Inversion of the Enantioselectivity in the Hydrogenation of (E)-2,3-diphenylpropenoic Acids over Pd Modified by Cinchonidine Silyl Ethers

Chiral tandem modifiers: highly efficient cinchonidine-derivative modifiers at low concentrations for the enantioselective hydrogenation of (E)-2,3-diphenylpropenoic acid over Pd/C

Chiral tandem modifiers linking two or three cinchonidine molecules at the 2′-position of the quinoline ring are highly effective at low concentrations for the enantioselective hydrogenation of PCA over Pd/C.

Plausible Pnicogen Bonding of epi-Cinchonidine as a Chiral Scaffold in Catalysis

As a non-covalent interaction of a chiral scaffold in catalysis, pnicogen bonding of epi-cinchonidine (epi-CD), a cinchona alkaloid, was simulated to consider whether the interaction can have the potential controlling enantiotopic face like hydrogen bonding. Among five reactive functional groups in epi-CD, two stable complexes of the hydroxyl group (X-epi-CD1) at C₁₇ and of the quinoline ring (X-epi-CD2) at N₁₆ with pnictide family analytes [X = substituted phosphine (PX), i.e., F, Br, Cl, CF₃, CN, HO, NO₂, and CH₃, and pnictide family analytes, i.e., PBr₃, BiI₃, SbI₃, and AsI₃] were predicted with intermolecular interaction energies, charge transfer (Q_Mulliken and Q_NBO), and band gap energies of HOMO-LUMO (Eg) at the B3LYP/6-31G(d,p) level of density functional theory. It was found that the dominant site of pnicogen bonding in epi-CD is the quinoline ring (N₁₆ atom) rather than the hydroxyl group (O₃₆ atom). In addition, the UV-Vis spectra of the complex were calculated by time-dependent density functional theory (TD-DFT) at the B3LYP/6-31+G(d,p) level and compared with experimental measurements. Through these calculations, two intermolecular interactions (H-bond vs. pnicogen bond) of epi-CD were compared.

Kinetic analysis of the asymmetric hydrogenation of (E)-2,3-diphenylpropenoic acid over cinchonidine derivative-modified Pd/C: quinoline ring modification

The substitutions at the 2′- and/or 6′-positions of the quinoline ring of cinchonidine reduce both the intrinsic enantioselectivity and adsorption strength for the enantioselective hydrogenation of α-phenylcinnamic acid over Pd/C.

Stereodivergent Catalysis

This review covers diastereo- and enantiodivergent catalyzed reactions in acyclic and cyclic systems using metal complexes or organocatalysts. Among them, nucleophilic addition to carbon-carbon and carbon-nitrogen double bonds, α-functionalization of carbonyl compounds, allylic substitutions, and ring opening of oxiranes and aziridines are considered. The diastereodivergent synthesis of alkenes from alkynes is also included. Finally, stereodivergent intramolecular and intermolecular cycloadditions and other cyclizations are also reported.