Synthesis and Reactions of Carbon Nanohoop

Abstract

Despite their intriguing structure and potential applications, the synthesis of structurally uniform carbon nanohoops has been a significant challenge until recently. The first synthesis of cycloparaphenylenes (CPPs), which are representative carbon nanohoops, nearly a decade ago considerably enhanced the availability of various carbon nanohoops, but the final products are usually only prepared on a mg scale. This review describes our endeavors to increase the availability of CPPs and their derivatives in large quantities. The three key reactions are 1) the one-pot, stereoselective two-fold addition of aryllithium to 1,4-benzoquinones to give U-shaped cyclization precursors, 2) subsequent nickel- or platinum-mediated selective cyclization, and 3) H₂SnCl₄-mediated reductive aromatization. This straightforward and high-yielding synthetic route provides gram quantities of various CPPs and their derivatives. Preliminary results on the applications of CPPs in electronic devices and the elucidation of CPP reactivity are also discussed.