Towards Uniform Iodine Catalysis: Intramolecular C-H Amination of Arenes under Visible Light

Cyclic Amine Synthesis via Catalytic Radical-Polar Crossover Cycloadditions

The rapid assembly of valuable cyclic amine architectures in a single step from simple precursors has been recognized as an ideal platform in term of efficiency and sustainability. Although a vast number of studies regarding cyclic amine synthesis has been reported, new synthetic disconnection approaches are still high in demand. Herein, we report a catalytic radical-polar crossover cycloaddition to cyclic amine synthesis triggered from primary sulfonamide under photoredox condition. This newly developed disconnection, comparable to established synthetic approaches, will allow to construct β, β-disubstituted cyclic amine and β-monosubstituted cyclic amine derivatives efficiently. This study highlights the unique utility of primary sulfonamide as a bifunctional reagent, which acts as a radical precursor and a nucleophile. The open-shell methodology demonstrates broad tolerance to various functional groups, drug derivatives and natural products in an economically and sustainable fashion.

Iodine(III)-Mediated Oxidation of Anilines to Construct Dibenzazepines

The development of an efficient process that produces bioactive medium-sized N-heterocyclic scaffolds from 2-substituted anilines using either iodosobenzene or (bis(trifluoroacetoxy)iodo)-benzene is reported. The tether between the sulfonamide and the aryl group can be varied to access dihydroacridine-, dibenzazepine-, or dibenzazocine scaffolds. While substitution on the aniline portion is limited to electron-neutral- or electron-poor groups, a broader range of functional groups are tolerated on the ortho-aryl substituent and site selective C-NAr bond formation can be achieved. Preliminary mechanistic investigations suggest that medium-ring formation occurs via radical reactive intermediates.

Nitrogen-Centered Radicals in Functionalization of sp2 Systems: Generation, Reactivity, and Applications in Synthesis

The chemistry of nitrogen-centered radicals (NCRs) has plentiful applications in organic synthesis, and they continue to expand as our understanding of these reactive species increases. The utility of these reactive intermediates is demonstrated in the recent advances in C-H amination and the (di)amination of alkenes. Synthesis of previously challenging structures can be achieved by efficient functionalization of sp² moieties without prefunctionalization, allowing for faster and more streamlined synthesis. This Review addresses the generation, reactivity, and application of NCRs, including, but not limited to, iminyl, aminyl, amidyl, and aminium species. Contributions from early discovery up to the most recent examples have been highlighted, covering radical initiation, thermolysis, photolysis, and, more recently, photoredox catalysis. Radical-mediated intermolecular amination of (hetero)arenes can occur with a variety of complex amine precursors, generating aniline derivatives, an important class of structures for drug discovery and development. Functionalization of olefins is achievable in high anti-Markovnikov regioselectivity and allows access to difunctionalized structures when the intermediate carbon radicals are trapped. Additionally, the reactivity of NCRs can be harnessed for the rapid construction of N-heterocycles such as pyrrolidines, phenanthridines, quinoxalines, and quinazolinones.

Environmentally friendly catechol-based synthesis of dibenzosultams

A scalable reaction for the synthesis of dibenzosultams in water with the aid of K2CO3 and air.

Iodonitrene: a direct metal-free electrophilic aminating reagent

Iodonitrene is a new type of reactive electrophilic aminating reagent that opens up opportunities for new discoveries.

Synthesis of Six-Membered N-Heterocycle Frameworks Based on Intramolecular Metal-Free N-Centered Radical Chemistry

The formation of intramolecular C-N bond represents a powerful strategy in organic transformation as the great importance of N-heterocycles in the fields of natural products and bioactive molecules. This personal account describes the synthesis of cyclic phosphinamidation, benzosultam, benzosulfoximine, phenanthridine and their halogenated compounds through transition-metal-free intramolecular oxidative C-N bond formation. Mechanism study reveals that N-X bond is initially formed under the effect of hypervalent halogen, which is very unstable and easily undergoes thermal or light homolytic cleavage to generate nitrogen radical. Then the nitrogen radical is trapped by the arene to give aryl radical. Rearomatization of aryl radical under the oxidant to provide corresponding N-heterocycle. Under suitable conditions, the N-heterocycles can be further transformed to halogenated N-heterocycles.

Transition-Metal-Free Tandem Cyclization/N-Arylation Reaction: A Method To Access Biaryl Sultam Derivatives via a Diradical Pathway

A novel procedure for the transition-metal-free tandem cyclization/N-arylation reaction sequence of an aryne with a 1,2,3,4-benzothiatriazine-1,1-dioxide is reported. This reaction goes through the intramolecular homolytic cyclization to generate an N-H biaryl sultam intermediate, which enables aryne insertion to access diversely functionalized biaryl sultam derivatives with high yields. The mechanism study indicates that homolytic cyclization is executed by a diradical species, initiated from the thermal decomposition of 1,2,3,4-benzothiatriazine-1,1-dioxide to release a nitrogen molecule.

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.

Crystal engineering of coordination-polymer-based iodine adsorbents using a π-electron-rich polycarboxylate aryl ether ligand

This work revealed that the synergy of microporous channels and convergent arrangements of halogen bonding and charge-transfer interaction sites within coordination polymers facilitated the iodine adsorption process.

Rh-Catalyzed Highly Enantioselective Synthesis of Aliphatic Sulfonyl Fluorides

Rh-catalyzed, highly enantioselective (up to 99.8% ee) synthesis of aliphatic sulfonyl fluorides was accomplished. This protocol provides a portal to a class of novel 2-aryl substituted chiral sulfonyl fluorides, which are otherwise extremely difficult to access. This asymmetric synthesis has the feature of mild conditions, excellent functional group compatibility, and wide substrate scope (51 examples) generating a wide array of structurally unique chiral β-arylated sulfonyl fluorides for sulfur(VI) fluoride exchange (SuFEx) click reaction and drug discovery.

Synthesis, characterisation, and reactivity of novel pseudocyclic hypervalent iodine reagents with heteroaryl carbonyl substituents

New heteroatom-containing pseudocyclic iodanes are being introduces as alternatives to the Koser reagent.

Regiospecific N-Arylation of Aliphatic Amines under Mild and Metal-Free Reaction Conditions

A transition metal‐free N‐arylation of primary and secondary amines with diaryliodonium salts is presented. Both acyclic and cyclic amines are well tolerated, providing a large set of N‐alkyl anilines. The methodology is unprecedented among metal‐free methods in terms of amine scope, the ability to transfer both electron‐withdrawing and electron‐donating aryl groups, and efficient use of resources, as excess substrate or reagents are not required.

Radical-mediated direct C-H amination of arenes with secondary amines

Direct radical-based substitution of aryl C–H bonds allows one-pot access to valuable polycyclic aryl amines from simple secondary amines.

Aryl dialkyl amines, valuable subunits of a wide range of effect chemicals, are accessed by intramolecular amination of aromatic C–H bonds employing UV photolysis of N-chloroamines. The reactions show good functional group tolerance and allow access to a range of fused and bridged polycyclic structures. The homogeneous reaction conditions allow for the one-pot conversion of secondary amines to their arylated derivatives. Experimental and theoretical evidence supports the involvement of electrophilic aminium radicals which react via direct ortho-attack on the arene.

Visible light catalyzed synthesis of quinolines from (aza)-Morita–Baylis–Hillman adducts

A mild and efficient protocol for the synthesis of quinoline scaffolds from (aza)-MBH adducts under visible light catalysis has been established.

Dehydrogenative Aromatic Ring Fusion for Carbazole Synthesis via C-C/C-N Bond Formation and Alkyl Migration

An intermolecular dehydrogenative annulation (IDA) for carbazole synthesis via sequential C-C/C-N bond formation with a selective alkyl group migration is reported. Using the hypervalent iodine(III) reagent PhI(OAc)₂ (PIDA), in a one-pot operation, up to five C(sp2)-H bonds, one N(sp3)-H bond functionalization, and one alkyl (Me, Et) group migration could all be achieved from non-prefunctionalized 1,3,5-trialkylbenzenes and anilides under ambient laboratory conditions. Mechanistically, it is shown that PIDA reacts with anilides to generate a nitrenium ion or an equivalent carbenium ion which influences the second aromatic ring to be activated for C-C/C-N bond formation. Strategically, regioselective fusion of arenes to anilides is described.

Synthesis of Aryl(2,4,6-trimethoxyphenyl)iodonium Trifluoroacetate Salts

The direct synthesis of aryl(2,4,6-trimethoxyphenyl)iodonium trifluoroacetate salts from aryl iodides is described. Stoichiometric quantities of trifluoroacetic acid and trimethoxybenzene are used as the counteranion and auxiliary precursors, respectively, under oxidizing conditions. The reaction occurs at mild temperature, is broad in scope, and does not require a separate anion exchange step to install the trifluoroacetate group. The intermediacy of two distinct dicarboxy aryl-λ³-iodanes is hypothesized in the mechanism.