Linked-BINOL: An Approach towards Practical Asymmetric Multifunctional Catalysis
β Scribed by Shigeki Matsunaga; Takashi Ohshima; Masakatsu Shibasaki
- Publisher
- John Wiley and Sons
- Year
- 2002
- Tongue
- English
- Weight
- 307 KB
- Volume
- 344
- Category
- Article
- ISSN
- 1615-4150
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β¦ Synopsis
The development and application of a novel linked-1,1'-binaphthol (linked-BINOL) as an approach towards practical asymmetric multifunctional catalysis is described. Linked-BINOL was first designed to increase the stability of a Ga-Li-BINOL complex against ligand exchange with 4-methoxyphenol. An oxygen-containing linked-BINOL, which is a semi crown ether, was effective in both promoting the formation of a monomer complex and increasing the stability of the Ga-Li complex. A Ga-Lilinked-BINOL complex promoted the epoxide opening reaction in up to 96% enantiomeric excess (ee). Second, based on the X-ray structural information of the Ga-Lilinked-BINOL complex, we designed a more stable lanthanide linked-BINOL complex. An air-stable, storable, and reusable La-linked-BINOL complex promoted the Michael reaction in up to > 99% ee. The catalyst activity remained unchanged after storage under air for 4 weeks. Calculations suggested that the linked-BINOL would function as a pentadentate ligand in a lanthanum complex, thus efficiently improving the stability of the complex. Finally, the linked-BINOL was applied to a new homobimetallic multifunc-tional catalysis. A dinuclear Zn-Zn-linked-BINOL complex promoted the enantio-and diastereoselective direct aldol reaction in up to 99% ee, where one Zn cation might function as a Lewis acid and the other Zn-phenoxide as a BrΛnsted base.
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