1-azabicyclic compounds. 22. Stereochemistry and13C NMR spectra of salts of pyrrolizidine and its homologs with protonic acids

Subbotin, O. A.; Skvortsov, I. M.

doi:10.1007/bf00842958

Cited by 2 publications

(11 citation statements)

References 10 publications

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“…Other evidence for the conformational heterogeneity (of the ring-fusion type) in compounds 9-11 was obtained during comparison of the 13 C NMR spectra of their protonated forms 12-14 and 15-17, formed as a result of reaction of the bases 9-11 with trifluoroacetic acid [18]. N In this paper the above-mentioned fact is regarded as evidence for the relatively large content of form 11A in the equilibrium mixture of conformations 11A and 11B.…”

Section: Detection Of Conformational Heterogeneity In Pyrrolizidines mentioning

confidence: 95%

“…The authors here started from the additivity of the contributions from the substituents to the basicity of the amines [52]. With allowance for the fact that compound 11 exists almost entirely in the trans-fused form A [17,18,24] pK a ≤ 9.9 was obtained.…”

Section: Basicitymentioning

confidence: 99%

“…From the collection of published data [17,18] it was possible to determine the parameters of the conformational equilibrium 9A 9B, calculated by two different methods. The first started from data on the integral intensities of the signals for the C (3) , C (5) , C (6) , C (8) , and C(Me) atoms in the 13 C NMR spectra of the salts 12 and 15, obtained during kinetically controlled protonation [60] of the base 9 by the absorption of its vapor with concentrated sulfuric acid at 25°C [18].…”

Section: Thermodynamics Of the Cis-trans Conversion Of Pyrrolizidine mentioning

confidence: 99%

“…This increases their strain and reduces the absolute value of the difference in free energies between forms 5B and 5A. Experiment shows that it becomes possible to observe a change in the conformational equilibrium 5A 5B with variation of temperature [16] and to determine the content of the individual conformers [17,18] even in the case of the smallest substituent Me.…”

mentioning

confidence: 99%

“…However, there are strong angular strains in forms A [2,14,15,17]. In spite of this many pyrrolizidine derivatives of types 6 and 7 exist preferentially in the trans-fused conformations A [14,[17][18][19][20][21][22][23], demonstrating the considerable supremacy of the cis-fused forms B with respect to strain that determines the preference for the A forms.…”

mentioning

confidence: 99%

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Cis-trans-conversion of the bicycle in pyrrolizidines: The effect of the preferred conformations on the properties of the bases and the thermodynamics of conformational transformation of the ring fusion type. (Review)

Skvortsov

2006

Chem Heterocycl Compd

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The cis-trans conversion in pyrrolizidines and the deciding effect of steric factors on their conformational equilibrium are discussed. Work on the synthesis and characteristics of sterically strained pyrrolizidines is analyzed and discussed. It is shown that such compounds (predominantly trans-fused) have a series of features in their properties that greatly distinguish them from unstrained pyrrolizidines. The first results from study of the thermodynamics of cis-trans conversion of the pyrrolizidine bicycle are summarized.

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Section: Detection Of Conformational Heterogeneity In Pyrrolizidines mentioning

confidence: 95%

Section: Basicitymentioning

confidence: 99%

Section: Thermodynamics Of the Cis-trans Conversion Of Pyrrolizidine mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Cis-trans-conversion of the bicycle in pyrrolizidines: The effect of the preferred conformations on the properties of the bases and the thermodynamics of conformational transformation of the ring fusion type. (Review)

Skvortsov

2006

Chem Heterocycl Compd

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Investigations on 1-azabicycles. 26*. IR spectra of the simplest pyrrolizidine alcohols in the region of the stretching vibrations of the hydroxyl group and their connection with the stereochemistry of the compounds

Tarasov

Kolesnikov

Levin

et al. 2009

Chem Heterocycl Comp

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The IR spectra in the hydroxyl group stretching vibration region of the simplest hydroxyalkylpyrrolizidines have been examined. The spectra were taken in the form of pure liquids, dilute solutions in carbon tetrachloride, and for individual bases in the gas phase. It was shown that in dilute solutions ∆ν OH depends on the geometric parameters of the intramolecular hydrogen bond (IMHB) . The energy of the IMHB of 3-(2-hydroxyethyl)pyrrolizidine was measured in dilute solution and in the gas phase.A large number of studies has been devoted to the synthesis and structure of pyrrolizidine alcohols, especially those forming the basis of pyrrolizidine alkaloids. In spite of this, problems linked with hydrogen bonds in pyrrolizidine alcohols have obtained only limited exposure. The investigation of aminodiols, the alkaloids platinecine and retronecine, in which the hydroxyl groups are connected with hydrogen bonds, are part of the previous work in this region [2].Meanwhile, regularities of the link of the structure of compounds with the character of the absorption in the region of stretching vibrations of the OH group, found for the simplest pyrrolizidine alcohols, are of interest not only in themselves but may also prove to be useful when investigating more complex compounds of this series.

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1-azabicyclic compounds. 22. Stereochemistry and13C NMR spectra of salts of pyrrolizidine and its homologs with protonic acids

Cited by 2 publications

References 10 publications

Cis-trans-conversion of the bicycle in pyrrolizidines: The effect of the preferred conformations on the properties of the bases and the thermodynamics of conformational transformation of the ring fusion type. (Review)

Cis-trans-conversion of the bicycle in pyrrolizidines: The effect of the preferred conformations on the properties of the bases and the thermodynamics of conformational transformation of the ring fusion type. (Review)

Investigations on 1-azabicycles. 26*. IR spectra of the simplest pyrrolizidine alcohols in the region of the stretching vibrations of the hydroxyl group and their connection with the stereochemistry of the compounds

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