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
Structure, Conformation and Stereodynamics of the Atropisomers of Highly Hindered Benzyl Ethers / D. Casarini; C. Coluccini; L. Lunazzi; A. Mazzanti. - In: JOURNAL OF ORGANIC CHEMISTRY. - ISSN 0022-3263. - STAMPA. - 71:(2006), pp. 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.
