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Absolute structure of the chiral pyrrolidine derivative (2 S )‐methyl ( Z )‐5‐(2‐ tert ‐butoxy‐1‐cyano‐2‐oxoethylidene)pyrrolidine‐2‐carboxylate, a compound with low resonant scattering
Author(s) -
Wang Ai,
Englert Ulli
Publication year - 2019
Publication title -
acta crystallographica section c
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.304
H-Index - 17
ISSN - 2053-2296
DOI - 10.1107/s2053229619012324
Subject(s) - pyrrolidine , absolute configuration , chemistry , enantiopure drug , molecule , carboxylate , intramolecular force , homo/lumo , enantiomer , stereochemistry , ligand (biochemistry) , crystallography , hydrogen bond , enantioselective synthesis , organic chemistry , biochemistry , receptor , catalysis
The enantiopure monopyrrolidine derivative (2 S )‐methyl ( Z )‐5‐(2‐ tert ‐butoxy‐1‐cyano‐2‐oxoethylidene)pyrrolidine‐2‐carboxylate, C 13 H 18 N 2 O 4 , ( 1 ), represents a potential ligand and an attractive intermediate for the synthesis of chiral metal complexes. At the molecular level, the compound features an intramolecular N—H…O hydrogen bond; neighbouring molecules interact via N—H…N contacts to form chains along [100]. Due to its elemental composition, resonant scattering of the target compound is entirely insignificant for diffraction experiments with Mo K α and small even for Cu K α radiation. A preliminary study with the harder radiation type confirmed the chiral space group and the suitability of the single crystal chosen; as expected, the results concerning the absolute structure remained completely inconclusive. A second data collection with the longer wavelength gave satisfactory quality indicators for the correct handedness of the molecule, albeit with high standard uncertainties. The absolute configuration has been assessed independently: CD spectra for both enantiomers of the target molecule were calculated and the spectrum for the S ‐configured stereoisomer was in agreement with the experiment. The Cotton effect of ( 1 ) may be ascribed to π–π* transitions from HOMO to LUMO and from HOMO to LUMO+1. As both independent techniques agree with respect to the handedness of the target molecule, the absolute structure may be assigned with a high degree of confidence.