2217-79-0Relevant articles and documents
Crystal Structures of Diaryliodonium Fluorides and Their Implications for Fluorination Mechanisms
Lee, Yong-Sok,Chun, Joong-Hyun,Hodo??ek, Milan,Pike, Victor W.
, p. 4353 - 4363 (2017)
The radiofluorination of diaryliodonium salts is of value for producing radiotracers for positron emission tomography. We report crystal structures for two diaryliodonium fluorides. Whereas diphenyliodonium fluoride (1 a) exists as a tetramer bridged by four fluoride ions, 2-methylphenyl(phenyl)iodonium fluoride (2 a) forms a fluoride-bridged dimer that is further halogen bonded to two other monomers. We discuss the topological relationships between the two and their implications for fluorination in solution. Both radiofluorination and NMR spectroscopy show that thermolysis of 2 a gives 2-fluorotoluene and fluorobenzene in a 2 to 1 ratio that is in good agreement with the ratio observed from the radiofluorination of 2-methylphenyl(phenyl)iodonium chloride (2 b). The constancy of the product ratio affirms that the fluorinations occur via the same two rapidly interconverting transition states whose energy difference dictates chemoselectivity. From quantum chemical studies with density functional theory we attribute the “ortho-effect” to the favorable electrostatic interaction between the incoming fluoride and the o-methyl in the transition state. By utilizing the crystal structures of 1 a and 2 a, the mechanisms of fluoroarene formation from diaryliodonium fluorides in their monomeric, homodimeric, heterodimeric, and tetrameric states were also investigated. We propose that oligomerization energy dictates whether the fluorination occurs through a monomeric or an oligomeric pathway.
The direct iodination of arenes with chromium(VI) oxide as the oxidant
Lulinski, Piotr,Skulski, Lech
, p. 1665 - 1669 (2007/10/03)
An easy and cheap laboratory method is presented for the direct mono- and diiodination of a number of activated and deactivated arenes. The main iodination reactions occurred at the temperatures not exceeding 65°C for 0.5-12 h in the anhydrous, strongly acidic liquid system, I2/AcOH/Ac2O/H2SO4, in the presence of prior dissolved CrO3 used as the oxidant. The yields of the pure iodinated products varied from 31% (for 3,5- diiodobenzoic acid) up to 90% (for 4-iodoanisole). So far, benzonitrile and some oxidizable aromatics, e.g. naphthalene, fluorene, xanthene, and thiophene, have been found to be unsuitable for the effective iodination. Nevertheless, this novel, simple method of direct iodination is worthy to be extended to other appropriate aromatics.
