Chelation-Induced Axially Chiral Palladium Complex System with Tetraoxazoline Ligands for Highly Enantioselective Wacker-Type Cyclization
作者:Yong Jian Zhang、Feijun Wang、Wanbin Zhang
DOI:10.1021/jo701469y
日期:2007.11.1
A new family of chelation-induced axiallychiral palladium complexes by using biphenyl ligands 2 with four identical chiral oxazoline groups at four ortho positions has been developed. Although there is no axialchirality in ligands 2 due to the molecular symmetry, when they chelated with one or two palladium ions, the axialchirality could be induced by destroying the molecular symmetry. Significantly
Two-Faced Reactivity of Alkenes: <i>cis</i>- versus <i>trans-</i>Aminopalladation in Aerobic Pd-Catalyzed Intramolecular Aza-Wacker Reactions
作者:Guosheng Liu、Shannon S. Stahl
DOI:10.1021/ja070424u
日期:2007.5.1
deuterated cyclopentene substrate reveals that four of the five catalyst systems (A, B, C, and E) promote exclusive cis-aminopalladation of the alkene, whereas both cis- and trans-aminopalladation occur with the N-heterocyclic-carbene (NHC) catalyst system. If stoichiometric Brønsted base (NaOAc, Na2CO3) is added to the latter reactionconditions, however, only cis-aminopalladation is observed. The identity
Pd(II)-catalyzed intramolecular Wacker-typecyclizations of o-trisubstituted allylphenols were studied. The chelation-induced axially chiral catalytic system, Pd(CF3COO)2-8 (1:1 molar ratio), showed excellent catalytic activities and enantioselectivities in the Wacker-typecyclizations of o-trisubstituted allylphenols with up to 94% ee.
Design and Preparation of 3,3‘-Disubstituted 2,2‘-Bis(oxazolyl)-1,1‘-binaphthyls (boxax): New Chiral Bis(oxazoline) Ligands for Catalytic Asymmetric Wacker-Type Cyclization
promoted by the oxazolyl groups. The 3,3'-disubstituted boxax ligands showed much higher enantioselectivity than the 3,3'-unsubstituted ones in the palladium(II)-catalyzed Wacker-typecyclization of an o-allylphenol. The cyclization of (E)-2-(2-methyl-2-butenyl)phenol (10) in the presence of a cationic palladium catalyst coordinated with (S)-2,2'-bis(4,4-dimethyloxazol-2-yl)-3,3'-bis(methoxycarbonyl)-1
Palladium-Catalyzed Oxidative Wacker Cyclizations in Nonpolar Organic Solvents with Molecular Oxygen: A Stepping Stone to Asymmetric Aerobic Cyclizations
作者:Raissa M. Trend、Yeeman K. Ramtohul、Eric M. Ferreira、Brian M. Stoltz