Reaction of Silyl Enol Ethers with Xenon Difluoride in MeCN:  Evidence for a Nonclassical Radical Cation Intermediate

Abstract

The reactions of xenon difluoride in MeCN solution in Pyrex flasks with a series of TMS enol ethers have been investigated. The types of products formed are dependent on the structures of individual enol ethers, but under these conditions all products are consistent with a mechanism involving single electron transfer to un-ionized XeF2 giving a radical cation and subsequent formation of an α-fluoroketone, together with some ketone formation. The results suggest that if the radical cation is particularly stable, fluorodesilylation leads to radical formation, and solvent-derived products are then observed. Using other solvents, such as CFCl3 and C6F6, much more complex mixtures of products are obtained, and this is attributed to a different mode of reaction of xenon difluoride involving ionization to FXe+.

ipso-Fluorination of aryltrimethylsilanes using xenon difluoride

“…They proposed a SET initiated mechanism in accord with our previous proposals that XeF 2 reacts with organic substrates via SET in MeCN solution. 9,11,12,21 Reaction of the boronic acid 12 with XeF 2 in CH 2 Cl 2 gave a dark brown fuming solution, which was shown to be a complex mixture containing a tiny amount of 4-fluorotoluene 4 (R¼F) ( 19 F NMR À119 ppm).…”

Synthesis and biological properties of radiohalogenated α,α‐disubstituted amino acids for PET and SPECT imaging of amino acid transporters (AATs)

“…The observation that syn ‐ and anti ‐3‐FMACBC were biologically as active as the parent anti ‐3‐FACBC led to the development of iodinated analogues of FMACBC where the fluoromethyl groups were replaced by iodovinyl moieties (Figure ). Thus, syn ‐ and anti ‐1‐amino‐3‐[2‐iodoethenyl]‐cyclobutane‐1‐carboxylic acids ( syn ‐3‐IVACBC ( 50 ), anti ‐3‐IVACBC ( 51 )), and 1‐amino‐3‐iodomethylene‐cyclobutane‐1‐carboxylic acid ( gem ‐3‐IVACBC ( 52 )) were prepared (Figure ) .…”

19F NMR and UV studies of xenon difluoride solution-vessel stability and its relevance to the fluorination of organic substrates

“…These mechanistic conclusions are supported by our studies of reactions of other substrates in which the product composition is determined by the combination of solvent and vessel. These include studies of TMS benzoates, 4 enol ethers 6 and carboxylic acids. 8 With the intention of supporting our preparative and mechanistic studies by identifying the species present in solution under organic reaction conditions, we have determined the 19 F NMR and UV spectra of xenon difluoride in various solvent/cell systems.…”

“…1,2 In a series of studies we have shown that both solvent and reaction vessel can profoundly influence the mode of reaction of xenon difluoride with organic substrates. [3][4][5][6][7][8][9] Although the instability of xenon difluoride in glassware has been known for some time, Pyrex ® flasks have been widely used, and advocated, 2 for carrying out organic reactions but, apart from our own work, 5 the role of the glass surface in determining the reaction pathway has not been recognised. We have shown, for example, that aryltrimethylsilanes are rapidly fluorinated by xenon difluoride at room temperature (Equation 1) but only in a Pyrex ® flask.…”