Development of new methodologies for the synthesis of expanded porphyrins and aspects of the conformational behavior of some previously unknown oligopyrrolic systems
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In spite of the considerable number of expanded porphyrin systems that are now known, methods for synthesizing these compounds remain quite limited. Aspects of this dissertation address this problem. For instance, in Chapter 2 a new methodology that allows, for the first time, the synthesis of quaterpyrrolecontaining expanded porphyrins is described. Specifically, using a Cr(VI)-based oxidative coupling approach, three previously unknown macrocycles were synthesized that were inaccessible using classic approaches. Likewise, in Chapter 4 the use of new Fe(III)-based oxidative couplings as a very effective way to produce previously unknown cyclopyrroles is detailed. The latter macrocycles, species of remarkable symmetry and potential utility, are prepared in high yields in a single synthetic step from readily available bipyrrolic precursors. Further, a modification of this strategy is presented that allows for the synthesis of linear quaterpyrrole, a species characterized structurally for the first time in the course of this work. The second major focus of this dissertation work was the study of conformational effects in oligopyrrolic macrocycles. A remarkable range of conformations is seen in many expanded porphyrins. This is not the result of rational design. Rather, it is an intrinsic feature of these systems, albeit an unexpected one. A desire to understand the origins of these effects has prompted the synthesis and study of four new expanded porphyrins. This work is presented in Chapter 3, wherein the use of simple symmetry considerations in the design and conformational analysis of previously unknown systems is described.