Enhanced nucleophilic fluorination and radiofluorination of organosilanes appended with potassium-chelating leaving groups

• Enhanced rates of fluorination at sterically congested silicon using simple potassium fluoride.
• New leaving groups chelate potassium cation to help stabilize charge build-up during substitution reaction.
• Method shows promising application in silicon radiofluorination with [18F]fluoride.

Here we aimed to explore the feasibility of enhancing the fluorination of organosilanes by appending potassium-chelating groups to the substrates. For this purpose, eight organosilanes were prepared in which a linear or cyclic leaving group, with putative potassium-chelating ability, was attached covalently to a congested silicon atom via an ether linkage to serve as a potential nucleophilic assisting leaving group (NALG). Organosilicon-NALGs with expected strong potassium-chelating capability enhanced reactions with potassium fluoride in acetonitrile to produce organofluorosilanes without any need to separately add phase transfer reagent. Similar rate enhancements were also observed with cyclotron-produced [18F]fluoride ion (t1/2 = 109.7 min, β+ = 97%) in the presence of potassium carbonate in MeCN–0.5% H2O. This study found that metal-chelating NALG units can accelerate fluorination and radiofluorination reactions at sterically crowded silicon atoms.

Figure optionsDownload as PowerPoint slide