Aryl iodides tetrafluoroborate

The reaction can be carried out efficiently using aryl diazonium tetrafluoroborates with crown ethers, polyethers, or phase transfer catalysts.103 In solvents that can act as halogen atom donors, the radicals react to give aryl halides. Bromotrichloromethane gives aryl bromides, whereas methyl iodide and diiodomethane give iodides.104 The diazonium ions can also be generated by in situ methods. Under these conditions bromoform and bromotrichloromethane have been used as bromine donors and carbon tetrachloride is the best chlorine donor.105 This method was used successfully for a challenging chlorodeamination in the vancomycin system. 

Entries 7 and 8 illustrate conversion of diazonium salts to phenols. Entries 9 and 10 use the traditional conditions for the Sandmeyer reaction. Entry 11 is a Sandmeyer reaction under in situ diazotization conditions, whereas Entry 12 involves halogen atom transfer from solvent. Entry 13 is an example of formation of an aryl iodide. Entries 14 and 15 are Schiemann reactions. The reaction in Entry 16 was used to introduce a chlorine substituent on vancomycin. Of several procedures investigated, the CuCl-CuCl2 catalysis of chlorine atom transfer form CC14 proved to be the best. The diazonium salt was isolated as the tetrafluoroborate after in situ diazotization. Entries 17 and 18 show procedures for introducing cyano and azido groups, respectively. 

The Stille coupling reaction has been performed in l-bntyl-3-methylimidazolium tetrafluoroborate. Use of this solvent system allows for facile recycling of the solvent and catalyst system, which can be used at least five times with little loss in activity. An interesting preference in starting catalyst oxidation state for nse with aryl bromides and aryl iodides was observed (Handy and Zhang, 2001). 

Palladium-catalyzed arylation of the electron-rich olefin bntyl vinyl ether has been accomplished in the ionic liquid l-butyl-3-methylimidazolium tetrafluoroborate using as the arylating agents aryl iodides and bromides instead of the commonly used, but commercially unavailable and expensive, aryl triflates. The reaction proceeds with high efficiency and remarkable regioselectivity, leading almost exclnsively to substitution by various aryl groups at the olefinic carbon a to the heteroatom of butyl vinyl ether (Xu et ak, 2001). 

As part of their study on gastric (H+/K+)-ATPase inhibitors, Kang et al. developed a simple and convenient synthetic approach to 1,2,3-trisubstituted pyrrolo[3,2-c]quinolines by means of Pd-catalyzed heteroannulation of 4-amino-3-iodoquinoline derivatives with internal alkynes [76]. The following scheme shows an example of a reaction using 4-arylamino-3-iodoquinoline derivative 180 with alkyne 181 to provide 1-arylpyrrolo [3,2-c]quinoline 182, illustrating the possibility of introducing diverse substituents to 1-arylpyrrolo[3,2-c]quinolines. In addition, a Pd-catalyzed domino hydroarylation/ cyclization process was reported to form substituted quinolines [77]. Thus, 3-arylquino-lines were prepared in 56-74% yield when 3,3-diethyl-l-phenyl-1-propyne and aryl iodide were refluxed in ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate [(bmim)BF4 ],in the presence of HCO2H, EtjN, and palladium catalyst. Meanwhile,... 

Conversion of diazonium compounds to aryl chlorides, bromides, or cyanides is usually accomplished using cuprous salts, and is known as the Sandmeyer reaction. Since a CN group is easily converted to a CO2H group (eq. 10.13), this provides another route to aromatic carboxylic acids. The reaction with KI gives aryl iodides, usually not easily accessible by direct electrophilic iodination. Similarly, direct aromatic fluorination is difficult, but aromatic fluorides can be prepared from diazonium compounds and tetrafluoroboric acid, HBF4. 

Packer et al. (1981) found that y-irradiation reduces arenediazonium tetrafluoro-borates to aryl radicals. Packer and Taylor (1985) investigated the y-irradiation of 4-chlorobenzenediazonium tetrafluoroborate by a 60Co source in the presence of 1 alone or I- +13 . The major product in the presence of iodide was 4,4 -dichloroazo-benzene. With I- + 1 ", however, it was 4-chloroiodobenzene. Two other investigations of the reactivity of aryl radicals with iodine-containing species are important for the understanding of the chain process of iodo-de-diazoniation that starts after formation of the aryl radical. Kryger et al. (1977) showed that, in the thermal decomposition of phenylazotriphenylmethane, the rate of iodine abstraction from I2 is extremely fast (see also Ando, 1978, p. 341). Furthermore, evidence for the formation of the radical anion V2 was reported by Beckwith and Meijs (1987) and by Abey-wickrema and Beckwith (1987) (see Sec. 10.11). 

The surprising stability of triaryloxonium ions has been demonstrated by the fact that reduction of the tris(4-nitrophenyl)oxonium tetrafluoroborate 35 can be performed to give the tris(4-aminophenyl)oxonium salt 36 without cleavage of aryl oxygen bonds [Eq. (4.21)]. Diazotation of this amino derivative and reaction with iodide leads to the tris(/v/ra-iodophenyl)oxonium salt 37 in excellent yields.104... 

Diphenylbromonium tetrafluoroborate gave 15% to 20% of the expected organometallics with Tl, Sn, Pb, Bi (but not Hg) powders (40). Perhaps, the better reactivity of the tetrafluoroborate as compared with the iodide may be explained in the same manner as with the diazonium arylation. This may be written as follows ... 

Arenediazonium tetrafluoroborates can be converted into aryl azides under mild conditions, by reaction with Me3SiN3 in an ionic liquid at room temperature. Analogously, aryl bromides and iodides are formed with MesSiX (X = Br, I). 

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