A Precisely Bromo-Functionalized [9]Cycloparaphenylene as a Platform for Late-Stage Multisite π-Extension Toward Chiral Nanohoops

Abstract

Selective functionalization of [n]cycloparaphenylenes ([n]CPPs) has remained a significant synthetic challenge due to their inherent ring strain. In this study, we present the synthesis of a [9]CPP derivative in which bromo groups are orderly introduced at the 2,5-positions of three benzene rings in the [9]CPP framework, each separated by two phenylene units. The use of our developed Au-mediated CPP synthetic method enabled efficient and scalable access to the target compound in five steps with an overall yield of 37%. The resulting molecule exhibited phosphorescence at low temperature, arising from the heavy-atom effect of the bromo substituents. Furthermore, post-functionalization through Pd-catalyzed coupling reactions demonstrated multisite π-extension and afforded a chiral nanohoop exhibiting exceptional chiroptical performance (|glum| = 0.100).