Radical cyclisations of methylenecyclopropane derivatives

Destabel, Christine (1994) Radical cyclisations of methylenecyclopropane derivatives. University of Southampton, Doctoral Thesis.

Abstract

This thesis is concerned with the synthesis of compounds containing a methylenecyclopropane moiety and their intramolecular radical cyclisations, in an effort to develop new approaches to ring systems.

The first chapter describes the synthesis of monosubstituted methylenecyclopropane radical precursors (82) and (95), and their radical cyclisation with tributyltin hydride and catalytic AIBN to give the unexpected cyclohexene (83) and methylenecyclohexane (84). A mechanism for the formation of compounds (83) and (84) is proposed. vskip 1.5cm

Chapter two describes the synthesis and radical cyclisation of disubstituted methylenecyclopropylalkyl derivatives (108) to (110) and (118) to (120). vskip 1.5cm

We found that methylenecyclopropylpropyl radicals cyclise in a 5-exo fashion, followed by a ring expansion to produce six-membered rings. In the case of methylenecyclopropylbutyl radicals, depending on the substitution of the cyclopropane ring, exo or endo cyclisation is favoured. If there is initial exo cyclisation, there is exo or endo opening of the intermediate cyclopropylmethyl radical depending on the substitution of the cyclopropane ring. No cyclised products were obtained with methylenecyclopropyl pentyl radicals under these conditions.

Chapter three describes the use of malonyl radicals with various chain lengths and substitution. Using the atom transfer methodology, methylenecyclopropylpropyl radicals cyclise almost exclusively in a 5-exo fashion, followed by endo opening of the intermediate cyclopropylmethyl radical to produce six-membered rings. Methylenecyclopropylbutyl and pentyl radicals cyclise preferentially in an endo fashion.

Finally, chapter four describes our preliminary approach to bicyclic systems by tandem cyclisation of methylenecyclopropylpropyl radical (207). vskip 1.7cm

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