Synthesis of rigid and C-2-symmetric 18-crown-6 type macrocycles bearing diamide-diester groups: enantiomeric recognition for alpha-(1-naphthyl) ethylammonium perchlorate salts

A series of rigid and chiral C-2-symmetric 18-crown-6 type macrocycles (S,S)-4, (S,S)-5, (S,S)-6 and (R,R)-2 bearing diamide-ester groups were synthesized. The binding properties of these macrocycles were examined for ot-(1-naphthypethylammonium perchlorates salts by an 1H NMR titration method. Taking into account the host employed, important differences were observed in the Ka values of (R)- and (S)-enantiomers of guests for macrocycles (S,S)-4 and (S,S)-6, Ks/KR = 3.6, and Ks/KR = 0.1 (KR/Ks = 10.3).6.,6,G= 3.19 and Delta Delta G= -5.77 kJ mol(-1), respectively. The results indicated excellent enantioselectivity of macrocyclic (S,S)-6 towards the enantiomers of alpha-(1-naphthyl)ethylammonium perchlorate salts. (C) 2010 Elsevier Ltd. All rights reserved.