From Targeted Synthesis to Serendipitous Discovery: Transforming Perfluorotoluene into Discotic Liquid Crystals and Dearomatized Spirofluorenes.

This study develops a one-pot synthetic system that concurrently produces two classes of functional materials via a previously unobserved transformation of perfluorotoluene under nucleophilic conditions. Building on prior work with fluorinated discotic systems, the reaction of 2,2'-dilithio-1,1'-biaryls with perfluorotoluene (C6F5-CF3) furnishes trifluoromethylated trifluorotriphenylene derivatives (TPFn, n = 1-4, 6, 8, 10, 8/2) alongside structurally distinct dearomatized spirofluorene analogues (TPFn-1). The formation of the spirofluorene compounds points to a competing pathway beyond classical aryl nucleophilic substitution. Based on structural evidence, a dearomatization process involving cleavage of four C-F bonds (one from the pentafluorophenyl ring and three from the CF3 group) and subsequent formation of new C-C bonds is proposed to account for the formation of the spiro-fused architecture. This side reaction sheds light on the moderate yields of the target TPFn series and highlights the complex reactivity of perfluorotoluene with 2,2'-dilithio-1,1'-biaryls. All TPFn compounds form thermally stable hexagonal columnar (Colhex) mesophases with large liquid-crystalline ranges, along with a strong modulation of the clearing temperatures with alkoxy chain lengths. Despite the presence of the bulky lateral CF3 group, the transition temperatures are surprisingly not greatly affected when compared to previously synthesized 4F-TPn homologous compounds (with no CF3 groups). Structural analysis, supported by X-ray crystallography of ditert-butyl model compound (tBuTPF), validates the molecular design and packing. This work thus provides a practical one-pot route to potentially fluorinated discotic semiconductors while revealing a competing transformation that advances the understanding of polyfluorinated arene chemistry and offers access to novel spiro-fused molecular architectures.