Modification of fluorene and fluorenone core via C–H functionalization

Abstract

We report the modification of fluorene and fluorenone cores, and the assembly of libraries of functionalized fluorenes/fluorenones involving the C(sp²)–H and C(sp³)–H functionalization route. Fluorene/fluorenone motifs are versatile components in materials science, and some are bioactive compounds. In this work, the C–H bonds of fluorene and fluorenone were subjected to C–H arylation, alkylation, benzylation, alkoxylation, and annulation reactions to afford modified fluorenes/fluorenones. Alternatively, various functionalized fluorenes/fluorenones were obtained by subjecting the C–H bonds of aryl or alkyl carboxamides to the C–H arylation process using iodofluorenes or iodofluorenones as the coupling partners. Overall, a comprehensive effort and synthesis of several C(1), C(2), C(3), and C(4) functionalized fluorenes, fluorenones, fluorene–fluorenone couples, fluorene–carbazole couples, π-extended bis fluorenes, and enantioenriched π-extended bis fluorenes are reported. Given the prominence of fluorene/fluorenone motifs, this work contributes to augmenting the library of fluorenes and fluorenones via a C(sp²)–H and C(sp³)–H functionalization strategy.