This thesis is divided into three sections, Parts 1, 2 and 3. Each part is divided into a number of principal sections, prefixed by capital letters, and these sections are further divided into sub-sections prefixed by Roman numerals or small letters. Part 1A deals with the relationship between azulene, indolizine and pyrrolo [2,1-b] thiazole, while part 1B consists of a review of the preparation and properties of thiones and thials. Part 2A-C is a discussion of results achieved in the course of investigations into the reactivity of indolizines and pyrrolo [2,1-b]-thiazoles towards electrophilic reagents. In Part 2D are described synthetic routes to some stable heterocyclic thiocarbonyl compounds, together with a preliminary investigation into the physical and spectral properties of these compounds. Part 3 is devoted entirely to a description of experimental details and is a complement to Part 2. Where reference is made to the chemical literature, this is indicated by a number in superscript, a key to which can be found at the end of part 3. The structural formulae which have been produced for illustrative purposes have been assigned Roman numerals, which correspond to the numbers which have been assigned to the relevant compounds in the text. The structure keys to Parts 1 and 2 are distinct. The structure key to part 3 is the same as that for Part 2.