Stereochemistry of a Spherand-Type Calixarene
- 10 April 2001
- journal article
- Published by American Chemical Society (ACS) in The Journal of Organic Chemistry
- Vol. 66 (9) , 2900-2906
- https://doi.org/10.1021/jo0016576
Abstract
The stereochemistry of the spherand-type calixarene 2a is analyzed in terms of the configuration of the three 2,2‘-dihydroxybiphenyl subunits (R or S) and the disposition of the methylene groups (crown or twist). X-ray crystallography indicates that the neutral 2a and its mono- or dianion (in form of the salts 2a-·C5H5NH+ and 2a2-·2Et3NH+) exist essentially in the same conformation (RRS/SSR-twist). This asymmetric RRS/SSR-twist form is the lowest energy conformer according to molecular mechanics calculations. Low-temperature 1H NMR data indicate the presence of a major conformer of C1 symmetry, in agreement with a RRS/SSR-twist form. The lowest energy topomerization pathway mutually exchanges two pairs of methylene protons and is ascribed to an enantiomerization process involving rotation around an Ar−Ar bond.Keywords
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