Selective Carbocation Functionalization by Catalytic Transchalcogenation Reactions

Introducing functionalities via acid‐mediated carbocation chemistry is conceptually straightforward, but typically lacks in selectivity and broad‐scale applicability, which is further hampered by the need for toxic reaction partners. Here, we show that small S‐ and Se‐based functionalities can be selectively and safely introduced into feedstock molecules via acid‐catalyzed transchalcogenation reactions. A designable y‐keto donor compound delivers the functionality through the formation of a trialkyl chalcogenonium intermediate that is prone to elimination in conjunction with the acid catalyst and its counteranion. We demonstrate how this strategy enables chemo‐, regio‐, and stereoselective construction of C(sp 3 )─S and ─Se bonds, offering clear advantages over classical acid‐catalyzed carbocation functionalization.