Synthesis of Ex^<i>n</i>Box Cyclophanes

Abstract

A rapid and efficient synthesis of the extended bipyridinium-based class of cyclophanesthat is, <b>Ex</b>^{<i><b>n</b></i>}<b>Box</b>^<b>4+</b> (<i>n</i> = 0–3), where <i>n</i> is the number of <i>p</i>-phenylene rings inserted between the pyridinium ringsis demonstrated, resulting in much higher yields of products along with a reduced output of oligomeric byproducts. Although each cyclophane can be synthesized readily without the use of a precise stoichiometric amount of template, <b>ExBox</b>^<b>4+</b> can be prepared in 66% yield (following crystallization) using six equivalents of pyrene in a template-directed protocol. This new methodology has been employed to synthesize, in modest yield, a nearly 2.5 nm long cyclophane consisting of 12 aromatic rings