This thesis is divided into three chapters. Chapter 1 provides brief reviews on the subjects of previous total syntheses of suaveoline, alstonerine and cytisine. In addition, a review concerning the Pictet–Spengler reaction mechanism and its application to the total syntheses of isoquinoline containing natural products has been included as well. Chapter 2 focuses on the research findings in the past three years. Two routes were investigated towards the total synthesis of (±)-suaveoline involving the decarboxylative Claisen rearrangement (dCr), N-sulfonylaziridine chemistry and subsequent nucleophilic ringopening of the latter by various sulfone-anions. Route A focused on the use of oxo-lithio chelation during aziridine ring-opening while route B employed selective weakening of the aziridine C–N bond proximal to the olefin by PiC–C→Sigma* C–N overlap (Scheme 0.1). Attempts towards total synthesis of (±)-alstonerine involved the preparation and subsequent screening of various sulfone-anions against the indolic hydroxy aziridine, followed by an interesting E1cB / Michael addition, cis-Pictet–Spengler cyclization and an ambitious global reduction step. Furthermore progress towards total synthesis of (–)-cytisine involved investigation towards the application of regioselective sulfone-anion hydroxy-aziridine opening mediated by oxolithio- chelation. Chapter 3 provides the experimental details and characterization data.