Recent Advances in the Synthesis of Nitrogen Heterocycles Using Arenediazonium Salts as Nitrogen Sources

Radical N2-Retention Cyclizations of Aryl Diazoniums: Access to 7/8/9-Membered Heterocycles

We report herein a modular approach to synthesizing diverse functionalized 7/8/9-membered poly-N-containing heterocycles via oxidative radical N2-retention cyclizations of allylic aryl diazonium salts using CF3SO2Na as a CF3 radical source. A range of trifluoromethylated benzotriazepines, benzotriazocines, and benzotriazonines were obtained in moderate to good yields. This transition-metal-free protocol demonstrates atom economy, safe conditions, broad functional group tolerance, and availability of readily accessible reagents.

2-Azabicyclo[3.2.1]octane scaffold: synthesis and applications

2-Azabicyclo[3.2.1]octanes are nitrogen containing heterocycles with significant potential in the field of drug discovery. This core has been applied as key synthetic intermediate in several total synthesis, while their unique structure can make them a challenging scaffold to acquire. This Minireview summarizes the synthetic approaches to access this bicyclic architecture and highlights its presence in the total synthesis of several target molecules.

Antileishmanial Effect of 1,5- and 1,8-Substituted Fused Naphthyridines

In the absence of a vaccine, there is a need to find new drugs for the treatment of neglected tropical diseases, such as leishmaniasis, that can overcome the many drawbacks of those currently used. These disadvantages include cost, the need to maintain a cold chain, the route of administration, the associated adverse effects and the generation of resistance. In this work we have evaluated the antileishmanial effect of 1,5- and 1,8-substituted fused naphthyridines through in vitro and ex vivo assays, using genetically modified axenic and intramacrophagic Leishmania infantum amastigotes. The toxicity of these compounds has been tested in the mammalian host cell using murine splenic macrophages, as well as in murine intestinal organoids (miniguts) in order to assess their potential for oral administration. The 1,8- derivatives showed greater leishmanicidal activity and the presence of a nitrogen atom in the fused ring to the naphthyridine was important to increase the activity of both types of molecules. The aromatization of the pyridine ring also had marked differences in the activity of the compounds.

Effect of rhizobium and gibberellin on the production of hydroponic green forage of red clover (Trifolium pratense L.) variety quiñequeli

The purpose of the present investigation was to determine the effect of rhizobium and gibberellin on the production of hydroponic green forage from red clover (Trifolium pratense L.) variety quiñequeli, four variables were measured: plant height, biomass weight, grass weight and root weight. The treatments were T0: 0%, T1: 10%, T2: 20%, T3: 30% and T4: 40% of Rhizobium before germination and Gibberellin T0: 0g, T1: 2.4g; T2: 3.3g; T3: 4.3 and T4: 5.3g each treatment with 6 repetitions, three applications on days 5, 10, 15 and 20 of growth. Data were analyzed with DCA, ANOVA and DUNCAN's multiple comparisons test; the results obtained were: first measurement with rhizobium without gibberellin there were no statistical differences, second and third measurement with Gibberellin application did not present statistical differences and the fourth measurement presented statistical difference (α=0.05), average height of the plant with a mean of 12.82 cm, T4 was higher, in biomass a statistical difference was obtained with a mean of 3.056 kg, T3 was higher, weight of grass and root did not present statistical differences; concluding that the use of rhizobium and gibberellin could be a usable alternative in the production of hydroponic green fodder, to alleviate the problems of fodder scarcity in dry season, its use being recommended in high Andean livestock.

Diazotization-Enabled Deaminative Late-Stage Functionalization of Primary Sulfonamides

We, for the first time, disclosed a simple and efficient strategy for the late-stage functionalization of primary sulfonamides by diazotization, leading to sulfonyl chlorides, sulfonates, and complex sulfonamides. This protocol obviates the requirement for the prefunctionalization of sulfonamides. Its applicability is exemplified by the late-stage functionalization of sulfonamide-type drugs.

Visible-Light-Promoted Aryl Cation Formation: Aromatic SN1 Reactions of Areneazo-2-(2-nitro)propanes

The visible light excitation of areneazo-2-(2-nitro)propane·HCl salts generated the singlet aryl cation that readily underwent aromatic SN1 reactions with a variety of nucleophiles. The in situ generated singlet aryl cation was stabilized by a counter nitronate anion that prevented other intersystem crossing and single electron transfer processes. With the improved safety features of neutral areneazo-2-(2-nitro)propane derivatives, the current visible-light-promoted aromatic SN1 reactions provide an alternative aryl Csp2-X bond forming strategy.

Access to Polyheterocyclic Compounds through Iron(II)-Mediated Radical Cascade Cyclization Utilizing 2-Ethynylbenzaldehydes and Aryl Isonitriles

An oxidative radical cascade addition cyclization approach for the synthesis of quinoline-based π-extended polyheterocyclic compounds is reported. Eco-friendly iron catalysis and inexpensive tert-butylhydroperoxide (TBHP) as the oxidant have been utilized in the transformation of various readily available ortho-alkynylated aromatic aldehydes as radical precursors with aryl isonitriles as radical acceptors. Indole and thiophene-based carbaldehydes allow the preparation of quinolines that are π-conjugated with an additional heteroarene moiety in a single sequence by applying the introduced method.

The Intramolecular Povarov Tool in the Construction of Fused Nitrogen-Containing Heterocycles

Nitrogen heterocycles are part of the structure of natural products and agents with important biological activity, such as antiviral, antibiotic, and antitumor drugs. For this reason, heterocyclic compounds are one of today's most desirable synthetic targets and the Povarov reaction is a powerful synthetic tool for the construction of highly functionalized heterocyclic systems. This process involves an aromatic amine, a carbonyl compound, and an olefin or acetylene to give rise to the formation of a nitrogen-containing heterocycle. This review illustrates advances in the synthetic aspects of the intramolecular Povarov reaction for the construction of intricate nitrogen-containing polyheterocyclic compounds. This original review presents research done in this field, with references to important works by internationally relevant research groups on this current topic, covering the literature from 1992 to 2022. The intramolecular Povarov reactions are described here according to the key processes involved, using different combinations of aromatic or heteroaromatic amines, and aliphatic, aromatic, or heteroaromatic aldehydes. Some catalytic reactions promoted by transition metals are detailed, as well as the oxidative Povarov reaction and some asymmetric intramolecular Povarov processes.

Formal [3 + 2] Cycloaddition of α-Imino Esters with Azo Compounds: Facile Construction of Pentasubstituted 1,2,4-Triazoline Skeletons

1,2,4-Triazole and 1,2,4-triazoline are important components of bioactive molecules and catalysts employed in organic synthesis. Therefore, the efficient synthesis of these components has received significant research attention. However, studies on their structural diversity remain lacking. Previously, we developed chiral phase-transfer-catalyzed asymmetric reactions of α-imino carbonyl compounds with α,β-unsaturated carbonyl compounds and haloalkanes. In this study, we demonstrate the formal [3 + 2] cycloaddition reaction of α-imino esters with azo compounds under Brønsted base catalysis, resulting in the corresponding 1,2,4-triazolines in high yields. The results revealed that a wide range of substrates and reactants can be applied, irrespective of their steric and electronic characteristics. The present reaction made the general preparation of 3-aryl pentasubstituted 1,2,4-triazolines possible for the first time. Furthermore, a mechanistic study suggested that the reaction proceeds without isomerization into the aldimine form.

Radical Fluorosulfonyl Heteroarylation of Unactivated Alkenes with Quinoxalin-2(1H)-ones and Related N-Heterocycles

The incorporation of sulfonyl fluoride groups into molecules has been proved effective to enhance their biological activities or introduce new functions. Herein, we report a transition-metal-free and visible-light-mediated radical 1-fluorosulfonyl-2-heteroarylation of alkenes, which could allow access to a series of SO₂F-containing quinoxalin-2(1H)-ones, which are a critical structural motif widely present in a number of biologically active molecules. Further application of the method to the modification of other heterocycles and drug molecules as well as ligation chemistry via SuFEx click reactions is also demonstrated.

A Review on The Medicinal And Industrial Applications of N-Containing Heterocycles

Nitrogen-containing heterocycles constitute an important division of organic chemistry. The structural and functional diversity in nitrogen-containing heterocyclic compounds emanates from the presence and nature of the heteroatom that optimizes the compound for a specific application. Nitrogen heterocycles have been found to mimic various endogenous metabolites and natural products, highlighting their pivotal role in current drug design. Their applications are manifold and are predominantly used as pharmaceuticals, corrosion inhibitors, polymers, agrochemicals, dyes, developers, etc. Additionally, their catalytic behavior has rendered these compounds notable precursors in synthesizing various important organic compounds. The rate at which nitrogen heterocycles are synthesized explains this organic chemistry domain's vitality and usefulness. The present review article focuses on nitrogen-containing heterocycles as a versatile scaffold for current applications of organic chemistry.

B2pin2-Mediated Cascade Cyclization/Aromatization Reaction: Facial Access to Functionalized Indolizines

Herein, a B₂pin₂-mediated radical cascade cyclization/aromatization reaction of enaminone with pyridine is described. This strategy provides a practical way for the construction of valuable functionalized indolizines under metal-, external oxidant-, and base-free conditions, which could be compatible with various kinds of functional groups, such as halogen, π-system, heterocycle, ferrocenyl, etc. A preliminary mechanism investigation indicated that the pyridine-boryl radical formed in situ triggered the reaction to occur.

Intermolecular C-H Aminocyanation of Indoles via Copper-iodine Cocatalyzed Tandem C-N/C-C Bond Formation

An efficient copper-iodine cocatalyzed intermolecular C-H aminocyanation of indoles with a broad substrate scope has been developed for the first time. This method enables highly step-economic access to 2-amino-3-cyanoindoles in moderate to good yields and provides a complementary strategy for the regioselective difunctionalization of carbon═carbon double bonds of interest in organic synthesis and related areas. Mechanistic studies suggest that these transformations are initiated by iodine-mediated C2-H amination with azoles, followed by copper-catalyzed C3-H cyanation with ethyl cyanoformate.

A practical and sustainable two-component Minisci alkylation via photo-induced EDA-complex activation

An operationally simple, open-air, and efficient light-mediated Minisci C-H alkylation method is described, based on the formation of an electron donor-acceptor (EDA) complex between nitrogen-containing heterocycles and redox-active esters. In contrast to previously reported protocols, this method does not require a photocatalyst, an external single electron transfer agent, or an oxidant additive. Achieved under mildly acidic and open-air conditions, the reaction incorporates primary-, secondary-, and tertiary radicals, including bicyclo[1.1.1]pentyl (BCP) radicals, along with various heterocycles to generate Minisci alkylation products in moderate to good yields. Additionally, the method is exploited to generate a stereo-enriched, hetereoaryl-substituted carbohydrate.

Rhodium(III)-catalyzed oxidative annulation of isoquinolones with allyl alcohols: synthesis of isoindolo[2,1-b]isoquinolin-5(7H)-ones

An efficient rhodium(III)-catalyzed direct C-H oxidative annulation of isoquinolones with allyl alcohols as C1 synthons has been successfully developed. This protocol enables the straightforward synthesis of structurally diverse isoindolo[2,1-b]isoquinolin-5(7H)-ones with high atom economy, tolerates a broad spectrum of functionalities, and is applicable to one-pot operation from readily available N-methoxybenzamides.

Aromatization as the driving force for single electron transfer towards C–C cross-coupling reactions

There is a strong current interest in C–H functionalization reactions under metal-free conditions. We report herein that the deprotonated form of dihydrophenazine (DPh) as a potent initiator under photochemical conditions...

A green polyol approach for the synthesis of Cu2O NPs adhered on graphene oxide: a robust and efficient catalyst for 1,2,4-triazole and imidazo[1,2-a]pyridine synthesis

Cu2O NPs immobilized on graphene oxide are used as a heterogeneous catalyst for the synthesis of a series of 1,2,4-triazoles and imidazo[1,2-a]pyridines under solvent-free conditions.

Direct Arylation of Distal and Proximal C(sp3)-H Bonds of t-Amines with Aryl Diazonium Tetrafluoroborates via Photoredox Catalysis

A visible light-mediated arylation protocol for t-amines has been reported through the coupling of γ- and α-amino alkyl radicals with different aryl diazonium salts using Ru(bpy)₃Cl₂·6H₂O as a photocatalyst. Structurally different 9-aryl-9,10-dihydroacridine, 1-aryl tetrahydroisoquinoline, hexahydropyrrolo[2,1-a]isoquinoline, and hexahydro-2H-pyrido[2,1-a]isoquinoline frameworks with different substitution patterns have been synthesized in good yield using this methodology.

Tris(pentafluorophenyl)borane-Catalyzed Carbenium Ion Generation and Autocatalytic Pyrazole Synthesis-A Computational and Experimental Study

In recent years, metal-free organic synthesis using triarylboranes as catalysts has become a prevalent research area. Herein we report a comprehensive computational and experimental study for the highly selective synthesis of N-substituted pyrazoles through the generation of carbenium species from the reaction between aryl esters and vinyl diazoacetates in the presence of catalytic tris(pentafluorophenyl)borane [B(C6 F5 )3 ]. DFT studies were undertaken to illuminate the reaction mechanism revealing that the in situ generation of a carbenium species acts as an autocatalyst to prompt the regiospecific formation of N-substituted pyrazoles in good to excellent yields (up to 81 %).

Pyrazole-Mediated C-H Functionalization of Arene and Heteroarenes for Aryl-(Hetero)aryl Cross-Coupling Reactions

Herein we introduce a transition-metal-free protocol that involves a commercially available, inexpensive pyrazole molecule to conduct C-C cross-coupling reactions at room temperature via a radical pathway. Using this method, an aryldiazonium salt has been coupled to a wide range of arenes and heteroarenes including benzene, mesitylene, thiophene, furan, benzoxazole to result the corresponding biaryl products. The full reaction mechanism is elucidated along with the crystallographic probation of an active initiator species. A potassium-stabilized deprotonated pyrazole steers single-electron transfer to the substrate and behaves as an initiator for the reaction.

Rhodium(III)-catalyzed oxidative alkylation of N-aryl-7-azaindoles with cyclopropanols

An efficient Rh(iii)-catalyzed C-H oxidative alkylation of N-aryl-7-azaindoles with cyclopropanols by merging tandem C-H and C-C cleavage was developed. This transformation features mild reaction conditions, high regioselectivity, and excellent functional group compatibility. The resulting β-aryl ketone derivatives can be readily transformed into 7-azaindole-containing π-extended polycyclic heteroarenes.

Catalytic Direct Construction of Cyano-tetrazoles

Cyano-tetrazole is the first reported compound that bears four nitrogen atoms in a single five-membered ring. This unique molecular scaffold has long been ignored after its discovery in 1885, mainly attributed to the scarcity of available synthetic methods. Indeed, the most popular approach to tetrazoles (that is the cycloaddition reaction between nitriles and azides) has inevitably excluded the possibility of introducing valuable cyano groups to decorate the final heterocyclic cores. Here, we describe a completely different disconnection strategy to the long time-pursued cyano-tetrazoles via a simple, direct, and practical cycloaddition transformation between readily accessible aryl diazonium salts and diazoacetonitrile. This method provides both regioisomers of disubstituted tetrazoles from the same set of starting materials in a metal cation controlled fashion.