Copper-promoted Chan-Lam coupling between enaminones and aryl boronic acids

A novel copper-promoted N-arylation of enaminones with aromatic boronic acids has been developed, which provides an efficient way to synthesize N-aryl enaminones with a broad substrate scope and excellent functional group compatibility. The N-aryl enaminones could be converted into a series of highly valuable building blocks and bioactive compounds. Notably, in comparison with traditional methods, this alternative approach provides accesses to N-aryl enaminones bearing multiple aromatic rings.     

CF3S(O)n-containing enaminones as precursors for the synthesis of pyrimidine-4(3H)-ones

Methyl 3-(dimethylamino) acrylates containing trifluoromethylsulfenyl-, trifluoromethylsulfinyl-, and trifluoromethylsulfonyl groups were synthesized and their utility demonstrated by reactions with aliphatic and aromatic amidines to produce 2,5-substituted 4(3H)-pyrimidones. Cyclization reactions of enaminones with urea or thiourea led to 5-substituted uracil or 2-thiouracil derivatives, respectively.     

Tautomerism in ketomethylquinolines—IV. The ultraviolet spectra of 2-ketomethylquinolines

Ultraviolet spectral data for a series of 36 2-ketomethylquinolines have been recorded. Members previously shown to be exclusively keto tautomers had spectra closely similar to that of 2-methylquinoline. Most of the rest, which were largely or exclusively in the enaminone forms, showed strong long wavelength absorptions. These are shown to be consistent with cis—s—cis enaminone structures. In aqueous acid, most of the enaminones protonated on carbon and those with electron-withdrawing groups were deprotonated in molar aqueous sodium hydroxide.     

Reactions of imines with 2,2-difluoro-2-fluorosulfonylacetyl fluoride

Selected N-alkyl ketoimines having at least one methyl group at the imino carbon were reacted in a Stork enamine reaction with 2,2-difluoro-2-fluorosulfonylacetyl fluoride to yield enaminones carrying one fluorosulfonyldifluoromethylene function. In the case of N-tertbutyl methyl aldimine two of these groups were present in a triketone derivative. Taking a ethylene bis(imine) also a ring closure reaction was observed, proven by X-ray structure analysis.     

One-pot synthesis of isoxazoles from enaminones: an application of Fe(II) as the catalyst for ring expansion of 2H-azirine intermediates

We report an application of FeCl₂ as an inexpensive, nontoxic, and efficient catalyst in a clean ring expansion reaction of 2H-azirine derivatives, an intermediate formed through the PhI(OAc)₂-mediated azirination of readily available enaminones. An alternative one-pot protocol for the synthesis of various substituted isoxazoles from their corresponding enaminones has been further established based on this reaction, and herein described.     

Efficient syntheses of novel indeno[1,2-b]chromenone derivatives via hetero-Diels-Alder reactions of 2-(arylmethylene)-1H-indene-1,3(2H)-diones with enaminones

Efficient syntheses of novel 10-aryl-5a-(arylamino)-9-hydroxy-5a,6,7,8-tetrahydroindeno[1,2-b]chromen-11(10H)-one derivatives has been reported by [4+2] cycloaddition reactions of electron-deficient 2-(arylmethylene)-1H-indene-1,3(2H)-dione heterodienes with electron-rich enaminones in [bmim]BF₄ at 80?°C and in acetic acid at 80?°C. Dimedone/cyclohexane-1,3-dione enaminones have been used as dienophiles in Inverse Electron Demand hetero-Diels-Alder reactions. The products were obtained in high yields by a simple work up.     

Synthesis of N-substituted carbazolones from α-iodo enaminones via Pd(0)-catalyzed intramolecular coupling under microwave irradiation

A variety of N-aryl and N-alkyl carbazolones were conveniently achieved in good to high yields via Pd₂(dba)₃-mediated intramolecular coupling of N-substituted α-iodo enaminones under microwave irradiation. The Pd(0)-catalyzed cyclization was found to proceed favorably with the more electron-deficient phenyl ring during the reactions involving unsymmetrical N,N-diaryl α-iodo enaminones. This unique property enables the construction of carbazolone skeleton containing nitro substituted benzenoid ring.     

Efficient synthesis of novel functionalized pyrazolo-pyranoquinoline and tetrahydrodibenzo-[1,8]naphthyridinone derivatives

The facile and efficient synthesis of 1,4-dihydropyrazolo-pyrano-[2,3-b]quinoline derivatives from the reaction of 2-chloroquinoline-3-carbaldehydes and pyrazolones is described. Moreover, a one-pot method for the development of functionalized tetrahydrodibenzo[b,g][1,8]naphthyridinone derivatives is reported by using a three-component reaction of 2-chloroquinoline 3-carbaldehydes, pyrazolone, and enaminones catalyzed by l-proline in EtOH.     

Reactions of carbethoxycarbene with enaminones. Formation of unexpected pyrroles

The reactions of carbethoxycarbene (:CH₂-CO₂Et, 2) with several acyclic enaminones (RCOCH=CR¹NHR², 3) lead to the unexpected formation of 2-Me, 3-CO₂Et, 4-H, 5-R¹-pyrroles 4 . Structural variations of the enaminones show that the structural fragments C(3)-CO₂Et and C(2)-Me are provided by 2 and that the fragment C(5)-R¹NHR² originates from the enaminones 3 , while the RCO group from 3 is eliminated during the course of reaction. Reactions with cyclic and nitrogen-hindered enaminones do not lead to pyrrole formation but occur by simple insertion of 2 to the Cα-H bond.     

Silver-catalysed hydroamination: synthesis of functionalised pyrroles

It has been shown that functionalised pyrroles can be efficiently prepared using a two-step sequence. This sequence involves the propargylation of secondary enaminones using n-BuLi and propargyl bromide, followed by intramolecular hydroamination catalysed by silver nitrate. The hydroamination can be carried out at room temperature (overnight) or in a domestic microwave oven (60 s).     

Acid-promoted metal-free synthesis of 3-ketoquinolines from amines,enaminones and DMSO

A metal-free p-toluenesulfonic acid (TsOH·H₂O) mediated synthesis of 3-ketoquinolines from anilines, enaminones and DMSO has been developed. In this transformation, DMSO was activated by TsOH·H₂O and provided the one-carbon unit of the 3-ketoquinolines. A plausible mechanism involving an electrophilic sulfenium ion intermediate was proposed.     

Regioselective addition of cyclic nitrones to Feist��s acid dimethyl ester

Cyclic nitrones, viz., tetrahydropyridine 1-oxide, 3,4-dihydroisoquinoline 2-oxide, and 2-methoxycarbonyl-4,5-dihydro-3H-pyrrole 1-oxide, regioselectively add to dimethyl 3-methylidenecyclopropane-1,2-dicarboxylate to form 5-spirocyclopropaneisoxazolidines. The latter undergo isomerization upon heating to give the corresponding tetrahydropyridin-4-ols and enaminones.     

Studies with enaminones and enaminonitriles: synthesis of 3-aroyl and 3-heteroaroyl-pyrazolo-[1,5-a]pyrimidines

The reaction of electron rich aromatics with cyanoacetic acid and acetic anhydride afforded 3-oxoalkanenitriles. Indium trichloride was used as a Lewis acid catalyst when the aromatic ring was not sufficiently reactive. The synthesized 3-oxoalkanenitriles were subsequently condensed with dimethylformamide dimethylacetal (DMFDMA) to yield enaminones that reacted readily with hydrazine hydrate to yield 4-aroylpyrazole-3-amines. The 4-aroylpyrazole-3-amines were condensed with enaminones to yield 3-aroylpyrazolo[1,5-a]pyrimidines.     

Reaction of [3-(Dimethylamino)-2-Azaprop-2-en-1-Ylidene] Dimethylammonium Chloride with Grignard Reagents

Abstract

We recently reported¹ that [3-(Dimethylamino)-2-azaprop-2-en-1-ylidene] dimethylammonium chloride² (1) could be reacted with anions derived from ketones or amides to produce enaminones or acylamidines, respectively.     

One‐Step Synthesis of 3,4‐Diphenyl‐2‐pyrrolinones by Solvent‐Free and Bi2O3‐Catalyzed Approaches and Cytotoxicity Screening Against Glioma Cells

Multifunctionalized 2‐pyrrolinones were synthesized from the formal aza‐[3 + 2] cycloaddition reaction of acyclic enaminones and diphenylcyclopropenone. For primary enaminones, solventless reaction under microwave heating was developed. On the other hand, catalysis by Bi₂O₃ under conventional heating was the more suitable strategy when secondary enaminones were employed. These conditions allowed the synthesis of a set of 2‐pyrrolinones with two vicinal phenyl substituents, which were evaluated for cytotoxicity against U251 and C6 glioblastoma cells. In general, all tested 2‐pyrrolinones with two vicinal phenyl rings were more active than those without this structural moiety, and 1‐butyl‐5‐methyl‐5‐(2‐oxopropyl)‐3,4‐diphenyl‐1,5‐dihydro‐2H‐pyrrol‐2‐one was the most cytotoxic and appears to be a new possibility as an antitumor scaffold to this aggressive brain tumor.     

Myrtine and epimyrtine,quinolizidine alkaloids from vaccinium myrtillus

The structures (including conformation and absolute configuration) of myrtine and epimyrtine, quinolizidine alkaloids from Vaccinium myrtillus, are reported. The two bases are obtainable from pelletierine by Mannich condensation with acetaldehyde, or can be derived stereospecifically by 1,4-nucleophilic addition to enaminones. They have been resolved with tartaric acid. The isomerization of myrtine is discussed.     

Enaminones as building blocks in organic synthesis: A novel route to polyfunctionally substituted benzonitriles,pyridines, eneylbenzotriazoles and diazepines

An efficient synthesis of enaminones 1a‐c is reported. Compounds 1a‐c reacted with diefhyl‐3‐amino‐2‐cyanopenten‐1,5‐dicarboxylate ( 3 ) to yield the benzonitriles 6 . On the other hand, the reaction of la‐c with 3‐amino‐2‐cyano‐2‐pentene dinitrile ( 7 ) afforded a mixture of benzonitriles 10 and pyridines 9 . The reaction of la‐c with 3‐aminocrotononitrile 11 has afforded the 4‐substituted‐3‐cyano‐2‐methylpyridines 15a‐c . The reaction of ethylene diamine with la‐c afforded 5‐substituted‐2,3‐dihydro‐lH‐[1,4]diazepines 18a‐c . On the other hand, la‐c reacted with o‐phenylenediamine to yield the 4‐(2‐aminopheynlamino)‐substituted enaminones 21 . Compounds 21 could be converted into the benzotriazolylenones 22 on treatment with sodium nitrite in acetic acid solution.     

Ruthenium catalyzed synthesis of enaminones

The Grubbs first-generation catalyst has been found to be an effective catalyst for the synthesis of enaminones by coupling thioamides with α-diazodicarbonyl compounds. The reaction is successful in converting primary, secondary, and tertiary thioamides into their corresponding enaminones. The reaction is also suitable for the synthesis of chiral enaminones.     

Enaminones as Synthons for a Directed C−H Functionalization: RhIII‐Catalyzed Synthesis of Naphthalenes

The use of enaminones as effective synthons for a directed C?H functionalization is reported. Proof‐of‐concept protocols have been developed for the Rh^III‐catalyzed synthesis of naphthalenes, based on the coupling of enaminones with either alkynes or α‐diazo‐β‐ketoesters. Two inherently reactive functionalities (hydroxy and aldehyde groups) are integrated into the newly formed cyclic framework and a broad range of substituents are tolerated, rendering target products readily available for further elaboration.     

Synthesis of 3-keto-quinolines from enaminones,anilines and DMSO: Transition metal free one pot cascade

An efficient and transition metal-free approach for the synthesis of functionalized 3-ketoquinolines from readily available anilines, enaminones and DMSO in the presence of K₂S₂O₈ has been conducted. This one pot tandem reaction proceeds through [3+2+1] cycloaddition reaction involving DMSO, enaminones and amines. In this environmental benign approach, DMSO acts as both a one carbon source and the solvent. A broad range of variously substituted amines and enaminones are successfully employed in this one pot tandem process to access a broad range of substituted 3-ketoquinolines.