Abstract

Since its discovery in 1949 by Brown and Farthing, paracyclophane has been intensely studied by chemists. Consisting of two benzene rings bound together by two ethano bridges, the paracyclophane core can undergo chemical transformations specific to both aliphatic and aromatic compounds, resulting in a wide variety of functionalized paracyclophanes. Because of the rigid molecular framework provided by the paracyclophane moiety and its short interannular distance, functional groups in pseudo-geminally substituted paracyclophanes are often held in such a position as to allow highly specific reactions to take place between them. Both the parent hydrocarbon and its derivatives have been used in asymmetric catalysis, optoelectronics and polymer synthesis. Acetylene-substituted paracyclophanes are important because of the ability of the acetylene moiety to easily undergo coupling and addition reactions, leading to new derivatives that contain one or more units of the paracyclophane core. Orthogonal π-bridges have been introduced into paracyclophanes by the reaction of the pseudo-geminal bisacetylene with various monoacetylenes and nitriles. Mono, pseudo-gem and pseudo-para ethynylcyclophanes and bis(azides) have been employed as addition partners in CuAAC reactions to design and build complex extended molecular scaffolds. The reactivity of the resulting triazoles was investigated under photochemical conditions. A variety of newly substituted paracyclophanes were identified; deazotization of pseudo-gem and pseudo-para adducts provided indolophane derivatives. A photochemical rearrangement from a pseudo-para adduct to a pseudo-ortho product was identified.