¹H NMR Chiral Analysis of Charged Molecules via Ion Pairing with Aluminum Complexes

Chiral analysis, such as determination of identity, concentration, and relative ratio of optically active (chiral) molecules, plays an indispensable role in contemporary synthetic, medicinal, and biological chemistry. Here, we describe the selective control of metal-centered chirality in an octahedral geometry to prepare negatively charged Al^III complexes, which can be used as versatile ¹H NMR chiral solvating agents for both positively and negatively charged chiral molecules in polar or nonpolar solvents. During the formation of ion pairs between the Al^III complexes and the chiral analytes such as amines and carboxylic acids, the metal-centered chirality in the Al complexes plays a crucial role in providing anisochronous chemical shifts to the ¹H NMR spectra. As a chiral solvating agent, Al^III complexes display an unprecedentedly broad substrate scope, good solvent compatibility, and operational simplicity

Stereoselective Chiral Recognition of Amino Alcohols with 2,2′‑Dihydroxybenzil

2,2′-Dihydroxybenzil is demonstrated to be a highly diastereoselective stereodynamic receptor for the chiral recognition of amino alcohols. The receptor by forming diimine compounds with amino alcohols showed good (11:1) to excellent (>50:1) diastereoselectivity in chloroform. The existence of intramolecular hydrogen bonding with amino alcohols only in an axial conformer is demonstrated by ¹H NMR and CD spectroscopy, X-ray crystallography, and DFT computations. The exciton chirality method can be used with diazo-attached 2,2′-dihydroxybenzil

2,2′-Dihydroxybenzil: A Stereodynamic Probe for Primary Amines Controlled by Steric Strain

A rational approach for generating 1,1′-binaphthalene-like axial chirality of a small organic receptor, 2,2′-dihydroxybenzil is presented. The receptor combines with 2 equiv of monodentate primary amines to form a diimine, of which axial chirality is controlled by steric strain with moderate (1.4:1) to good (4.7:1) stereoselectivity. The observed circular dichroism (CD) spectra have been closely simulated by TD-DFT computations and can be used for determining the absolute chirality and enantiomeric excess of primary amines

Bicyclic Bridgehead Phosphoramidite (Briphos) Ligands with Tunable π‑Acceptor Ability and Catalytic Activity in the Rhodium-Catalyzed Conjugate Additions

A new type of bicyclic bridgehead phosphoramidites (briphos) is reported, where the geometrical constraints significantly enhance the π-acceptor ability compared with its monocyclic analogs. The briphos is shown to be highly efficient and tunable for Rh­(I)-catalyzed conjugate additions of aryl boronic acids to α,β-unsaturated ketones and <i>N</i>-tosyl ketimines