Preparation and temperature-dependent enantioselectivities of homochiral phenolic crown ethers having aryl chiral barriers: thermodynamic parameters for enantioselective complexation with chiral amines

Homochiral crown ether (S,S)-1 containing I-naphthyl groups as chiral barriers together with the phenol moiety was prepared by using (S)-3 as a chiral subunit which was resolved in enantiomerically pure form by lipase-catalyzed enantioselective acylation of (+/-)-3. Homochiral phenolic crown ether (S,S)-2, containing phenyl groups as chiral barriers, was also prepared from (S)-5 which was derived from (S)-mandelic acid. The association constants for their complexes with chiral amines in CHCl(3) were determined at various temperatures by the UV-visible spectroscopic method demonstrating that the crown ethers (S,S)-1 and (S,S)-2 displayed the large Delta(R-S)Delta G values of 6.2 and 6.4 kJ mol(-1), respectively, towards the amine 21 at 15 degrees C. Thermodynamic parameters for complex formation were also determined and a linear correlation between T Delta(R-S)Delta S and Delta(R-S)Delta H values was observed. (C) 1998 Elsevier Science Ltd. All rights reserved.