Pd(0)-Catalyzed Cross-Coupling of 1,1-Diboronates with 2,2′-Dibromobiphenyls: Synthesis of 9H-Fluorenes

Abstract

An efficient and mild synthesis of 9H-fluorene derivatives through a Pd(0)-catalyzed cross-coupling reaction of 1,1-diboronates with 2,2'-dibromobiphenyls has been developed. This reaction features high yields, operational simplicity, and mild reaction conditions, thus providing an excellent alternative to published methods for 9H-fluorene synthesis.

Alkylated Selenophene-Based Ladder-Type Monomers via a Facile Route for High-Performance Thin-Film Transistor Applications

“…2,1,3-Benzothiadiazole-4,7-bis-(boronic acid pinacol ester) (6) was purified by recrystallization from hexane before use. (3,3′-Dibromo-[2,2′-biselenophene]-5,5′diyl)bis(trimethylsilane) (1), 43 bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)methane, 44 2,5-dibromoselenophene (7), 45 and 1,4-dibromo-2,5-diiodobenzene (10) 46 were synthesized by the reported methods. 1 H and 13 C NMR spectra were recorded on a Bruker AV-400 (400 MHz), using the residual solvent resonance of CDCl 3 or d 2 -1,1,2,2-tetrachloroethane, and the chemical shifts are given in parts per million.…”

Palladium-Catalyzed Double-Suzuki–Miyaura Reactions Using Cyclic Dibenziodoniums: Synthesis of o-Tetraaryls

“…López-Romero employed p -dibromobiphenyl derivatives in coupling reactions, but monocoupling products were preferentially obtained . Very recently, Li and Wang reported a double-cross-coupling reaction of 2,2′-dibromobiphenyls with 1,1-diboronates where 9 H -fluorenes were synthesized in excellent yields …”

Palladium-Catalyzed Cyclization of Alkenes with Organohalides

“…Wu et al merged the Pd-catalyzed cycloisomerization and subsequent retro-aldol condensation in this manner (Scheme , II ) . Recently, tosylhydrazones and 1,1-diboronates were used in the construction of ring systems through a suitable design (Scheme , III and IV ). However, most of these reactions suffer drawbacks of harsh conditions, limited starting materials ( ortho -disubstituted arenes), and low functional group tolerance.…”

“…As such, intense research interest has been paid to explore some practical synthetic strategies, including Brønsted or Lewis acid promoted intramolecular Friedel–Crafts alkylation, transition-metal-catalyzed/mediated cyclization utilizing C–H bond activation or carbene C–H insertion, and even radical reactions . Among them, palladium-catalyzed tandem reaction, which allows efficient access to substituted fluorene derivatives, leads to major progress (Scheme , a). − For example, Hu and co-workers disclosed the cascade coupling of dihalobenzenes with methylphenylmagnesium bromide or 2-tolylboronic acid to fluorenes (Scheme , I ) . Wu et al merged the Pd-catalyzed cycloisomerization and subsequent retro-aldol condensation in this manner (Scheme , II ) .…”