Straightforward access to novel indolo[2,3-b]indoles via aerobic copper-catalyzed [3+2] annulation of diarylamines and indoles

Copper-Catalyzed Dearomative [3 + 2] Annulation of Indoles with 2-Iodoacetic Acid

An efficient copper-catalyzed dearomative [3 + 2] annulation of indoles with 2-iodoacetic acid is developed. By employing Cu(OTf)2/2,2'-bis(2-oxazoline) as the catalyst and LPO as the oxidant, a series of indoline-fused butyrolactones were synthesized in moderate to good yields. The reaction features mild conditions, a broad substrate scope, and readily available starting materials. Furthermore, synthetic transformations of the products were conducted to demonstrate the practical utility of this reaction.

Copper-catalyzed aerobic annulation of hydrazones with dienones: an efficient route to pyrazole-linked hybrid molecules

A copper-catalyzed aerobic [3 + 2] annulation reaction to access various pyrazole-bound chalcones starting from readily available and cost-effective hydrazones and dienones is reported. These pyrazole-bound chalcones were further utilized effectively to prepare a series of pyrazole-linked hybrid molecules, such as pyrazole-pyrazoline, pyrazole-aziridine, and pyrazole-pyridine hybrids by efficient simple transformations. Synthetically challenging hybrid molecules were obtained in a simple, two-step process with high atom economy under aerobic copper catalysis.

Regioselective Electrooxidative [3+2] Annulation between Indole and Aniline Derivatives to Construct Functionalized Indolo[2,3-b]indoles

A protocol for the electrooxidative [3+2] annulation to generate indolo[2,3-b]indoles in an undivided cell is reported. It exhibits good yields with excellent regioselectivities and tolerates various functional groups without external chemical oxidants. Cyclic voltammetry and density functional theory calculations indicate that the [3+2] annulation is initiated by the simultaneous anodic oxidation of indole and aniline derivatives, and the step to determine the rate relies on the combination of radical cations.

NBS-induced intramolecular annulation reactions for the divergent synthesis of fused- and spirocyclic indolines

An NBS-induced intramolecular annulation of 3-(1H-indol-3-yl)-N-alkoxypropanamide is described. The reactions proceed well and quickly under mild conditions with the help of a base. It was found that C2-substituents on the indole ring in 3-(1H-indol-3-yl)-N-alkoxypropanamide have a great influence upon the reaction. By using C2-methyl- and C2-phenyl-3-(1H-indol-3-yl)-N-alkoxypropanamide as templates, practical protocols for the divergent synthesis of fused- and spirocyclic indoline compounds were studied and established.

Copper-catalyzed construction of (Z)-benzo[cd]indoles: stereoselective intramolecular trans-addition and SN-Ar reaction

Substituted benzo[cd]indoles are one of the most attractive frameworks because of their wide range of biological and optical activities. Herein, a copper-catalyzed one-step synthesis of biologically important polysubstituted benzo[cd]indoles starting from 8-alkynyl-1-naphthylamine derivatives is reported. In this protocol, many substituents tolerated the reaction conditions and produced (Z)-benzo[cd]indoles in good yields. Preliminary mechanistic studies indicated that the reaction proceeds via a stereoselective intramolecular trans-addition and S_N-Ar reaction with high selectivity and high yields. The synthesized polysubstituted (Z)-benzo[cd]indoles possess sulfonamide building blocks, which make them candidates for bioactive molecules.

Chemodivergent Synthesis of Indeno[1,2-b]indoles and Isoindolo[2,1-a]indoles via Mn(III)-Mediated or Electrochemical Intramolecular Radical Cross-Dehydrogenative Coupling

Chemodivergent synthesis of indeno[1,2-b]indoles and isoindolo[2,1-a]indoles from the same starting materials involving radical cross-dehydrogenative couplings have been developed. Mn(OAc)₃·2H₂O selectively promoted an intramolecular radical C-H/C-H dehydrogenative coupling reaction to provide indeno[1,2-b]indoles, while an intramolecular radical C-H/N-H dehydrogenative coupling reaction could proceed via electrochemistry to deliver isoindolo[2,1-a]indoles. Plausible mechanisms of the chemodivergent reactions were proposed.

Substrate-directed divergent synthesis of fused indole polycycles through Rh(II)-catalyzed cascade reactions of bis(diazo)indolin-2-ones

Herein, we report a substrate-directed diverse synthetic strategy toward two kinds of structurally intriguing fused indole polycycles through Rh(II)-catalyzed cascade reactions of bis(diazo)indolin-2-ones with enaminones. The subtle structural changes in enaminones lead to different reactivities. Cyclic enaminones produce indolo[2,3-b]indoles, whereas acyclic ones afford oxazolo[3,2-a]indoles.

Recent Advances towards the Synthesis and Material Applications of Indoloindoles

An important class of N -heteroacenes is indoloindoles which are air-stable, electron-rich and possesses many tuneable properties. Initially, indoloindoles were explored for potential biological applications but current interest is based on their performance as photovoltaic materials. With growing applications of indoloindoles across multiple facets as organic functional materials, the need for efficient methods to synthesize and functionalize indoloindoles has taken a centre stage. Over the years, synthetic routes leading to indoloindoles have evolved from multistep protocols to one-pot multicomponent synthesis. Present literature boasts of a variety of reports that employ metals such as Cu, Ru, Rh, Pd, or Au to mediate the reaction towards indoloindoles. As alternatives to such metal-mediated methods, researchers have also developed metal-free and catalyst-free conditions. Indoloindoles, which are fundamentally fused-indoles, are often synthesized by transforming indole derivatives but methods that employ anilines or arynes as the starting substrates are equally abundant. The present review highlights the rich diversity and versatility of recent literature for the synthesis of indolo[3,2- b ]indoles, indolo[2,3- b ]indoles, indolo[7,6- g ]indoles, and indolo[5,4- e ]indoles. This review discusses protocols that were explicitly designed to obtain the above-mentioned indoloindoles and also explores several other methods that can be adapted to access said heteroacenes. Available mechanistic details pertaining to novel transformations have been detailed for the readers. Various applications where indoloindoles function as organic light-emitting diodes, organic field-effect transistors, solar cells, etc. have also been delved into before concluding with an outlook on future research.

Iron–iodine co-catalysis towards tandem C–N/C–C bond formation: one-pot regioselective synthesis of 2-amino-3-alkylindoles

An efficient intermolecular C2,3-H aminoalkylation of indoles with 9H-xanthenes and azoles via iron–iodine co-catalyzed tandem C–N/C–C bond formation has been developed.

Copper-iodine Co-catalyzed C−H Aminoalkenylation of Indoles via Temperature-controlled Selectivity Switch: Facile Synthesis of 2-Azolyl-3-alkenylindoles

An efficient copper-iodine co-catalyzed 2,3-difunctionalization of indoles with azoles and phenols via temperature-controlled selectivity switch has been developed for the green synthesis of 2-azolyl-3-alkenylindoles. The strategy involves the simultaneous establishment...

Copper dual-atom catalyst mediated C3–H amination of indoles at room temperature

An efficient zeolite supported copper dual-atom catalyst for C–H amination of indoles has been developed for the green synthesis of 3-diarylaminoindoles.

Synthesis of 3-halogenated 2,3'-biindoles by a copper-mediated 2,3-difunctionalization of indoles

A copper-mediated 2,3-difunctionalization of indoles to afford 3-halogenated 2,3'-biindoles is described herein. The protocol uses readily available feedstocks and a naturally abundant copper catalyst system, which allows the regioselective formation of C-C and C-X (X = Cl & Br) bonds in one single operation. Here the copper metal salt serves not only as a catalyst but also as a reactant to provide the source of halogen. This operationally simple procedure avoids the utilization of environmentally unfriendly reagents and displays good functional group compatibility. Noteworthily, the introduction of halogen into molecules would offer great potential for further chemical transformations.

Synthesis of functionalized benzimidazoles via oxidative tandem quartic C-H aminations and cleavage of C-N and C-C bonds

Via aerobic copper-catalyzed tandem quartic C-H aminations, we herein present an unprecedented approach for the synthesis of functionalized benzimidazoles from aniline derivatives and 2-substituted cyclic amines. The cyclic amines act as the CN building blocks and are involved in the annulation reaction by cleavage of inert α-C-N and β-C-C bonds. The synthetic protocol features high selectivity, no need for specific aminating agents, mild conditions, and the use of a naturally abundant [Cu]/O₂ catalyst system.

CF3SO3H-enabled cascade ring-opening/dearomatization of indole derivatives to polycyclic heterocycles

A novel dearomatization process to produce fused polycyclic indolines via a CF3SO3H-mediated cascade ring-opening of a β-lactam and hydroaminative cyclization is demonstrated. It provides a new strategy for the synthesis of important polycyclic indoline-2-amine derivatives in moderate to excellent yields, as well as with good functional group tolerance. Moreover, transformation of the product was performed to deliver the corresponding acid, alcohol and amide smoothly.

Diastereoselective and Reversed Regioselective Annulations of N-Alkyl Anilines to Julolidines and Lilolidines

A three-component annulation reaction of N-alkyl anilines, cyclic 1,3-dicarbonyl compounds, and aryl aldehydes to julolidines and lilolidines is reported. The 6π-electrocyclization enabled the annulation to proceed with reversed regioselectivity as compared with the annulation that occurs in the Povarov reaction. Both cyclic and acyclic N-alkyl anilines participated in the reaction to provide a wide range of julolidines and lilolidines as the single regio- and diastereoisomers in good to excellent yields.

Is Cu(iii) a necessary intermediate in Cu-mediated coupling reactions? A mechanistic point of view

The different pathways have been summarized to disclose the key intermediate in copper-mediated coupling reactions.

One-electron oxidative dehydrogenative annulation and cyclization reactions

This review focuses on the recent advances in one-electron oxidation involved oxidative dehydrogenative annulations and cyclizations for the intermolecular and intramolecular construction of valuable ring structures.