Primary and Secondary Amines by Flavin‐Photocatalyzed Consecutive Desulfonylation and Dealkylation of Sulfonamides

Abstract

AbstractAlkane‐, arene‐, and perfluoroalkanesulfonyl groups are widely used in organic synthesis to protect amino functionalities or to facilitate their installation. Protection of amino functions by a sulfonyl group to form sulfonamides is advantageous as they are easy to purify and tolerate various reaction conditions. On the other hand, sulfonyl group removal is difficult. Herein, we present a versatile metal‐free photocatalytic reductive method for desulfonylation of sulfonamides and aryl sulfonates to the parent amines mediated by flavin derivatives, namely deazaisoalloxazines and deazaalloxazines, and visible light. Photocatalysis with 5‐deazalloxazines is shown to even mediate the cleavage of perfluoroalkanesulfonamides (triflylamides and nonaflylamides), which is significantly more difficult than that of other sulfonamides and has previously not been achieved by photochemical means. The method is shown to perform consecutive desulfonylation and dealkylation of N‐alkyl‐N‐phenylperfluoroalkanesulfonamides affording primary anilines. This occurs via consecutive reductive and oxidative catalytic cycles mediated by the flavin catalyst. The perfluoroalkylsulfonyl group fulfils a dual role serving as a protecting group and, after removal by the reductive cycle, as the species driving the oxidative dealkylation reaction.