Iridium-Catalyzed Aryl C–H Sulfonamidation and Amide Formation Using a Bifunctional Nitrogen Source

Ammonia surrogates in the synthesis of primary amines

Primary amines are derivatives of ammonia in which one hydrogen atom is replaced by an alkyl or aryl group. Ammonia serves as the primary nitrogen source in amination reactions, and its utilization in solution or as a pure gas has witnessed notable advancements. However, the use of gaseous ammonia remains problematic in academic laboratory settings, while employing aqueous ammonia poses challenges in highly water-sensitive transformations. Consequently, the search for alternative sources of ammonia has garnered considerable attention among the organic chemistry community. This comprehensive literature review focuses on the use of ammonia surrogates in amination reactions, irrespective of the resulting intermediate. The review emphasizes the formation of the C-N bond and underscores the importance of generating intermediate products that can be readily transformed into primary amines through well-established reactions.

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.

Palladium-catalyzed Ugi-type reaction of 2-iodoanilines with isocyanides and carboxylic acids affording N-acyl anthranilamides

The first palladium-catalyzed Ugi-type multicomponent reaction for the synthesis of N-acyl anthranilamides from isocyanides, 2-iodoanilines and carboxylic acids has been developed. This method provides expeditious and highly efficient access to structurally diverse N-acyl anthranilamides from readily available starting materials with good functional group compatibility. The utility of this method has been demonstrated by the late stage functionalization of two commercial drugs: Flurbiprofen and Loxoprofen.

Catalytic Decarboxylative C-N Formation to Generate Alkyl, Alkenyl, and Aryl Amines

Transition-metal-catalyzed sp² C-N bond formation is a reliable method for the synthesis of aryl amines. Catalytic sp³ C-N formation reactions have been reported occasionally, and methods that can realize both sp² and sp³ C-N formation are relatively unexplored. Herein, we address this challenge with a method of catalytic decarboxylative C-N formation that proceeds through a cascade carboxylic acid activation, acyl azide formation, Curtius rearrangement and nucleophilic addition reaction. The reaction uses naturally abundant organic carboxylic acids as carbon sources, readily prepared azidoformates as the nitrogen sources, and 4-dimethylaminopyridine (DMAP) and Cu(OAc)₂ as catalysts with as low as 0.1 mol % loading, providing protected alkyl, alkenyl and aryl amines in high yields with gaseous N₂ and CO₂ as the only byproducts. Examples are demonstrated of the late-stage functionalization of natural products and drug molecules, stereospecific synthesis of useful α-chiral alkyl amines, and rapid construction of different ureas and primary amines.

Redox-Neutral P(O)-N Coupling between P(O)-H Compounds and Azides via Dual Copper and Photoredox Catalysis

We report a redox-neutral P(O)-N coupling reaction of P(O)-H compounds with azides via photoredox and copper catalysis, providing new access to useful phosphinamides, phosphonamides, and phosphoramides. This transformation tolerates a wide range of nucleophilic functionalities including alcohol and amine nucleophiles, which makes up for the deficiency of classical nitrogen nucleophilic substitution reactions. As a demonstration of the broad potential applications of this new methodology, late-stage functionalization of a diverse array of azido-bearing natural products and drug molecules, a preliminary asymmetric reaction, and a continuous visible-light photoflow process have been developed.

Theoretical studies on the N–X (X = Cl, O) bond activation mechanism in catalytic C–H amination

A favorable S_N2-type N–Cl bond cleavage mechanism are proposed for Rh-catalysed C–H amination, which also works for N–O bond cleavage in Rh, Ru, and Pd analogous systems. These results could provide new understanding of C–H amination.

Iridium-Catalyzed Cross-Coupling Reactions of Alkenes by Hydrogen Transfer

A range of Ru-, Rh-, or Pd-catalyzed vinylic C-H/C-H cross-coupling reactions of olefins have been demonstrated to provide 1,3-dienes, using a quantitative amount of metal oxidants. Although transfer hydrogenation and C-H alkenylation are two important areas that evolved independently, we herein report the first iridium-catalyzed cross-coupling reactions of alkenes by integration of directed C(alkenyl)-H alkenylation and transfer hydrogenation to obviate the usage of a metal oxidant, employing a hydrogen acceptor such as inexpensive chloranil.

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.

Iridium-catalyzed alkenyl C–H allylation using conjugated dienes

An iridium-catalyzed olefinic C–H allylation of acrylamides with conjugated dienes was developed, providing an atom economic synthesis of skipped dienes.

Synergistic combination of visible-light photo-catalytic electron and energy transfer facilitating multicomponent synthesis of β-functionalized α,α-diarylethylamines

A synthetic strategy which takes advantage of the synergistic combination of electron and energy transfer processes using only one photocatalyst has been developed for the multicomponent synthesis of the α,α-diarylalkylamine skeleton.

Cobalt-catalysed unactivated C(sp3)–H amination: two-state reactivity and multi-reference electronic character

A remarkable two-state reactivity scenario and an unusual multi-reference character have been computationally found in Co-catalysed C(sp³)–H amination. In addition, the investigation on the additive, aminating reagent, metal center, and auxiliary ligand provides implications for development of new catalytic C–H functionalization systems.

Iridium-Catalyzed Unreactive C(sp3)-H Amination with 2,2,2-Trichloroethoxycarbonyl Azide

An additive-assisted iridium-catalyzed directed C(sp³)-H amination with 2,2,2-trichloroethoxycarbonyl azide as an amino source is reported. Both carboxylate anions and the corresponding cations in the additives are crucial to achieve satisfactory efficiency. Sodium acetate or n-pentanoic acid can promote the amination of various primary C(sp³)-H bonds adjacent to secondary, tertiary, and quaternary carbons in ketoximes or N-aromatic heterocycles, respectively, providing a practical route to versatile β-amino ketoxime and N-heteroaryl ethanamine derivatives. The amination products can be treated as isocyanate analogues and can be converted to other useful amino functionalities. An iridacyclic compound was isolated and identified as a plausible intermediate.