317-71-5

Upstream product

• 86-73-7 9H-fluorene 
• 6630-33-7 ortho-bromobenzaldehyde 
• 1073-06-9 3-fluorobromobenzene 
• 60081-02-9 (2-bromophenyl)(3-fluorophenyl)methanol 

Relevant academic research and scientific papers

Efficient palladium-catalyzed C(sp2)-H activation towards the synthesis of fluorenes

A facile protocol for the synthesis of fluorene derivatives has been developed through palladium-catalyzed cyclization of 2′-halo-diarylmethanes via activation of arylic C-H bonds. The reactions occurred smoothly and allowed both electron-rich and electron-deficient substrates to convert into their corresponding fluorenes in good to excellent yields. Studies revealed that this Pd-catalyzed cyclization was also available for the substrates of 2′-chloro-diarylmethanes and no catalyst poisoning occurred for 2′-iodo-diphenylmethane.

Fluorination of fluorene, dibenzofuran and their open analogues with caesium fluoroxysulfate and related fluorinating reagents

Fluorination of fluorene (1) with caesium fluoroxysulfate (CFS), 2,6-dichloro-l-fluoropyridinium tetrafluoroborate (FP-B800) and 1-fluoro-4-hydroxy-1,4-diazoniabicyclo[2.2.2]-octane bis(tetrafluoroborate) (Accufluor NFTh) occurred only on the aromatic ring in the position ortho and para to the biphenyl central bond with the ratio 2-fluoro- (2a) vs 4-fluorofluorene (2b) 1.7-2.4:1. Regioselectivity of fluorination of both open-chain analogues - diphenylmethane (3a) and biphenyl (3b) was different and more ortho-fluorinated product was formed. Furthermore, the reaction of diphenylmethane (3a) with CFS occurred also on central carbon forming benzophenone (6) and fluorodiphenylmethane (7), while fluorination with FP-B800 and Accufluor NFTh occurred only at the aromatic ring. Similar effect of the structure of fluorinating reagent on the regioselectivity was also observed with dibenzofuran (8) and its open-chain analogues diphenyl ether (10) and biphenyl (3b), where the regioselectivity of fluorination with CFS (1- (9a):2- (9b):3- (9c) = 27:46:27) was similar to fluorination with Selectfluor. Product distribution of fluorination of fluorene (1) and dibenzofuran (8) with CFS is similar to nitration and is in accordance with the calculated HOMO electron density, which indicates the presence of the electron transfer pathway.

The role of geometry on regioselectivity and rate of fluorination of fluorene and diphenylmethane with selectfluor F-TEDA-BF4

Diphenylmethane and fluorene were used as target molecules in an investigation of the effect of the geometry of aromatic molecules on the regioselectivity and rate of fluorination with 1-chloromethyl-4-fluoro-1,4-diazonia-bicyclo[2.2.2]octane bis(tetrafluoroborate) (Selectfluor F-TEDA-BF4). In acetonitrile at 80°C ring fluorination of diphenylmethane was accompanied by oxidation of the saturated carbon atom, while in trifluoroacetic acid only ring fluorination with an ortho-para regioselectivity of 1.8:1 was observed. Fluorene was converted in acetonitrile as well as in trifluoroacetic acid into 2- and 4-fluoro substituted products in the relative ratio of 2:1 and 1.2:1, respectively. The reactions in acetonitrile obey a simple rate equation: v = d[F-TEDA]/dt=k2 × [F-TEDA] × [Substrate] and the second order rate constants for the reactions in acetonitrile at 65°C were determined; values of 0.6 × 10-4 M-1 s-1 for diphenylmethane and 35.5 × 10-4 M-1 s-1 for fluorene were obtained. The reaction rates for the various functionalisations of fluorene relative to those for diphenylmethane were found to be considerably influenced by the type of functionalisation. Relative rate factors (krel=k2(fluorene)/k2(diphenylmethane)) with values between 59 for fluorination and 712 for chlorination were determined, while the corresponding data for the biphenyl/diphenylmethane pair were only slightly dependent on the type of functionalisation. A reaction pathway involving electron transfer, thus forming cation radical intermediates, was proposed as the main process in the case of fluorination of fluorene with F-TEDA-BF4.