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This thesis describes synthetic studies towards the recently isolated and previously unsynthesised cytotoxin aruncin B, a small molecule inhibitor of the Bcl-2 family antiapoptotic proteins. An initial approach relying on an Achmatowicz reaction is first presented. This method was unsuccessful. An alternative approach relying on a RCM / ethoxyselenation-selenoxide elimination was then envisaged. This method successfully delivered the Na salts of the Z- and E- isomer of the originally proposed structure of aruncin B, along with a third closely related isomeric Na salt. The free acids could not be obtained from these salts, suggesting structural misassignment of aruncin B. An alternative g-alkylidenebutenolide structure is proposed, and its synthesis using a related RCM / hydroxyselenation-selenoxide sequence is presented. This sequence confirmed the true structure of aruncin B, but suffered from reproducibility issues. An alternative sequence based on b-iodo MBH followed by Sonogashira cross-coupling-5- exo-dig-lactonisation was successfully applied to the synthesis of the true structure of aruncin B, as well as 15 analogues for biological evaluation.