Equilibrium and bite-back strategy for the control of diasteroselectivity in radical cyclisations

Hannam, Joanne Clare (1998) Equilibrium and bite-back strategy for the control of diasteroselectivity in radical cyclisations. University of Southampton, Doctoral Thesis.

Abstract

This thesis is concerned with the development of novel diastereoselective radical cyclisations. It is notable that the methodology utilises thiyl radicals and a bite-back strategy to control the stereoselectivity. It is shown that dienes such as diethyl diallylmalonate can be converted to the corresponding cis fused tetrahydrothiophenes. The scope and limitations of the reaction are investigated.

The use of dihydropyranones as 1,5-diketone synthons is presented and then applied to a short synthesis of the sesquiterpenoid, α-herbertenol. The synthetic route makes use of titanium reagents to effect an intramolecular pinacol coupling to construct the cyclopentane fragment and then to create the adjacent quaternary centres in the cyclopentane.

A mild and effective route to highly substituted furanones that uses a sulfur mediated radical-polar crossover reaction is developed. It is demonstrated that using this methodology simple maleate esters can be converted to fumarate esters using thiyl radicals.

Approaches to rubioncolin B, a naturally occurring naphthoquinone, are described.

A literature review of sulfur-centred radical cyclisations is presented.

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