Synthesis, Structural Analysis, and Chiral Investigations of Some Atropisomers with EE-Tetrahalogeno-1,3-butadiene Core

Abstract

The atropenantiomers of stable 1,2,3,4-tetrahalo-1,3-butadiene derivatives (where halogeno stands for bromine or iodine) were separated with use of chiral HPLC. The barriers for the enantiomerization process were determined on-line by dynamic HPLC (DHPLC) or off-line by classical kinetic measurements. In the case of the tetrachloro compound, the barrier was too low for DHPLC and its value was obtained by dynamic NMR experiments. The obtained barriers for chloro, bromo, and iodo derivatives correlate with the van der Waals radii of the halogens. The absolute configuration of the isolated enantiomers of the tetraiodo and tetrabromo compounds was assigned by comparison of the experimental and conformations averaged calculated VCD spectra. The identification of a signature band of the absolute configuration of the butadiene core, the sign and location of which are independent from the different conformations and substituents, allowing the safe assignment of the absolute configuration of the enantiomers of chiral 1,3-butadienes, is also reported.

Stereoselective Halogenation of Integral Unsaturated C‐C Bonds in Chemically and Mechanically Robust Zr and Hf MOFs

“…In contrast to our solution of the crystal structures of 1‐Br 2 and 2‐Br 2 , it was only possible to collect unit cell parameters for 3‐Br 4 . We would expect the lowest energy arrangement of the bdb‐Br 4 2− linker to result in the tetrabromodialkene unit being geometrically frustrated both horizontally and vertically as a consequence of the steric bulk of the bromo substituents; this conformation has been observed in the crystal structure of a tetrabromodialkene analogue34 (Figure 2 f) and in our energy minimisation of bdb‐Br 4 ‐H 2 (Figure 2 g). As the linker sits along a linear vector in the framework, the resultant MOF 3‐Br 4 will exhibit significant disorder.…”

“…Comparisons of the d)  1 H NMR spectra (the asterisk denotes residual benzoic acid) and e) Raman spectra of 3 and 3‐Br 4 , with both techniques suggesting quantitative conversion. f) Crystal structure of a rare tetrabromodialkene‐containing compound (CCDC deposition RUWROR)34 highlighting both the vertical and horizontal displacements as a result of the steric bulk of the Br atoms. g) A molecular dynamics minimised (UFF) representation of the similarly expected arrangement of bdb‐Br 4 ‐H 2 .…”

“…There exists little literature concerning the bromination of butadiynes to tetrabromodialkene units,34 but nonetheless the bromination of 3 was initially attempted by exposing bulk microcrystalline samples to solutions of neat Br 2 (15 equivalents per alkyne unit) in CHCl 3 , with the transformation followed using a number of experimental techniques (see Supporting Information, Section S5).…”

A Forgotten Chiral Spiro Compound Revisited: 3,3'‐Dimethyl‐3H,3'H‐2,2'‐spirobi[[1,3]benzothiazole]

“…On cooling, a typical plateau shape chromatogram was obtained, indicating an exchange between two enantiomers on the column (Fig. ) …”

Liquid Chromatography Enantioseparations of Halogenated Compounds on Polysaccharide‐Based Chiral Stationary Phases: Role of Halogen Substituents in Molecular Recognition

“…Three chiral halogenodienes iodo-(36), bromo-(37) and chlorosubstituted (38) were enantioseparated by Roussel and colleagues on three polysaccharide-based columns: Chiralpak IA, IB, and IC (250 × 4.6 mm). 78 The introduction of bromine or iodine onto the 1,3-butadiene core has a beneficial effect on enantioseparation compared to chlorine (Table 16).…”