Studies towards the asymmetric synthesis of Dictyoxetane

The brown alga, Dictyota dichotoma, collected from the Indian Ocean has proven to be a prolific source of new diterpenes. The diterpene, dictyoxetane, isolated from the brown alga, is structurally related to the dollabellane class of natural products. Dictyoxetane is the only known natural product having the 2,7-dioxatricyclo[4.2.1.0]nonane ring subunit. Chapter 1 of this thesis describes the isolation, structure and proposed biosynthesis of dictyoxetane. The methods reported in the literature for the preparation of the dioxatricyclic framework are discussed, which might be applied in a synthesis of dictyoxetane. The Grainger group has previously reported the synthesis of the trans-hydrindane core of dictyoxetane starting from a Robinson annulation-derived bicyclic enone. Asymmetric approaches to the starting hydrindanone in this synthesis and the Hajos-Parrish ketone are also presented. Chapter 2 reports the efforts to address the current limitations of this approach, namely the low-yielding Robinson annulation of an expensive starting material, 2-methylcyclopentanone. An asymmetric synthesis of the trans-hydrindane ring system starting from the Hajos-Parrish ketone, involving chemoselective radical-based deoxygenation, is reported. Studies towards dioxatricyclic ring annulation are described in Chapter 3. A number of strategies such as radical cyclisation, ring-expansion and [4+3] cycloaddition are investigated towards 7-membered ring formation. The Lee [5+2] annulation using allylsilane acetals and olefin metathesis both provided a way to annulate a 7-membered ring to the hydrindanone system en route to dictyoxetane