New highlights of the syntheses of pyrrolo[1,2-a]quinoxalin-4-ones

Modular synthesis of pyrrole-fused heterocycles via glucose-mediated nitro-reductive cyclization

A novel biomass-derived glucose-mediated one-pot multicomponent nitro-reductive cyclization method is presented for the direct synthesis of diverse pyrrole-fused heterocycles. The process involves two-component reactions of alkyl (NH)-pyrrole-2-carboxylates and 2-fluoronitroarenes, yielding pyrrolo[1,2-a]quinoxalin-4(5H)-ones, as well as three-component reactions utilizing (NH)-pyrroles, nitroarenes, and DMSO as carbon sources, resulting in various pyrrolo[1,2-a]quinoxaline derivatives. High yields were achieved with broad substrate scope and gram-scale synthesis capability, including pharmaceuticals featuring pyrroloquinoxaline scaffolds. The method's key innovation lies in enabling three or four reactions in a single-pot setup, previously unexplored in pyrrole chemistry. The simplicity of nitro group reduction by biomass-derived glucose ensures practical safety during scale-up, while mechanistic insights from control experiments reveal a new paradigm in pyrrole chemistry. The tandem process demonstrates low PMI values and high step and atom economies, aligning well with green chemistry principles.

Ultrasound assisted synthesis of hybrid quinoline-imidazole derivatives: a green synthetic approach

A green, straightforward and efficient study for obtaining hybrid quinoline-imidazole derivatives under ultrasound (US) irradiation as well as under conventional thermal heating (TH) has been presented. The reaction pathway involves only two steps: the N-alkylation of imidazole ring and a Huisgen [3 + 2] dipolar cycloaddition reaction of ylides to dimethyl acetylenedicarboxylate (DMAD). For both types of reactions, a green workup procedure under US irradiation has been presented. Under US irradiation, the N-alkylation of nitrogen atoms from the imidazole nucleus has outstanding benefits in terms of reaction time, energy consumption and yields, and can thereby be considered an environmentally friendly method. Forty new hybrid quinoline-imidazole compounds have been synthesized: 18 salts, 8 dihydro-benzopyrrolo imidazolo quinoline, 9 benzopyrrolo-imidazolo quinoline and 5 dihydro-pyrroloquinoxaline quinoline cycloadducts.

Acid-Catalyzed Multicomponent Rearrangements via 2-((Quinoxalin-3(4H)-on-2-yl)(aryl)methylene)malononitriles, Generated In Situ, for Divergent Synthesis of Pyrroles with Different Substitution Patterns

New three-component domino reactions, providing divergent approaches to multifunctionalized pyrroles with different substitution patterns, have been established (47 examples). In this work, a new rearrangement of quinoxalinones with the participation of the in situ-generated 2-en-1-imine moiety of the substituent at C3 makes it possible to construct two new heterocyclic systems, namely, a benzimidazolone and a pyrrole, simultaneously under one-pot reaction conditions. The reaction is easy to perform simply by mixing three common reactants of acetic acid with heating. Secondary amines or primary alcohols as the third component of the reaction, along with quinoxalin-3(4H)-ones and malononitrile, not only initiate the rearrangement but also are responsible for the nature of substituents at position 5 of the pyrrole ring in the newly formed new biheterocyclic system. The reaction proceeds smoothly and can be finished within 7 h, which makes workup convenient to give up to 97% chemical yields.

The construction of fluorophoric thiazolo-[2,3-b]quinazolinone derivatives: a multicomponent domino synthetic approach

Acid-mediated one-pot domino reactions of substituted 2-amino thiazoles, substituted benzaldehydes and cyclic diketones have been developed for the synthesis of novel and architecturally unique thiazolo[2,3-b]quinazolinone derivatives under microwave irradiation. In this protocol, a series of thiazolo[2,3-b]quinazolinone derivatives have been synthesized and the excellent fluorescence behaviors of some of the molecules have been reported based on the incorporation of different electron-donating and electron-withdrawing substituents on the aryl moieties of the target molecules.

A library of unique fluorophoric thiazolo[2,3-b]quinazolinones were synthesized under acid catalyzed one pot microwave irradiation technique.

Iron-catalyzed [3 + 2]-cycloaddition of in situ generated N-ylides with alkynes or olefins: access to multi-substituted/polycyclic pyrrole derivatives

An iron-catalyzed one-pot three-component reaction of 1-substituted benzimidazoles with diazoacetates and electron-deficient alkynes or alkenes has been reported. Mechanistically, the reaction goes through a 1,3-dipolar cycloaddition of catalytically generated benzimidazolium N-ylides with various activated alkynes or alkenes, leading to multi-substituted and polycyclic fused pyrrole derivatives, respectively.

Schiff bases containing a furoxan moiety as potential nitric oxide donors in plant tissues

Stable Schiff bases containing a furoxan moiety are synthesized as single regioisomers by the reaction of 3-methyl-2-oxy-furazan-4-carbaldehydewith various amino compounds at room temperature. The structures of synthesized compounds were fully characterized by multinuclear NMR spectroscopy and X-ray crystallography. The effect of synthesized Schiff bases containing a furoxan moiety on biological generation of reactive oxygen species and nitric oxide in plant tissues was investigated for the first time by fluorescence microscopy and the released NO identified as nitrite with Griess reagent. There is a good correlation between the biological generation of NO determined by fluorescence microscopy and with Griess reagent. Some of the synthesized compounds exhibited both nitric oxide and reactive oxygen species generation abilities and represent potential NO donors in plant tissues.

Isoxazole derivatives as new nitric oxide elicitors in plants

Several 3,5-disubstituted isoxazoles were obtained in good yields by regiospecific 1,3-dipolar cycloaddition reactions between aromatic nitrile oxides, generated in situ from the corresponding hydroxyimidoyl chlorides, with non-symmetrical activated alkynes in the presence of catalytic amounts of copper(I) iodide. Effects of 3,5-disubstituted isoxazoles on nitric oxide and reactive oxygen species generation in Arabidopsis tissues was studied using specific diaminofluoresceine dyes as fluorescence indicators.

The Cycloaddition of the Benzimidazolium Ylides with Alkynes: New Mechanistic Insights

New insights concerning the reaction mechanism in the cycloaddition reaction of benzimidazolium ylides to activated alkynes are presented. The proposed pathway leading both to 2-(1H-pyrrol-1-yl)anilines and to pyrrolo[1,2-a]quinoxalin-4(5H)-ones involves an opening of the imidazole ring from the cycloaddition product, followed by a nucleophilic attack of the aminic nitrogen to a proximal carbonyl group and the elimination of a leaving group. The mechanistic considerations are fully supported by experimental data, including the XRD resolved structure of the key reaction intermediate.

Indolizines and pyrrolo[1,2-c]pyrimidines decorated with a pyrimidine and a pyridine unit respectively

The three possible structural isomers of 4-(pyridyl)pyrimidine were employed for the synthesis of new pyrrolo[1,2-c]pyrimidines and new indolizines, by 1,3-dipolar cycloaddition reaction of their corresponding N-ylides generated in situ from their corresponding cycloimmonium bromides. In the case of 4-(3-pyridyl)pyrimidine and 4-(4-pyridyl)pyrimidine the quaternization reactions occur as expected at the pyridine nitrogen atom leading to pyridinium bromides and consequently to new indolizines via the corresponding pyridinium N-ylides. However, in the case of 4-(2-pyridyl)pyrimidine the steric hindrance directs the reaction to the pyrimidinium N-ylides and, subsequently, to the formation of the pyrrolo[1,2-c]pyrimidines. The new pyrrolo[1,2-c]pyrimidines and the new indolizines were structurally characterized through NMR spectroscopy. The X-ray structures of two of the starting materials, 4-(2-pyridyl)pyrimidine and 4-(4-pyridyl)pyrimidine, are also reported.