Stereochemistry of a spherand-type calixarene

K Agbaria; S E Biali; V Böhmer; J Brenn; S Cohen; M Frings; F Grynszpan; J M Harrowfield; A N Sobolev; I Thondorf

doi:10.1021/jo0016576

Stereochemistry of a spherand-type calixarene

J Org Chem. 2001 May 4;66(9):2900-6. doi: 10.1021/jo0016576.

Authors

K Agbaria¹, S E Biali, V Böhmer, J Brenn, S Cohen, M Frings, F Grynszpan, J M Harrowfield, A N Sobolev, I Thondorf

Affiliation

¹ Department of Organic Chemistry, The Hebrew University of Jerusalem, Jerusalem, 91904, Israel.

PMID: 11325251
DOI: 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(-) 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.