Peroxides double-bonded oxygen functional groups

TABLE 3. Enthalpies of formation of hydroperoxides and peroxides containing double-bonded oxygen functional groups (kJ mol )... 

As a further example of a hydroxyl-assisted epoxidation, geraniol and nerol bearing two isolated C=C double bonds were regioselectively epoxidized with TS-1 at the 2-position (near the OH group), as reported by Kumar et al. (795). On the basis of these results, Kumar et al. (195) proposed that the transition state of the epoxidation of allylic alcohols involves coordination of the alcoholic functional group to the Ti active site and that the double bond interacts with one of the peroxidic oxygen atoms, not with the titanium site (Scheme 9). 

The structure of ophiobolin A (5.137) was established by chemical degradation and by X-ray crystallography of a bromo derivative. The spectroscopic characteristics of ophiobolin A led to the identification of the oxygen functions and the double bonds. The relationship between the aldehyde and the cyclo-pentanone was revealed by the formation of a y-lactone on reduction and partial re-oxidation. A cyclic pyridazine was formed with hydrazine. Tetra-hydro-ophiobolin A formed an unusual cyclic peroxide involving these two groups. Vigorous oxidation of tetrahydro-ophiobolin A afforded a heptanoic acid lactone, which revealed the structure of the side-chain. 

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