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Edge‐to‐Face CH/π Aromatic Interaction and Molecular Self‐Recognition in epi ‐Cinchona‐Based Bifunctional Thiourea Organocatalysis
Author(s) -
Tárkányi Gábor,
Király Péter,
Varga Szilárd,
Vakulya Benedek,
Soós Tibor
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200800197
Subject(s) - bifunctional , chemistry , thiourea , quinuclidine , cinchona , cinchona alkaloids , squaramide , hydrogen bond , molecular recognition , crystallography , organocatalysis , enantioselective synthesis , computational chemistry , stereochemistry , organic chemistry , molecule , catalysis
The impact of cooperativity between intermolecular interactions is demonstrated by the molecular self‐recognition properties of highly enantioselective epi ‐cinchona bifunctional thiourea organocatalysts. Low‐temperature NMR experiments in inert solvents have revealed two sets of nonequivalent resonances in equal population for thiourea‐modified members of the epi ‐quinine and epi ‐quinidine families. In solution, the predominance of an asymmetric ( C 1 ) dimeric self‐assembly with noteworthy structural motifs became evident: simultaneous intra‐ and intermolecular thiourea hydrogen bonding and a CH/π interaction were observed. Both the stereochemical and the diverse conformational features of the system favor the observed quinoline T‐shaped aromatic π–π stacking interaction. The structure findings are supported by quantitative proton–proton distance data that were available from NOE buildup curves. The 3D structure of the dimeric assembly has been modeled in agreement with the H–H distance restraints. Owing to the geometrical preference associated with the dimerization process, the self‐assembled bifunctional system is interpreted as a charge‐transfer complex with the potential for catalyst self‐activation.