Synthesis of furan-fused 1,4-dihydrocarbazoles via an unusual Garratt-Braverman Cyclization of indolyl propargyl ethers and their antifungal activity

The reactivity of indole based bis-propargyl ethers 4a-4g under Garratt-Braverman condition (KOBu^t in refluxing toluene) has been studied. Interestingly, these propargyl systems with one arm attached with substituted 3-indolyl derivatives leaving the other arm unsubstituted produced the 3,4-furan fused dihydrocarbazole derivatives 6a-6g (and not the expected carbazole derivatives) as the predominant product (70–82%) making this methodology to access such derivatives an attractive route. The results are supported by computational studies and some of the carbazole derivatives showed good antifungal activities.     

A straightforward synthesis of indole and benzofuran derivatives

A new methodology for the synthesis of indole and benzofuran derivatives has been devised. The starting materials, ortho-substituted aryl diynes, have been easily converted into new unsaturated bis-indolyl and bis-benzofuran derivatives and into 2-ethynylindole and 2-ethynylbenzofuran. Both these products have been further elaborated into more complex unsaturated indole-benzofuran and bis-benzofuran derivatives.     

Synthesis of benz[5,6]azepino[4,3-b]indoles by 1,7-electrocyclisation of azomethine ylides

A new, general route to the benz[5,6]azepino[4,3-b]indole ring system has been developed via the 1,7-dipolar electrocyclisation reactions of azomethine ylides derived from easily available 3-formyl indole derivatives. The intermediacy of azomethine ylides was shown by the trapping of the proposed α,β:γ,δ-conjugated dipole with N-phenylmaleimide.     

A free radical cyclization approach to indolo-benzodiazocine derivatives

A versatile route to indolo[2,1-d][1,5]benzodiazocine derivatives has been developed based on a free radical cyclization approach from 1-substituted indole derivatives with appropriately positioned haloacetamide functionalities. Fair yields of the indole- and dihydroindole-fused eight-membered ring derivatives were obtained from N-substituted iodo- and bromoacetamide precursors. Synthetic and mechanistic aspects of the regiospecific cyclization are discussed.     

Synthesis of novel 1,7-annulated 4,6-dimethoxyindoles

A range of new 1,7-annulated indole derivatives has been prepared via a ring-closing metathesis approach starting from N-allyl-7-formyl indoles.     

p-TsOH promoted Fischer indole synthesis of multi-substituted 2-trifluoromethyl indole derivatives

A p-TsOH promoted one-pot synthesis of multi-substituted 2-trifluoromethyl indole derivatives, for instance, 2-trifluoromethyl-3-phenylindoles, 2-trifluoromethyl-indole-3-propanoates, and 2-trifluoromethyl-indole-3-butanoates from reactions of 1,1,1-trifluoro-3-phenylacetone and simply prepared ω-trifluoromethyl substituted δ and ?-ketoesters with arylhydrazines via Fischer indole synthesis has been developed.     

Synthesis of new fluorescent building blocks via the microwave-assisted annulation reaction of 1,1,2-trimethyl-1H-benzo[e]indole with acrylic acid and its derivatives

The reaction of 1,1,2-trimethyl-1H-benzo[e]indole with acrylic acid and its derivatives was employed for the preparation of novel fluorescent building blocks. Treatment of 1,1,2-trimethyl-1H-benzo[e]indole with acrylic acid, acrylamide or tert-butyl acrylate in an autoclave or a microwave reactor at 180–200 °C afforded benzo[e]pyrido[1,2-a]indole derivatives. Various chemical transformations of the latter compounds have been performed to yield functionalized benzo[e]indole scaffolds. The structure assignments were based on data from ¹H and ¹³C NMR spectroscopy and single crystal X-ray analyses. The optical properties of the obtained benzo[e]indoline derivatives were studied by UV–vis and fluorescence spectroscopy.     

Studies on the biological activity of gem-difluorinated 3,3-spirocyclic indole derivatives

The biological activities of a series of 3,3-spirocyclic indole derivatives containing CF₂, phosphine oxide,indole, and cyano functional groups were evaluated, and these derivatives were found to exhibit antiTMV, fungicidal, and insecticidal activities.     

Synthesis of new series of iboga analogues

Synthesis of new iboga-analogues, replacing the indole ring with a benzofuran moiety has been described. Starting materials are the suitably substituted benzofuran derivatives and have been synthesized by Pd-catalyzed reactions. The conversion of endo-6-methylcarboxylate substituted dehydroisoquinuclidine to exo-isomer, a key component of iboga-alkaloids has been achieved in the presence of NaOMe in methanol under reflux conditions.     

Chromone-3-carboxaldehydes in Diels-Alder reactions with indole-o-quinodimethane. Synthesis of tetrahydrochromeno[2,3-b]carbazoles

An efficient route to a new class of indole derivatives, tetrahydrochromeno[2,3-b]carbazoles, has been developed. The cycloaddition reactions of chromone-3-carboxaldehydes with indole-o-quinodimethane gave a diastereomeric mixture of Diels-Alder cycloadducts in good yields after in situ deformylation.     

Simple route to 3-(2-indolyl)-1-propanones via a furan recyclization reaction

A simple route to 1-R-3-(2-indolyl)-1-propanones has been elaborated based on recyclization of 2-(2-aminobenzyl)furan derivatives. Being a modification of the Reissert indole synthesis, our approach employs the furan ring as a source of carbonyl function. This approach is general and allows varying of substituents in aromatic ring as well as in 3-position of indole nucleus.     

An efficient regioselective reaction of indole with 2H-chromenes for the synthesis of new 4H-chromenes in environmentally benign media

An efficient regioselective, catalyst free, and green protocol has been developed for the synthesis of a novel class of 4H-chromene scaffolds at room temperature in ionic liquid. The method is general and applicable for a series of 2H-chromenes as well as indole derivatives.     

Visible-light-irradiated tandem sulfonylation/cyclization of indole tethered alkenes for the synthesis of tetrahydrocarbazoles

A visible-light-mediated reaction of indole derivatives employing arylsulfonyl chlorides as sulfonyl surrogates has been developed, which proceeds via the sequence of reduction of sulfonyl chloride, sulfonylation, and intramolecular cyclization. This mild protocol transforms a diverse array of indole tethered alkenes and simple sulfonyl chlorides into highly valuable functionalized tetrahydrocarbazoles in good yields. This reaction is also suitable for gram-scale synthesis, which provides an efficient and green access to multi-substituted tetrahydrocarbazoles.     

Fluorinated N-[2-(haloalkyl)phenyl]imidoyl chloride, a key intermediate for the synthesis of 2-fluoroalkyl substituted indole derivatives via Grignard cyclization process

Fluorinated N-[2-(haloalkyl)phenyl]imidoyl chloride, which was readily available from the corresponding anilines by using Uneyama's one-pot synthesis of fluorinated imidoyl chloride, was found to be a key intermediate for the facile synthesis of 2-fluoroalkyl substituted indole derivatives via the Grignard cyclization process. The bromination of 3-methyl group of 3-methyl-2-trifluoromethyl indole with NBS/CCl₄ led to the formation of 3-bromomethyl substituted indole which can be further utilized to synthesize some new and biologically interested indole derivatives.     

Prenylated indole alkaloids and chromone derivatives from the fungus Penicillium sp. SCSIO041218

Four new prenylated indole alkaloids (1–4), and four new chromone derivatives (7–10), together with six known compounds (5, 6, and 11–14), have been isolated from the mangrove sediment derived fungus Penicillium sp. SCSIO041218, cultured in the 1% NaCl PDB substrate. The structures of new compounds were determined by analysis of the NMR and MS spectroscopic data. The absolute configuration of the prenylated indole alkaloids were elucidated based on the comparison of ECDs with known analogues. The absolute configurations of the chromone derivatives were determined by time-dependent density functional theory calculations of the ECD spectra. In all of these isolated compounds, penixanthones A and B (12 and 13) exhibited antiallergic activities in vitro.     

The configuration of esters of β-(indol-3- yl)-α-nitroacrylic acid

It has been shown by PMR spectroscopy that for the methyl and benzyl esters of β-(indol-3-yl)-α-nitroacrylic acid and their N-acetylated derivatives the isomers with the cis arrangement of the nitro group and the indole nucleus are the more stable.     

H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript>-catalyzed one-pot synthesis of <Emphasis Type="Italic">bis</Emphasis>(indole) derivatives under silent and ultrasonic irradiation conditions in aqueous media

A convenient and direct approach has been developed for the preparation of bis(indole) derivatives by one-pot four-component condensing of indole, aldehydes and active methylene compounds in the presence of 12-tungstophosphoric acid in aqueous media under silent and ultrasound methods. The remarkable advantages are the simplicity of the experimental procedures, short reaction times and high yields with the green aspects by avoiding toxic catalysts and solvents.     

Diversified Synthetic Strategies for Pyrroloindoles: An Overview

In current scenario, heterocyclic compounds' role in medicinal chemistry has been tremendously increased as they possess wide number of pharmacological activities. One of the common heterocycles include indole skeleton with well‐established biological significance in field of medicinal chemistry. Fusion of indole nucleus with pyrrole heterocycle constitutes pyrroloindole scaffold, which further modifies the existing properties of indole alone. Pyrroloindole is a privileged scaffold found in various types of bioactive entities including natural compounds and exhibits wide variety of pharmacological activities like muscle relaxant, antifungal, antitumor, and antibiotic. Therefore, it is considered as attractive template for drug discovery. From several years, numbers of synthetic strategies have been reported for the synthesis of pyrroloindole and its derivatives, including also natural compounds such as amauromine, yuremamine, and chimonanthines. Here, in this review, we have tried to compile various synthetic strategies of pyrroloindole and its derivatives.     

New synthesis of condensed hydropyridazine derivatives. VI

The reactivity of some indole derivatives towards the semicarbazone of ω-bromoacetophenone has been reported. Substituents at position 1 and 2 of the indole ring greatly affect the course of the reaction. 1,4,4a,9a-Tetrahydro-9H-pyridazino[3,4-b]indole derivatives or 3-indolyl derivatives were obtained depending on the substituents. The structures were assigned on the basis of satisfactory analytical and spectroscopic data.     

Intramolecular Pd-catalyzed C–H functionalization: construction of fused tetracyclic bis-indole alkaloid analogues

An efficient Pd-catalyzed intramolecular indole-C2-arylation protocol for the synthesis of pharmaceutically active bis-indole alkaloid analogues from simple and readily available and 3,3′-Bis(1H-indol-3-yl)methanes derivatives has been developed. The corresponding products could be obtained in moderate to excellent yields, which permits selective modification on either one of the two indole moieties independently.