title: Structure, conformation, and stereodynamics of the atropisomers of highly hindered benzyl ethers.
abstract: 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 4), 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(-1), could be measured for all the examined compounds. In two cases (compounds 3 and 5), the minor antiperiplanar (ap) atropisomer has been also observed, and the sc to ap interconversion barrier measured (11.7 and 11.9 kcal mol(-1), respectively). In addition, restricted rotation of the isopropyl and tert-butyl substituents has been detected, and the corresponding barriers have been determined.
authors.affiliation: Department of Chemistry, University of Basilicata, Potenza, Italy.
authors.forename: Daniele
authors.initials: D
authors.lastname: Casarini
authors.forename: Carmine
authors.initials: C
authors.lastname: Coluccini
authors.forename: Lodovico
authors.initials: L
authors.lastname: Lunazzi
authors.forename: Andrea
authors.initials: A
authors.lastname: Mazzanti