Synthetic approaches to polyoxygenated chromone and chromanome natural products

The work described in this thesis is concerned with the chemistry ofpolymethoxylated aromatic carbonyl compounds bearing a 2,6-dioxygenatedsubstitution pattern, with particular regard to establishing synthetic routes tobiologically active chromone and chromanone systems. Syntheses of keyintermediates in the approaches to the natural products stigmatellin, baicalein andLL-D253(x (and related products) were undertaken.In chapter one the reactions of nucleophiles at the carbonyl moieties of 2,6-dioxygenated benzene carbonyl compounds are reviewed. This type of processocan present special difficulties and was to prove particularly significant at variousstageso f the work describedi n subsequenct hapters.Chapter two is a review of the provenance, abundance, biosynthesis, and previoussyntheses of the natural products stigmatellin, baicalein and LL-D253(x, thesebeing the targets of the synthetic work undertaken in the course of the project.Chapter three is concerned with an approach to a fragment of the stigmatellinmolecule (referred to as stigmatellin fragment A) using the Vilsmeier formylationreaction, while chapter four is concerned with an alternative approach tostigmatellin fragment A using Friedel-Crafts acylation methodology. Thestrategies and the results obtained are described and analysed in detail.In chapter five a strategy for the synthesis of baicalein trimethyl ether is describedand the results obtained are discussed