Cross-dehydrogenative coupling macrocyclization for the construction of donor-acceptor nanohoops

Donor (D) and acceptor (A) (D-A) architectures in cycloparaphenylenes (CPPs), or nanohoops, offer property tunability beyond what can be controlled by ring size. However, the synthesis of D-A nanohoops using traditional cross-coupling requires monomer prefunctionalization, which reduces step and atom economy. We report a catalytic cross-dehydrogenative coupling (CDC) macrocyclization strategy to access the [8]nanohoop cyclo(2,5-thienylene)(perfluoro-1,4-phenylene) ([8]CTPFP) with D-A architecture. A strain-relieving L-shaped precursor bearing thiophene termini is used in a Pd-catalyzed C-H/C-H cross-coupling reaction with 1,2,4,5-tetrafluorobenzene to form the precursor macrocycle pre[8]CTPFP in an atom- and step-economic route, circumventing the use of organometallic reagents. Subsequently, a BBr₃-mediated reductive aromatization at room temperature is shown to furnish the target nanohoop [8]CTPFP. The overall synthetic route presents a reduced synthetic complexity compared to those reported for comparable [8]nanohoops with D-A architecture. X-ray crystallographic analysis reveals that the intrinsic nanotubular assembly of [8]CTPFP in the solid state is perturbed by π-rich solvent inclusion. A significantly red-shifted emission is observed, despite lacking internal charge-transfer (ICT) character. This work provides a proof-of-concept for catalytic C-H activation as a tool for the streamlined syntheses of D-A nanohoop architectures.