PMID: 11325251Apr 28, 2001Paper

Stereochemistry of a spherand-type calixarene

The Journal of Organic Chemistry
K AgbariaI Thondorf

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(-) x C(5)H(5)NH(+) and 2a(2)(-) x 2Et(3)NH(+)) 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 (1)H NMR data indicate the presence of a major conformer of C(1) 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.

Citations

Apr 21, 2012·Chemistry : a European Journal·Changjiang YuErhong Hao
Jul 19, 2019·Chemical Communications : Chem Comm·Ryo KurosakiHiroko Yamada
Apr 28, 2001·The Journal of Organic Chemistry·K AgbariaI Thondorf
Aug 4, 2001·The Journal of Organic Chemistry·K Agbaria, S E Biali

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