1044221-72-8Relevant academic research and scientific papers
A chiral frozen hydrogen bonding in C4-symmetric inherently chiral resorcin[4]arenes: NMR, X-ray, circular dichroism, and theoretical study
Kuberski, Bogumil,Pecul, Magdalena,Szumna, Agnieszka
experimental part, p. 3069 - 3078 (2009/05/07)
Chiral C4-symmetric resorcinarenes, substituted with L-amino acid derivatives at upper rims, were synthesized by the modified Mannich reaction and subsequent N-substitution reactions. Compounds of that type (5a-e) can exist in two relatively stable inherently chiral C4-symmetric conformations, (M) and (P), stabilized by the formation of seams of hydrogen bonds. However, because of diastereomeric preferences the amino acid substituted resorcinarenes exhibit considerable diastereomeric excesses for the induced conformational inherent chirality (up to ≥95%). The relatively slow exchange allowed the determination of the directions of the hydrogen bond ring closures through the combined application of NMR (ROESY) and X-ray analysis. It was also possible to correlate the absolute conformation with the sign of the Cotton effects observed for the transitions within the resorcinol chromophore in the CD spectra (solution and solid state). The ab initio calculations (TDDFT/B3LYP/DZVP and TDDFT/CAMB3LYP/6-31++G*) for model compounds showed that the chiral arrangement of the hydrogen bonding in resorcinarenes can produce substantial CD effects, which are amplified by exciton coupling. However, it was also shown that the neighboring urea, amide, or phenyl groups have crucial effects on the direction of electric transition dipoles and, as the result, on the signs of the exciton-coupled bands.
