products 6a-o in good to excellent yields. Cyclic and acyclic secondary amines were proficient nucleophiles (6a-c), including the proline methyl ester, forming 6c in 95% yield. A common issue with N-alkylation strategies is the challenge to avoid over-alkylation. Thus, we were pleased to achieve selective monoalkylation of primary amine nucleophiles, with no detectable trace of dialkylated products. The methodology was compatible with a range of functionalities e.g. olefins, alkenyls, furanyl and thionyl groups (6d-h). Even the ambident nucleophile 2-aminoethanol reacted with complete selectivity for the C-N bond formation, giving 6i in 81% yield. Anilines could also be employed in the ring-opening, despite being weaker nucleophiles, and could be used for incorporation of an indolyl functionality and for derivatization of the commercial pharmaceutical cytadren, affording 6j-l in 61-84% yield. While an ortho-blocked phenol was efficient in the ring opening of 4a to provide 6m, unhindered phenols underwent a competing SNAr pathway with the ammonium moiety as the leaving group (see SI section 3.4). Halogenations were easily achieved with CsCl and KBr, providing products 6n and 6o in 80% and 88% yield, respectively. Some nucleophiles proved incompatible with the conditions of method A, either due to competing pathways (ArOH, CsF, KCN) or by causing decomposition of 4a (S-nucleophiles). Method B was designed to overcome this limitation through the use of substrates 3-OTs (Scheme 4). Upon formation of ammonium salts 4-OTs, direct ring-opening by the tosylate takes place, giving products 7 in quantitative yield with 100% atom economy (see SI section 3.3). Compounds 7 then undergo an in situ SN2 reaction with the external nucleophile to yield the target products 6. A short optimization revealed that the second SN2 reaction was more efficient in DMF at 70 °C for 4 h (see SI Table ). Fluorine incorporation into organic molecules has spurred a large research interest due to the favorable medicinal properties and the importance of 18 F radiolabeled pharmaceuticals.