| Summary: | <p>The work presented in this thesis mainly describes the development of new reactions of β-lithiooxyphosphonium ylides to access stereodefined substituted alkenes in a highly convergent fashion.</p> <p>Firstly, β-lithiooxy ylides prepared from aldehydes and phosphonium ylides were shown to react with halogen electrophiles to provide a highly stereoselective route to <em>E</em>-alkenyl bromides and iodides. This methodology was successfully applied to the first total synthesis of naturally occurring (5<em>E</em>,9<em>Z</em>)-6-bromohexadeca-5,9-dienoic acid.</p> <p>Secondly, an experimentally straightforward method was developed for the stereocontrolled formation of trisubstituted Z-allylic esters by <em>in situ</em> trapping of β-lithiooxyphosphonium ylides with readily available halomethyl esters. The synthetic utility of this methodology was demonstrated with the synthesis of plaunotol [(2<em>Z</em>,6<em>E</em>)-2-((<em>E</em>)-4,8-dimethylnona-3,7-dien-1-yl)-6-methylocta-2,6-diene-1,8-diol] and the first asymmetric synthesis of the naturally occurring geranylgeraniol-derived diterpene (6<em>S</em>,7<em>R</em>,<em>Z</em>)-7-hydroxy-2-((E)-6-hydroxy-4-methylhex-4-enylidene)-6,10-dimethylundec-9-enyl acetate. Furthermore, the chemistry of β-lithiooxyphosphonium ylides was expanded to access synthetically useful disubstituted Z-allylic esters. The synthetic utility of Z-allylic esters was also demonstrated in a versatile and diastereoselective Ireland-Claisen rearrangement to access γ,δ-unsaturated acids.</p> <p>Finally, the synthesis of the side-chain of the 6,7-dideoxysqualestatin H5 was also investigated. It was demonstrated that the side-chain of 6,7-dideoxysqualestatin H5 could be accessed by a convergent and stereoselective organozinc-based strategy</p>
|
|---|