This thesis describes the synthesis of pyrrolizidines, indolizidines and pyrroloazepines from the reaction of cyclopropenones with a wide range of five, six and seven-membered cyclic imines. These three alkaloids nuclei are widespread in nature and have shown many potential pharmaceutical properties. The cyclic imines were typically synthesised by thionation and alkylation of their corresponding lactams, although other cyclic imines were investigated. The imines were then reacted with diphenylcyclopropenone (DPP). The pyrrolizidine, indolizidine and pyrroloazepine reactivity was exploited by oxidising the bridgehead group (X = S) with m-CPBA, giving rise to new products, including a sulfoxide elimination product, and an unexpected hydroxy compound. This was a useful discovery, given the presence of such a bridgehead OH in the jenamidine natural products. This thesis explores ways in which this may have occurred and also looks at alternative methods. The synthesis of cyclopropenones other than DPP is described along with attempts at reacting them with 5-membered cyclic imines (1-pyrrolines). Also included is a study of nitrile oxides as traditional 1,3-dipoles and their reaction with 1- pyrrolines. Finally, an exploration of the reactivity of diphenylcyclopropenone with acyclic imines derived from Ellman’s 2-methyl 2-propanesulfinamide is included, which gave unexpected access to an indenone.