Synthesis of pyrrolo[1,2-a]quinoxalines by 1,3-dipolar cycloaddition reaction. An additional reaction mechanism via an aziridine intermediate

The reaction of the 2-substituted 6-chloroquinoxaline 4-oxides 1a or 1b with 2-fold molar amount of methyl propiolate resulted in the 1,3-dipolar cycloaddition reaction to give 8-chloro-1,3-bismethoxycarbonyl-4-(piperidin-1-yl)pyrrolo[1,2-a]quinoxaline 4a or 8-chloro-1,3-bismethoxycarbonyl-4-(morpholin-4-yl)pyrrolo-[1,2-a]quinoxaline 4b , respectively. Compound 4a or 4b was transformed into 8-chloro-3-methoxycarbonyl-4-(piperidin-1-yl)pyrrolo[1,2-a]quinoxaline 5a or 8-chloro-3-methoxycarbonyl-4-(morpholin-4-yl)pyrrolo[1,2-a]-quinoxaline 5b , respectively. The structure of 4a,b was confirmed by the NOE measurement among the C₁ -H , C ₂-H and C ₉-H proton signals of 5a,b . An additional reaction mechanism was proposed for the ring transformation of isoxazolo[2,3-a]quinoxalines into pyrrolo[1,2-a]quinoxalines.     

Synthesis of quinoxaline derivatives via condensation of aryl-1,2-diamines with 1,2-Diketones using (NH4)6Mo7O24.4H2O as an efficient, mild and reusable catalyst

Ammonium heptamolybdate tetrahydrate [(NH₄)₆Mo₇O₂₄.4H₂O] efficiently catalyzes the condensation of aryl-1,2-diamines with 1,2-diketones in EtOH/H₂O as a green media at room temperature to afford quinoxaline derivatives as biologically interesting compounds. Ease of recycling of the catalyst is one of the most advantages of the proposed method.     

One‐Pot,Four‐Component Synthesis of Novel Spiro[indeno[2,1‐b]quinoxaline‐11,4′‐pyran]‐2′‐amines

A one‐pot, four‐component reaction for the efficient synthesis of novel spiro[indeno[2,1‐b]quinoxaline‐11,4′‐pyran]‐2′‐amines by using InCl₃ is described. The syntheses are achieved by reacting ninhydrin with 1,2‐diaminobenzenes to give indenoquinoxalines, which are trapped in situ by alkyl malonates and various α‐methylencarbonyl compounds through cyclization, providing multifunctionalized spiro‐substituted indeno[2,1‐b]quinoxaline‐11,4′‐pyran‐2′‐amines.     

Synthesis of pyrrolo[1,2-a]quinoxaline derivatives by the reaction of 2-hydroxy-1,5-diketones with o-phenylenediamine

The reaction of 2-hydroxy-1,5-diketones with o-phenylenediamine leads to the formation of 4,5-dihydropyrrolo[1,2-a]quinoxaline derivatives, which are dehydrogenated by the action of MnO₂ to give the corresponding pyrrolo[1,2-a]quinoxaline derivatives.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 112–115, January, 1992.     

Iodine-Promoted Domino Oxidative Cyclization for the One-Pot Synthesis of Novel Fused Four-Ring Quinoxaline Fluorophores by sp3 C−H Functionalization

A method for the synthesis of novel fused four-ring quinoxaline skeleton has been described by an I₂ promoted sp³ C−H functionalization between 1,2,3,3-tetramethyl-3H-indolium iodides and 1,2-diamines. This transformation proceeds smoothly under metal- and peroxide-free conditions through a sequential iodination, oxidation, annulation and rearrangement. Moreover, 8,9-dichloro-5,12,12-trimethyl-2-(trifluoromethyl)-5,12-dihydroquinolino[2,3-b]quinoxaline showed good photophysical properties and was used in live cell imaging, indicating the potential value of this skeleton as a fluorophore in probes.     

Oxidation of alkynes using PdCl2/CuCl2 in PEG as a recyclable catalytic system: one-pot synthesis of quinoxalines

Alkynes were oxidized efficiently using the catalytic amount of PdCl₂ and CuCl₂ in PEG-400 in the presence of water, providing excellent yields of the corresponding 1,2-diketones. A variety of alkynes were well-suited substrates for the oxidation under the described conditions. Further, the optimized conditions were successfully utilized for the one-pot synthesis of 2,3-disubstituted quinoxaline derivatives.     

A rapid and efficient method for 1,3-dithiolane synthesis

A mild, efficient and solvent-free protocol for conversion of aldehydes and ketones into their corresponding 1,3-dithiolanes using 1,2-ethanedithiol in the presence of a catalytic amount of SnCl₂·2H₂O is reported.     

Room temperature Fe(NO3)3·9H2O/TEMPO/NaCl-catalyzed aerobic oxidation of homopropargylic alcohols

A practical and eco-friendly aerobic oxidation of homopropargylic alcohols using Fe(NO₃)₃·9H₂O/TEMPO/NaCl as catalysts at room temperature under atmospheric pressure was developed affording corresponding homopropargylic ketones with moderate to good yields. Aryl, heteroaryl as well as alkyl 1,2-allenic ketones were obtained by the isomerization of corresponding terminal homopropargylic ketones through column chromatographic workup on silica gel.     

Selective 1,2-dihalogenation and oxy-1,1-dihalogenation of alkynes by N-halosuccinimides

1,2-Dihalogenation and oxy-1,1-dihalogenation of alkynes by N-halosuccinimides can be selectively realized through using different reaction conditions. α,β-Dihalo alkenes were obtained exclusively using THF as solvent without using any catalyst, while α,α-dihalo ketones were synthesized using a mixed solvent of THF and H₂O in the presence of FeCl₃·6H₂O. Terminal aromatic alkynes are smoothly transformed into α,α-dihalo ketones on water without a catalyst.     

An efficient and convenient protocol for the synthesis of quinoxalines and dihydropyrazines via cyclization-oxidation processes using HClO4·SiO2 as a heterogeneous recyclable catalyst

A convenient and straightforward method has been developed for the synthesis of quinoxalines and dihydropyrazines (DHPs) using α-bromo ketones and 1,2-diamines in the presence of silica supported perchloric acid (HClO₄·SiO₂) at room temperature. The quinoxalines and DHPs were presumably formed via cyclization-oxidation. The catalyst works under heterogeneous conditions and can be recycled.     

A simple and efficient route to 2-arylimidazo[1,2-a]pyridines and zolimidine using automated grindstone chemistry

A green and efficient mechanochemical method for the synthesis of a series of 2-arylimidazo[1,2-a]pyridines was developed using an electrical grinder. I₂ catalyzed mechanochemical grinding facilitates the cyclocondensation reaction between various aryl methyl ketones and 2-aminopyridines to afford 2-arylimidazo[1,2-a]pyridines in good yields at ambient temperature. The method was successfully used for the gram-scale synthesis of a marketed drug, zolimidine. The noticeable advantages of this environmentally sustainable protocol include mild conditions, simple instrumentation, inexpensive catalyst, atom economy, short reaction time etc.     

A mild and variable synthesis of α-ketoesters

The ZnCl₂ promoted addition of 1,2-diethoxy-1,2-disilyloxyethylene 1 with electrophiles such as aldehydes, ketones, α,β-unsaturated ketones or tertiary alkyl halides allows for a simple synthesis of α-ketoesters.     

Diversity‐Oriented Synthesis of Novel 2′‐Aminospiro[11H‐indeno[1,2‐b]quinoxaline‐11,4′‐[4H]pyran] Derivatives via a One‐Pot Four‐Component Reaction

A sequential one‐pot four‐component reaction for the efficient synthesis of novel 2′‐aminospiro[11H‐indeno[1,2‐b]quinoxaline‐11,4′‐[4H]pyran] derivatives 5 in the presence of AcONH₄ as a neutral, inexpensive, and dually activating catalyst is described (Scheme 1). The syntheses are achieved by reacting ninhydrin ( 1 ) with benzene‐1,2‐diamines 2 to give indenoquinoxalines, which are trapped in situ by malono derivatives 2 and various α‐methylenecarbonyl compounds 4 through cyclization, providing the multifunctionalized 2′‐aminospiro[11H‐indeno[1,2‐b]quinoxaline‐11,4′‐[4H]pyran] analogs 5 . This chemistry provides an efficient and promising synthetic way of proceeding for the diversity‐oriented construction of the spiro[indenoquinoxalino‐pyran] skeleton.     

Expeditious synthesis of diverse spiro fused quinoxaline derivatives using magnetically separable core–shell CoFe2O4@SiO2‐SO3H nanocatalyst under ultrasonication

A magnetically separable core–shell CoFe₂O₄@SiO₂‐SO₃H nanocatalyst has been successfully exploited as a heterogeneous acid catalyst in the synthesis of diversely substituted biologically important spiro fused pyrrolo/indolo[1,2‐a]quinoxaline derivatives through the condensation of N‐(2‐aminophenyl)pyrroles/indoles and various cyclic conjugated 1,2‐diones in ethanol under ultrasonic irradiation. Room temperature synthesis, short reaction time, wide substrate scope, good to excellent yield of products and use of a magnetically separable and recyclable nanocatalyst make this method attractive and practicable.     

Asymmetric Hydrogenation of α-Hydroxy Ketones: A Reaction Sensitive toward Electronic Effect of Substrates

以[RuCl2(benzene)]2 和 SunPhos为原料现场制备的催化剂,催化不对称氢化α-羟基酮类化合物可获得手性1, 2-二醇类化合物,ee值最高达99%。     

Lithium bromide as an efficient,green, and inexpensive catalyst for the synthesis of quinoxaline derivatives at room temperature

Abstract

An efficient, simple, and green procedure for the synthesis of quinoxaline derivatives is described. The condensation of 1,2-diamines with 1,2-diketones using lithium bromide (LiBr) in H₂O/EtOH as a green reaction media at room temperature affords the title compounds in high to excellent yields and in short reaction times.     

Reactive organoallyl species generated from aryl halides and allene: allylation of α,β-unsaturated aldehydes and cyclic ketones employing Pd/In transmetallation processes

Allylation of α,β-unsaturated aldehydes and cyclic ketones promoted by Pd/In transmetallation processes has been studied. The unsaturated aldehydes underwent regioselective 1,2-addition to afford secondary homoally alcohols. The reactions have been performed using Pd(OAc)₂/PPh₃ as catalytic system and metallic indium affording the products in good yields. The same transformation with unsaturated ketones proved to be less efficient, while saturated cyclic ketones delivered generally excellent yields in the presence of CuI. In these latter processes the presence of a distal heteroatom influences the reaction rate.     

Rhodium-catalyzed α-methylthiolation reaction of unactivated ketones using 1,2-diphenyl-2-methylthio-1-ethanone for the methylthio transfer reagent

In the presence of catalytic amounts of RhH(PPh₃)₄, 1,2-bis(diphenylphosphino)ethane (dppe), and dimethyl disulfide, ketones without α-activating groups were α-methylthiolated with 1,2-diphenyl-2-methylthio-1-ethanone giving α-methylthio ketones. The reaction of unsymmetrical ketones proceeded at the more substituted carbons. The initial formation of kinetic α-methylthiolated products followed by their rearrangement to thermodynamic products was observed in the reaction of α-phenyl ketones. Aldehydes, phenylacetate, and phenylacetonitrile were also α-methylthiolated under these conditions.     

A chain of π‐stacked molecules in 4‐(2‐chlorophenyl)pyrrolo[1,2‐a]quinoxaline and a hydrogen‐bonded sheet in (4RS)‐4‐(1,3‐1,3‐benzodioxol‐6‐yl)‐4,5‐dihydropyrrolo[1,2‐a]quinoxaline

In the molecule of 4‐(2‐chlorophenyl)pyrrolo[1,2‐a]quinoxaline, C₁₇H₁₁ClN₂, (I), the bond lengths are consistent with electron delocalization in the two outer rings of the fused tricyclic system, with a localized double bond in the central ring. The molecules of (I) are linked into chains by a π–π stacking interaction. In (4RS)‐4‐(1,3‐benzodioxol‐6‐yl)‐4,5‐dihydropyrrolo[1,2‐a]quinoxaline, C₁₈H₁₄N₂O₂, (II), the central ring of the fused tricyclic system adopts a conformation intermediate between screw‐boat and half‐chair forms. A combination of N—H...O and C—H...π(arene) hydrogen bonds links the molecules of (II) into a sheet. Comparisons are made with related compounds.     

One-pot synthesis of pyrrolo[1,2-a]quinoxaline and pyrrolo[1,2-a]pyrazine derivatives via the three-component reaction of 1,2-diamines,ethyl pyruvate and α-bromo ketones

A simple synthetic protocol has been developed involving the three-component reaction between 1,2-diamines, ethyl pyruvate and a-bromo ketones in the presence of Fe Cl3 as a catalyst. A number of pyrrolo[1,2-a]quinoxaline and pyrrolo[1,2-a]pyrazine derivatives were synthesized in excellent yields using this protocol.