Synthesis and Structures of Carbon Nanohoops Containing Three Picene Units with Each Having Two Carbomethoxy...

Carbon nanohoops are an emerging class of cyclic conjugated molecules that have drawn significant attention for their unique optoelectronic properties and potential applications in nanomaterials. We report herein the synthesis of two novel carbon nanohoops with structures as [9]cycloparaphenylene ([9]CPP) derivatives having three picene units with each substituted by two carbomethoxy groups. A substrate bearing a hexahydropicene unit with the two bromophenyl groups cis to each other through the Diels-Alder reaction with dimethyl acetylenedicarboxylae was prepared in four steps from 6-bromo-1-tetralone. A subsequent Ni(cod)₂/bpy-mediated macrocyclization reaction followed by a DDQ-promoted oxidation step of the central six-membered ring and the dimethylene linkages produced a pair of cyclic anti- and syn-trimers because of the slow rotation of the dicarbomethoxy-substituted picene units. This work not only introduces new CPP architecture but also provides insights into the potential extension of this methodology toward the synthesis of cyclophenacenes as carbon nanobelts.