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2,5‐disubstituted N,N'‐alkylpiperazines represent an interesting target in organic synthesis both for pharmaceutical or agrochemical applications and as a promising class of ligands in coordination chemistry. We report here a microwave‐enhanced synthesis of these compounds starting from non‐activated N‐alkyl aziridines in the presence of catalytic amounts of simple ammonium metallates. A remarkable TOF of 2787.9 h−1 has been observed in the case of [TBA]2[ZnI4] as the catalyst (catalyst loading 0.1 mol %) and with an almost complete selectivity (up to 97 %) in favor of both diastereoisomers (meso and chiral form) of the target 2,5‐disubstituted piperazines, obtained in 1 : 1 ratio. The two isomers are easily separated, because the meso form precipitates in pure from the reaction crude. A stereochemical investigation and the unprecedented isolation of 2,6‐disubstituted N,N'‐alkylpiperazines allowed us to shed light on the reaction mechanism. [ABSTRACT FROM AUTHOR]

We present a method for the synthesis of substituted indolo[1,2‐a]quinoline‐5(6H)‐ones starting from 1‐(2‐ethynylphenyl)‐1H‐indoles. The transformation involves gold‐catalyzed oxidation of the triple bond followed by acid‐promoted intramolecular cyclization at the indole C2 position. Demonstrating noteworthy versatility, the reaction tolerates a wide array of substituents on the indole core and proceeds in good to excellent yields (up to 93 %). [ABSTRACT FROM AUTHOR]

A photoredox‐promoted approach for the synthesis of [1,4]diazepino[1,7‐a]indol‐6(7H)‐ones starting from N‐indolyl phenylacrylamides and aroyl chlorides as radical source is reported. This method, that involves a cascade radical addition on C−C double bond followed by intramolecular cyclization at indole C2‐position, affords two diastereomeric indole‐fused 1,4‐diazepinones characterized by a N−C(aryl) axial chirality in yields ranging from 51 to 99%. [ABSTRACT FROM AUTHOR]

We describe an alternative and more sustainable method for the synthesis of 2,2'‐disubstituted 3,3'‐biindoles starting from 2,2'‐diaminotolanes and (hetero)arylaldehydes. The key feature of the approach is the use of an acidic Deep Eutectic Solvent (DES) able to exploit a double activity, i. e. solvent and Brønsted Acid (BA) catalyst, avoiding the use of Volatile Organic Compounds (VOCs) as solvents and additional acid catalysts. By this way, we synthesized twenty‐five biindoles, including eighteen new compounds. The reactions run quickly under mild conditions by microwave heating at 70 °C, with yields ranging from good to very good. The reaction scope is rather broad. The medium demonstrated to be reusable at least five times with only a slight reduction in yields. Based on experimental evidence and previous literature findings, a plausible mechanism is proposed. [ABSTRACT FROM AUTHOR]

A redox umpolung strategy for the synthesis of complex tetrahydrocarbazoles is reported. The reaction involves a visible light promoted radical cation [4+2] cycloaddition between 2-vinylindoles and conjugated alkenes that proceeds with good yields and diastereoselectivity. [ABSTRACT FROM AUTHOR]

An enantioselective phosphine‐catalyzed [3+2] cycloaddition between aza‐aurones and allenoates is here described. The reaction proceeded under mild reaction conditions to afford 2‐spirocyclopentyl indolin‐3‐one derivatives as single γ‐isomer and with high levels of stereocontrol. [ABSTRACT FROM AUTHOR]

The development of alternative benign reaction conditions to perform multicomponent reactions is an interesting and desirable strategy to increase the sustainability of organic synthesis. In this paper, we report a new version of A3‐coupling MCR for the preparation of differently substituted propargylamines starting from aldehydes, alkynes and amines in an acidic DES as reaction media, under dielectric heating, and in the presence of a tetraaza‐macrocyclic silver complex as catalyst. The reaction scope is broad in terms of aldehyde partners. Electron‐rich phenylacetylenes are the more reactive alkynes partners, whereas the nature of the amine is the more serious limitation as only secondary cyclic amines are tolerated. [ABSTRACT FROM AUTHOR]

Research has been conducted on the 2-amino-3-hydroxynorbornene-2-carboxylic acid derivatives. The results of the enantioselective synthesis of these derivatives carried out via the Diels-Alder reaction between cyclopentadiene and various dienophiles are discussed.

The Cover Feature shows the synthesis of substituted indolo[1,2‐a]quinoline‐5(6H)‐ones starting from 1‐(2‐ethynylphenyl)‐1H‐indoles and N‐oxides by a gold‐catalyzed oxidation of the triple bond, followed by an acid‐promoted intramolecular cyclization at the indole C‐2 position. More information can be found in the Research Article by E. Brambilla, V. Pirovano and co‐workers (DOI: 10.1002/ejoc.202400083). Cover design by Dominica Del Grosso...By Elisa Brambilla; Mariaclara Gugiatti; Silvia Rizzato; Giorgio Abbiati and Valentina PirovanoReported by Author; Author; Author; Author; Author [Extracted from the article]

The reaction between epoxides and CO2 to yield cyclic carbonates is efficiently promoted under solvent‐free and relatively mild reaction conditions (0.5 mol % catalyst loading, 0.8 MPa, 125 °C) by zinc(II) complexes of pyridine containing macrocyclic ligands (Pc−L pyridinophanes). The zinc complexes have been fully characterized, including X‐ray structural determination. The [Zn(II)X(Pc−L)]X complexes showed good solubility in several polar solvents, including cyclic carbonates. The scope of the reaction under solvent‐free conditions has been studied and good to quantitative conversions with excellent selectivities have been obtained, starting from terminal epoxides. When solvent‐free conditions were not possible (solid epoxides or low solubility of the catalyst in the oxirane) the use of cyclic carbonates as solvents has been successfully investigated. The remarkable stability of the catalytic system has been demonstrated by a series of consecutive runs. [ABSTRACT FROM AUTHOR]

Spiroindolenines were employed as cyclic imine substrates in formal aza-Diels--Alder reactions with Danishefsky's diene or silyloxy-substituted electron-rich dienes for the synthesis of the corresponding tetrahydropyrido[1,2-α]spiroindolinones. The reactions occur under mild conditions in the presence of ytterbium triflate as Lewis acidic catalyst delivering the desired compounds in good yield. The reaction results in the preparation of a small library of a new class of conformational constrained heterocyclic derivatives that easily undergo selective and efficient manipulations. [ABSTRACT FROM AUTHOR]

In this paper, we describe a new silver catalysed domino approach to 6‐substituted benzoxazino isoquinolines starting from 2‐alkynylbenzaldehydes and 1‐substituted‐(2‐aminophenyl)methanols. The strategy is characterized by good reaction yields, and can be performed at room temperature as well as under heating (conventional or dielectric) in different reaction times. Best results have been obtained by using silver complexes of macrocyclic pyridine‐containing ligands (PcL) as catalysts. The stereoselectivity of the transformation has been investigated by using chiral reaction partners and chiral catalysts, but unfortunately, modest stereoselectivities have been achieved. On the other hand, this approach represents an alternative synthetic strategy for the preparation of 6‐substituted benzoxazino isoquinolines, which are the key scaffold of some compounds endowed of biological activity. [ABSTRACT FROM AUTHOR]

In this paper, we describe the synthesis of neglected 1‐aminoisochromene derivatives starting from 2‐alkynylbenzaldehydes and electron‐poor anilines. The domino reaction is catalyzed by original [AgIPcL] complexes and occurs with complete regioselectivity under mild conditions. The approach well‐tolerates different aryl, heteroaryl, alkyl and cycloalkyl substituents on alkyne terminus to give the desired products in modest to very good yields. [ABSTRACT FROM AUTHOR]

The reactivity of vinyl‐/furoindole derivatives with gold‐activated π‐systems is the subject of extensive investigation. In the presence of these electrophilic partners, the realized transformations allow for the construction of different and fascinating architectures via cycloaddition and cyclization reactions often included in cascade processes. The reactions realized involving in these processes an external substituent at the indole moiety are the subject of the present minireview. [ABSTRACT FROM AUTHOR]

A palladium-mediated multicomponent domino reaction leading to 2-aryl-4-amino-quinolines and 2-aryl-4-amino[1,8]naphthyridines is reported. The scope of the reaction was examined using carbon monoxide, two 2-ethynyl-arylamines, four aryl iodides, and 10 primary amines as substrates.

The synthesis of the pyrazinol[1,2-a]indole nucleus was achieved by intramolecular cyclization of several 2-carbonyl-1-propargylindoles in the presence of ammonia. It is indicated that cyclization of 1-alkynylindole-2-carbaldehydes was easily accomplished under standard heating conditions, whereas microwave heating contributed to reduced reaction times and improved overall yields.

Research has been conducted on indole 2-carboxamide derivatives. The authors report that these compounds can produce beta-carbolinones or pyrazino[1,2-a]indoles via palladium-catalyzed intramolecular cyclization reactions.

Research has been conducted on pyridines. The authors describe the synthesis of these compounds carried out from the reaction of dialkyl acyclic/cyclic ketones, aryl/heteroaryl ketones, methyl and aldehydes.

In this paper, we describe the use of p‐TSA based Deep Eutectic Solvents (DESs) as alternative environmental‐friendly "active" solvents for the microwave‐mediated synthesis of 6‐substituted 3,4‐fused 2‐pyranones, and in particular isocoumarins, starting from 2‐alkynyl‐(hetero)arylcarboxylates. When the alkyne terminus bears a neutral or an electron‐donating group (EDG), the reactions are fast, clean and highly regioselective, to give the 6‐endo‐dig cyclization products in good to excellent yields. For substrates bearing an electron‐withdrawing group (EWG) on the alkyne end, the regioselectivity can be tuned by adding a small amount of silver(I) triflate as co‐catalyst. DES was demonstrated to be reusable without loss of efficiency in terms of reaction yields. Based on experimental evidence and previous findings, two competitive mechanisms working simultaneously are proposed to explain the outcomes and the regioselectivity issues. An acidic Deep Eutectic Solvent is an alternative environmental‐friendly "active" media for the microwave‐mediated synthesis of 6‐substituted 3,4‐fused 2‐pyranones. [ABSTRACT FROM AUTHOR]

The review summarizes the most recent achievements in the chemistry of 2-vinylindoles and 3-vinylindoles. In particular, we focus on the behavior of these compounds as dienes in cycloaddition reactions. The majority of the literature in this field deals with [4+2] cycloaddition, and only one report of [4+1] cycloaddition has appeared in the literature until now. Thus, the main section reviews [4+2] cycloaddition with activated cyclic and acyclic dienophiles under Lewis-acid catalysis or organocatalysis conditions. In addition, cycloadditions performed with simple p-systems as dienophiles, occurring through activation by transition-metal catalysts, are reviewed. This section mainly involves the use of allenes as dienophiles under gold catalysis conditions. In both cases, the authors report excellent levels of diastereoselectivity and enantioselectivity. Two separate subsections deal with the synthesis of natural compounds and with the use of methyleneindolinones as dienophiles. [ABSTRACT FROM AUTHOR]

The gold-catalyzed synthesis of tetrahydrocarbazoles through dearomative [4+2] cycloaddition reactions of 3/2-substituted 2/3-vinylindoles with allenamides is reported. In particular, we optimized the enantioselective variant of these cycloadditions. Using allenamides as dienophiles 3-substituted 2-vinylindoles gave the corresponding carbazoles with high chemo-, regio- and enantioselectivity. Good results were obtained also with 2-methyl 3-vinylindoles even if mixtures of ( Z) and ( E) isomers were isolated in high er and in excellent overall yields. [ABSTRACT FROM AUTHOR]

We report herein the first example of the silver triflate catalysed synthesis of 1,3-dicarbo-substituted isochromene derivatives starting from 2-alkynyl(hetero)arylaldehydes and enolizable ketones. The reaction proceeds in a cascade fashion under mild heating with complete regioselectivity and moderate-to-good yields. In some cases, the reaction gives unexpected homodimeric products. Two competitive mechanistic paths for the formation of the desired isochromene derivatives and the homodimeric products are described. [ABSTRACT FROM AUTHOR]

A gold(I)-catalyzed cascade [3,3]-propargylic rearrangement and [4+2] cycloaddition reaction of 2-vinylindoles with propargylic esters is reported. The reaction leads to the synthesis of highly substituted tetrahydrocarbazole derivatives in high yields and diasteroselectivities. Furthermore, a preliminary screening for an asymmetric version of this reaction is described. [ABSTRACT FROM AUTHOR]

Silver(I) complexes of pyiridine-containing macrocyclic ligands (Pc-L) have already been demonstrated as active catalysts for some domino and multicomponent reactions. Here, we report new chiral [AgI(Pc-L*)] cationic complexes that have been synthesized and fully characterized, including structural determination by single-crystal X-ray diffraction. The complexes show a rich coordination chemistry, demonstrating both the σ-philic (alcohol and nitrile coordination) and the π-philic (alkyne coordination) nature of silver. The η2 coordination mode of the naphthyl pendant arm of the ligands on silver has been observed in solution by NMR spectroscopic experiments. 2D NMR spectroscopy revealed the presence of positive cross peaks resulting from rotational processes and the rate of rotation was measured by using 2D exchange spectroscopy (EXSY). [ABSTRACT FROM AUTHOR]