Enaminones in Heterocyclic Synthesis

Synthesis, Theoretical Study, and Anticonvulsant Evaluation of N-Arylenaminones

N-Arylenaminones are highly versatile compounds which can be synthesized in relatively simple ways. In this work we explored the synthesis of the four monosubstituted N-(4-R-phenyl)enaminones 3 a (R=NO2), 3 b (R=F), 3 c (R=H), and 3 d (R=OMe) with the goal of determining the influence of the substituents' electronic effects on tautomer stability and biological activity. These compounds were analyzed by means of Density Functional Theory calculations (DFT), to evaluate the relative stability of the possible tautomers. We found that the enaminone structure is the most stable with respect to the ketoimine and iminoenol forms. In addition, all four compounds display anticonvulsant activity, with 3 d being the one that mostly increased latency and mostly decreased the number of convulsions with respect to the control group. The suggested mechanism of action involves blockage of the voltage-dependent Na+ channels, considering that these molecules meet the structural characteristics needed to block the receptor, as is the case of the positive control molecules phenytoin (PHT) and valproic acid (VPA).

Iodine promoted cyclization of N,N′-diphenylthiocarbamides with enaminones: a protocol for the synthesis of poly-substituted 2-iminothiazolines

An iodine promoted cyclization reaction between N,N′-diphenylthiocarbamides and enaminones was achieved, providing a series of poly-substituted 2-iminothiazolines.

(3E)-4-[(Naphthalen-1-yl)amino]pent-3-en-2-one hemihydrate

The title compound, C15H15NO·0.5H2O, was prepared from α-naphthylamine and 2,4-pentanedione in a 1:1 ratio. An intramolecular N—H...O hydrogen bond in the N-naphthylpent-3-en-2-one molecule involving the amine and carbonyl groups strengthens the structure. The water molecule interacts with two symmetry-related N-naphthylpent-3-en-2-one molecules viaby O—H...O hydrogen bonds.

Syntheses and structures of two benzoyl amides: 2-chloro-4-eth-oxy-3,5-dimeth-oxy-N-(3-oxo-cyclo-hex-1-en-1-yl)benzamide and 2-chloro-N-(5,5-dimethyl-3-oxo-cyclo-hex-1-en-1-yl)-4-eth-oxy-3,5-di-meth-oxy-benzamide

The first title benzoyl amide, C₁₇H₂₀ClNO₅ (3a), crystallizes in the monoclinic space group P2₁/c with Z = 4 and the second, C₁₉H₂₄ClNO₅ (3b), also crystallizes in P2₁/c with Z = 8 (Z' = 2), thus there are two independent mol-ecules in the asymmetric unit. In 3a, the phenyl ring makes a dihedral angle of 50.8 (3)° with the amide moiety with the C=O group on the same side of the mol-ecule as the C-Cl group. One meth-oxy group is almost in the plane of the benzene ring, while the eth-oxy and other meth-oxy substituent are arranged on opposite sides of the ring with the eth-oxy group occupying the same side of the ring as the C=O group in the amide moiety. For one of the two mol-ecules in 3b, both the amide and 5,5-dimethyl-3-oxo-cyclo-hex-1-en-1-yl moieties are disordered over two sets of sites with occupancies of 0.551 (2)/0.449 (2) with the major difference between the two conformers being due to the conformation adopted by the cyclo-hex-2-en-1-one ring. The three mol-ecules in 3b (i.e., the undisordered mol-ecule and the two disorder components) differ in the arrangement of the subsituents on the phenyl ring and the conformation adopted by their 5,5-dimethyl-3-oxo-cyclo-hex-1-en-1-yl moieties. In the crystal of 3a, N-H⋯O hydrogen bonds link the mol-ecules into a zigzag chain propagating in the [001] direction. For 3b a combination of C-H⋯O and N-H⋯O inter-molecular inter-actions link the mol-ecules into a zigzag ribbon propagating in the [001] direction.

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.

An Unexpected Reaction of Isodehydracetic Acid with Amines in the Presence of 1-Ethyl-3-(3-dimethylaminopropyl) Carbodiimide Hydrochloride Yields a New Type of β-Enaminones

The reaction of isodehydracetic acid with amines was serendipitously found to afford β-enaminones in the presence of the coupling agent 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC). Under the optimal reaction condition, 23 examples of α-aminomethylene glutaconic anhydride were obtained at approximately 30−80% yields. This is a concise, operationally simple method to expediently synthesize a new type of β-enaminone-containing compound.

Metal-Free Method for Direct Synthesis of Functionalized β-Ketoenamines

A new method for direct synthesis of β-ketoenamines was developed by a BF₃·OEt₂-catalyzed cyclization of 1-iodoalkyne and α-keto acid followed by an amine-mediated ring-opening in one pot. Its metal-free conditions allowed the easy synthesis of those products bearing the transition metal-sensitive functional groups. Its three-component process achieved wide range of functionalized products.

Special feature of kinetics of ZcE isomerization of β-N-methylaminovinyl trifluoromethyl ketone in Ar matrix exposed to UV radiation and spontaneous E⇌Z isomerization of α-methyl-β-N-methylaminovinyl trifluoromethyl ketone

Although it is well known that reactivity of α,β-unsaturated enaminoketones is closely associated with spatial and electronic structure but until now little attention was devoted to quantitative investigation of interconversion of different stereoisomeric forms of enaminoketones. In present work we studied peculiarities of kinetics of Z⇌E isomerization of enaminoketone 4-(N-methylamino)-1,1,1-trifluorobut-3-en-2-one F₃C-COCHCHNH(CH₃) (1) in Ar-matrix exposed to UV-radiation (λ=340nm) with IR Fourier and 2D correlation spectroscopy and we found that Z-s-Z-s-trans isomer transforms primarily into two E-isomers, E-s-E-s-trans and E-s-Z-s-trans which further turn into the E-s-E-s-cis and E-s-Z-s-cis conformers all interconversion rate constants being comparable in magnitude. Along with this process long-term exposure to the UV-radiation results in proton transfer from nitrogen of methylamino group to carbonyl oxygen with simultaneous isomerization of 'cyclic' iminoenol form into 'linear'one. In solution of enaminoketone 4-(N-methylamino)-1,1,1-trifluoro-3-methylbut-3-en-2-one F₃C-CO-C(CH₃)CH-NH(CH₃) (2) we observed reversed process, namely, spontaneous interconversion of the E-s-E-s-trans and E-s-Z-s-trans conformers into the Z-s-Z-trans isomer. It was found that rate constants of the dimeric forms of the E-s-E-s-trans and E-s-Z-s-trans conformers are higher than those of the monomers and are independent on total enaminoketone concentration. Addition of highly polar HMPA promotes proton transfer from nitrogen to oxygen in the Z-s-Z-s-trans isomer of 2 with subsequent isomerization into the linear imino-enol product but the rate constant of this transformation is ten-fold smaller than that for 1 in the Ar matrix exposed to UV radiation.

Oxazaborinines from Vinylogous N-Allylic Amides: Reactivities of Underexplored Heterocyclic Building Blocks

Access to a new class of oxazaborinines using an efficient transition-metal-catalyzed rearrangement is demonstrated. The method overcomes the synthetic challenge of achieving an aza-Claisen rearrangement of vinylogous N-allylic amide substrates, giving rise to a variety of highly modifiable oxazaborinine products. An investigation of the unique reactivity of these boron-based heterocycles has unveiled their underexplored potential as valuable building blocks and intermediates for organic synthesis.

Recent developments in chemical reactivity of N,N-dimethylenamino ketones as synthons for various heterocycles

This review demonstrates the high number of synthetic applications of enaminones in the preparation of acyclic, carbocyclic, heterocyclic and fused heterocyclic compounds.

Trivedi E, Török B, Dembinski R. Regioselective “hydroamination” of alk-3-ynones with non-symmetrical o-phenylenediamines. Synthesis of diversely substituted 3H-1,5-benzodiazepines via (Z)-3-amino-2-alkenones

Reaction of alk-3-yn-1-ones with non-symmetricalo-phenylenediamines provides an effective method with high atom economy for the synthesis of diversely substituted 1,5-benzodiazepines and conjugated enaminones.

Synthesis of α-enamino esters via Cu(ii)-promoted dehydrogenation of α-amino acid esters: application to the synthesis of polysubstituted pyrroles

α-Enamino esters are synthesized from α-amino acid esters using Cu(ii)-promoted dehydrogenation. Application of the α-enamino esters to the synthesis of polysubstituted pyrroles is achieved through oxidative coupling with alkynes under Cu(ii)-promoted conditions.

Efficient synthesis of functionalized spiro[indoline-3,4'-pyrrolo[3,4-b]pyridines] via one-pot three-component reaction

Diverse functionalized spiro[indoline-3,4'-pyrrolo[3,4-b]pyridines] were efficiently synthesized by the three-component reaction of 3-arylamino-1-methyl-H-pyrrole-2,5-dione, isatins and malononitrile (ethyl cyanoacetate) in ethanol in the presence of triethylamine. This reaction not only provided a convenient synthetic method for the construction of a versatile spirooxindole system, but also access to reactive β-enaminone and its derivatives for organic and medical chemistry.

A catalyst-free multicomponent domino sequence for the diastereoselective synthesis of (E)-3-[2-arylcarbonyl-3-(arylamino)allyl]chromen-4-ones

The three-component domino reactions of (E)-3-(dimethylamino)-1-arylprop-2-en-1-ones, 3-formylchromone and anilines under catalyst-free conditions afforded a library of novel (E)-3-(2-arylcarbonyl-3-(arylamino)allyl)-4H-chromen-4-ones in good to excellent yields and in a diastereoselective transformation. This transformation generates one C–C and one C–N bond and presumably proceeds via a reaction sequence comprising a Michael-type addition–elimination reaction, a nucleophilic attack of an enamine to a carbonyl reminiscent of one of the steps of the Bayllis–Hilman condensation, and a final deoxygenation. The deoxygenation is assumed to be induced by carbon monoxide resulting from the thermal decomposition of the dimethylformamide solvent.