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Reactions of Arylsulfonate Electrophiles with NMe₄F: Mechanistic Insight, Reactivity, and Scope

Schimler, Sydonie D., Froese, Robert D. J., Bland, Douglas C., Sanford, Melanie S.
Journal of organic chemistry 2018 v.83 no.18 pp. 11178-11190
Lewis acids, chemical reactions, chemical structure, fluorides, monitoring, nuclear magnetic resonance spectroscopy, sulfates, tetramethylammonium compounds
This paper describes a detailed study of the deoxyfluorination of aryl fluorosulfonates with tetramethylammonium fluoride (NMe₄F) and ultimately identifies other sulfonate electrophiles that participate in this transformation. ¹⁹F NMR spectroscopic monitoring of the deoxyfluorination of aryl fluorosulfonates revealed the rapid formation of diaryl sulfates under the reaction conditions. These intermediates can proceed to fluorinated products; however, diaryl sulfate derivatives bearing electron-donating substituents react very slowly with NMe₄F. Based on these findings, aryl triflate and aryl nonaflate derivatives were explored, since these cannot react to form diaryl sulfates. Aryl triflates were found to be particularly effective electrophiles for deoxyfluorination with NMe₄F, and certain derivatives (i.e., those bearing electron-neutral/donating substituents) afforded higher yields than their aryl fluorosulfonate counterparts. Computational studies implicate a similar mechanism for deoxyfluorination of all the sulfonate electrophiles.