In Chapter I some of the chemical, biological and physical properties of purine analogues, particularly benzimidazole N-oxides, are briefly discussed. In Chapter II, the preparations of 4-, 5-, 6-, and 7-amino-1H-benzimidazole 3-oxides are described. The methods employed involve base-induced cyclisation of suitably protected aminonitrophenyl glycine derivatives (esters or nitriles) followed by hydrolysis of the ester or nitrile and decarboxylation. In Chapter III, attempts are made to prepare imidazopyridine N-oxides, an area of N-oxide chemistry little explored. Although few derivatives of this class of compound are synthesised, the preparation of the parent 3H-imidazo[4 ,5-b]pyridine 1-oxide is accomplished. In Chapter IV, the possibility of preparing 1-methylbenzimidazole 3-oxides by the methods used in Chapters II and III is investigated, but unexpected results are obtained e.g. cyclisation of O-nitropheny1-sarcosine esters gives 1-hydroxy-4-methylquinoxaline-2, 3-diones. These reactions have instigated an investigation into the general mechanism for the base-induced cyclisations discussed in this thesis.