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. 2018 May 20;23(5):1225.
doi: 10.3390/molecules23051225.

Conformational Aspects of the O-acetylation of C- tetra(phenyl)calixpyrogallol[4]arene

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Free PMC article

Conformational Aspects of the O-acetylation of C- tetra(phenyl)calixpyrogallol[4]arene

José Luis Casas-Hinestroza et al. Molecules. .
Free PMC article

Abstract

Reaction between pyrogallol and benzaldehyde results in a conformational mixture of C-tetra(phenyl)pyrogallol[4]arene (crown and chair). The conformer mixture was separated using crystallization procedures and the structures were determined using FTIR, ¹H-NMR, and 13C-NMR. O-acetylation of C-tetra(phenyl)pyrogallol[4]arene (chair) with acetic anhydride, in pyridine results in the formation of dodecaacetyl-tetra(phenyl)pyrogallol[4]arene. The structure was determined using ¹H-NMR and 13C-NMR finding that the product maintains the conformation of the starting conformer. On the other hand, the O-acetylation reaction of C-tetra(phenyl)pirogallol[4]arene (crown) under same conditions proceeded efficiently, and its structure was determined using ¹H-NMR and 13C-NMR. Dynamic ¹H-NMR of acetylated pyrogallolarene was studied by means of variable temperature in DMSO-d₆ solution, and it revealed that two conformers are formed in the solution. Boat conformations for acetylated pyrogallolarene showed a slow interconversion at room temperature.

Keywords: acetylation; conformers; macrocycles; pyrogallolarenes.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Scheme 1
Scheme 1
Synthesis of C-tetra(phenyl)pyrogallol[4]arene.
Figure 1
Figure 1
(A) 1H-NMR spectrum of conformational mixture: crown conformation 1a and chair conformation 1b; (B) 1H-NMR spectrum of pure conformer 1a; and (C) 1H-NMR spectrum of pure conformer 1b.
Figure 2
Figure 2
HMQC spectrum of conformer 1b.
Scheme 2
Scheme 2
Synthesis of C-tetraphenylpyrogallol[4]arene acetylated.
Figure 3
Figure 3
Comparison of the fragments of 1H-NMR spectra of the conformer 2a (A) and 2b (B).
Figure 4
Figure 4
Coalescence of the peaks in the aromatic zone for conformer 2a.
Figure 4
Figure 4
Coalescence of the peaks in the aromatic zone for conformer 2a.

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