Catalytic, Highly Enantio- and Diastereoselective Pinacol Coupling Reaction with a New Tethered Bis(8-quinolinolato) Ligand
摘要:
A new class of chiral ligand, tethered bis(8-quinolinol) (TBOxH), is developed. Its chromium complex, TBOxCrCl (3 mol %), effectively catalyzes the pinacol coupling reaction of aromatic aldehydes at room temperature with high yield (up to 94%), high diastereoselectivity (up to dl:meso = 98:2), and high enantioselectivity (up to 98%). The scope of the present method turns out not to be limited to aromatic aldehyde derivatives, as cyclohexanecarboxaldehyde undergoes pinacolization as well (44% yield, dl:meso = 93:7, 84% ee). The method provides an efficient access to enantioenriched 1,2-diols.
The TBOxCrIIICl/TBOxCrII system is ideal for catalytic asymmetric redox process. Because of the electron density of the TBOxH ligand high turnover numbers are expected, hence allowing decrease in t...
Catalytic Enantioselective Pudovik Reaction of Aldehydes and Aldimines with Tethered Bis(8-quinolinato) (TBOx) Aluminum Complex
作者:Joshua P. Abell、Hisashi Yamamoto
DOI:10.1021/ja803859p
日期:2008.8.13
New chiral tethered bis(8-quinolinolato) (TBOx) aluminum(III) complexes effectively catalyze the addition of phosphites to aldehydes and aldimines to give enantioenriched alpha-hydroxy and a-amino phosphonates in high yields and enantioselectivities with unprecedented reactivity (TON = 100 as high as 200). The catalyst is optimized with the low catalyst loading of 0.5 - 1.0 mol %. The modular synthesis of the catalyst allows for potential to tune the reaction for maximum catalytic activity. To date there are few examples with broad substrate scopes that can catalyze both aldehydes and aldimines with such high selectivity and no reports utilizing such low catalyst loading.