Changing the course of radical reactions through solid phase immobilisation : radical reactions in solution and on solid phase

Abstract

The work described in this thesis concerns our attempts to exploit a dichotomy between solid and solution phase reaction kinetics to develop new and useful radical cyclisation strategies.  The thesis begins with a review of radical reactions conducted on solid supported substrates.  2-Bromostilbenes were subjected to tributyltin-mediated radical forming conditions with cyclisation occurring via 6-exo/endo-trig pathway to give the corresponding phenanthrenes in good yield.  Similar reactions on solid phase showed that the desired phenanthrene was the minor product of the reaction – the major component being the trans-stilbene.

2-iodostilbenes are known to give poor results with a mixture of dihydrophenanthrene and direct reduction products present.  When the PS-Wang immobilised analogue was subjected to the same reaction and then cleaved into solution with 95% TFA, we noted that the yield of dihydrophenanthrene was greatly improved and that no products derived from the direct reduction.  Instead, another radical intermediate – a biaryl, was present as the minor component.  Related examples and extensions will be discussed.  Methods used to analyse our supported substrates will be highlighted, together with new solid phase cyclisation results of stilbenes where there is at least one halo substituent on both rings.

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