Nickel-Catalyzed Intramolecular Direct Arylation of Imines toward Diverse Indoles

p-TsOH-Mediated Intramolecular C2-Arylation on NH-Indoles: Access of 5,10-Dihydroindeno[1,2-b]indoles

5,10-Dihydroindeno[1,2-b]indole has served as an important starting precursor for BARAC-fluor reagent in medicinal chemistry. Herein, an unprecedented p-TsOH assisted intramolecular C2-arylation of NH-indoles via C(sp2)-CN/C(sp2)-H coupling, offering a series of 5,10-dihydroindeno[1,2-b]indoles with moderate to good yields, has been showcased under redox-neutral conditions. Furthermore, successful scalability and synthetic applications highlight the practical nature of the method.

N-Heterocyclic carbene-catalyzed enantioselective annulation of 2-amino-1H-indoles and bromoenals for the synthesis of chiral 2-aryl-2,3-dihydropyrimido[1,2-a]indol-4 (1H)-ones

An efficient N-heterocyclic carbene (NHC)-catalyzed enantioselective [3 + 3] annulation of 2-bromoenals with 2-amino-1H-indoles has been developed. A series of functionalized 2-aryl-2,3-dihydropyrimido[1,2-a]indol-4(1H)-ones were synthesized using NHCs as the catalyst in good yields with high to excellent enantioselectivities.

Synthesis of Indolo[2,1-a]isoquinolines by Nickel-Catalyzed Mizoroki-Heck/Amination Cascade Reaction

An efficient Mizoroki-Heck/amination cascade reaction of o-dihaloarenes with cyclic imines was realized by combining nickel and a sterically bulky N-heterocyclic carbene ligand. This protocol provides access to a variety of indole[2,1-a]isoquinolines from readily available starting materials. This cascade approach could be applied to produce straightforward synthesis of the natural product cryptowoline.

Synthesis of Indoles via Domino Reactions of 2-Methoxytoluene and Nitriles

2-Arylindoles are privileged structures widely present in biologically active molecules. New sustainable synthetic routes toward their synthesis are, therefore, in high demand. Herein, a mixed base-promoted benzylic C-H deprotonation of commercially available ortho-anisoles, addition of the resulting anion to benzonitriles, and S_NAr to displace the methoxy group provide indoles. A diverse array of 2-arylindoles is prepared with good yields (>30 examples, yields up to 99%) without added transition metal catalysts.

Pd(II)/Lewis Acid Catalyzed Intramolecular Annulation of Indolecarboxamides with Dioxygen through Dual C-H Activation

Transition-metal ion catalyzed intramolecular dual C-H activation to construct polycyclic heteroarene skeletons is merited for its step and atom-economic advantages in organic synthesis. However, in most cases, stoichiometric oxidants, elevated temperature, and other harsh conditions were commonly faced for this reaction, which apparently block the synthetic applications. Herein, we report a Pd(II)/LA (LA: Lewis acid) catalyzed intramolecular dual C-H activation to construct indoloquinolinone derivatives under mild conditions with dioxygen as the sole oxidant. It was found that adding LA such as Sc³⁺ to Pd(OAc)₂ sharply improved its catalytic efficiency, whereas Pd(OAc)₂ alone was very sluggish. The activity improvement was attributed to the linkage of the Sc³⁺ cation to the Pd(II) species through a diacetate bridge that significantly enhanced the electrophilic properties of Pd(II) for dual C-H activation.

Reduction of Substituted Benzo-Fused Cyclic Sulfonamides with Mg-MeOH: An Experimental and Computational Study

A study involving the use of Mg-MeOH for the double reductive cleavage of both N–S and C–S bonds in a series of 11 benzo-fused cyclic sulfonamides is reported. Examples where the sulfonamide nitrogen atom is part of a pyrrolidine ring effectively undergo reduction, as long as a methoxy substituent is not para-positioned in the aromatic ring, relative to the sulfonyl group. In contrast, if the nitrogen atom is contained within an aromatic ring (pyrrole or indole), the presence of a para-methoxy substituent does not prohibit reduction. If deuterated methanol is used, aromatic ortho-deuterium incorporation was observed. To better understand how structure affects reactivity, density functional theory calculations were performed using three functionals. Results using CAM-B3LYP were found to best correlate with experimental observations, and these demonstrate the impact that the different aromatic substitution patterns and types of N-atom have on the lowest unoccupied molecular orbital (LUMO) energies and adiabatic electron affinities.

Three-component synthesis of α-indole-β-sulfonyl tetrahydrofurans under metal-free conditions

An efficient multi-component reaction has been developed for the synthesis of 2,3-disubstituted tetrahydrofurans in a “one pot” manner, starting from readily available 2-arylindoles, arylsulfonyl azides, and tetrahydrofuran under simple and easily operated reaction conditions.

A Tandem Nucleophilic Aminopalladation and Carbene Insertion Sequence for Indole Fused Polycycles

An efficient tandem nucleophilic aminopalladation and carbene insertion sequence is described for the synthesis of indole fused polycycles. The reaction process provides a variety of substituted indeno[1,2-b]indoles in up to 99% yields.

Nickel-Catalyzed Mizoroki-Heck/Amination Cascade Reactions of o-Dihaloarenes with Allylamines: Synthesis of Indoles

An efficient Mizoroki-Heck/amination cascade reaction of o-dihaloarenes with allylamines has been developed using nickel and IPr carbene ligand as catalyst. This protocol enables the synthesis of a broad range of substituted indoles by a cascade process, from readily available starting materials. Mechanistic studies suggest that the Mizoroki-Heck reaction occurred first under IPr-nickel catalysis.

Facile synthesis of 9H-pyrrolo[1,2-a]indoles via Brønsted acid catalyzed cascade reactions

A Brønsted acid system promotes the Friedel–Crafts alkenylation/1,6-addition/condensation cascade reaction of ynones with indoles to access 9H-pyrrolo[1,2-a]indoles.