An efficient metal-free synthesis of 2-(pyrazin-2-yl)benzimidazoles from quinoxalinones and diaminomaleonitrile via a novel rearrangement

2,3-Diaminomaleonitrile: A Multifaceted Synthon in Organic Synthesis

2,3-Diaminomaleonitrile (DAMN), a tetramer of hydrogen cyanide, displays weakly basic properties and has reactivity comparable to o-phenylenediamine. It has emerged as a versatile, cheap as well as a readily accessible building block towards the synthesis of a variety of organic compounds. The present review focuses on the applications of 2,3-diaminomaleonitrile for the synthesis of Schiff's base, imidazoles, pyrazines, quinoxolines, benzodiazocines, 1,4-diazepines, purines, pyrimidines, pyrazine-tetrazole hybrids, triazoles, thiadiazole, thiazolidines, porphyrazines, formamidines, 1,3,5-triazepines, pyrrolo[3,4-b][1,4]diazepin-6(3H)-ones, triaza[22]annulenes, pyrrolo[3,4-f][1,3,5]triazepines, spiro compounds, pyrazoles and 2,3-dicyano-5,7-bismethylthieno[3,4-b]pyrazine.

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.

Antimicrobial evaluation and docking study of some new substituted benzimidazole-2yl derivatives

Benzimidazoles incorporated biologically active heterocycles such as quinoline, triazine-3-thione, thiazole and thiadiazole, were synthesized utilizing 2-acetylbenzimidazole as a building block. The structures of the newly synthesized benzimidazoles were assured by their spectral data (IR, ¹H NMR, ¹³C- NMR and MS spectra). Most of the synthesized candidates were screened for their in vitro antimicrobial activity against Staphylococcus aureus, Escherichia coli, Bacillus pumilus and antifungal activity against (Saccharomyces cerevisiae). As a result, 2-(2-(1-(1H-benzo[d]imidazol-2-yl)ethylidene)hydrazineyl)-5-(furan-2-yl)-1,3,4-thiadiazole (14) had the most potent inhibitory activity against all tested bacteria with no antifungal inhibition. Furthermore, to gain insight into the mode of action of the synthesized compounds as antibacterial agents, docking studies were performed for the synthesized compounds in order to evaluate their activity as anti-bacterial agents. Virtual screening of the most promising compounds was performed against two bacterial proteins (DNA gyrase subunit B, and penicillin binding protein 1a) that are known targets for some antibiotics.

Acid-Catalyzed Rearrangement of 3-Cyanoquinoxalin-2(1H)-ones When Exposed to 1,2-Diaminobenzenes: Synthesis of 2,2'-Bibenzimidazoles

A novel and efficient protocol for the synthesis of diversely substituted 2,2'-bibenzimidazoles from the reaction of 3-cyanoquinoxalin-2(1H)-ones with 1,2-diaminobenzenes has been developed, which proceeds through sequential nucleophilic addition and electrophilic substitution followed by a Mamedov rearrangement. The synthetic utility of this strategy was illustrated by the concise, one-pot synthesis of 5,5'-bi(2,2'-bibenzimidazoles) and aza-analogues of 2,2'-bibenzimidazole.

One-Pot Synthesis of 7-(Benzimidazol-2-yl)thioxolumazine and -lumazine Derivatives via H2SO4-Catalyzed Rearrangement of Quinoxalinones When Exposed to 5,6-Diamino-2-mercapto- and 2,5,6-Triaminopyrimidin-4-ols

A facile approach to a range of substituted 7-(benzimidazol-2-yl)thioxolumazines [7-(benzimidazol-2-yl)-2-thioxo-2,3-dihydropteridin-4(1 H)-ones] and 7-(benzimidazol-2-yl)lumazines [7-(benzimidazol-2-yl)pteridine-2,4(1 H,3 H)-diones] is described. These new biheterocyclic systems are obtained via H₂SO₄-catalyzed rearrangement of quinoxalin-2-ones in the presence of 5,6-diamino-2-mercapto- and 2,5,6-triaminopyrimidin-4-ols. Thus, benzimidazole and pteridine rings are constructed in one synthetic step. A plausible ANRORC ( addition of nucleophile, ring opening and ring closure)-type reaction mechanism is proposed. Applying the rearrangement to the aza-analogue of 3-benzoylquinoxalin-2(1 H)-one-i.e., 3-benzoylpyrido[2,3- b]pyrazin-2(1 H)-one-with 5,6-diamino-2-mercaptopyrimidin-4-ol makes it possible to synthesize inaccessible 7-(1 H-imidazo[4,5- b]pyridin-2-yl)-6-phenyl-2-thioxo-2,3-dihydropteridin-4(1 H)-one. 7-(Benzimidazol-2-yl)-6-(2-fluorophenyl)-2-thioxo-2,3-dihydropteridin-4(1 H)-ones undergoes intramolecular nucleophilic substitution of fluorine by a nitrogen of the benzimidazole fragment with the formation of benzo[4',5']imidazo[1',2':1,2]quinolino[4,3- g]pteridine-2,4(1 H,3 H)-diones as new heterocyclic systems.

Recent advances in the synthesis of benzimidazol(on)es via rearrangements of quinoxalin(on)es

The review describes all the quinoxaline-benzimidazole rearrangements as a whole and the new quinoxalinone-benzimidazol(on)e rearrangements in particular when exposed to nucleophilic rearrangements which can be used for the synthesis of various biheterocyclic motifs.

Reaction for the synthesis of benzimidazol-2-ones, imidazo[5,4-b]-, and imidazo[4,5-c]pyridin-2-ones via the rearrangement of quinoxalin-2-ones and their aza analogues when exposed to enamines

A synthetically useful protocol has been developed for the preparation of highly functionalized N-pyrrolylbenzimidazol-2-ones. The reaction of variously substituted 3-aroyl- and 3-alkanoylquinoxalin-2(1H)-ones with commercially available enamines in acetic acid results in a rapid rearrangement and formation of N-pyrrolylbenzimidazol-2-ones in modest to excellent yields. The key step of the rearrangement involves the novel ring contraction of 3-aroyl- and 3-alkanoylquinoxalin-2(1H)-ones with enamines. In this case, the atom of carbon which is displaced from the pyrazine ring of quinoxalin-2(1H)-one becomes the fourth carbon atom of the newly formed pyrrole ring. The method is applicable for the aza analogues of quinoxalin-2(1H)-ones.