Structurally Diverse Second-Generation [2.2]Paracyclophane Ketimines with Planar and Central Chirality: Syntheses, Structural Determination, and Evaluation for Asymmetric Catalysis
A set of 20 novel [2.2]paracyclophaneketimines with planar and centralchirality has been synthesized from enantiomerically pure and racemic 5-acyl-4-hydroxy[2.2]paracyclophane and alpha-branched chiral amines. Their X-ray structures were determined to elucidate the three-dimensional structures and the absolute configuration. The ketimines were used as catalysts in the asymmetric 1,2-addition reactions
Co-Metal-Free Enantioselective Conjugate Addition Reactions of Zinc Reagents
作者:Sefer Ay、Martin Nieger、Stefan Bräse
DOI:10.1002/chem.200801676
日期:——
Asymmetric conjugate addition of diethylzinc to cinnamaldehyde in a co-metal-free fashion by usingN,O-ligands with planar and central chirality is described. Different modulations of the ligand structure, including several combinations of the chiral units, indicate that a [2.2]paracyclophane backbone is essential for the activity and the enantioselectivity of the generated active catalyst. By using
Novel chiral tridentate Schiff base ligands of the [2.2]paracyclophane series: synthesis and application
作者:Tatyana I. Danilova、Valeria I. Rozenberg、Elena V. Sergeeva、Zoya A. Starikova、Stefan Bräse
DOI:10.1016/s0957-4166(03)00326-4
日期:2003.7
The first example of the efficient application of chiral tridentate N,O-[2.2]paracyclophaneligands of the imino type for enantioselective diethylzinc addition to aliphatic and aromaticaldehydes is presented. The enantiomeric excess of the resulted secondary alcohols is up to 93% e.e.
Regioselective Fries Rearrangement and Friedel−Crafts Acylation as Efficient Routes to Novel Enantiomerically Enrichedortho-Acylhydroxy[2.2]paracyclophanes
Two useful approaches to ortho-acylhydroxy[2.2]paracyclophanes, starting from 4-hydroxy[2.2]paracyclophane, have been developed. TiCl4-catalyzed Fries rearrangement and direct acylation occur regioselectively (to the ortho position with respect to the hydroxy group), leading to 4-acetyl-5-hydroxy[2.2]paracyclophane (3) and 4-benzoyl-5-hydroxy[2.2]paracyclophane (4) in high to excellent chemical yields
Second-Generation Paracyclophane Imine Ligands for the Dialkylzinc Addition to Aldehydes. Optimization of the Branched Side Chain leads to Improvement for Aliphatic Aldehydes
diastereomeric [2.2]paracyclophaneketimineligands (SP,S)-2 and (RP,S)-2, which unite a planar chiral element and a central chiral element, were used towards the enantioselective diethylzinc addition onto aliphaticaldehydes. These improved second-generationligands, which are stable in air and water and are easy to obtain, showed significant improvements with respect to the ligands that were previously