Palladium(II)-Catalyzed Intramolecular Oxidative C–H/C–H Cross-Coupling Reaction of C3,N-Linked Biheterocycles: Rapid Access to Polycyclic Nitrogen Heterocycles

POCl3/Sulfoxide-Promoted Synthesis of Indolizino[8,7-b]indoles

A mild chlorocyclization of pyrrole-tethered indoles has been realized using POCl3 as the chlorine source and tetramethylene sulfoxide as the promoter. A variety of chlorinated indolizino[8,7-b]indole derivatives have been constructed efficiently under this reaction system in moderate to good yields (19 examples, up to 93% yield).

Synthesis of fused bis-indazoles/indazoles via a one-pot sequential strategy

We report here an efficient synthesis of fused bis-indazoles/indazoles via a one-pot sequential strategy starting from o-azido aldehydes and amines. This novel method involves the sequential formation of 2H-indazole followed by a Pd-catalyzed intramolecular cross-dehydrogenative coupling reaction. Overall, this one-pot sequential reaction involved the formation of new five bonds, resulting in the formation of three heterocyclic rings.

Phenotype Screening of an Azole-bisindole Chemical Library Identifies URB1483 as a New Antileishmanial Agent Devoid of Toxicity on Human Cells

We report the evaluation of a small library of azole-bisindoles for their antileishmanial potential, in terms of efficacy on Leishmania infantum promastigotes and intracellular amastigotes. Nine compounds showed good activity on L. infantum MHOM/TN/80/IPT1 promastigotes with IC₅₀ values ranging from 4 to 10 μM. These active compounds were also tested on human (THP-1, HEPG2, HaCaT, and human primary fibroblasts) and canine (DH82) cell lines. URB1483 was selected as the best compound, with no quantifiable cytotoxicity in mammalian cells, to test the efficacy on intracellular amastigotes. URB1483 significantly reduced the infection index of both human and canine macrophages with an effect comparable to the clinically used drug pentamidine. URB1483 emerges as a new anti-infective agent with remarkable antileishmanial activity and no cytotoxic effects on human and canine cells.

Synthesis of Azacarbolines via PhIO2-Promoted Intramolecular Oxidative Cyclization of α-Indolylhydrazones

An unprecedented synthesis of polysubstituted indole-fused pyridazines (azacarbolines) from α-indolylhydrazones under oxidative conditions using a combination of iodylbenzene (PhIO₂) and trifluoroacetic acid (TFA) has been developed. This transformation is conducted without the need for transition metals, harsh conditions, or an inert atmosphere.

Synthesis of N-Fused Triazole-Piperazine-Quinazolinones via One-Pot Tandem Click Reaction and Cross-Dehydrogenative Coupling

Herein, a one-pot protocol to synthesize tetracyclic triazole-piperazine-quinazolinone-fused N-heterocyclic scaffolds is reported. In this strategy, a tandem approach of two highly efficient synthetic reactions, click and cross-dehydrogentive coupling reactions, with high atom economy were employed to obtain the target N-fused scaffolds. Being highly functional group tolerable, this method has broad substrate scope. Interestingly, some of these derivatives showed strong white solid-state fluorescence.

Copper-catalyzed tandem annulation of 2-alkynoyl-2′-iodo-1,1′-biphenyls with isocyanoacetates: a rapid access to pyrrole-fused tetracyclic skeletons

A copper-catalyzed [3 + 2] cycloaddition/C–C coupling tandem process was developed based on the concept of trapping organocuprate intermediates.

Synthesis of Polycyclic Fused Indoline Scaffolds through a Substrate-Guided Reactivity Switch

Zn(II)-catalyzed divergent synthesis of functionalized polycyclic indolines through formal [3 + 2] and [4 + 2] cycloadditions of indoles with 1,2-diaza-1,3-dienes (DDs) is reported. The nature and type of substituents of substrates are found to act as a chemical switch to trigger two distinct reaction pathways and to obtain two different types of products upon the influence of the same catalyst. The mechanism of both [4 + 2] and [3 + 2] cycloadditions was investigated and fully rationalized by density functional theory (DFT) calculations.

Application of Palladium-Catalyzed Cross-Coupling Reactions in Organic Synthesis

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Palladium-catalyzed cross-coupling reactions have gained a continuously growing interest of synthetic organic chemists. The present review gives a brief account of applications of the palladium-catalyzed cross-coupling reactions in comprehensive synthesis, viz., the Heck, Stille, Suzuki–Miyaura, Negishi, Sonogashira, Buchwald–Hartwig, Ullmann and the Oxidative, decarboxylative cross-coupling reactions, with particular emphasis on the synthesis of heterocyclic compounds.

Pd-Catalyzed asymmetric [5 + 2] cycloaddition of vinylethylene carbonates and cyclic imines: access to N-fused 1,3-oxazepines

A facile route to access enantioenriched N-fused 1,3-oxazepines via Pd-catalyzed asymmetric [5 + 2] cycloaddition of vinylethylene carbonates and cyclic imines has been developed.

Synthesis of imidazopyridine-fused indoles via one-pot sequential Knoevenagel condensation and cross dehydrogenative coupling

A simple and efficient strategy for the synthesis of imidazopyridine-fused indoles has been developed that involves one-pot sequential Knoevenagel condensation of readily available active methylene azoles with N-substituted-1H-indole-3-carboxaldehydes or N-substituted-1H-indole-2-carboxaldehydes followed by palladium-catalyzed intramolecular cross dehydrogenative coupling reaction. A series of 36 derivatives was prepared by using this strategy. The products were obtained in moderate to excellent (32-94%) yields and showed broad substrate scope with tolerance of various functional groups and was amiable for gram scale preparation without problems.

Convenient construction of tetrahydrochromeno[4',3':2,3]indolizino[8,7-b]indoles and tetrahydroindolizino[8,7-b]indoles via one-pot domino reaction

The functionalized tetrahydrochromeno[4′,3′:2,3]indolizino[8,7-b]indoles were conveniently synthesized in high yields by one-pot domino reaction of tryptamines, alkyl propiolates and 2-aryl-3-nitro-2H-chromenes. Under similar conditions, the one-pot reaction of tryptamines, alkyl propiolates and β-nitroalkenes resulted in functionalized tetrahydroindolizino[8,7-b]indoles. The reaction mechanism involved sequential generation of β-enamino ester, Michael addition, Pictet–Spengler reaction and annulation process. The reaction showed high atomic economy and met the goals of sustainable chemistry.

The functionalized tetrahydrochromeno[4′,3′:2,3]indolizino[8,7-b]indoles were conveniently synthesized in high yields by one-pot domino reaction of tryptamines, alkyl propiolates and 2-aryl-3-nitro-2H-chromenes.

Palladium-catalyzed oxidative C–H/C–H cross-coupling of imidazopyridines with azoles

A palladium-catalyzed oxidative C–H/C–H cross-coupling of imidazopyridines with azoles using air as the oxidant has been developed.

Transition-metal-free oxidative intermolecular cyclization reaction: synthesis of 2-aryl-4-quinolones

Herein, a novel and efficient intermolecular cyclization of 2-aminoacetophenones with aldehydes was developed for the synthesis of 2-aryl-4-quinolones through C–C and C–N bond formation.