Structure, Conformation, and Stereodynamics of the Atropisomers
of Highly Hindered Benzyl Ethers
Daniele Casarini
Carmine Coluccini
Lodovico Lunazzi
Andrea Mazzanti
10.1021/jo0603173.s002
https://acs.figshare.com/articles/journal_contribution/Structure_Conformation_and_Stereodynamics_of_the_Atropisomers_of_Highly_Hindered_Benzyl_Ethers/3076555
Low-temperature and NOE NMR spectra of four of the title compounds indicate that they adopt a synclinal
(sc) conformation, in agreement with the prediction of ab initio computations. In the case of the most-hindered derivative (compound <b>4</b>), the conformation is syn-periplanar (sp), as is also shown by X-ray
diffraction. Such stereolabile sp- or sc-atropisomers exist as two conformational enantiomers: the
corresponding enantiomerization barriers, covering the range 6.6 to 9.7 kcal mol<sup>-1</sup>, could be measured
for all the examined compounds. In two cases (compounds <b>3</b> and <b>5</b>), the minor antiperiplanar (ap)
atropisomer has been also observed, and the sc to ap interconversion barrier measured (11.7 and 11.9
kcal mol<sup>-1</sup>, respectively). In addition, restricted rotation of the isopropyl and <i>tert</i>-butyl substituents has
been detected, and the corresponding barriers have been determined.
2006-06-09 00:00:00
ap interconversion barrier
mol
range 6.6
conformation
title compounds
NOE NMR spectra
enantiomerization barriers
compounds 3
sc
ab initio computations
kcal
Such stereolabile sp