Lewis acid mediated cyclisation of methylenecyclopropane derivatives

Abstract

This thesis is concerned with the synthesis, and cyclisation of compounds containing a methylenecyclopropane moiety. Special interest is given to the Lewis acid mediated cyclisation of methylenecyclopropyl ketones and ketals, which proceed with high yields of highly functionalised carbocycles.

Chapter 1 discussed the synthesis and the cyclisation of methylenecyclopropyl ketones and aldehydes 122, which gave cyclised compounds 125 and 126. (Fig. 8562A).

In addition, a rapid method for the preparation of precursors for the Lewis acid mediated cyclisation of methylenecyclopropane derivatives was developed with addition of methylenecyclopropyl cuprate to conjugated ketones.

Chapter 2 focused on the cascade process of 1,2-disubstituted methylenecyclopropanes with first cyclisation induced by Lewis acid to give an allyl cation intermediate which can be trapped in a cycloaddition reaction.

Chapter 3 also discussed the cyclisation of 1,1-disubsittuted methylenecyclopropane derivatives mediated by Lewis acid, especially the synthesis of spirocycle compounds.

Chapter 4 discussed the effect of a silyl group on the cyclisation reaction. Ketone 300 gave, under treatment with Lewis acid, cyclised compounds 303 and 304 in very good yields, due presumably to the ability of silicon to stabilise β-carbocation intermediate 301. (Fig. 8562B).

Chapter 5 is concerned with the development of a cascade process as the silicon atom can be used to transfer allyl and phenyl groups. (Fig. 8562C).

Finally Chapter 6 is concerned with an attempt, which failed, to synthesise the natural product Norketoagarofuran.

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