title: Enantioselective formation of a dynamic hydrogen-bonded assembly based on the chiral memory concept.
abstract: In this paper, we report the enantioselective formation of a dynamic noncovalent double rosette assembly 1a(3).(CYA)(6) composed of three 2-pyridylcalix[4]arene dimelamines (1a) and six butylcyanuric acid molecules (BuCYA). The six 2-pyridyl functionalities of the assembly interact stereoselectively with chiral dicarboxylic acids 3a-e via two-point hydrogen-bonding interactions. One of the two enantiomeric assemblies (P- or M-) 1a(3).(CYA)(6) is formed in excess as the result of the complexation of the chiral diacids, resulting in formation of optically active assemblies. The complexations with dibenzoly tartaric acids D-3a and L-3a (3 equivalent), respectively, leading to the formation of diastereomeric assemblies (P)-1a(3).(BuCYA)(6).(D-3a)(3) and (M)-1a(3).(BuCYA)(6).(L-3a)(3) with 90% diastereomeric excess. The diastereomeric excess in (M)-1a(3).(BuCYA)(6).(L-3a)(3) is "memorized" when L-3a is removed by precipitation with ethlylenediamine (EDA). The assembly (M)-1a(3).(BuCYA)(6) is still optically active (90% enantiomeric excess), although none of its individual components are chiral. (M)-1a(3).(BuCYA)(6) has a high kinetic stability toward racemization (E(a) = 119 kJ mol(-)(1), half-life of (M)-1a(3).(BuCYA)(6) is ca. 1 week at 20 degrees C).
authors.affiliation: Laboratory of Supramolecular Chemistry and Technology, MESA(+) Research Institute, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands.
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Ishi-I
authors.forename: Mercedes
authors.initials: M
authors.lastname: Crego-Calama
authors.forename: Peter
authors.initials: P
authors.lastname: Timmerman
authors.forename: David N
authors.initials: DN
authors.lastname: Reinhoudt
authors.forename: Seiji
authors.initials: S
authors.lastname: Shinkai