Synthesis and reactivity of 7-azaindole (1H-pyrrolo[2,3-b]pyridine)

Programmed Heterocycle Synthesis Using Halomucononitriles as Pyridinimine Precursors

Herein we report a method to convert primary amines, ubiquitous motifs found in pharmaceutical libraries, to either imidazo[1,2-a]pyridines or 7-alkyl azaindoles in two steps from known compounds. Using halomucononitrile reagents, we can directly access 5-bromo-6-imino-1-alkyl-1,6-dihydropyridine-2-carbonitriles (pyridinimines) in a single step from primary amines (25-93% yield) through the cyclization of transient aminomucononitrile intermediates. We then demonstrate that these compounds can be readily converted to 7-alkylazaindoles using Sonogashira cross-coupling conditions (13 examples, up to 91% yield). Under oxidative conditions, the pyridinimines serve as directing groups for C-H functionalization reactions to afford imidazo[1,2-a]pyridines. We also studied the mechanism of the cyclization event using DFT calculations and propose that this takes place via sequential base-mediated E/Z isomerization and cyclization steps.

Cobalt(III)-Catalyzed Directed C-7 Selective C-H Alkynylation of Indolines with Bromoalkynes

A cobalt(III)-catalyzed directed C-7 alkynylation of indolines with easily accessible bromoalkynes has been developed. The reaction has a broad substrate scope with excellent yields and represents a powerful route to the synthesis of 7-alkynyl-substituted indolines. In addition, the reaction can be extended to the coupling of N-aryl 7-azaindoles, highlighting the synthetic practicability of the strategy.

Palladium-Catalyzed Heck Cyclization with P(O)H Compounds to Construct Phosphinonyl-Azaindoline and -Azaoxindole Derivatives

We report herein a concise method for the construction of phosphinonyl-azaindoline and -azaoxindole derivatives via a palladium-catalyzed cascade cyclization with P(O)H compounds. Various H-phosphonates, H-phosphinates, and aromatic secondary phosphine oxides are all tolerated under the reaction conditions. Furthermore, the phosphinonyl-azaindoline isomer families such as 7-, 5-, and 4-azaindolines could be synthesized in moderate to good yields.

A Survey on the Synthesis of Variolins, Meridianins, and Meriolins-Naturally Occurring Marine (aza)Indole Alkaloids and Their Semisynthetic Derivatives

Marine natural products are a source of essential significance due to a plethora of highly diverse biological properties. The naturally occurring (aza)indole alkaloids variolin B (1), meridianins (2), and their synthetic hybrids meriolins (3) exhibit potent kinase inhibitory activities and have aroused considerable interest in the past two decades. Therefore, the immense demand for versatile synthetic accesses to these structures has considerably increased. This review surveys the synthetic pathways to these naturally occurring alkaloids and their semisynthetic derivatives.

Fused pyrrolo-pyridines and pyrrolo-(iso)quinoline as anticancer agents

This work emphasizes the synthesis strategies and antiproliferative related properties of fused pyrrolo-pyridine (including indolizine and azaindoles) and pyrrolo-(iso)quinoline derivatives recently reported in literature.

Alkali-Amide Controlled Selective Synthesis of 7-Azaindole and 7-Azaindoline through Domino Reactions of 2-Fluoro-3-methylpyridine and Aldehydes

Azaindoles and azaindolines are important core structures in pharmaceuticals and natural products, which have found wide applications in the field of medicinal chemistrty. In this study, we developed a novel...

Cu(II)-Catalyzed C-N, C-O, C-Cl, C-S, and C-Se Bond Formation via C(sp2)-H Activation Using 7-Azaindole as an Intrinsic Directing Group

A general protocol has been developed for the construction of carbon-heteroatom (C-N, C-Cl, C-O, C-S, and C-Se) bonds using the bench stable, earth-abundant, and environmentally benign copper catalyst. Only oxygen is sufficient to regenerate the copper catalyst. Control experiments suggested that the proto-demetalation step is reversible. Depending on the coupling partner, the reaction follows either disproportionation or radical pathways to complete the catalytic cycle. The synthetic utility of the developed protocol has been demonstrated via various functional group transformations.

Iridium-catalyzed C3-selective asymmetric allylation of 7-azaindoles with secondary allylic alcohols

The development of efficient synthetic methods of 7-azaindoles has been desired due to the useful biological activities and physical properties. We report the first example of the iridium-catalyzed C3-selective asymmetric allylation of 7-azaindoles with racemic secondary allylic alcohols to give only branched allylation products in good to high yields with high enantioselectivity (up to >99.5% ee). Allylic alcohols and 7-azaindoles with a variety of functional groups including halogen and heteroaromatic groups are compatible with the reaction conditions. Furthermore, transformations of the obtained allylation products are demonstrated without a significant loss of enantiomeric excess.

Recent developments in the synthesis of azaindoles from pyridine and pyrrole building blocks

The azaindole framework is ubiquitous in bioactive natural products and pharmaceuticals. This review highlights the synthetic approaches to azaindoles with advantages and limitations, mechanistic pathways and biological importance.

Anti-selective [3+2] (Hetero)annulation of non-conjugated alkenes via directed nucleopalladation

2,3-Dihydrobenzofurans and indolines are common substructures in medicines and natural products. Herein, we describe a method that enables direct access to these core structures from non-conjugated alkenyl amides and ortho-iodoanilines/phenols. Under palladium(II) catalysis this [3 + 2] heteroannulation proceeds in an anti-selective fashion and tolerates a wide variety of functional groups. N-Acetyl, -tosyl, and -alkyl substituted ortho-iodoanilines, as well as free -NH2 variants, are all effective. Preliminary results with carbon-based coupling partners also demonstrate the viability of forming indane core structures using this approach. Experimental and computational studies on reactions with phenols support a mechanism involving turnover-limiting, endergonic directed oxypalladation, followed by intramolecular oxidative addition and reductive elimination.

Photosensitized Intramolecular [2+2] Cycloaddition of 1H-Pyrrolo[2,3-b]pyridines Enabled by the Assistance of Lewis Acids

The [2+2] photocycloaddition of alkenyl-tethered 1H-pyrrolo[2,3-b]pyridine derivatives sensitized with 3',4'-dimethoxyacetophenone under irradiation by a high-pressure mercury lamp through Pyrex glass was dramatically accelerated by the addition of Lewis acids, preferably Mg(OTf)₂, to give the products stereoselectively in high yields. The reaction without a Lewis acid gave only small amounts of the [2+2] cycloaddition products. Conformational fixation of the substrates by coordination with a Lewis acid was presumed to facilitate the cycloaddition.

Recent advances in the global ring functionalization of 7-azaindoles

The 7-azaindole building block has attracted considerable interest in the field of drug discovery in the current portfolio. Because of their powerful medicinal properties, the development of synthetic, elegant techniques for the functionalization of 7-azaindoles continues to be an active area of research. Advances in metal-catalyzed chemistry have recently supported the successful development of a number of novel and effective methods for functionalization of the 7-azaindole template. This review reports state-of-the-art functionalization chemistry of 7-azaindoles with an aspiration to highlight the global ring functionalization of 7-azaindoles that are potential as pharmacophores for various therapeutic targets. Other relevant reviews focused on 7-azaindole synthesis, properties and applications have also been reported. However, none of these reviews have been dedicated to the results achieved in the field of metal-catalyzed cross-coupling/C-H bond functionalized reactions. So we wish to discuss and summarize the advances made since 2011 in this field toward 7-azaindole functionalization.

The importance of indole and azaindole scaffold in the development of antitumor agents

With some indoles and azaindoles being successfully developed as anticancer drugs, the design and synthesis of indole and azaindole derivatives with remarkable antitumor activity has received increasing attention and significant progress has been made. This paper reviews the recent progress in the study of tumorigenesis, mechanism of actions and structure activity relationships about anticancer indole and azindole derivatives. Combining structure activity relationships and molecular targets-related knowledge, this review will help researchers design more effective, safe and cost-effective anticancer indoles and azindoles agents.

Synthesis of Highly Substituted Pyridines via [4 + 2] Cycloadditions of Vinylallenes and Sulfonyl Cyanides

A convergent strategy for the synthesis of multisubstituted pyridines is described. Vinylallenes combine with commercially available arylsulfonyl cyanides in Diels-Alder cycloadditions to generate isopyridine cycloadducts that are converted to pyridines upon further heating or addition of a base. The 2-sulfonylpyridine products undergo nucleophilic aromatic substitution reactions with oxygen and carbon nucleophiles to provide access to a variety of highly substituted pyridines.

Regioselective deoxygenative chalcogenation of 7-azindole N-oxides promoted by I2/PEG-200

We developed a general and sustainable approach for the regioselective deoxygenative chalcogenation of 7-azindole N-oxides; the combination of an internal oxidant and a green solvent has been used successfully for the synthesis of mono- and dichalcogenyl 7-azaindoles which are of pharmaceutical interest. The regioselectivity is tunable by the variation of the reaction conditions. I2/PEG was established as an efficient and reusable catalytic system for C-H chalcogenation. This developed methodology has great potential for practical utility, with a broad substrate scope, green reaction conditions, and operational simplicity.

7-Azaindole Analogues as Bioactive Agents and Recent Results

Azaindoles have been accepted as important structures having various biological activities in medicinal chemistry in novel drug discovery. Various azaindole derivatives have been used commercially and newer analogues are synthesized continuously. As in literature, azaindole is a very potent moiety, its derivatives displayed a number of biological activities such as kinase inhibitors, cytotoxic agents, anti-angiogenic activity, CRTh2 receptor antagonists, melanin agonists, nicotine agonists, effectiveness in alzheimer disease, cytokinin analogs, Orai inhibitors in asthma and chemokine receptor- 2 (CCR2) antagonists. This review consists of biological activities of various azaindole analogs, reported so far, and their structure activity relations, along with future perspectives in this field.

Substituted 1H-1,2,3-Triazol-4-yl-1H-pyrrolo[2,3-b]pyridines by De Novo One-Pot Ring-Forming Coupling/Cyclization/Desilylation Cu Alkyne/Azide Cycloaddition (AAC) Sequence

Substituted 1H-1,2,3-triazol-4-yl-pyrrolo[2,3-b]pyridines are efficiently prepared by a one-pot coupling/cyclization/desilylation Cu alkyne/azide cycloaddition (CuAAC) sequence in the sense of a consecutive three-component fashion. The key feature of this new de novo formation of azole and triazole anellation is the sequentially Pd/Cu-catalyzed process employing tri(iso-propyl)silyl (TIPS) butadiyne as a four-carbon building block. In addition, the sequence can be expanded in a four-component fashion also employing the in situ formation of the required azides.

Visible Light-Mediated Decarboxylative Alkylation of Pharmaceutically Relevant Heterocycles

A net redox-neutral method for the decarboxylative alkylation of heteroarenes using photoredox catalysis is reported. Additionally, this method features the use of simple, commercially available carboxylic acid derivatives as alkylating agents, enabling the facile alkylation of a variety of biologically relevant heterocyclic scaffolds under mild conditions.

Recent developments in palladium-catalysed non-directed coupling of (hetero)arene C–H bonds with C–Z (Z = B, Si, Sn, S, N, C, H) bonds in bi(hetero)aryl synthesis

This review article describes the palladium-catalysed non-directed coupling of (hetero)arene C–H bonds with C_(Ar)–Z (Z = B, Si, Sn, S, N, C, H) bonds for facile bi(hetero)aryl synthesis in the past 10 years.

Domino cyclization/trifluoromethylation of 2-alkynylanilines using fluoroform-derived CuCF3: synthesis of 3-(trifluoromethyl)indoles

A domino cyclization/trifluoromethylation strategy for the construction of indole cores with concomitant installation of a CF₃ group is described.

Iridium-catalyzed C–H phosphoramidation of N-aryl-7-azaindoles with phosphoryl azides

An iridium-catalyzed C–H phosphoramidation of N-aryl-7-azaindoles with phosphoryl azides was developed, affording a series of 7-azaindole phenylphosphoramidates.

Catalytic Reductive Synthesis and Direct Derivatization of Unprotected Aminoindoles, Aminopyrroles, and Iminoindolines

A titanium(III)-catalyzed radical cyclization to unprotected 3-aminoindoles, 3-aminopyrroles, or 3-iminoindolines is reported. The reaction is non-hazardous, scalable, and allows facile isolation of the free products by extraction. The method is demonstrated on a large substrate scope and it further allows the direct installation of various nitrogen protecting groups or the synthesis of building blocks for peptide chemistry in a single sequence. Fused bisindoles can be directly accessed from the cyclization products.

Access to π-conjugated azaindole derivatives via rhodium(iii)-catalyzed cascade reaction of azaindoles and diazo compounds

Diazo compounds play an important role as a coupling partner to access unique π-conjugated 7-azaindole derivatives via rhodium(iii)-catalyzed double C–H activation/cyclization.

Crystal structure of 3-tert-butyl-7-azadioxindole, C11H14N2O2

C11H14N2O2, orthorhombic, P212121 (no. 19), a = 7.3227(3) Å, b = 10.9955(4) Å, c = 26.3709(9) Å, V = 2123.30(14) Å3, Z = 8, Rgt(F) = 0.0372, wRref(F2) = 0.0907, T = 150 K.