Remarkable Effect of Subtle Structural Change of Chiral Pseudo-18-Crown-6 on Enantiomer-Selectivity in Complexation with Chiral Amino Alcohols
作者:Keiji Hirose、Yoshito Tobe、Pakatip Aksharanandana、Michiko Suzuki、Kiyoshi Wada、Koichiro Naemura
DOI:10.3987/com-05-s(k)42
日期:——
Chiral receptors [(S,S)-1] and [(S,S,S,S)-2] having 1,2-dialkoxy-1-(3,5-dimethylphenyl)ethane and 1,2-dialkoxy-1-(3,5-dimethyl phenyl)cyclohexane as chiral building blocks, respectively, were prepared. Thermodynamic parameters of complexations of these and structurally related receptors [(S,S)-3] and [(S,S,S,S)-4] with 2-amino-1-propanol (5), 2-amino-2-phenylethanol (6), and 3-methylbutan-1-ol (7) in chloroform were determined. It was found that the host-guest systems that have same enantiomer-selectivity at 25 degrees C showed opposite selectivity in the enthalpy term. For example, complexations of both (SS)-1 and (SS)-3 with 5 are R-selective at 25 degrees C (Delta Delta G = 2.2 and 3.8 kJ mol(-1), respectively), whereas In terms of the enthalpy of complexation the former is S-selective (Delta Delta H = 22 kJ mol(-1)) but the latter is R-selective (Delta Delta H = 10 kJ mol(-1)).