Abstract
D.Sc. (Chemistry)
Two different projects with the central theme of oxidation are discussed, namely the
ozonation of saturated hydrocarbons and the total synthesis of an unusual steroid
glycoside.
The oxidation of saturated hydrocarbons by ozone with the so-called dry ozonation
technique was investigated. This study led to the development of improved
procedures in which the rate, yield and selectivity of the reaction between ozone and
various saturated substrates could be controlled. Subsequently the dry ozonation of
a broadspectrum of long straight chain saturated hydrocarbons, including waxes, was
investigated. Reaction with these highly unreactive compounds gave almost
exclusively ketones as products in high yields. The average amount of keto
functionalities in the products is dependent on the reaction conditions as well as the
chain length of the substrate. Therefore, a reliable method has been developed for
the selective oxidation of straight chain saturated hydrocarbons, a process that is of
great chemical, industrial as well as commercial importance.
The dry ozonation of various straight chain monoketo compounds was also studied.
Poliketo compounds are mainly formed in these reactions. This investigation showed
that keto functionalities in the substrates exert a deactivating effect on neighbouring
methylene groups, so that oxidations do not take place at these positions. Therefore,
it was possible to predict the product distribution formed during the dry ozonation of
shorter chain length monoketo compounds (Cg) .
An effective synthesis of an unusual steroid glycoside similar to orbicusides A-C,
compounds that contain extraordinary carbohydrate and A-ring moieties, was
developed. Oxidation reactions played a prominent role in this reaction sequence.
A substantial effort was also directed towards obtaining the correct stereochemistry
at the various stereocentres of the carbohydrate moiety. This facilitated ring closure
to a final product that contained carbohydrate and A-ring moieties similar to
orbicusides A-C. As a result of this work, a method was developed for the
introduction of a vicinal cis-diol on the sterically hindered face of an alkene. This
method is especially suited for substrates where acid labile functional groups are
present.