Conformational study of chiral heterocyclic enamino ketones

An assumption regarding the existence of a homoconjugation effect involving enaminoketo and phenyl groups as a result of the drawing together in space of their orbitals was made on the basis of circular dichroism (CD) data and an examination of the preferred conformations of two-ring enamino ketones with -phenylethyl and -benzylethyl substituents. A study of enamino ketones with a chiral alkyl substituent attached to the nitrogen atom made it possible to confirm this assumption.Communication XLIX from the series Stereochemical Studies. See [1] for communication XLVIII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1230–1233, September, 1978.     

Synthesis and rotatory dispersion of cisoid bicyclic enamino ketones

Optically active cisoid, bicyclic, enamino ketones — N-(-phenylethyl)-4-keto-^9,10-octa-hydroquinoline and N-(-phenylethyl)-4-keto-^8,9-hexahydropyridine — were synthesized by the condensation of ethyl -[N-(-phenylethyl)amino]propionate with cyclohexanone and cyclopentanone, while ethyl -(N-benzylamino)propionate and cyclohexanone gave N-benzyl-4-keto-^9,10-octahydroquinoline. A study of the rotatory dispersion of the compounds obtained demonstrated that a strong positive Cotton effect at 330–350 nm, which is associated with the presence of a cis-enamino ketone chromophore, is characteristic for them.Communication XXVIII of the series Stereochemical Investigations. See [1] for communication XXVII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 541–545, April, 1972.     

Novel photochemical reactions of enamino ketones

Irradiation of the conjugated N-aryl enamino ketone (V) yielded the indole (VI) resulting from a novel decomposition of the ylide intermediate.     

Synthesis of enamino ketones from 4,5-dihydropyrazoles

Enamino ketones were synthesized in 97–99% yield by reactions of 4,5-dihydropyrazoles with 1,3-dicarbonyl compounds.     

Novel and facile synthesis of fluorinated enamino ketones and amino alcohols

Selected imines and one bis-imine react via their enamine tautomers with terminal perfluorinated epoxides, e.g. hexafluoropropene oxide to produce fluorinated enamino ketones or imino ketones. In contrast, internal perfluorinated linear epoxides and one cyclic epoxide yield intermediate imino alcohols, which in one case added hexafluoroacetone, furnishing a new imino diol investigated by X-ray diffraction.     

Conformational analysis of medium-ring ketones

The conformations of cyclooctanone, cyclooctane-1,5-dione, cyclononanone, ayclodecanone, cyclodecane-1,6-dione, and cycloundecanone are discussed.     

Functionalized silicon-containing imino enols and enamino ketones prepared by hydrolytic condensation

A mixture of two isomers of organosilicon carbofunctional compounds, 4-(3′-triethoxysilylpropylimino)pent-2-en-2-ol (EtO)₃Si-CH₂CH₂CH₂-N=C(Me)-CH=C(Me)-OH (Ia, 83%) and 4-(3′-triethoxysilylpropylamino)pent-3-en-2-one (EtO)₃-CH₂CH₂CH₂-NH-C(Me)=CH-C(O)Me (Ib, 17%) was prepared by reaction of 3-aminopropyltriethoxysilane with acetylacetone. The use of trimethylsilyl ether of acetylacetone instead of acetylacetone yields Ia (84%) and silylated derivatives (Me₃SiO)_n(EtO)_3?n Si-CH₂CH₂CH₂-N=C(Me)CH=C(Me)OH (II) (16%). Solid, liquid, or resinous products were prepared by hydrolytic condensation of I and II. Compositions for preparing transparent sol-gel films were developed.     

Cross-dehydrogenative coupling between enamino esters and ketones: synthesis of tetrasubstituted pyrroles

Tetrasubstituted pyrroles have been synthesized via the cross-dehydrogenative coupling between enamino esters and acetone. Silver carbonate proved to be an effective oxidant, and no transition metal catalyst is necessary.     

Conformational studies by nuclear magnetic resonance—III: ASIS and protonation studies of the rotational isomerism of enamino aldehydes and ketones

The s-cis ? s-trans equilibrium of several enamino ketones and aldehydes, has been evaluated based on the results of aromatic solvent induced shift measurements and of protonation of the title compounds. In contrast to α,β-unsaturated ketones bearing no heteroatom, the Δδ_3,cis value but not the Δδ_3,trans, proved to be useful in conformational assignments. Protonation, which occurs mainly on oxygen, enhances the rotational barrier, thus enabling the observation of both rotamers at room temperature. Steric hindrance to conjugation enhances the rate of protonation at the carbon C².     

Principal component analysis of the 13C NMR spectra of enamino ketones

The ¹³C NMR spectra of eleven 3-N,N-dialkylamino-5,5-dimethylcyclohex-2-en-1-ones have been determined. The chemical shifts of the three sp² carbons and of the two methylene carbons on the cyclohexenone moiety have been subjected to factor analysis. Two factors are necessary and sufficient to account for more than 93% of the total variance. The more important axis (79%) corresponds to a factor closely related to the inductive and steric effects of the alkyl nitrogen substituents. The second parameter is more difficult to interpret and could correspond to the ‘ipso effects’ of amino groups.     

Tetrazole compounds. 8. Synthesis of tetrazolylpyrimidines from tetrazolyl-substituted enamino ketones

Tetrazolyl-substituted enamino ketones 1 react with various amidines 2 to give 5-(1-phenyl-1H-tetrazol-5-yl)pyrimidines 3 . In the case of the chloroacetyl enamine 4 4-(N,N-dimethylaminomethyl)-substituted tetra-zolylpyrimidines 5 were obtained. Subsequent hydrolysis of the 4-trifluoromethyl derivatives 3b, 3d and 3g afforded the corresponding 5-(1-phenyl-1H-tetrazol-5-yl)pyrimidine-4-carboxylic acids 6 .     

Conformational studies by nuclear magentic resonance—II: The effect of steric factors on hindered rotation in enamino aldehydes and ketones

Rotational barriers of the dimethylamino group in different enamino aldehydes and ketones have been applied for evaluation of their conformation. It has been maintained that repulsion between bulky substituents causes twisting of the molecule rather than planar deformations. Arguments for and against these alternative concepts based on the analysis of J_HH and J(¹³CH) coupling constants in different fragments of the molecule have been discussed.     

Enamines. 9. Polarographic reduction of enamino ketones in aqueous media

The mechanism of the polarographic reduction of cyclic enamino ketones of the pyrrolidine, piperidine, and hexahydroazepine series of two types, viz., compounds in which the -carbon atom of the enamine is included in the azoheteroring, and enamino ketones in which the double bond is located outside the cyclic system, was investigated. The acyclic analogs were also studied. It is shown that the two- or four-electron reduction depends substantially on the structures of the investigated compounds and the pH of the medium; this in turn is associated with a change in the character, rate, and site of protonation of the enamino ketones and the compounds formed as a result of their reduction.See [1] for communication 8.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 357–364, March, 1981.     

Enamines. 8. Polarographic study of the reactions of a number of enamino ketones with nucleophilic reagents

The hydrolysis and hydrazinolysis of cyclic enamino ketones of the pyrrolidine, piperidine, and hexahydroazepine series, as well as their noncyclic analogs, were investigated. It is shown that these processes have several principles in common. A bell-shaped dependence of kobs on the pH of the medium is characteristic for hydrolysis; the reaction of the enamino ketones with hydrazine hydrate in absolute ethanol is accelerated in the presence of p-toluenesulfonic acid. It is shown that the rates of hydrolysis and hydrazinolysis depend on the size of the saturated azaheteroring and change in the order 6 > 5 > 7. A possible mechanism for the processes in which the slow step is C-protonation and(or) attack by the nucleophilic reagent in the enamine position is discussed.See [1] for Communication 7.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No, 3, pp. 352–356, March, 1981.     

Conformational study on some β-phenyl-α,β-unsaturated ketones

The conformation of three (E)-β-phenyl-α,β-unsaturated ketones and their corresponding (Z)-isomers 1, 2, and 3 was established by IR and ASIS. (Z)-1 and (E)-1 have exclusively the s-trans conformation. The two isomers of 2 occur in both conformations but there is a higher s-cis to s -trans ratio with the (Z) than with the (E)-isomer. (Z)-3 appears to exist exclusively in the s-cis conformation, the (E)-isomer has a small content of the s-trans conformation. It was concluded that the ASIS for H_b, is a measure of the s-cis content of the conformational equilibrium.     

Carbon-13 magnetic resonance spectra of quaternary ammonium salts derived from enamino ketones

¹³C magnetic resonance spectra of nine quaternary ammonium salts of the general formula R¹C¹(O)C²H?C³HNR₃⁴Cl (where R¹, R⁴ = alkyl) were obtained and compared with those of the parent amino compounds. The chemical shift differences between these two classes of compounds are qualitatively accounted for by π-electron density changes. Steric effects and hyperconjugation of the alkyl substituents are also discussed.     

Selective amidoalkylation of cyclic enamino ketones with N-acyliminium salts of 3,4-dihydroisoquinolines

A series of cyclic enaminoketones were selectively amidoalkylated at the α-carbon in reactions with acyliminium reagents derived from 3,4-dihydroisoquinolines.