Atroposelective Haloamidation of Indoles with Amino Acid Derivatives and Hypohalides

Merging of Two Photoredox Cycles with One Perovskite Catalyst Achieving Dual Functionalization: N-Heterocyclization and Site-Selective Bromination of N-Arylamines

Dual functionalization in organic synthesis represents a powerful strategy aimed at achieving multiple transformations within a single reaction cycle, thereby streamlining synthetic processes, enhancing efficiency, and imparting economic paths for complex molecules. Here, we report a heterogeneous perovskite nanocrystal (NC) photocatalytic system that can simultaneously drive two photoredox cycles in a single reaction. The dual process incorporates two distinct functional groups (N-heterocycles and bromines) into N-arylamines under the influence of a single catalyst (CsPbBr3 NCs), allowing for the concurrent formation of two distinct architectures of 3-bromo-N-arylindoles. Mechanistically, long-lived charge separation and charge carrier accumulation at the NC surface enable perovskite to drive these two photoredox cycles simultaneously. The dual approach exploits light-induced holes to drive an amine oxidation in one cycle (I) and cooperatively utilizes dibromomethane (CH2Br2), a solvent-grade mild reagent for site-selective bromination, to achieve the other photoredox cycle (II). We find that chiral perovskite induces enantioselective axial C-N bond formation, but is inactive for axial C-C bond formation of arylindoles. Merging two photoredox cycles simultaneously to achieve dual functionalization is rare; thus, the perovskite NC photocatalysis not only aligns with the principles of green chemistry but also holds immense potential for the rapid and economical design of complex molecules.

A stereodivergent multicomponent approach for the synthesis of C-N atropisomeric peptide analogues

A four-component Ugi reaction is described for the stereoselective synthesis of novel C-N atropisomeric peptide analogues. Using this approach, a combination of simple, readily available starting materials (ortho-substituted anilines, aldehydes, carboxylic acids and isocyanides) could be combined to access complex products possessing both central and axial chirality in up to 92% yield and >95 : 5 d.r. Variation of the reaction temperature enabled the development of stereodivergent reactions capable of selectively targeting either diastereoisomer of a desired product from a single set of starting materials with high levels of stereocontrol. Detailed experimental and computational studies have been performed to probe the reaction mechanism and stereochemical outcome of these reactions. Preliminary studies show that novel atropisomeric scaffolds prepared using this method display inhibitory activity against M. tuberculosis with a significant difference in activity observed between different atropisomers.

Modular Synthesis of Tripeptide Analogs with an Aminobitriazole Skeleton Using Diynyl Benziodoxolone as a Trivalent Platform

A new synthesis method of tripeptide analogs with an aminobitriazole skeleton was proposed. The method involves assembling three amino acid-derived modules at the amino group site and onto a triisopropylsilyl diynyl benziodoxolone by copper-catalyzed electrophilic diynylation of amino acid-derived sulfonamides, chemoselective azide-alkyne cycloadditions with amino acid-derived azides, and deprotection. Various complex aminobitriazoles substituted with pyrene, nucleoside, and N-acetylglucosamine were also synthesized. The produced aminobitriazoles have three sp3 chiral centers and a C-N axial chirality.

Iodine-mediated oxidative triple functionalization of indolines with azoles and diazonium salts

We report an innovative synthetic strategy for the generation of polysubstituted indoles from indolines, aryldiazonium salts, and azoles. The methodology encompasses an electrophilic substitution reaction affording C5-indoline intermediates which undergo an iodine-mediated oxidative transformation coupled with C-H functionalization to yield the indole derivatives.

Brønsted Acid-Catalyzed Reaction of N-arylnaphthalen-2-amines with Quinone Esters for the Construction of Carbazole and C-N Axially Chiral Carbazole Derivatives

We demonstrated here an efficient synthetic method of carbazole derivatives from readily available N-arylnaphthalen-2-amines and quinone esters catalyzed by Brønsted acid. With this strategy, a series of carbazole derivatives were obtained in good to excellent yields (76 to >99) under mild conditions. Large scale reaction illustrated the synthetic utility of this protocol. Meanwhile, a series of C-N axially chiral carbazole derivatives were also constructed in moderate to good yields (36-89% yield) with moderate to excellent atroposelectivities (44-94% ee) by using chiral phosphoric acid as a catalyst, which provides a novel strategy for the atroposelective construction of C-N axially chiral compounds and a new member of the C-N atropisomers.

NaClO-Mediated Cross Installation of Indoles and Azoles Benefits Anticancer Hit Discovery

Innovations in synthetic chemistry have a profound impact on the drug discovery process, and will always be a necessary driver of drug development. As a result, it is of significance to develop novel simple and effective synthetic installation of medicinal modules to promote drug discovery. Herein, we have developed a NaClO-mediated cross installation of indoles and azoles, both of which are frequently encountered in drugs and natural products. This effective toolbox provides a convenient synthetic route to access a library of N-linked 2-(azol-1-yl) indole derivatives, and can be used for late-stage modification of drugs, natural products and peptides. Moreover, biological screening of the library has revealed that several adducts showed promising anticancer activities against A549 and NCI-H1975 cells, which give us a hit for anticancer drug discovery.

Atroposelective Amination of Indoles via Chiral Center Induced Chiral Axis Formation

The construction of an N-C chiral axis for N-aryl indole derivatives is meaningful as they widely exist in functionalized molecules. This work provides a novel method for this purpose via amination of amino acid derivatives at the C2 position of the indole and chiral center induced chiral axis formation. The protocol of this transformation is easily accessible, not requiring metal or an organic chiral catalyst, endowing this method with great potential in the construction of axis chiral N-aryl indoles.

Palladium-catalyzed oxidative C-H activation/annulation of N-alkylanilines with bromoalkynes: access to functionalized 3-bromoindoles

A straightforward approach to the synthesis of 3-bromoindoles via palladium-catalyzed oxidative C-H activation/annulation of N-alkylanilines with bromoalkynes has been described. This protocol features high atom economy, excellent chemo- and regioselectivities, and good functional group tolerance. Moreover, the resultant 3-bromoindoles can be transformed to various functionalized indole derivatives, which demonstrates the practicability of this method in organic synthesis.

Copper-Catalyzed Enantioselective C-H Arylation between 2-Arylindoles and Hypervalent Iodine Reagents

The copper-catalyzed enantioselective C-H arylation between 2-arylindoles and hypervalent iodine reagents has been successfully developed, which provides a convenient and economical route to the highly atroposelective synthesis of axially chiral indole derivatives with a 2-aryl structure (up to 99% ee). Density functional theory calculations and wave function analysis show that the key "sandwich" intermediate leads to high enantioselectivity of the reaction.

Unprecedented Reactivity of γ-Amino Cyclopentenone Enables Diversity-Oriented Access to Functionalized Indoles and Indole-Annulated Ring Structures

Observation of an unexpected, Lewis acid promoted displacement of latent reactive γ-amino group on cyclopentenone presented unparalleled opportunity for enone functionalization and annulations with indole derivatives, which is developed in the current study. Herein, a vast range of C3/N-indolyl enones and indole alkaloid-like compound were accessed in excellent yields (up to 99 %) and selectivity through a one-pot operation. The mechanism most likely involves an unprecedented trait of Piancatelli-type rearrangement where influence of the gem-diaryl group appeared crucial.

Electrochemical Iodoamination of Indoles Using Unactivated Amines

An environmentally friendly electrochemical approach for iodoamination of various indole derivatives with a series of unactivated amines, amino acid derivatives, and benzotriazoles (more than 80 examples) has been developed. This strategy was further applied in late-stage functionalization of natural products and pharmaceuticals and gram-scale synthesis and radiosynthesis of ¹³¹I-labeled compounds. Fundamental insights into the mechanism of the reaction based on control experiments, density functional theory calculation, and cyclic voltammetry are provided.

Transition-Metal-Free Stereospecific Oxidative Annulative Coupling of Indolines with Aziridines

Tandem C-N bond formation for the oxidative annulation of indolines with aziridines is accomplished employing the combination of DDQ and NaOCl at ambient conditions. Optically active aziridine can be coupled with high enantiomeric purity (>99% ee). The substrate scope, stereocontrol with the enantioenriched substrate, and scale-up are the important practical advantages.