Simultaneous freezing of chirality and in-out conformation of a macropentacyclic cryptand by protonation.
Compound 1, a cryptand-derived macropentacycle, is a flexible molecule that encompasses many conformations (symmetrical, unsymmetrical, and chiral ones) depending on the observation temperature (VT 1H NMR). Selective monoprotonation of this molecule leads to a totally unsymmetrical, rigidly chiral species in solution (1H NMR). Helical chirality and in-out conformation of monoprotonated 1 are observed in the solid state by X-ray diffraction analysis, as well as the proton location. The latter is bound to the endo bridgehead nitrogen atom and involved in hydrogen-bonding interactions with the three closest sulfurs. Significant induction of chirality is triggered by reaction of 1 with the optically active (R)-(-)-1,1'-binaphthyl-2,2'-diylphosphoric acid. It proceeds with a maximum 24% diastereomeric excess, as shown by the splitting, in the 62:38 intensity ratio, of several 1H NMR signals. These correspond to the two indistinguishable diastereomeric ion pairs: (Lambda-[1-H])((R)-(-)-BNP) and (Delta-[1-H])((R)-(-)-BNP).
Bonnot
Clément
C
Laboratoire d'Ingénierie Moléculaire pour la Séparation et les Applications des Gaz (CNRS, UMR 5633), Université de Bourgogne, 6 boulevard Gabriel, 21100 Dijon, France.
Chambron
Jean-Claude
JC
Espinosa
Enrique
E
D000588:Amines / Q000737:chemistry; D001555:Benzene Derivatives / Q000737:chemistry*; D043844:Crown Ethers / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004220:Disulfides / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D011522:Protons; D013237:Stereoisomerism
D000588:Amines; D001555:Benzene Derivatives; D043844:Crown Ethers; D004220:Disulfides; D011522:Protons; C063841:tert-butylbenzene