Some new protocols for the assignment of absolute configuration by NMR spectroscopy using chiral solvating agents and CDAs

Abstract

The utility of enantiopure BINOL (1,10-Bi-2-naphthol), in a ternary ion-pair complex, which is obtained using a carboxylic acid and an organic base, as a versatile chiral solvating agent (CSA) has been demonstrated for chiral analysis and the absolute configuration assignment of hydroxy acids. Another protocol where the utility of NOBIN as a CSA has been developed for discrimination and absolute configuration assignment of acids, hydroxy acids and their derivatives with a distinct strategy where a third ingredient, p-toluenesulfonic acid (p-TsOH) serves as a linker. In addition some three component chiral derivatization protocols have been introduced, such as the use of 2-formylphenylboronic acid and enantiopure mandelic acid or a primary amine for the determination of the configuration of primary amines and hydroxy acids, respectively. A simple, rapid and highly efficient three component chiral derivatizing protocol has also been discussed which was developed for assigning the absolute configuration of chiral α-hydroxy acids and their derivatives, which involves the coupling of 2-formylphenylboronic acid with (R)-[1,1-binaphthalene]-2,2-diamine, and (S)-[1,1-binaphthalene]-2,2-diamine separately. In a few examples, the DFT based theoretical calculations have been carried out to determine the geometry optimized structures of the complexes.