Design and synthesis of helical acetylenic carbo- and heterocyclic cyclophanes

Abstract

The purpose of this research project was to synthesize new acetylenic cyclophanes. These cyclophanes have unusual and aesthetically pleasing structures, pose synthetic challenges, have peculiar reactivity, and often exhibit interesting spectroscopic and physical properties. In addition to the successful synthesis of a number of new cyclophanes, several new synthetic strategies and methods were developed. A one-pot preparation of arylbutadiynes 95 from chloroenyne 83 and arylhalides was accomplished. This method was used to prepare a variety of arylbutadiynes in 80--95% yields. A procedure was also developed for the in situ desilylation/dimerization of bulky silylalkynes. A molecular modeling study provided insight into the observed dimerization reaction products of alpha,o-dialkyne precursors. Termini separation distances (r) less than 7 A gave intermolecular coupling, while distances greater than 10 A gave intermolecular reactions. Mixtures of intra- and intermolecular reaction products were obtained when 7 < r > 10 A. The synthesis of two new C60 acetylenic cyclophanes revealed that the substitution pattern of the capping group controlled the conformation of the molecule. Cyclophane 113 with para-substituted capping groups adopted a helical (chiral) conformation and the isomeric meta-capped cyclophane 123 had a different molecular folding pattern with the potential to be planar. Two classes of unsaturated cyclophanes were synthesized as ligands for the preparation of chiral, non-racemic helical complexes: A tetramethoxybenzene-capped, C60 acetylenic cyclophane as a potential eta12-bis(arene) ligand, and phenanthrolinophanes as tetradentate pi-coordination ligands. Cyclophane 170 was successfully prepared, but metal complexes of 170 could not be prepared. Phenanthrolinophanes 200, 217, and 227 and their corresponding copper complexes were synthesized by a new, metal-templated procedure. Copper coordination was found to raise the helical isomerization barrier height by over 7 kcal/mol; however, isomerization still occurred at room temperature so enantiopure phenanthrolinophanes could not be isolated. The first pentacenes with functional groups on the A and E rings have also been synthesized. A highlight of the rapid, four-step synthesis of pentacenes 274 and 275 was the absence of any chromatographic purification. The commercial potential of these new pentacene compounds as organic semiconductors is being investigated in collaboration with the National Research Council of Canada.* *Please refer to dissertation for diagrams.