Conformational studies by dynamic NMR. 64. Stereomutations of atropisomers and of conformational enantiomers in ethers of hindered naphthylcarbinols

被引:23
作者
Casarini, D
Lunazzi, L
Mazzanti, A
Foresti, E
机构
[1] Univ Bologna, Dept Organ Chem A Mangini, I-40136 Bologna, Italy
[2] Univ Bologna, Chem Dept G Ciamician, Bologna, Italy
关键词
D O I
10.1021/jo9804801
中图分类号
O62 [有机化学];
学科分类号
070303 ; 081704 ;
摘要
Methyl or ethyl ethers of 1-naphthyl carbinols ArCR2OR' (Ar = 1-naphthyl, R' = Me, Et) can occur in a range of rotational conformations whose population varies with the nature of the substituents R. The passage between such conformation minima is achieved by rotation, during which one group R or OR' passes either the 2- or the 8-position of the naphthalene, and depending on the nature of R and OR', some of these interconversions are slow on the NMR time scale. Dynamic NMR experiments, supported by molecular mechanics calculations, show that different minima are preferred as the R group changes. These conformations are identified, their populations are determined, and the barriers to their interconversions are measured. In particular when R is a tert-butyl group, two atropisomers (with the OMe moiety near the 2- or 8-position) could be physically separated and their structures determined by NOE experiments in solution and X-ray diffraction in the solid state. Each of these exists as a pair of stereolabile enantiomers, with a barrier of 9-10 kcal mol(-1) for interconversion.
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页码:4746 / 4754
页数:9
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