(Alkynylphenyl)triazenes and phenylacetylene macrocycles for the synthesis of heterocycles and aromaticity probes

Triazenes are a useful and diverse class of compounds. They have been used for a variety of purposes, including medicinal chemistry, combinatorial chemistry, as well as to produce haloarenes useful in phenylacetylene synthesis. Chapter I is a review of the chemistry of triazenes and introduces several applications that are specifically addressed in subsequent chapters.; In Chapters II and III, a new route to isoindazoles and cinnolines through the cyclization of (2-alkynylphenyl)triazenes is presented. The products that result from heating the starting triazenes in MeI depend on both the type of alkyne ortho to the triazene functionality and the temperature used. Replacing MeI with 1,2-dichlorobenzene as solvent allows for the general cyclization of (2-ethynylphenyl)dialkyltriazenes. Heating to 170°C results in a mixture of isoindazole and cinnoline products, whereas the cinnolines are produced exclusively in high yield at 200°C. Alternatively, the isoindazoles can be obtained in good to excellent yield by stirring a 1,2-dichloroethane solution of the starting triazene with CuCl overnight at 50°C. Chapter II will discuss our findings on these unusual cyclizations as well as their scope.; The mechanistic aspects of the cyclization of (2-ethynylphenyl)triazenes under both thermal and copper-mediated conditions were also studied. For cyclization to an isoindazole, a carbene mechanistic pathway is proposed. DFT calculations support a pseudocoarctate pathway for this type of cyclization. Thermal cyclization to give a cinnoline from (2-ethynylphenyl)triazenes is proposed to occur through a pericyclic pathway. DFT calculations predict a zwitterionic intermediate that is supported by trapping experiments. Chapter III is devoted to these mechanistic studies.; At the very core of our interest in triazenes is their utilization in the construction and study of dehydrobenzoannulenes (DBAs). Our study of the cyclization of (alkynylphenyl)triazenes was in fact an offshoot of this type of research. One of the key concepts in the study of DBAs is the question of their aromaticity. Much debate exists regarding this subject, although our research has repeatedly suggested that DBAs have properties consistent with aromatic annulenes. Chapter IV concerns the use of an experimental probe, dimethyldihydropyrene (DDP), to investigate the extent of aromaticity of DBAs. Several DBA/DDP hybrids are reported and characterized, as well as preliminary studies regarding the potential of these systems to act as photoisomerizable switches. This application has to do with the ability of certain types of DDP hybrids to photoisomerize between the pyrene and cyclophanediene structures.; This dissertation includes both my previously published and unpublished coauthored materials.