Bioisosteres provide valuable design elements for medicinal chemists to adjust the structural and pharmacokinetic characteristics of bioactive compounds towards viable drug candidates. Aryl oxetane amines offer exciting potential as bioisosteres for benzamides, an extremely common pharmacophore, but are rarely examined due to the lack of available synthetic methods. Here, we describe a new class of reactions for sulfonyl fluorides to form aminooxetanes by an alternative pathway to the established SuFEx (sulfonyl-fluoride exchange) click reactivity. An unprecedented defluorosulfonylation forms planar oxetane carbocations simply on warming. This disconnection, comparable to a typical amidation, will allow the application of vast existing amine libraries. The reaction is tolerant to a wide range of polar functionalities and is suitable for array formats. Ten oxetane analogues of bioactive benzamides and marketed drugs are prepared.Kinetic and computational studies support the formation of an oxetane carbocation as the rate determining step, followed by a chemoselective nucleophile coupling step.New reaction classes have enormous potential to access underexplored chemical space and influence molecular design. 1,2 A limited set of reliable and predictable reactions continue to have a disproportionate influence on the ability to construct medicinal and agrochemical compounds. 3 Such reactions can enable rapid access to derivatives, while also influencing, and limiting, molecular design. Most notably, click reactions have had an enormous impact in the chemical and biological sciences, which proceed on complex substrates without stringent conditions. 4,5,6,7 In drug discovery, amide bond formation continues to be the most common reaction, 3 exploiting vast amine and carboxylic acid libraries available to pharmaceutical companies. Amides are therefore prevalent in marketed pharmaceutical and agrochemical compounds, and display valuable features being more stable than other carbonyl derivatives, powerful H-bond donors and acceptors, and ubiquitous as critical bonding units in natural peptides and proteins. 8 Nonetheless, the amide sub-structure will frequently not provide the subtle balance of properties that is required for a successful active ingredient. Consequently, bioisosteres of amides are also common, providing a mimic of the features of the amide and adjusting the global properties of a compound. 9,10,11 While amidation is extensively investigated, with powerful, mostly stoichiometric coupling reagents, 12 the same cannot be said for amide-isosteres, which often require bespoke synthetic efforts (Fig. 1a).3,3-Disubstituted oxetanes have garnered considerable interest as carbonyl replacements, due to the similar dipole moments, hydrogen-bonding capacity, and oxygen lone pair orientation. 13,14 Their use as a bioisostere or replacement group also introduces a more 3-dimensional element to a drug compound that can have beneficial binding and solubility effects. 15 The motif is exemplified by antiviral Ziresovir, bear...