This thesis describes results obtained during the investigation of peptide thioester formation and regioselective dihalohydration reactions of propargylic alcohols. Chapter 1 explores the formation of peptide thioesters via N S acyl transfer. Firstly, native chemical ligation (NCL) will be introduced as a powerful tool to join a peptide thioester and a peptide fragment containing an N terminal cysteine. The challenges of making a peptide thioester will be discussed. Following this, the synthesis of model peptides will be reported, including the first synthesis of boronocysteine. The model peptides are then used to investigate the rate of peptide thioester formation. Alongside this, the effects of guanidine hydrochloride and the thiol additive will be explored. Chapter 2 describes regioselective dihalohydration reactions of propargylic alcohols. Previous research in this area will be reviewed, including previous work within the Sheppard group involving dichloro- and diiodohydration reactions. Following this, the development of the dibromohydration reaction will be detailed which was used to synthesise a wide range of dibromoketoalcohols and dibromolactols. These products have been further manipulated to give a wide variety of products. The difluorohydration reactions of propargylic alcohols will be briefly explored. Chapter 3 details the experimental procedures and compound characterisation for the results discussed in Chapters 1 and 2
