A. De Groot

INVESTIGATIONS INTO THE TOTAL SYNTHESIS OF INSECT ANTIFEEDANT CLERODANES. THE TOTAL SYNTHESIS OF (.+‐.)‐4‐EPI‐AJUGARIN

Among the still growing group of clerodane type diterpenes, those compounds possessing insect antifeedant activity have drawn much attention. Surprisingly, at the beginning of our investigations, only a few attempts towards the total synthesis of clerodanes had been made. During the last few years the number of investigators studying the synthesis of these diterpenes steadily increased and in 1979 Takahashi et al. achieved the first success in this field with the total synthesis of annonene (see chapter 2.7). However, up to the time of writing no total synthesis of physiologically active clerodanes has been reported. The main object of the investigations described in this thesis was to develop synthetic methods for the construction of the clerodane basic skeleton. This skeleton should contain functionalities that allow the total synthesis of the highly oxygenated clerodanes. At a later stage these results could be employed in the synthetic approach to the interesting insect antifeedant clerodanes. This also offered the possibility to arrive at analogous compounds which may contribute to the knowledge of structure-activity relationships of the antifeedant activity.

Rearrangements and hydrogen—deuterium exchange in ferrocenylcarbenium ions

Abstract The rearrangement of the t-butyl group in t-butylferrocenyl carbenium ions (VI) and the hydrogen—deuterium exchange in the methyl group of methylferrocenyl carbenium ions (XVI) has been studied. The reaction rates depend on the size of the substituents at the carbenium ion center, an increase in the size of the substituents causing an increase in the rate. This effect is attributed, on the basis of the Gleiter and Cais models of ferrocenyl substituted carbenium ions, to increased steric hindrance between the substituents and the unsubstituted cyclopentadienyl ring.