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Synlett 2006(20): 3545-3547  
DOI: 10.1055/s-2006-956496
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© Georg Thieme Verlag Stuttgart · New York

Catalytic Enantioselective Epoxidation of Unfunctionalized Olefins: Utility of a Ti(Oi-Pr)4-Salan-H2O2 System

Kazuhiro Matsumoto, Yuji Sawada, Tsutomu Katsuki*
Department of Chemistry, Faculty of Science, Graduate School, Kyushu University 33, Hakozaki, Higashi-ku, Fukuoka, 812-8581, Japan
Fax: +81(92)6422607; e-Mail: katsuscc@mbox.nc.kyushu-u.ac.jp;
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Publication History

Received 4 September 2006
Publication Date:
08 December 2006 (online)

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Abstract

Salan ligands bearing an ortho-substituted phenyl group at C3 and C3′ were found to serve as an effective auxiliary of a Ti(Oi-Pr)4-salan-H2O2 system for enantioselective epoxidation. Simple olefins were converted into the corresponding epoxides in good to excellent enantioselectivity.

Key words

asymmetric catalysis - epoxidations - titanium - hydrogen peroxide - salan ligand

    References and Notes

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  • 7 General Experimental Procedure. To a CH2Cl2 solution of salan ligand (6 mol%, 0.50 mL) was added a CH2Cl2 solution of Ti(Oi-Pr)4 (5 mol%, 0.50 mL) under nitrogen atmosphere and the resultant solution was stirred at r.t. After 1 h, olefin (0.10 mmol)and subsequently 30% H2O2 (0.11 mmol) were added and the mixture was stirred at r.t. for 9 h. The solvent was removed under reduced pressure and the residue was purified by silica gel chromatography to give an epoxide. An ee was determined by HPLC analysis using a chiral stationary phase described in the footnote to Table 2
5

We have already reported that the in situ prepared titanium-salan complex was equally efficient to the isolated di-µ-oxo titanium-salan complex (1, ref. 4).

6

Compound 2e: 47%, 92% ee; compound 2n: 23%, 87% ee.