This thesis is split into two sections describing syntheses of heterocyclic systems. The introduction gives a brief discussion on heterocycles and their uses as drugs. The first section is devoted to sulfoximines and their preparation and uses. The approach described in this thesis is a one-pot procedure from sulfinimines and methyl-2-bromobutenoate via an Aza -Darzens reaction, giving tri-substituted aziridines, which undergo a radical-based rearrangement to form sulfoximines. Different groups have been tested and the yields were significantly improved in comparison with the two-step procedure. This novel approach gives easy access to cyclic sulfoximines. From here sulfoximines could be functionalised, reduced or deprotected and used for the synthesis of natural products.