Electron-Withdrawing, Biphenyl-2,2′-diol-Based Compounds for Asymmetric Catalysis

Role of Chiral Skeleton in Chiral Phosphoric Acids Catalyzed Asymmetric Transfer Hydrogenation: A DFT Study

Chiral phosphoric acids (CPAs) have received considerable attention due to their high activity for enantioselective transformations. However, the role of various chiral skeletons of CPAs in regulating the mechanism and enantioselectivity of asymmetric transfer hydrogenation has remained unclear. Density functional theory (DFT) calculations are performed to elucidate the role of chiral skeletons on the acidity, mechanism, enantioselectivity, and kinetic stabilities of transition states (TSs) in Asymmetric Transfer Hydrogen (ATH) reaction catalyzed by five CPAs. We found that the acidity of CPAs is strongly dependent on the chiral skeleton. The origin of enantioselectivity of ATH reaction arises from the differential noncovalent interactions between TSs and CPAs. Moreover, the shape and size of the catalyst pocket depending on chiral skeletons play key roles in the stability of TSs and the enantioselectivity of ATH. This study might facilitate to design and computationally screening of CPAs and guide the strategic choice of CPA skeletons to reduce the experimental workload.

Counterion-Enhanced Pd/Enamine Catalysis: Direct Asymmetric α-Allylation of Aldehydes with Allylic Alcohols by Chiral Amines and Achiral or Racemic Phosphoric Acids

We report a straightforward and efficient Pd/enamine catalytic procedure for the direct asymmetric α-allylation of branched aldehydes. The use of simple chiral amines and easily prepared achiral or racemic phosphoric acids, together with a suitable Pd-source resulted in a highly active and enantioselective catalyst system for the allylation of various α-branched aldehydes with different allylic alcohols. The reported procedure could provide an easy access to both product antipodes. Furthermore, two possible orthogonal derivatizations of the enantioenriched aldehydes were performed without any decrease in enantioselectivity.

Accessible bidentate diol functionality within highly ordered composite periodic mesoporous organosilicas

Periodic mesoporous organosilicas containing biphenol bridging groups were modified post-synthesis to prepare aryl phosphate esters from the free diols.

Crystal structure of 5,5'-di-bromo-3,3'-di-tert-butyl-6,6'-di-methyl-biphenyl-2,2'-diol

The whole mol-ecule of the title compound, C22H28Br2O2, is generated by twofold rotation symmetry. The dihedral angle of the biphenyl moiety is 85.05 (11)°. The hy-droxy groups show intra-molecular O-H⋯π inter-actions without any other hydrogen-bond acceptors. In the crystal, there are no other significant inter-molecular inter-actions present.