine 1-oxide derivatives

A tandem annulation reaction triggered by rhodium(iii)-catalyzed C–H bond functionalizations has been well developed for highly efficient synthesis of dihydrobenzo thiadiazine 1-oxide derivatives from free NH-sulfoximine and two-component benzyl azides.

Cp*Co(iii)-catalyzed ortho-amidation of azobenzenes with dioxazolones

Herein we have reported a decarboxylative ortho-amidation of azobenzene via cobalt catalyzed C–H amidation with dioxazolone.

Ionic Liquid Promoted Diazenylation of N-Heterocyclic Compounds with Aryltriazenes under Mild Conditions

An efficient, mild, and metal-free approach to direct diazenylation of N-heterocyclic compounds with aryltriazenes using Brønsted ionic liquid as a promoter has been developed for the first time. Many N-heterocyclic azo compounds were synthesized in good to excellent yields at room temperature under an open atmosphere. Notably, the promoter 1,3-bis(4-sulfobutyl)-1H-imidazol-3-ium hydrogen sulfate could be conveniently recycled and reused with the same efficacies for at least four cycles.

Rhodium-Catalyzed Selective Mono- and Diamination of Arenes with Single Directing Site "On Water"

A Rh(III)-catalyzed selective C-H amination of 2-phenylpyridine derivatives is reported. With pyridine as a directing group, the reaction has high mono- or diamination selectivity, and a wide range of effective substrates, including electron-deficient and -rich aryl azides. Water helps to promote C-H activation, and the concept of a water promoted rollover mechanism is postulated for the diamination step. The reactions were conducted using a Schlenk flask and proceeded smoothly "on water" under atmospheric conditions with nitrogen gas as the only byproduct.

Synthesis of isoquinolines via Rh-catalyzed C–H activation/C–N cyclization with diazodiesters or diazoketoesters as a C2 source

Synthesis of isoquinolines based on efficient C–C and C–N bond formation through Rh(iii)-catalyzed C–H functionalization and subsequent intramolecular cyclization is reported. Diazodiesters serving as a C₂ source in the newly formed heterocycles are first demonstrated.

Azobenzenes and catalysis

Azobenzene is the most extensively used class of chromophore in a large variety of applications.

Acylsilanes in Iridium-Catalyzed Directed Amidation Reactions and Formation of Heterocycles via Siloxycarbenes

Exposing ortho-amido aroylsilanes to visible light or heat leads to cyclization reactions that provide N-heterocyclic compounds via siloxycarbenes as key intermediates. The previously unreported starting materials have been prepared by directed amidations of aromatic acylsilanes in the presence of an iridium catalyst followed by N-alkylation.

Rhenium-catalyzed C-H aminocarbonylation of azobenzenes with isocyanates

The first C-H aminocarbonylation of azobenzenes with isocyanates is achieved by using rhenium-catalysis, which provides an expedient and atom-economical access to varied o-azobenzamides from readily available starting materials. The reaction efficiency can be enhanced by the catalytic use of sodium acetate via accelerated C-H bond activation.

Iridium-Catalyzed Direct C-H Sulfamidation of Aryl Nitrones with Sulfonyl Azides at Room Temperature

Ir(III)-catalyzed direct C-H sulfamidation of aryl nitrones has been developed to synthesize various sulfamidated nitrones in moderate to excellent yields with excellent regioselectivity and broad functional group tolerance. This transformation could proceed smoothly at room temperature with low catalyst loading in the absence of external oxidants, acids, or bases. Molecular nitrogen was released as the sole byproduct, thus providing an environmentally benign sulfamidation process. And this protocol could efficiently apply to synthesize the substituted benzisoxazoline via one-step transformation from the product.