Amino-oxetanes as amide isosteres by an alternative defluorosulfonylative coupling of sulfonyl fluorides

Bioisosteres provide valuable design elements that medicinal chemists can use to adjust the structural and pharmacokinetic characteristics of bioactive compounds towards viable drug candidates. Aryl oxetane amines offer exciting potential as bioisosteres for benzamides—extremely common pharmacophores—but are rarely examined due to the lack of available synthetic methods. Here we describe a class of reactions for sulfonyl fluorides to form amino-oxetanes by an alternative pathway to the established SuFEx (sulfonyl–fluoride exchange) click reactivity. A 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. Sulfonyl fluorides typically react with nucleophiles exclusively at sulfur, leading to the substitution of fluoride, as is the case in SuFEx reactions. Now, an alternative defluorosulfonylative reaction has been developed, coupling 3-aryloxetane sulfonyl fluorides with amines to generate amino-oxetanes. The mild conditions and high functional group tolerance enable the preparation of oxetane analogues of benzamide drugs via oxetane carbocation intermediates.