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 also shown by X-ray diffraction. Such stereolabile sp- or sc-atropisomers exist as two conformational enantiomers: the corresponding enantiomerisation 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
D. Casarini, C. Coluccini, L. Lunazzi, A. Mazzanti (2006). Structure, Conformation and Stereodynamics of the Atropisomers of Highly Hindered Benzyl Ethers. JOURNAL OF ORGANIC CHEMISTRY, 71, 4490-4496 [10.1021/jo0603173].
Structure, Conformation and Stereodynamics of the Atropisomers of Highly Hindered Benzyl Ethers.
LUNAZZI, LODOVICO;MAZZANTI, ANDREA
2006
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 also shown by X-ray diffraction. Such stereolabile sp- or sc-atropisomers exist as two conformational enantiomers: the corresponding enantiomerisation 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 apI documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
