Resolution of inherently chiral anti-O,O′-dialkylated calix[4]arenes and determination of their absolute stereochemistries by CD and X-ray methods

Qualitative analysis of the helical electronic energy of inherently chiral calix[4]arenes: an approach to effectively assign their absolute configuration

For all microhelices on aromatic rings of inherently chiral calix[4]arene, an expression was derived from one approximation and one hypothesis on the basis of the electron-on-a-helix model of Tinoco and Woody as follows: , where µ = 1 for the right-handed microhelix and µ = −1 for the left-handed microhelix; and H and K are constant and greater than zero. The expression correlates microhelical electronic energy (E) with the atom polarizability difference (Δα) on both microhelix ends, which intuitively and clearly shows the impact of helical substituent polarizability on helical electronic energy. The case analysis almost entirely proves that the qualitative analysis of the helical electronic energy of inherently chiral Calix[4]arenes with the expression is scientific and can be used to effectively assign their absolute configuration.

Inherently chiral concave molecules--from synthesis to applications

This tutorial review covers the recent development in the synthesis and application of molecules and finite assemblies that are chiral owing to their curvature. A modified definition of inherent chirality is provided. Various classes of chiral concave molecules are presented including salphen complexes, cyclic amides, derivatives of sumanene, trioxatricornan or subphthalocyanine, cyclotriveratrylenes, homooxacalix[3]arenes, calixarenes, resorcinarenes, phthalocyanines, corannulenes and cavitands. Some of these bowl shaped compounds exhibit high inversion barriers, comparable with the stability of classical carbon chirality centres, while the others (e.g. hydrogen bonded assemblies) can only be detected by NMR. This review is focused on practical aspects of synthesis, resolution and applications in chiral recognition and asymmetric synthesis.

Absolute configuration assignment of inherently chiral calix[4]arenes using DFT calculations of chiroptical properties

The racemate of an inherently chiral meta-substituted calix[4]arene derivative 3 has been resolved via enantioselective HPLC. Measured optical rotation dispersion and electronic circular dichroism have been compared with DFT theoretical predictions. The comparison indicates that the absolute configuration of the dextrorotatory enantiomer (+)-3 is cS. The procedure has been successfully tested against a literature precedent confirming the validity of the method.

A New Approach to Enantiopure Inherently Chiral Calix[4]arenes: Determination of Their Absolute Configurations

A new approach to the synthesis of meta-substituted enantiopure inherently chiral calix[4]arenes by introducing L-Boc-proline as dual functions of the chiral auxiliary has been described. Moreover, the absolute configurations of the enantiomers were determined by CD spectra, X-ray crystallographic analysis, and the chemical derivative method.

Diastereoselective Lower Rim (1S)-Camphorsulfonylation as the Shortest Way to the Inherently Chiral Calix[4]arene

[structure: see text]. A diastereomeric mixture of chiral 25-(1S)-camphorsulfonyloxy-26-isopropoxycalix[4]arene 2a (de 15%) and 25-isopropoxy-26-((1S)-10-camphorsulfonyl)calix[4]arene 2b has been obtained by asymmetrical lower rim (1S)-camphorsulfonylation of the monoisopropoxycalix[4]arene. Pure diastereomer 2a has been obtained by simple crystallization, and its absolute configuration has been determinated by X-ray analysis. Enantiomerically pure inherently chiral 5,11-dibromo-26-isopropoxycalix[4]arene 4 has been synthesized by the upper rim dibromination of the diastereomer 2a followed by hydrolytical removal of the auxiliary camphorsulfonyl group.