Effects of the structure of reagents on the halogenation of organic molecules

Following very intensive research in the area of the halogenation of organic molecules especially stressing in selective fluorination under mild reaction conditions we sistematically studied reactions of modern fluorinating reagents: N-F reagents (derivates of N-fluoro-1,4-diazoniabicyclo(2.2.2)octane, N-fluoro pyridinium salts, N-fluoro sulfonimides), caesium fluoroxysulphate and xenon difluoride with selected model aromatic molecules (phenoles, aromatic ethers, alky aromatics) and bicyclo alkenes (norbornene). Room temperature xenon difluoride fluorination of fluorene resulted in two ring fluoro-substituted products: 2-fluoro- and 4-fluorofluorene in 2:1 relative ratio. Fluorination of debenzofuran gave three products 1-fluoro-, 2-fluoro-, and 3-fluorodibenzofuran in 1:1:2 relative ratio and ion radicals were postulated as reactive intermediates. The ortho regioselectivity of fluorine introduction into a substrates within the group of diphenyl substituted aromatic molecules increases in the series: biphenyl, diphenylmethane, diphenyl ether. (J.Org.Chem. 1998, 63, 878). In the reaction of norbornene in acetonitrile with N-F reagents (F-TEDA-BF4, NFTh, NFSi, FPD-T) the formation of 2-exo-acetamido-7-syn-fluoro and 2-exo-acetamido-7-anti-fluoronorbornane was observed and the reaction pathway including carbonium ions intermediates was postulated (Chem. Lett. 1998, 641). In the reactions of phenols and anisole derivatives with F-L reagents the competition between three reaction proccesses : orho fluorofunctionalisation, ipso substitution, and addition-elimination was observed their relative intensity beeing depended on the structure of the reagent and the substrate.