Temperature dependent inversion of enantiomer selectivity in the complexation of optically active azophenolic crown ethers containing alkyl substituents as chiral barriers with chiral amines 1

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Abstract
Azophenolic crown ethers (S,S)-1, (R,R)-2 and (S,S)-3 have been prepared in enantiomerically pure forms by using (S)-1-(1′-adamantyl)ethane-1,2-diol, (R)-3,3-dimethylbutane-1,2-diol and (S)-propane-1,2-diol, respectively, as chiral subunits, and the association constants for their complexes with chiral amines have been determined by 1H NMR or UV–VIS spectroscopic methods at various temperatures. The enantiomer selectivities of crown ethers (S,S)-1 and (R,R)-2 in complexation with 2-aminopropan-1-ol are reversed at ca. 6 °C and increase with increasing temperature above the isoenantioselective temperature.

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