The formation and Si-29 NMR spectroscopic characterization of silicon cations that are intramolecularly stabilized by a dialkeyl thioether are described. The chemical stability of the silicon sulfur Lewis pair and, hence, the viability Of the approach, were probed with a 2-[(alkylthio)methyl]phenyl-substituted hydrosilane as a proxy before three different motifs with chiral binaphthyl backbones were prepared in multistep sequences. The degree of shielding of the silicon atom in these cations was found to depend on the substitution pattern at the silicon atom and the ring size generated by the silicon sulfur interaction: These sulfur-stabilized silicon cations are sufficiently reactive to promote Diels-Alder reactions of cyclohexa-1,3-diene with various dienophiles; the same set of reactions with cyclopentadiene is also reported. One of the three chiral Lewis acids induces low, but promising, enantioselectivity, and 24% ee is the highest Value so far obtained with a cationic tetracoordinate silicon catalyst.
Switchable Smiles Rearrangement for Enantioselective <i>O</i>-Aryl Amination
作者:Xihao Chang、Qinglin Zhang、Chang Guo
DOI:10.1021/acs.orglett.9b01848
日期:2019.6.21
atropisomeric anilines from abundant and readily available precursors is one of the most challenging but valuable processes in organic synthesis. The use of highly efficient Smiles rearrangement to accomplish switchable enantioselective amination reactions of O-arenes provides access to nonsymmetric 2′-amino[1,1′-binaphthalen]-2-ol (i.e., NOBIN-type) and [1,1′-binaphthalene]-2,2′-diamine (i.e., BINAM-type)
effective chiral dialkylsulfide organocatalysts remain relatively rare and under‐developed, despite the potential utility of dialkylsulfide catalysts. Herein, we report the development of chiral bifunctional dialkylsulfide catalysts possessing a urea moiety for regio‐, diastereo‐, and enantioselective bromolactonization. The importance of the bifunctional design of chiral sulfide catalysts was clearly
Catalyst-Controlled Regio- and Stereoselective Bromolactonization with Chiral Bifunctional Sulfides
作者:Ayano Tsuchihashi、Seiji Shirakawa
DOI:10.1055/s-0037-1610716
日期:2019.9
Highlyregioselective 5-exo bromolactonizations of stilbene-type carboxylic acids bearingelectron-withdrawing substituents are achieved for the first time via the use of chiral bifunctional sulfide catalysts possessing a urea moiety. The chiral phthalide products are obtained in moderate to good enantioselectivities as the result of 5-exo cyclizations.
A Versatile Method for Kinetic Resolution of Protecting‐Group‐Free BINAMs and NOBINs through Chiral Phosphoric Acid Catalyzed Triazane Formation
作者:Wei Liu、Qianwen Jiang、Xiaoyu Yang
DOI:10.1002/anie.202009395
日期:2020.12.21
azodicarboxylates. A series of mono‐N‐protected and unprotected BINAMs, diphenyl diamines and NOBIN derivatives could be kinetically resolved with excellent performances (with s factor up to 420). The gram‐scale reactions and facile derivatizations of the chiral products demonstrate the potential of these methods in the asymmetric synthesis of chiral catalysts and ligands.
Intramolecularly Sulfur-Stabilized Silicon Cations with Chiral Binaphthyl Backbones: Synthesis of Three Different Motifs and Their Application in Enantioselective Diels–Alder Reactions
作者:Volker H. G. Rohde、Maria F. Müller、Martin Oestreich
DOI:10.1021/acs.organomet.5b00351
日期:2015.7.13
The formation and Si-29 NMR spectroscopic characterization of silicon cations that are intramolecularly stabilized by a dialkeyl thioether are described. The chemical stability of the silicon sulfur Lewis pair and, hence, the viability Of the approach, were probed with a 2-[(alkylthio)methyl]phenyl-substituted hydrosilane as a proxy before three different motifs with chiral binaphthyl backbones were prepared in multistep sequences. The degree of shielding of the silicon atom in these cations was found to depend on the substitution pattern at the silicon atom and the ring size generated by the silicon sulfur interaction: These sulfur-stabilized silicon cations are sufficiently reactive to promote Diels-Alder reactions of cyclohexa-1,3-diene with various dienophiles; the same set of reactions with cyclopentadiene is also reported. One of the three chiral Lewis acids induces low, but promising, enantioselectivity, and 24% ee is the highest Value so far obtained with a cationic tetracoordinate silicon catalyst.