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By Roger A. Sheldon (auth.), Renato Ugo (eds.)

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The regioselective epoxidation of the bis-allylic alcohol (XXVI) to the bisepoxide (XXVII) is the crucial step in a synthesis of juvenile hormone from farnesol [166]. VO(OCOC)2 TBHP (97) ~ (XXVII) (XXVI) Similarly, the regioselective epoxidation of (XXVIII) to the monoepoxide (XXIX) has been reported [167]. ~OH VO(ococ ). TBHP (98) • OH (XXVIII) (XXIX) The stereoselectivity of epoxidations of unsaturated alcohols with metal catalyst/alkyl hydroperoxide reagents has been studied in detail by several groups [72,73,165-170].

The Lewis acidity of a catalyst is obviously influenced by the electronic properties of coordinating ligands and one would expect the ligands to have a significant effect on catalytic activity. In practice, however, a ligand effect may be observable only during the initial stages of reaction due to rapid destruction of the original ligands under the oxidizing conditions of these reactions. In one study [89] the rates of molybdenum-catalysed epoxidations were shown to become independent of the structure of the molybdenum complex Epoxidations with alkyl hydroperoxides 27 used, after an initial phase in which the rates were changing.

In this case no extra solvent is needed. This means, for example, that epoxidations with ethyl benzene hydroperoxide are generally carried out in ethylbenzene as solvent. g. allyl chloride, it is often attractive to use the olefin itself as the solvent in order to obtain reasonably high rates of reaction and selectivities. 8. Effect of structure of tbe bydroperoxide In studies of alkylaromatic hydroperoxides it was shown [81,105] that electron-attracting substituents in the aromatic ring increased the rate of epoxidation, presumably by increasing the electrophilicity of the peroxide oxygens.

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