Highly Efficient Asymmetric Hydrogenation Catalyzed by Iridium Complexes with Tridentate Chiral Spiro Aminophosphine Ligands

Abstract

This work demonstrates that replacing the planar pyridine group of Ir-SpiroPAP catalysts with a relatively bulky thioether group creates a more crowded chiral environment around the catalytic center and thus remarkably improves the enantioselectivity of asymmetric hydrogenation of β-alkyl-β-ketoesters.

Recent Progress in the Synthesis of Silaspiranes

“…The obtained chiral spirosilabindane 6 was further converted into SPSiOL 9 (Scheme 5), the silyl analog of the well‐known spirocarbon‐centered SPINOL 8 [14] developed by Zhou [4b,e–g,k] . Compared with SPINOL 8 , SPSiOL 9 had a larger dihedral angle between the two phenyl rings (92.2° vs. 64.2°) and a longer O−O distance (5.155 Å vs. 3.439 Å), probably as a result of the hybridization of Si and the longer C−Si bond (C Ar −Si vs C Ar −C: 1.86 Å vs 1.52 Å; C sp3 −Si vs C sp3 −C: 1.88 Å vs 1.56 Å) due to the larger atomic radius of silicon than carbon (111 pm vs 91 ppm).…”

Co-SAC catalyzed utilization of methanol and ethanol in the transfer hydrogenation of azo bonds: experimental and theoretical studies

“…The TH of polar unsaturated bonds, compared to that of iso-propanol, methanol and ethanol, has been less explored. [47][48][49][50][51][52][53][54][55][56][57][58][59][60] Notably, among the reported protocols, the TH of nonpolar bonds is rare. [61][62][63]64 During the preparation of this manuscript, the Xu group demonstrated a protocol for the TH of azoarenes using ethanol, catalyzed by a (NC)Ru(II)complex; however, this catalytic system was incapable of complete hydrogenation of the -NvNbond, and produced hydroazoarenes as the major product.…”

Asymmetric hydrogenation of all-carbon tetrasubstituted α-acylpyrazole-β-alkyl cycloalkenes

“…One of the most straightforward approaches to access such frameworks would be asymmetric hydrogenation of the corresponding tetrasubstituted cycloalkenes. [7][8][9][10][11][12][13][14][15] However, achieving efficient enantioselective hydrogenation remains challenging, particularly when all substitutions involve carbon, because steric congestion in the substrate inhibits its reaction with the ligand-metal complex. Chelating or directing groups might mitigate this problem, yet they may also inactivate the catalyst by binding too strongly to it.…”