Gold(III) chloride catalyzed regioselective synthesis of pyrano[3,4-b]indol-1(9H)-ones and evaluation of anticancer potential towards human cervix adenocarcinoma

Base-Catalyzed Cascade Cyclization of 2-Nitrochalcones and Isocyanides to Access Pyrano[3,4-b]indol-1(9H)-one Frameworks

An unexpected cascade reaction of 2-nitrochalcones with isocyanoacetates has been reported for the efficient synthesis of indole carboxylic esters and pyranoindoles. The conversion was achieved by KOH-catalyzed cyclization and elimination of the nitro group with final decarbonylation-aromatization. The method was used to synthesize a series of potentially biologically active indole derivatives (49 examples) in 67-85% yields under transition-metal-free catalytic conditions.

Efficient Synthesis of 1H-Benzo[4,5]imidazo[1,2-c][1,3]oxazin-1-one Derivatives Using Ag2CO3/TFA-Catalyzed 6-endo-dig Cyclization: Reaction Scope and Mechanistic Study

A small library of 1H-benzo[4,5]imidazo[1,2-c][1,3]oxazin-1-one derivatives was prepared in good to excellent yields, involving a Ag₂CO₃/TFA-catalyzed intramolecular oxacyclization of N-Boc-2-alkynylbenzimidazole substrates. In all experiments, the 6-endo-dig cyclization was exclusively achieved since the possible 5-exo-dig heterocycle was not observed, indicating the high regioselectivity of this process. The scope and limitations of the silver catalyzed 6-endo-dig cyclization of N-Boc-2-alkynylbenzimidazoles as substrates, bearing various substituents, were investigated. While ZnCl₂ has shown limits for alkynes with an aromatic substituent, Ag₂CO₃/TFA demonstrated its effectiveness and compatibility regardless of the nature of the starting alkyne (aliphatic, aromatic or heteroaromatic), providing a practical regioselective access to structurally diverse 1H-benzo[4,5]imidazo[1,2-c][1,3]oxazin-1-ones in good yields. Moreover, the rationalization of oxacyclization selectivity in favor of 6-endo-dig over 5-exo-dig was explained by a complementary computational study.

3,6-Dihydro-5H-pyrazolo [4′,3′:5,6]pyrano[3,4-b]indol-5-one

Pyrano [3,4-b]indol-1(9H)-ones and indolo [2,3-c]coumarins are important classes of heterocyclic compounds with versatile biological activities. Herein, we describe a straightforward and scalable synthesis of 3,6-dihydro-5H-pyrazolo [4′,3′:5,6]pyrano [3,4-b]indol-5-one, a pyrazolo-fused pyrano [3,4-b]indolone, via a three step approach including Fischer-indole synthesis and intramolecular esterification. The compound is fully characterized by means of 1H and 13C NMR spectra, using direct and long-range heteronuclear correlation experiments (HMBC and HMQC).

Efficient One-pot Synthesis of 3,3-di(indolyl)indolin-2-ones from Isatin and Indole Catalyzed by VOSO4 as Non-Sulfonamide Carbonic Anhydrase Inhibitors

Background A high yielding green protocol has been developed and delineated for the synthesis of 3,3-di(indolyl)indolin-2-ones, potentially bioactive compounds, involving one pot aqueous medium condensation of isatin with indole in the presence of VOSO4. The synthesized compounds were screened for their carbonic anhydrase inhibitory activity against human (h) isoforms hCA I, hCA II, hCA IX and hCA XII. These non-sulfonamide derivatives selectively inhibited hCA II in the micromolar range. Objective To develop a high yielding green protocol to synthesize 3,3-diindolyl oxindole derivatives using water as solvent media and screening of the synthesized molecules for their carbonic anhydrase inhibitory activity. Methods The target compound is obtained by taking isatin, indole, VOSO4and H2O in one-pot at 70 oC. Results The designed molecules were synthesized by using the new method. The molecules were screened for their CA inhibitory activity which shows selective inhibition toward hCA II.The result shown an excellent yield without any loss or decrease in catalytic activity, hence proved the performance and recyclability of the catalyst. Conclusion An efficient, simple and green protocol was established that provides a facile and straightforward approach for the preparation of 3,3-diindolyl oxindole derivatives (3a-r) from Isatin and Indole by using 10 mol % VOSO4 in high yields in a short period of time by a one-pot coupling reaction. Furthermore, the catalyst can also be recovered and reused for three consecutive catalytic cycle without any loss of its efficiency which was confirmed by performing the experiment with 3a. The newly synthesized molecules (3a-r) were screened for their carbonic anhydrase inhibition potency against four isoforms, hCA I, II, IX and XII and most of the compounds were found potent against hCA II with potency low to submicromolar range.

Functionalized Bipyrroles and Pyrrolyl-Aminopyrones from Acylethynylpyrroles and Diethyl Aminomalonate

An efficient method for the synthesis of 1H,1′H-2,3′-bi­pyrroles (up to 72% yield) by the cyclocondensation of easily available 2-(acylethynyl)pyrroles with diethyl aminomalonate hydrochloride has been developed. The reaction proceeds under reflux in MeCN (6 h) in the presence of Cs2CO3. Under the same conditions, 2-(acylethynyl)pyrroles with bulky (benzyl and octyl) substituents at nitrogen atom react with diethyl aminomalonate to afford 1H,2′H-2,3′-bipyrroles and pyrrolyl-aminopyrones.

Emergence of 2-Pyrone and Its Derivatives, from Synthesis to Biological Perspective: An Overview and Current Status

Pyrone moieties are present in natural products and can be synthesized by a diverse range of synthetic methods, resulting in the formation of various derivatives through chemical modifications. Many pyrone-based derivatives are commercially available and are biocompatible. They are building blocks of various intermediates in organic synthesis. They possess remarkable biological properties including antimicrobial, antiviral, cytotoxic, and antitumor activity. These characteristics have made them valuable for the development of drugs. We have summarized recent developments in the synthesis of 2-pyrone and its derivatives and their potential applications. With regard to synthetic approaches, the focus has been on metal-free and transition metal-catalyzed reactions.

Cycloisomerization of π-Coupled Heteroatom Nucleophiles by Gold Catalysis: En Route to Regiochemically Defined Heterocycles

Since the dawn of millennium, catalytic gold chemistry is at the forefront to set off diverse organic reactions via unique activation of π-bonded molecules. Within this purview, cycloisomerization of heteroatom nucleophiles linked to a π-system is one of the well recognized chemistry for the construction of numerous heterocyclic cores. Though the rudimentary aspects of this transformation are reviewed by several groups in different timeline, a holistic view on regiochemistry of such reactions went largely overlooked. Hence, this account emphasizes the gold catalyzed regioselective cycloisomerization of structurally distinctive π-connected hetero-nucleophiles leading to different heterocycles documented in the last two decades. From an application perspective, this account also highlights those methodologies which find a role in the total synthesis of natural products. Wherever appropriate, mechanistic details and contributing factors for selectivity are also discussed.

Alkynoates as Versatile and Powerful Chemical Tools for the Rapid Assembly of Diverse Heterocycles under Transition-Metal Catalysis: Recent Developments and Challenges

Heterocycles, heteroaromatics and spirocyclic entities are ubiquitous components of a wide plethora of synthetic drugs, biologically active natural products, marketed pharmaceuticals and agrochemical targets. Recognizing their high proportion in drugs and rich pharmacological potential, these invaluable structural motifs have garnered significant interest, thus enabling the development of efficient catalytic methodologies providing access to architecturally complex and diverse molecules with high atom-economy and low cost. These chemical processes not only allow the formation of diverse heterocycles but also utilize a range of flexible and easily accessible building units in a single operation to discover diversity-oriented synthetic approaches. Alkynoates are significantly important, diverse and powerful building blocks in organic chemistry due to their unique and inherent properties such as the electronic bias on carbon-carbon triple bonds posed by electron-withdrawing groups or the metallic coordination site provided by carbonyl groups. The present review highlights the comprehensive picture of the utility of alkynoates (2007-2019) for the synthesis of various heterocycles (> 50 types) using transition-metal catalysts (Ru, Rh, Pd, Ir, Ag, Au, Pt, Cu, Mn, Fe) in various forms. The valuable function of versatile alkynoates (bearing multifunctional groups) as simple and useful starting materials is explored, thus cyclizing with an array of coupling partners to deliver a broad range of oxygen-, nitrogen-, sulfur-containing heterocycles alongside fused-, and spiro-heterocyclic compounds. In addition, these examples will also focus the scope and reaction limitations, as well as mechanistic investigations into the synthesis of these heterocycles. The biological significance will also be discussed, citing relevant examples of drug molecules highlighting each class of heterocycles. This review summarizes the recent developments in the synthetic methods for the synthesis of various heterocycles using alkynoates as readily available starting materials under transition-metal catalysis.

Gold-Catalyzed Addition of Carboxylic Acids to Alkynes and Allenes: Valuable Tools for Organic Synthesis

In this contribution, the application of gold-based catalysts in the hydrofunctionalization reactions of alkynes and allenes with carboxylic acids is comprehensively reviewed. Both intra- and intermolecular processes, leading respectively to lactones and linear unsaturated esters, are covered. In addition, cascade transformations involving the initial cycloisomerization of an alkynoic acid are also discussed.

Synthesis of Highly Functionalized 2-Pyranone from Silyl Ketene

We report a highly functionalized 2-pyranone small molecule prepared from tert-butyl diphenyl silyl ketene using an alkoxide catalyst and thermally induced rearrangement. Treatment of the silyl ketene with a substoichiometric amount of alkoxide led to the formation of a trimer which was isolated and fully characterized; heating this trimer in a 1,4-dioxane solution induced a thermal rearrangement, yielding the product 2-pyranone. The isolated intermediate and product are characterized by 1D and 2D nuclear magnetic resonance (NMR) spectroscopies, mass spectrometry, and single crystal X-ray diffraction. A mechanism for the thermally induced rearrangement is proposed based on ¹H NMR studies, and a rate law is derived from the proposed mechanism with steady-state approximation. This work illustrates a route for the formation of highly functionalized and modifiable 2-pyranone motifs with potential biological activity. The formation of the trimer, and thus the functionalized 2-pyranone, is highly dependent on the silyl substituents and alkoxide counterion and thus indicates the intriguing reactivity of highly functionalized small molecules.

New D–π-A push–pull chromophores as low band gap molecular semiconductors for organic small molecule solar cell applications

Low band gap molecular semiconductors based on push–pull systems with appropriate HOMO–LUMO energy levels for organic photovoltaic applications were accomplished.

MCM-41-Accelerated PWA Catalysis of Friedel-Crafts Reaction of Indoles and Isatins

Ordered mesoporous siliceous material has been identified as one of the key elements of the catalysis concept. Here we report an efficient Friedel-Crafts reaction of indoles with isatins catalyzed by PWA/MCM-41, which got the di(indolyl)indolin-2-ones derivatives with high yield. Moreover, the catalysts were characterized by XRD and SEM/EDS, the EDS spectrum indicated that the catalyst used in this reaction also contains tungsten, and the proposed mechanism for the synthesis of 3,3-di(indolyl)indolin-2-ones was also discussed. Finally, the catalyst can be reused repeatedly for several times without obvious loss of activity.

One-Pot Consecutive Sulfonamidation/ipso-Cyclization Strategy for the Construction of Azaspirocyclohexadienones

Harnessing of Morita-Baylis-Hillman (MBH) carbonates of acetylenic aldehydes as handy synthons has allowed a facile synthesis of azaspirocyclohexadienones by sequential DABCO-promoted sulfonamidation/ICl-mediated ipso-iodocyclization reactions. A variety of MBH-carbonates having aryl or heteroaryl groups on the alkyne functionality fruitfully participated in the one-pot ipso-annulation reaction to provide the corresponding 3-iodo spirocyclohexadienones. The sulphonamide functionality was further utilized to construct the tricyclic fused-sultam framework.

When Indolizine Meets Quinoline: Diversity-Oriented Synthesis of New Polyheterocycles and Their Optical Properties

Fluorescence-based technologies play a pivotal role in various biomedical applications. Here we report an efficient route to a new class of fluorophores, indolizino[3,2-c]quinolines, via the oxidative Pictet-Spengler cyclization strategy. The condensation of several 2-methylpyridines with 2-bromo-2'-nitroacetophenone allowed for the rapid assembly of indolizines with a 2-nitrophenyl group at the C2 position. The subsequent reduction of the nitro group under mild conditions followed by oxidative Pictet-Spengler cyclization with various aryl aldehydes in the presence of a catalytic amount of FeCl3 furnished the indolizino[3,2-c]quinolines in good overall yields. We also examined the photophysical properties of this new series of polyheterocyclic compounds. Several indolizino[3,2-c]quinolines were found to have unique and desirable optical properties, suggesting that these compounds may be suitable for use as prospective fluorescent probes in aqueous systems.

Recent advances in the synthesis of 2-pyrones

The present review summarizes the recent progresses in the synthesis of 2-pyrones and the application to the synthesis of marine natural products. Especially, much attention was placed on the transition metal catalyzed synthetic methodologies in this review.

Synthesis of 4-hydroxyindole fused isocoumarin derivatives and their fluorescence “Turn-off” sensing of Cu(ii) and Fe(iii) ions

A simple and efficient protocol has been developed for the synthesis of 4-hydroxyindole fused isocoumarins from easily available starting materials.

Cu(OTf)2 catalyzed three component strategy for the synthesis of thienopyridine containing spirooxindoles and their cytotoxic evaluation

Compound 5v docked in caspase-3 (−10.5 kcal mol⁻¹).

Selectivity, Compatibility, Downstream Functionalization, and Silver Effect in the Gold and Palladium Dual-Catalytic Synthesis of Lactones

The chemo- and regioselectivity and functional group compatibility in gold and palladium cooperatively catalyzed cross-coupling reactions were determined in the synthesis of lactones; the selectivity in the gold and palladium dual-metal catalysis system was distinct from that available for the same class of substrates in systems with only gold catalysis or only palladium catalysis rather than dual catalysis. The dual-catalytic rearrangement reaction selectively promoted oxidative addition at the C-O bond over the C-Br bond, providing a useful C-Br bond handle for downstream functionalization showcased via Suzuki-Miyaura and Sonogashira coupling reactions. Product classes were expanded from isocoumarins to three previously unpublished ring classes: pyrone, indolepyrone, and furopyrone.

Cu(II)-mediated ortho C-H alkynylation of (hetero)arenes with terminal alkynes

Cu(II)-promoted ortho alkynylation of arenes and heteroarenes with terminal alkynes has been developed to prepare aryl alkynes. A variety of arenes and terminal alkynes bearing different substituents are compatible with this reaction, thus providing an alternative disconnection to Sonogashira coupling.