Total synthesis of (+/-)-murrayazoline

Asymmetric Total Synthesis of (+)-Verrubenzospirolactone and (+)-Capillobenzopyranol

The first asymmetric total synthesis of (+)-verrubenzospirolactone (1), a distinctive highly fused benzosesquiterpenoid, characterized by a pentacyclic skeletal structure, is realized through a concise 10-step synthetic pathway with an impressive 22.8% overall yield. Notable highlights of this synthetic endeavor include (i) the introduction of a Ru-catalyzed ortho C-H activation step, (ii) the application of Pd-catalyzed asymmetric allylic alkylation to establish a pivotal stereocenter at C-3 with an excellent enantiomeric excess, (iii) B-alkyl Suzuki-Miyaura coupling to construct a Diels-Alder precursor, and, ultimately, (iv) the successful deployment of an intramolecular Diels-Alder reaction to complete the synthesis of (+)-verrubenzospirolactone without erosion of the enantiomeric excess.

Mini-review on the novel synthesis and potential applications of carbazole and its derivatives

Microporous organic polymers (MOPs) are a new type of porous materials, which have advantages of synthetic diversity, chemical and physical stability, microporous size controllability, etc. MOPs indicate broad applications in various fields such as heterogeneous catalysis, gas adsorption, separation, and storage. In recent years, MOPs have attracted an enormous attention in greenhouse gas capture due to their great potential in physisorptive gas storage. Carbazole and its derivatives have been studied extensively as Metal-Organic Polyhedra (MOPs) building blocks due to their unique structural features and versatile functionalization possibilities. This paper systematically reviews the synthesis, characterization and application of carbazole-based polymers, and relationship of structures and properties of these polymers. The application of the polymers in carbon dioxide (CO₂) capture field is analysed taking advantage of their adjustable microporous structure and electron rich properties. This review also provides novel insights regarding functional polymer materials that have high ability of greenhouse gas capture and absorbing selectivity will be obtained by reasonable molecular design and efficient synthesis.

Recent synthetic strategies for the construction of functionalized carbazoles and their heterocyclic motifs enabled by Lewis acids

This article demonstrates recent innovative cascade annulation methods for preparing functionalized carbazoles and their related polyaromatic heterocyclic compounds enabled by Lewis acid catalysts. Highly substituted carbazole scaffolds were synthesized via Lewis acid mediated Friedel-Crafts arylation, electrocyclization, intramolecular cyclization, cycloaddition, C-N bond-formations, aromatization and cascade domino reactions, metal-catalyzed, iodine catalyzed reactions and multi-component reactions. This review article mainly focuses on Lewis acid-mediated recent synthetic methods to access a variety of electron-rich and electron-poor functional groups substituted carbazole frameworks in one-pot reactions. Polyaromatic carbazole and their related nitrogen-based heterocyclic compounds were found in several synthetic applications in pharma industries, energy devices, and materials sciences. Moreover, the review paper briefly summarised new synthetic strategies of carbazole preparation approaches will assist academic and pharma industries in identifying innovative protocols for producing poly-functionalized carbazoles and related highly complex heterocyclic compounds and discovering active pharmaceutical drugs or carbazole-based alkaloids and natural products.

Palladium(0)-catalyzed aryne annulation: a powerful strategy for the synthesis of thio-bridged compounds

A method for the construction of various thio-bridged compounds is developed using readily available o-(trimethylsilyl)aryl triflates as a source of aryne precursor, catalyzed by simple Pd(dba)₂/dppe complex. This operationally simple and modular protocol allows thio-bridged compound via C(sp²)-C(sp²) and C(sp²)-C(sp³) bond formation in promising yields with a broad substrate scope. The key part is in situ generation of an aryne from o-(trimethylsilyl)aryl triflates and their subsequent intermolecular annulation.

Phosphine-Mediated Sequential [2+4]/[2+3] Annulation to Construct Pyrroloquinolines

A domino [2+4]/[2+3] sequential annulation reaction of MBH carbonates with N-unprotected indoles has been developed to provide various pyrroloquinoline derivatives in ≤94% yield and 20:1 dr. The reaction could be either mediated by stoichiometric PCy₃ or catalyzed by R₃PO via P^III/P^V═O redox cycling in the presence of phenylsilane. This method assembles polycyclic 1,7-fused indoles in one step diastereoselectively.

Palladium-catalyzed synthesis and nucleotide pyrophosphatase inhibition of benzo[4,5]furo[3,2-b]indoles

A two-step palladium-catalyzed procedure based on Suzuki–Miyaura cross coupling, followed by a double Buchwald–Hartwig reaction, allows for the synthesis of pharmaceutically relevant benzo[4,5]furo[3,2-b]indoles in moderate to very good yield. The synthesized compounds have been analyzed with regard to their inhibitory activity (IC₅₀) of nucleotide pyrophosphatases h-NPP1 and h-NPP3. The activity lies in the nanomolar range. The results were rationalized based on docking studies.

New Triphenylamine-Based Oligomeric Schiff Bases Containing Tetraphenylsilane Moieties in the Backbone

Three new triphenylamine-based oligomeric Schiff bases (polySB1, polySB2 and polySB3) containing tetraphenylsilane core (TPS-core) in the main chain were obtained from TPS-core-based diamines and bis(4-formylphenyl)phenylamine by a high-temperature polycondensation reaction. These new oligomers were structurally characterized by FT-IR, NMR and elemental analysis. All polySBs were highly soluble in common organic solvents, such as chloroform, tetrahydrofuran and chlorobenzene. Samples showed moderate molecular average molecular weight (Mw) and a high thermal stability above 410 °C. Likewise, polySBs showed absorption near 400 nm in the UV-vis range and photoluminescence. The HOMO levels and band-gap values were found in the ranges of -6.06 to -6.18 eV and 2.65⁻2.72 eV, respectively. The lowest band-gap value was observed for polySB2, which could be attributed to a more effective π-conjugation across the main chain. The results suggest that silicon-containing polySBs are promising wide-band-gap semiconductors materials for optoelectronic applications.

Mixed er-NHC/phosphine Pd(ii) complexes and their catalytic activity in the Buchwald–Hartwig reaction under solvent-free conditions

A single catalyst for solvent-free Buchwald–Hartwig amination with both primary and secondary amines.

Applications of Friedel-Crafts reactions in total synthesis of natural products

Over the years, Friedel-Crafts (FC) reactions have been acknowledged as the most useful and powerful synthetic tools for the construction of a special kind of carbon-carbon bond involving an aromatic moiety. Its stoichiometric and, more recently, its catalytic procedures have extensively been studied. This reaction in recent years has frequently been used as a key step (steps) in the total synthesis of natural products and targeted complex bioactive molecules. In this review, we try to underscore the applications of intermolecular and intramolecular FC reactions in the total syntheses of natural products and complex molecules, exhibiting diverse biological properties.

Synthesis of furo[3,2-b:4,5-b']diindoles and their optical and electrochemical properties

An efficient two-step palladium catalyzed synthesis of furo[3,2-b:4,5-b']diindoles, a hitherto unknown symmetrical heterocyclic core structure, was developed. The synthesis is based on a regioselective Suzuki-Miyaura cross coupling reaction of tetrabromofuran and subsequent double N-arylation. Selected compounds were studied with regard to their optical and electrochemical properties. The compounds show fluorescence with high quantum yields and non-reversible oxidation events. The compounds possess similar HOMO-LUMO band gaps compared to their sulfur and nitrogen analogs. Variation of the substituents hardly affects the HOMO-LUMO gap, but allows for some fine-tuning of the electron affinity and ionization potential as well as quantum yields. The compounds prepared represent interesting candidates for the development of organic electronic materials.

Rhodium-catalyzed intramolecular cascade sequence for the formation of fused carbazole-annulated medium-sized rings by cleavage of C(sp2)-H/C(sp3)-H bonds

The rhodium(iii)-catalyzed intramolecular annulation of alkyne-tethered 3-(indol-3-yl)-3-oxopropanenitriles for the synthesis of fused carbazole scaffolds via C-H activation has been developed. A series of six-, seven-, and eight-membered hydroazepino[3,2,1-jk]carbazoles were achieved. This reaction proceeded under mild reaction conditions and with a broad substrate scope. The reaction involved sequential cleavage of C(sp2)-H/C(sp3)-H bonds and annulation with the tethered alkyne.

Rh(III)-Catalyzed C-H Activation/Intramolecular Cyclization: Access to N-Acyl-2,3-dihydro-1H-carbazol-4(9H)-ones from Cyclic 2-Diazo-1,3-diketones and N-Arylamides

A Rh(III)-catalyzed C-H activation/cyclization cascade reaction is described. The reaction involves cyclic 2-diazo-1,3-diketones and N-arylamides, and it proceeds via an intermolecular C-C bond formation and subsequent intramolecular C-N bond formation. A variety of N-acyl-2,3-dihydro-1H-carbazol-4(9H)-ones were obtained under mild conditions in good to excellent yields (65-90%). Key features of this strategy include high-efficiency, operational simplicity, scalability, and broad functional-group tolerance. In addition, H2O and N2 are the only byproducts. Carbazole derivatives with free NH groups can be easily obtained through N-deprotection reactions.

Applications of Palladium-Catalyzed C-N Cross-Coupling Reactions

Pd-catalyzed cross-coupling reactions that form C–N bonds have become useful methods to synthesize anilines and aniline derivatives, an important class of compounds throughout chemical research. A key factor in the widespread adoption of these methods has been the continued development of reliable and versatile catalysts that function under operationally simple, user-friendly conditions. This review provides an overview of Pd-catalyzed N-arylation reactions found in both basic and applied chemical research from 2008 to the present. Selected examples of C–N cross-coupling reactions between nine classes of nitrogen-based coupling partners and (pseudo)aryl halides are described for the synthesis of heterocycles, medicinally relevant compounds, natural products, organic materials, and catalysts.

Naturally Occurring Carbazole Alkaloids from Murraya koenigii as Potential Antidiabetic Agents

This study identified koenidine (4) as a metabolically stable antidiabetic compound, when evaluated in a rodent type 2 model (leptin receptor-deficient db/db mice), and showed a considerable reduction in the postprandial blood glucose profile with an improvement in insulin sensitivity. Biological studies were directed from the preliminary in vitro evaluation of the effects of isolated carbazole alkaloids (1-6) on glucose uptake and GLUT4 translocation in L6-GLUT4myc myotubes, followed by an investigation of their activity (2-5) in streptozotocin-induced diabetic rats. The effect of koenidine (4) on GLUT4 translocation was mediated by the AKT-dependent signaling pathway in L6-GLUT4myc myotubes. Moreover, in vivo pharmacokinetic studies of compounds 2 and 4 clearly showed that compound 4 was 2.7 times more bioavailable than compound 2, resulting in a superior in vivo efficacy. Therefore, these studies suggested that koenidine (4) may serve as a promising lead natural scaffold for managing insulin resistance and diabetes.

Tissue-based metabolic labeling of polysialic acids in living primary hippocampal neurons

The posttranslational modification of neural cell-adhesion molecule (NCAM) with polysialic acid (PSA) and the spatiotemporal distribution of PSA-NCAM play an important role in the neuronal development. In this work, we developed a tissue-based strategy for metabolically incorporating an unnatural monosaccharide, peracetylated N-azidoacetyl-D-mannosamine, in the sialic acid biochemical pathway to present N-azidoacetyl sialic acid to PSA-NCAM. Although significant neurotoxicity was observed in the conventional metabolic labeling that used the dissociated neuron cells, neurotoxicity disappeared in this modified strategy, allowing for investigation of the temporal and spatial distributions of PSA in the primary hippocampal neurons. PSA-NCAM was synthesized and recycled continuously during neuronal development, and the two-color labeling showed that newly synthesized PSA-NCAMs were transported and inserted mainly to the growing neurites and not significantly to the cell body. This report suggests a reliable and cytocompatible method for in vitro analysis of glycans complementary to the conventional cell-based metabolic labeling for chemical glycobiology.

A greener approach towards double heteroarylation of N, O and S nucleophiles: synthesis of bioactive polynuclear fused N-heteroarenes

We report first general and common strategy for double heteroarylation of N, O and S nucleophiles leading to polynuclear N-heteroarenes.

Carbazole incorporated ratiometric chemosensor for Zn2+

An electron donating carbazole incorporated thiazole (3) based Zn(2+) selective intrinsic chemosensor has been synthesized and investigated. It was found that electron donating substituents such as methyl and carbazole on chemosensor (1) produce remarkable red shift in emission upon complexation with Zn(2+). The sensor shows a selective fluorescence response with Zn(2+) over biologically relevant cations (Ca(2+), Mg(2+), Na(+), and K(+)) and biologically non-relevant cations (Cd(2+), In(3+) and Ga(3+)) in an aqueous ethanol system. It also produce an enhancement in the quantum yield and a longer emission wavelength shift on Zn(2+) binding with the potential of a ratiometric assay.

Diastereoselective intramolecular carbamoylketene/alkene [2 + 2] cycloaddition: enantioselective access to pyrrolidinoindoline alkaloids

A novel and highly diastereoselective intramolecular carbamoylketene/alkene [2 + 2] cycloaddition has been developed, and the methodology was successfully applied to the enantioselective syntheses of (-)-esermethole and Takayama's intermediate for (+)-psychotrimine.

Double N-arylation reaction of polyhalogenated 4,4'-bipyridines. Expedious synthesis of functionalized 2,7-diazacarbazoles

Unusual 2,7-diazacarbazoles were prepared in one step from readily available tetra-halogenated 4,4'-bipyridines by using a double N-arylation reaction in the presence of the Pd-XPhos catalyst system. Moderate to good yields were obtained in this site-selective Buchwald-Hartwig double amination. The functionalization of these tricyclic derivatives was performed by using Pd-catalyzed cross-coupling reactions such as the Stille and Suzuki couplings. Two compounds were analyzed by X-ray diffraction and show π-π stacking involving the diazacarbazole moieties and the phenyl rings of functionalized groups.

Palladium- and copper-mediated N-aryl bond formation reactions for the synthesis of biological active compounds

N-Arylated aliphatic and aromatic amines are important substituents in many biologically active compounds. In the last few years, transition-metal-mediated N-aryl bond formation has become a standard procedure for the introduction of amines into aromatic systems. While N-arylation of simple aromatic halides by simple amines works with many of the described methods in high yield, the reactions may require detailed optimization if applied to the synthesis of complex molecules with additional functional groups, such as natural products or drugs. We discuss and compare in this review the three main N-arylation methods in their application to the synthesis of biologically active compounds: Palladium-catalysed Buchwald-Hartwig-type reactions, copper-mediated Ullmann-type and Chan-Lam-type N-arylation reactions. The discussed examples show that palladium-catalysed reactions are favoured for large-scale applications and tolerate sterically demanding substituents on the coupling partners better than Chan-Lam reactions. Chan-Lam N-arylations are particularly mild and do not require additional ligands, which facilitates the work-up. However, reaction times can be very long. Ullmann- and Buchwald-Hartwig-type methods have been used in intramolecular reactions, giving access to complex ring structures. All three N-arylation methods have specific advantages and disadvantages that should be considered when selecting the reaction conditions for a desired C-N bond formation in the course of a total synthesis or drug synthesis.

One-pot synthesis of new substituted 1,2,3,4-tetrahydrocarbazoles via Petasis reaction

The one-pot synthesis of a new substituted 1,2,3,4-tetrahydrocarbazoles has been described via Petasis reactions. These tetrahydrocarbazoles exhibits various medicinal importance and might be suitable for elaboration into larger peptides at carboxy termini. The scope and limitations of this method have been examined.