X ‐ray Crystallography and 1 H NMR Anisotropy Methods for Determination of Absolute Configurations

Abstract

In the stereoselective synthesis of drugs and natural products, it is critical to determine the absolute configurations (ACs) of reaction products. To determine the ACs of chiral compounds, many spectroscopic and diffraction methods have been developed. Among them, X‐ray crystallographic Bijvoet and circular dichroism (CD) exciton chirality methods enable one to determine ACs in a nonempirical manner. On the other hand, X‐ray crystallography using a chiral internal reference and 1 H nuclear magnetic resonance (NMR) spectroscopy using a chiral anisotropy reagent are relative and/or empirical methods, but they are more practical for organic synthetic studies because the methods have the advantage of preparing enantiopure compounds by high‐performance liquid chromatography (HPLC) separation and of establishing unambiguously the ACs. As chiral reagents useful for both the preparation of enantiopure compounds by HPLC separation and the simultaneous determination of their ACs, we have developed camphorsultam‐dichlorophthalic acid (CSDP acid) for X‐ray crystallography and 2‐methoxy‐2‐(1‐naphthyl)propionic acid (MαNP acid) for 1 H NMR spectroscopy and X‐ray crystallography. In this chapter, the outline and applications of these X‐ray and NMR methods are explained using various interesting data.