Transition-metal-catalyzed methods for synthesis of fluorenes

This report aims to summarize recent advances in syntheses of fluorenes and derivatives thereof by using methods based on catalytic or stoichiometric transformations of various aromatic compounds induced by transition metal compounds. These methods encompass various inter- and intramolecular processes such as cross-coupling reactions, carbonylations, CH activations, electrophilic aromatic substitutions, cycloaddition reactions of alkenes and alkynes.     

Study of the substituent groups effect on the room-temperature phosphorescent emission of fluorene derivatives in solution

We present here the first study of the effect of substituent groups and the chemical structure of fluorene derivatives on phosphorescent emission. A group of fluorene derivatives have been studied with a new methodology of room-temperature phosphorescence emission called heavy atom induced room-temperature phosphorescence (HAI-RTP). This methodology makes use of RTP emission directly from the compound in fluid solution, without a protective medium but only with the presence of high concentrations of heavy atom perturbers and an oxygen scavenger. These experimental conditions permit sufficient interaction between the perturbers and the phosphors to produce effective population of the triplet states of the latter and, consequently, intense phosphorescent emission. Good deoxygenation conditions are obtained using sodium sulfite as the oxygen scavenger. We show here that it is possible that many fluorene derivatives can exhibit RTP emission in aqueous solutions in the absence of a protective medium. Phosphorescence spectral characteristics of these compounds (excitation and emission wavelengths and lifetime) and the optimization of the chemical variables involved in the phosphorescence phenomenon are reported. Under optimal experimental conditions, calibration graphs and detection and quantification limits in the ng ml⁻¹ level have been established.     

Highly efficient synthesis of polysubstituted fluorene via iron-catalyzed intramolecular Friedel-Crafts alkylation of biaryl alcohols

An efficient and mild Fe(III)-catalyzed intramolecular Friedel-Crafts alkylation of biaryl methanol derivatives has been developed to achieve the substituted fluorene derivatives. The present reaction provides an excellent alternative to published methods because of its high yields, operational simplicity, mild conditions, and use of inexpensive and sustainable catalyst.     

A general and efficient synthesis of substituted fluorenes and heterocycle-fused indenes containing thiophene or indole rings utilizing a Suzuki-Miyaura coupling and acid-catalyzed Friedel-Crafts reactions as key steps

A general and efficient synthesis of fluorenes or heterocycle-fused indenes including 3-thia-cyclopenta[a]indenes, 9-thia-indeno[1,2-a]indenes, 5,6-dihydroindeno[2,1-b]indoles has been developed. This methodology is realized by a multistep protocol involving first preparation of ortho-formylbiaryls through Suzuki-Miyaura coupling of o-bromobenzaldehydes with arylboronic acids or the coupling of aryl halides with 2-formylbenzene boronic acid, this is followed by Grignard addition and Friedel-Crafts cyclization reactions catalyzed by Brønsted or Lewis acid to form the desired fluorene or indene rings. The method offers several advantages such as high yields, high selectivities, mild reaction conditions, easily accessible starting materials, and so on.     

Novel 5-(oligofluorenyl)-1,10-phenanthroline type ligands: synthesis, linear and two-photon absorption properties

The synthesis and characterization of new 1,10-phenanthroline-based chromophores LT1, LT2 and LD1 featuring fluorene unit(s) are reported. Their absorption and emission as well as their two-photon absorption properties in the 450-650 nm spectral range are discussed in comparison with the parent 1,10-phenanthroline and already described ligands L1 and L2.     

A Convenient Way to Methylated 2-Imidazolines. Syntheses of Fluorene and Triazine Cyclic Diamidines

Summary. One N-methyl- and 4-substituted 2-imidazolines are described. Fluorene bisimidazolines were obtained in good yield (64–92%), starting from 2,7-dicyanofluorene and ammonium sulfide. In a two-step procedure the crude bisthioamide was reacted with excess diaminoalkane-ethanol (1:1 mixture) in an oil bath. This new procedure is superior over standard methods. For the sake of comparison, a new triazine bisimidazoline was prepared by direct conversion of the appropriate bisnitrile. Preliminary in vitro studies have shown an interesting anticancer activity of this compound (NSC 710607) against diverse human cancer types, including colon, CNS, melanoma, breast, non-small cell lung, and ovarian.