Synthesis of quinoxalines through iodine-catalyzed one-pot annulation of alkynes with o-phenylenediamines

The synthesis of N-heterocycles of quinoxalines has been developed by an efficient protocol of one-pot annulation of alkynes with o-phenylenediamines. A variety of quinoxalines were prepared in good to high yields in the presence of catalytic amount of iodine as a catalyst.     

Novel succinct routes to quinoxalines and 2-benzimidazolylquinoxalines via the Ugi reaction

This Letter reveals a unique, user-friendly, concise two-step, one-pot protocol for the synthesis of highly substituted quinoxalines. Conducting the Ugi reaction with appropriately functionalized classical Ugi reagents with subsequent acid treatment of the Ugi adduct affords collections of diversified quinoxalines in good to excellent yields. The methodology exploits what may be viewed as a ‘convertible carboxylic acid’, which in addition may be captured in an intramolecular sense to generate structurally complex 2-benzimidazolylquinoxalines in a mere two steps.     

Logic design and synthesis of quinoxalines via the integration of iodination/oxidation/cyclization sequences from ketones and 1,2-diamines

A novel protocol for the synthesis of quinoxalines has been developed from simple ketones and 1,2-diamines. This process underwent a logic approach to bis-substituted quinoxalines via a consecutive iodination/Kornblum oxidation/cyclization in the presence of I₂/CuO/DMSO and to mono-substituted quinoxalines via an iodination/cyclization/aromatization in the presence of I₂/CuO/K₃PO₄·3H₂O.     

A highly divergent Pictet-Spengler approach for pyrrolo[1,2-a]quinoxalines from aryl amine using 1,2-dinitrobenzene as an oxidant

A convenient Pictet-Splengler approach for the synthesis of substituted pyrrolo[1,2-a]quinoxalines from aryl amine and 1-(2-aminoaryl)-pyrrole has been developed. This is the first domino protocol involving formation of benzaldehyde as an intermediate from benzyl amines and benzyl alcohols using 1,2-DNB as an oxidant, followed by its endo cyclization with 1-(2-aminophenyl)-pyrrole to furnish the pyrrolo[1,2-a]quinoxalines. Notably, this procedure exhibits good functional group tolerance as well as good to moderate yield of pyrrolo[1,2-a]quinoxaline.     

Development of an unexpected reaction pathway for the synthesis of 1,2,4-trisubstituted pyrrolo[1,2-a]quinoxalines through palladium-catalyzed cascade reactions

1,2,4-trisubstituted pyrrolo[1,2-a]quinoxalines are synthesized through the multi-component reaction of 3-substituted 2-chloroquinoxalines, propargyl bromide, and excess secondary amines in the presence of a palladium copper catalytic system. This one-pot process provides an unexpected synthesis of new trisubstituted pyrrolo[1,2-a]quinoxalines by the introduction of two amine substituents onto the fused pyrrole rings in a single reaction procedure. The compounds formed are fully characterized by the analytical spectral data and X-ray analysis. A number of synthesized pyrrolo[1,2-a]quinoxaline derivatives are also screened against the three bacterial strains Micrococcus luteus, Pseudomonas aeruginos, and Bacillus subtilis. According to the results obtained, compounds 3b, 3c, and 3e are active against M. luteus, compounds 3b and 3e are active against Ps. Aeruginos, and only compound 3f is active against all the three bacterial strains.     

One-pot palladium-catalyzed synthesis of functionalized 10H-pyrido[1,2-a]quinoxalin-10-ones under copper-free conditions

Reactions of 3-substituted-2-chloroquinoxalines, terminal alkynes, and 1,3-dicarbonyl compounds in the presence of palladium catalyst afforded a number of 6,8,9-trisubstituted-10H-pyrido[1,2-a]quinoxalin-10-ones in 60–86% reaction yields. This one-pot protocol provided an efficient, practical, and direct method for the synthesis of pyrido[1,2-a]quinoxalines from readily available starting materials in the absence of a copper salt.     

Combinatorial synthesis of 4-oxo-4H-imidazo[1,5-a]quinoxalines and 4-oxo-4H-pyrazolo[1,5-a]quinoxalines

A combinatorial synthetic route yielding imidazo[1,5-a]quinoxalines and pyrazolo[1,5-a]quinoxalines is described. The use of 2-fluoroaniline and 1H-imidazole-4-carboxylic acid, respectively, 1H-pyrazole-3-carboxylic acid in the Ugi-reaction (U-4CR) followed by a nucleophilic aromatic substitution (S_NAr) affords the imidazo- as well as the pyrazolo-[1,5-a]quinoxaline moiety in good yield and high diversity.     

One-pot synthesis of 1,2-disubstituted pyrrolo[2,3-b]quinoxalines via palladium-catalyzed heteroannulation in water

The reaction of N-alkyl-3-chloroquinoxaline-2-amines with 1-alkynes, catalyzed by Pd-Cu, in the presence of sodium lauryl sulfate as the surfactant in water, leads to the one-pot formation of 1,2-disubstituted pyrrolo[2,3-b]quinoxalines in good-to-high yields.     

Regioselective synthesis of 2,3-disubstituted 1-alkyl pyrrolo[2,3-b] quinoxalines through palladium-catalyzed Heck reaction of chalcones and evaluation of their anti-bacterial activities

The regioselective synthesis of 1-alkyl-2-aryl-3-acyl pyrrolo[2,3-b]quinoxalines through palladium-catalyzed Heck coupling reaction/heteroannulation was reported. The reaction of N-alkyl/benzyl-3-chloroquinoxaline-2-amines with chalcones catalyzed by Pd(OAc)₂ in the presence of KO^tBu, as the base, in DMSO afforded the desired products in good-to-high yields. The MIC and MBC determinations revealed that these compounds could be used in the future research works for the development of antibiotics.     

Synthesis of isoxazolo[2,3-a]quinoxalines and pyrrolo[1,2-a]quinoxalines by 1,3-dipolar cycloaddition reaction

The isoxazolo[2,3-a]quinoxalines 11a,b and pyrrolo[1,2-a]quinoxalines 12a,b were selectively synthesized from the 2-substituted 6-chloroquinoxaline 4-oxides 10a,b . The pyrrolo[1,2-a]quinoxalines 12a,b were clarified to be produced by the ring transformation of the isoxazolo[2,3-a]quinoxalines 11a,b . The pyrrolo[1,2-a]quinoxalines 14a,b were obtained from both 2,6-dichloroquinoxaline 4-oxide 9 and compounds 12a,b .     

One-pot synthesis of 2-substituted quinoxalines using K10-montmorillonite as heterogeneous catalyst

An efficient one-pot synthesis of 2-substituted quinoxalines from 1,2-diamines and phenacyl bromides is developed using K10-montmorillonite (K10 clay) as a catalyst at 50 °C in acetonitrile medium. This method offers an easy route for the synthesis of substituted quinoxalines in high yields. A plausible mechanism is proposed in which quinoxalines are formed via dehydration–dehydrohalogenation–cyclization sequence. Further, the K10 clay catalyst is recovered by simple filtration and reused six times without any loss in its catalytic activity.     

喹喔啉衍生物与缺电子烯烃的激光闪光光解研究

利用时间分辨激光诱导瞬态吸收光谱装置,以一台Nd：YAG激光器四倍频后的266nm激光作为激发光源,详细研究了两种喹喔啉衍生物激发三重态在乙腈体系中的动力学过程,得到激光脉冲作用后不同时间的瞬态吸收光谱及激发三重态自猝灭反应动力学常数．并以五种缺电子烯烃作为猝灭剂,得到了基态缺电子烯烃对喹喔啉衍生物激发三重态的猝灭反应动力学常数,阐明了猝灭反应机理．     

Dipolar cycloaddition of ethyl isocyanoacetate to 3-chloro-2-(methylthio)/2-(methylsulfonyl)quinoxalines: highly regio- and chemoselective synthesis of substituted imidazo[1,5-a]quinoxaline-3-carboxylates

An efficient route for regio- and chemoselective synthesis of substituted 3-(carboethoxy)imidazo[1,5-a]quinoxalines and novel diimidazo[1,5-a:5',1'-c]quinoxalines via base-induced cycloaddition of ethyl isocyanoacetate to unsymmetrically substituted 3-chloro-2-(methylthio)/2-(methylsulfonyl)quinoxalines has been reported.     

A selective synthesis of novel isoxazolo[2, 3-a]-quinoxalines and pyrrolo[1, 2-a]quinoxalines

The isoxazolo[2, 3-a]quinoxalines 11a, b and pyrrolo[1, 2-a]quinoxalines 12a, b were selectively synthesized from the 2-substituted 6-chloroquinoxaline 4-oxides 10a, b . The pyrrolo[1, 2-a]quinoxalines 12a, b were clarified to be produced by the ring transformation of the isoxazolo[2, 3-a]quinoxalines 11a, b .     

Pyrrolo[1,2-<Emphasis Type="Italic">a</Emphasis>]quinoxalines based on quinoxalines (Review)

Published data on methods for the synthesis of pyrrolo[1,2-a]quinoxalines, based on derivatives of quinoxalines and also on compounds that are not initially derivatives of quinoxalines or pyrroles are summarized and classified.     

Chemoselective synthesis of quinoxalines and benzimidazoles by silica gel catalysis

Treatment of nitroolefins and o-phenylenediamine with silica gel catalyst produced quinoxalines mainly in THF, but gave benzimidazoles efficiently in water. Such a solvent-dependent chemoselective reaction has prominent features of affording two cyclized products selectively with the same substrate, short reaction time, operational simplicity, as well as available starting materials and nontoxic catalysts. In addition, the scope and limitations were explored and a plausible reaction mechanism is proposed.     

3-(α-azidoalkyl)quinoxalin-2(1H)-ones and related alkylquinoxalinyl ketones

A convenient method has been developed for the synthesis of 3-alkanoyl-and 3-benzoyl-2-oxo-1,2-dihydroquinoxalines from the corresponding 3-(α-azidoalkyl)quinoxalines using acetic acid. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 574–577, 2007.     

A new and versatile Ugi/SNAr synthesis of fused 4,5-dihydrotetrazolo[1,5-a]quinoxalines

A combinatorial synthetic route yielding fused tetrazolo[1,5-a]quinoxalines is described. The use of 2-fluorophenylisocyanide in the Ugi-tetrazole reaction (tetrazole-U-4CR) followed by a nucleophilic aromatic substitution (S_NAr) affords the tricylic tetrazolo[1,5-a]quinoxaline moiety in good yields and with high diversity.     

Efficient diverse approach for quinoxaline‐derived glycosylated and morphinylated analogs

Sulfanyl‐glycosides have been synthesized by reaction of 2,3‐dimercaptoquinoxaline ( 1 ) with acetohalo sugars in presence of base to give the thioglycosides‐derived quinoxalines 5 , 6 , 7 and 9 . Similarly, the acyclic analogs 23 , 24 , 25 , 26 were prepared by coupling of 1 with different acyclo‐alkylating agents. The preparation of 3‐morpholinyl‐quinoxalines 10 and 11 allowed the synthesis of 3‐glycosylsulfanyl‐2‐morpholinyl‐quinoxalines 12 , 13 , 14 and 17 as well as the acyclic analogs 27 , 28 , 29 . Microwave irradiation of the reactants turned out to be preferred over the conventional method for achieving the synthetic goals. This study made an available venue to the synthesis of diverse quinoxaline derivatives. J. Heterocyclic Chem., 2011.     

Application of the Pictet-Spengler reaction to aryl amine substrates linked to deactivated aromatic heterosystems

Three new substrates with an aryl amine moiety attached to quinoxalines, triazoles and tetrazoles either via C or N have been used for the Pictet-Spengler reaction. The substrates have been designed by applying the concept of ‘aryl amine attached to a deactivated heteroaromatic ring’ in a manner to facilitate endo cyclization. This is in contrast to the substrates used traditionally and reported earlier by us that are based on either aliphatic or aryl amine, respectively, attached to an activated heterocyclic ring. The Pictet-Spengler condensation of the three substrates with aldehydes led to the synthesis of novel N-rich polyheterocyclic system hitherto not reported. Our modified strategy opens up possibilities to design novel substrates with aryl amines linked via C or N to either deactivated or activated heterocyclic privileged structure, which in turn can be used for the synthesis of novel fused polyheterocyclic skeletons.