Self‐association promoted conformational transition of (3R,4S,8R,9R)‐9‐[(3,5‐bis(trifluoromethyl)phenyl))‐thiourea](9‐deoxy)‐epi‐cinchonine

The conformational diversity of the (3R,4S,8R,9R)‐9‐(3,5‐bis(trifluoromethyl)phenyl))‐thiourea](9‐deoxy)‐epi‐cinchonine organocatalyst is discussed. Low‐temperature NMR experiments confirmed a self‐association process, which promotes the quinoline rotation between two intramolecularly hydrogen‐bonded monomeric conformers of the catalyst. The balanced population of the coexisting monomeric and dimeric species allowed us to conduct a structural study of a rather complex conformational dynamics of the pure catalyst. The study is extended by a comparison with other members of the bifunctional amine‐thiourea organocatalyst family. Changes in the molecular structure of the catalysts influence the interplay between intra‐ and intermolecular hydrogen bonding, and yield different extent of catalyst self‐association. By assessing the conformation of the individual states, we established the thermodynamic model of a self‐association promoted conformational transition. Copyright © 2009 John Wiley & Sons, Ltd.