Bogdan J. Kurtev

β-Ureido acids and dihydrouracils—VII: Applications of proton resonance spectroscopy—XXXII nmr spectra and conformation of dihydrouracils and related compounds

Abstract The NMR spectia of the cis and trans -isomers of 5,6-tetramethylenedihydrouracil (2,4-dioxo-decahydroquinazoline, TMDHU), 5,6-dimethyldihydrouracil (DMeDHU), 5,6-diphenyldihydrouracil (DPhDHU), 5-methyldihydroorotic acid (MeDHO), as well as those of dihydroorotic acid (DHO) and its methyl ester, and 6-phenyldihydrouracil (PhDHU) are reported. The J trans and J 16 coupling constants of these and other dihydrouracils are used in the conformational analysis. Contrary to earlier suggestions 3,4 of widely varying distortion of the dihydrouracil ring, the variation of cis J 56 and J 16 is best explained by electronegativity and equilibrium effects. Carboxy and methoxycarbonyl groups at C-6 prefer the axial orientation. A phenyl group at C-6. and the two phenyls in trans -DPhDHU, are predominantly axial in dimethyl sulphoxide, but equatorial in trifluoroacetic acid. The coupling constants of the cis and trans isomers of 2-ureidocyclohexane carboxylic (UCHA) and of the erytho and threo isomers of 2-methyl-3-ureidobutyric acid (MeUBA) and of 2,3-diphenyl-3-ureidopropionic acid (DPhUPA) indicate that with both isomers of MeUBA conformers with gauche hydrogens are preferred, while in the case of DPhUPA trans hydrogens predominate.

Thin-layer chromatography on silica gel as a method for assigning the relative configurations to some aliphatic diastereomeric compounds

Abstract Separation of 37 diastereomeric pairs of compounds from the group ArCH(X)CH(Y)Ar′ (X and Y are polar groups; Ar and Ar′ are phenyl or m -, p -alkoxy substituted phenyl groups) is achieved by thin-layer chromatography on silica gel. In all cases the erythro-isomers have higher R F values than do the corresponding threo-isomers, irrespective of the polarity of the developing solvents as well as of the formation of an intramolecular hydrogen bond between X and Y. The phenomena are explained on the basis of the preferred conformations of the diastereomers. Thin-layer chromatography on silica gel is proposed as a method for assigning the relative configurations of diastereomeric pairs of compounds of the above type.

Chromatographic behaviour of diastereoisomers : X. Thin-layer chromatographic retentions on silica of some (E)- and (Z)-oxazolones and related cinnamates as a function of mobile phase effects or Hammett constants

The thin-layer chromatographic behaviour of twenty diastereoisomeric 1,1-disubstituted 2-arylethenes [(Z)- and (E)-oxazolones and -cinnamates] on silica was studied using 40 mobile phases. The (E)-oxazolone and the (Z)-cinnamate were the stronger adsorbing isomers in all instances. The relative retentions and the retentions themselves were correlated with solvent selectivity effects or Hammett constants of the various substituents on the aryl group. Solvent selectivity effects were approximated on the basis of Snyders theory by the parameter localization, m, for experiments with mobile phases of constant strength, e, and by the molar fraction of one of the solvents for the experiments with binary mobile phases of increasing e. According to the data obtained, electronic effects determine the model of adsorption of any Z/E pair and steric effects modify it, controlling the relative retention which is not affected by solvent selectivity effects and the nature of the aryl group.

Circular dichroism of optically active 1,2-disubstituted 1,2-diphenylethanes—Part I: The cotton effects within the α-band

Resume Die zwei Phenylchromophore eines optisch aktiven 1,2-disubstituierten 1,2-Diphenylethans geben unabhangig voneinander Cotton-Effekte innerhalb des Wellenlangenbereichs der α-Bande. Durch Bildung der Summen-und Differenz-CD-Kurve fur ein threo/erythro Paar erhalt man CD-Spektren, die fur jedes “Halbmolekul” charakteristisch sind, und die im allgemeinen zwei 0-0—Linien um 37230 cm -1 aufweisen. Aus deren Vorzeichen kann die absolute Konfiguration an jedem der Chiralitatszentren eindeutig bestimmt werden.

Synthese und Konfiguration von Methylestern der diastereomeren (±)-3-Amino-2,3-diarylpropansäuren, der (±)-3-Amino-2,3-diarylpropanole und ihrer Derivate

ZusammenfassungDurch Umsetzung von “Hydramiden” mit am aromatischen Ring m,p-dialkoxysubstituierten Arylessigsäureestern in Gegenwart von wasserfr. AlCl3 entstehen Gemische aus Estern der (±)-erythro- und (±)-threo-3-Amino-2,3-diarylpropansäuren. Bei der Umsetzung von “Piperonalhydramid” mit dem Methylester der Homoveratrumsäure konnte lediglich daserythro-Diastereomere isoliert werden.Die diastereomeren Ester wurden zu den jeweiligen (±)-erythro- und (±)-threo-3-Amino-2,3-diaryl-1-propanolen reduziert, die als N,O-Dibenzoylderivate charakterisiert wurden. Ihre relativen Konfigurationen und die der zugehörigen Ester wurden auf Grund der IR-Spektren der diastereomeren Aminopropanole bestimmt. Die NMR-Spektren eines Diastereomerenpaares von Aminopropanolen bestätigen die ihnen chemisch zugeordneten Konfigurationen und ermöglichen den Nachweis auch ihrer bevorzugten Konformationen.AbstractReaction of “hydramides” with m,p-dialkoxysubstituted arylacetates in the presence of anhydrous AlCl3 generally leads to mixtures of the esters of the (±)-erythro- and (±)-threo-3-amino-2,3-diarylpropanoic acids. However, in the reaction of piperonal “hydramide” with methyl homoveratrate, only the correspondingerythro-diastereomer was obtained.Reduction of the diastereomeric esters gives the corresponding (±)-erythro- and (±)-threo-3-amino-2,3-diaryl-1-propanols, which can be characterized as N,O-dibenzoyl derivatives. Relative configurations of both alcohols and esters were determined by means of their IR spectra. Configurations were confirmed for one pair of diastereomeric amino alcohols by means of NMR spectra and preferred conformations deduced.

The circular dichroism of some derivatives of tetrahydro-1,3-oxazine, tetrahydro-1,4-oxazine(morpholine)and 1,3-oxazolidine

Abstract The circular dichroism of some derivatives of tetrahydro-1,3-oxazine, tetrahydro-1,4-oxazine and 1,3-oxazolidine is described, and discussed in terms of configuration and preferred conformations.

Linear free energy–steric strain energy relationships for the gem-di-methyl effect. Acid-catalysed ring closure of methyl-substituted 3-ureidopropionic acids

The rate data for the acid-catalysed ring closure of eight methyl-substituted 3-ureidopropionic acids constitute an isokinetic series according to Exners statistical criteria. Linear relationships were obtained for the free energies in the reaction series for rates and equilibria exhibiting the gem-dimethyl effect with steric strain energies estimated from enthalpies of formation of homomorphic hydrocarbons. These estimates were obtained by means of Istomin and Palms procedure and are of two kinds, the P values measuring the total strain energy and ΔP values measuring the strain between two fragments in the model hydrocarbon. Some reaction series correlated with ΔP values when one of the functional groups was taken as an invariable fragment and the rest of the molecule as a variable substituent. Other reaction series correlated with P values. The approach has the advantage that it takes into account directly the non-additivity of gauche-interactions and permits evaluation of the data for substituents at various positions of the chain in a single correlation. For cyclization to five- and six-membered rings, the data form a single reaction series when the rates for the parent compounds are close in value. Only certain hydrocarbon models and manners of fragmentation lead to satisfactory correlations. These, and the correlation with P or with ΔP values, or whether a correlation can be obtained at all, indicate the steric requirements of the reaction and thus its mechanism. Linear relationships with strain energies were obtained for reaction series where the rate accelerations have been attributed to entropy effects.

β-Ureido-acids and dihydrouracils. Part IX. Kinetics and mechanism of alkaline hydrolysis of dihydrouracils

The kinetics of alkaline hydrolysis of dihydrouracils are of the first and second order in hydroxide ion, reverting to first (apparent zero) order at high alkalinity. The reaction is general base-catalysed. A mechanism is suggested involving reaction only of the un-ionised species with rate-determining general base-catalysis by water and decomposition by hydroxide ion of the tetrahedral addition intermediate changing to rate-determining formation of the addition intermediate at high alkalinities.

The aldol stage of the Perkin reaction

The interaction of benzaldehyde, phenylacetic acid, acetic anhydride, and triethylamine at room temperature leads to a mixture of α-phenyl-trans-cinnamic acid and the diastereomeric 3-acetoxy-2,3-diphenylpropionic acids. At –24° the acetoxy-acids are the main product, with the erythro-isomer predominant. No isomerisation could be detected under the conditions used. Some suggestions have been made with regard to the mechanism of the aldol stage of the Perkin reaction.