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DOI: 10.1055/s-2007-968734
Titanium-Mediated Olefin Epoxidation Using Hydrogen Peroxide
Contributor(s):Mark Lautens, Michael LangerKyushu University, Fukuoka, Japan
Titanium-Catalyzed Asymmetric Epoxidation of Non-Activated Olefins with Hydrogen Peroxide
Angew. Chem. Int. Ed. 2007, 46: 4559-4561
Publication History
Publication Date:
24 July 2007 (online)
Key words
epoxidation - hydrogen peroxide - titanium
Significance
Enantioenriched epoxides are versatile intermediates in organic synthesis. The synthetic methods developed so far often involve oxidants of low atom economy or require the use of activated substrates. The authors found that di-µ-oxo titanium(salalen) complex 1 epoxidizes conjugated olefins with high TON in the presence of hydrogen peroxide as oxidant. They extended the methodology to unactivated olefins bearing only alkyl groups on the alkene. See also previous work: Angew. Chem. Int. Ed. 2005, 44, 4935; Angew. Chem. Int. Ed. 2006, 45, 3478.
Comment
The catalyst can successfully differentiate between an alkyl group and hydrogen, methyl-, methylene-, and methine groups of the Z-alkene. Branching in the α-position leads to a decrease in activity but an increase in enantioselection. Terminal, less electron-rich double bonds are epoxidized preferentially and the method is selective for Z-olefins. However, the epoxidation of internal alkenes bearing different n-alkyl groups remains challenging.