Synlett 2002(12): 2011-2014
DOI: 10.1055/s-2002-35570
LETTER
© Georg Thieme Verlag Stuttgart · New York

A New Highly Selective Method for the Catalytic Epoxidation of Chiral Allylic Alcohols by Sandwich-Type Polyoxometalates with Hydrogen Peroxide

Waldemar Adama, Paul L. Alstersb, Ronny Neumannc, Chantu R. Saha-Möllera, Dorit Sloboda-Roznerc, Rui Zhang*a
a Institute of Organic Chemistry, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany
Fax: +49(931)8884756; e-Mail: adam@chemie.uni-wuerzburg.de;
b DSM Fine Chemicals, Advanced Synthesis and Catalysis, 6160 MD Geleen, Netherlands
c Department of Organic Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
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Publikationsverlauf

Received 5 September 2002
Publikationsdatum:
20. November 2002 (online)

Abstract

Oxidatively and solvolytically persistent sandwich-type polyoxometalates, namely [WZnM2(ZnW9O34)2]q- [M = Mn(II), Ru(III), Fe(III), Zn(II)], catalyze chemoselectively, diastereoselectively and regioselectively the epoxidation of chiral allylic alcohols with 30% hydrogen peroxide through a tungsten peroxo species, in which the allylic alcohol is coordinated as alcoholate (template effect).

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General Procedure for Catalytic Epoxidations of Allylic Alcohols 1 by Sandwich-Type Polyoxometalates: Substrate 1 (0.50 mmol) and dimethyl isophthalate (0.20 mmol), as internal standard, were dissolved in a stock solution of the particular methyltricaprylammonium M-POM catalyst (0.50 mL, 1.0 mM). The reaction was initiated by addition of 30% hydrogen peroxide (110 mL, 1.0 mmol) to the above solution at ca. 20 °C, and the resulting biphasic mixture was stirred at a constant rate (ca. 1000 rpm) for all runs. The reaction progress was monitored by 1H NMR spectroscopy or TLC, and after the required reaction time, the organic phase of the reaction medium was separated, dried over Na2SO4, and the solvent removed at reduced pressure (20 °C/50 mbar). The conversions, product ratios and diastereomeric ratios of the epoxides 2 were determined by 1H NMR analysis directly on the crude mixture and the data are given in Table [1] and Table [2] . The epoxides 2a-e, obtained by M-POM-catalyzed epoxidation, are literature known and have been identified on the basis of their NMR data.