MeCN, 100 °C, Using method B, efficient fluorination was achieved in quantitative yield, allowing straightforward isolation of the pure product 6p by filtration. Furthermore, a range of C-, S-and Onucleophiles with varying nucleophilicity could be employed, such as cyanide, aromatic/aliphatic thiols, thioamides, phenols and carboxylic acids, to afford products 6q-w in good to excellent yields. Notably, the competing SNAr pathway observed for phenols with method A was circumvented, and even complex substrates such as the steroid estrone could be derivatized into 6u in 77% yield. Moreover, the unprotected natural product cholic acid, with three competing nucleophilic hydroxy groups, underwent selective alkylation of the carboxylate moiety, to give product 6w in 88% yield. Some nucleophiles reacted in unexpected ways with 4a. For instance, the addition of water resulted in amide product 8 in 55% yield (see SI section 3.3), rather than the intended ring opening by hydroxide. The formation of 8 can be rationalized through a Ritter-type reaction in the presence of the MeCN solvent. Surprisingly, also DMF could be used as a productive nucleophile for the ring opening of 4a. When 3a was heated in DMF instead of MeCN, followed by addition of piperidine at room temperature, the formate product 9 was obtained in 88% yield. Furthermore, when the reaction was performed without addition of an external nucleophile, the primary alcohol product 10 was obtained in quantitative yield after aqueous workup. We anticipate that products 9 and 10 stem from an iminium intermediate formed through the ring opening of 4a by DMF in similarity with the Vilsmeier-Haack intermediate (see SI section 3.3). Ammonium salt 4 are potentially interesting compounds since organic ammonium salts find various industrial applications owing to their antimicrobial, 21 antistatic 22 and surfactant properties. To demonstrate the efficient preparation of 4, a small set of these products were synthesized by heating of 3, and isolated in good to excellent yields by simple evaporation of the solvent (Scheme 5).