Conformational Analysis in Solution of a Chiral BisoxazolineMolecule: Vibrational Circular Dichroism Spectroscopy and DensityFunctional Theory Study

A Aamouche,P J Stephens

doi:10.1155/2011/905045

Abstract

The conformations of the chiral bisoxazoline: 2,2′‐methylenebis[3a,8a‐dihydro‐8H‐indeno[1,2‐d]oxazole] (also named IndaBOX), have been studied. Density functional theory (DFT) calculations identify four inequivalent stable conformations. Two, I and II have, C2 symmetry; two, III and IV, have C1 symmetry. The electronic energies of I–IV are ordered: I < II < III < IV. The span in energy is <1.0 kcal/mole. Vibrational unpolarised absorption and circular dichroism spectra have been predicted for the four conformations using DFT. Comparison of population‐weighted spectra to experimental spectra of CHCl3 and CDCl3 solutions in mid‐IR region strongly supports the DFT predictions of the number, structures, and relative energies of the conformations of IndaBOX. This shows that DFT predicts spectra with a high degree of reliability. We will undoubtedly illustrate the advantage added by vibrational circular dichroism spectroscopy in conformational analysis and in the absolute configuration determination.

Highlights

We report a study of the conformations of a chiral bisoxazoline: 2,2 -methylenebis[3a,8a-dihydro-8H-indeno[1,2d]oxazole], 1, in solution using ab initio vibrational spectroscopy
The X-ray structures of several metal complexes of chiral bisoxazolines have been reported [6,7,8,9,10], there appear to have been no structural studies of chiral bisoxazolines alone
We report a study of the bisoxazoline, 1, using ab initio density functional theory (DFT) [11, 12], in combination with vibrational unpolarised absorption (IR) and vibrational circular dichroism (VCD) [13,14,15,16] spectroscopies. 1 is a flexible molecule; internal rotation can occur about the CC1 and CC2 bonds

Summary

Introduction

We report a study of the conformations of a chiral bisoxazoline: 2,2 -methylenebis[3a,8a-dihydro-8H-indeno[1,2d]oxazole], 1, in solution using ab initio vibrational spectroscopy. In combination with metal salts, chiral bisoxazolines catalyse a wide variety of asymmetric transformations, in many cases with high enantioselectivity [1,2,3,4,5]. We report a study of the bisoxazoline, 1, using ab initio density functional theory (DFT) [11, 12], in combination with vibrational unpolarised absorption (IR) and vibrational circular dichroism (VCD) [13,14,15,16] spectroscopies. We seek to establish the structures and relative energies of the stable conformations of 1

Methods

Results

Conclusion