This thesis is concerned with the total synthesis of the two natural products peyssonol A and peyssonol B, which were isolated from a Red Sea Alga, Peyssonnelia sp. They were shown to display inhibition of HIV Reverse Transcriptases. Syntheses of several related natural products containing the same sesquiterpene skeleton, such as avarol and ilimiquanone, are reviewed in the first chapter. The second chapter describes our first route towards the total synthesis of peyssonol A. We intended to synthesise the decalin portion fist and then couple it to the aromatic moiety. The key step in the formation of the decalin ring is a 6-exo-trig intramolecular radical cyclisation. Samarium (II) iodide intramolecular radical cyclisation was also investigated. Entries based on the Robinson annulation and the related Robinson-Mannich base methiodide method are also described. An alternative route towards the total synthesis was developed, in which the key step involved a Ring Closure Metathesis reaction. A synthesis of the aromatic portion is also described. Studies on the introduction of an electrophilic group on the aromatic portion to facilitate the coupling with the decalin ring are then discussed. Finally, studies relating to a Mukayiama reaction are described as this too could provide a method of introducing the aromatic moiety. A third route towards the total synthesis is described. It is based on work by Laube et al and their total synthesis of the natural product zonarol. Lewis acid intramolecular cyclisation is involved as a key step. Studies on an alternate Mn(OAc)₃ intramolecular reductive cyclisation complete the discussion.