Cyclopropenium Sulfide as Lewis Base Catalyst for Chemoselective and Regioselective Electrophilic Selenylation of Phenols

Soft Lewis basic sulfides are frequently employed as catalysts in the electrophilic functionalization of unsaturated compounds because the reactions can be operated under mild conditions. Among these reactions, electrophilic selenylation reactions are less reported, partly due to the lack of sufficiently strong Lewis base catalysts. Herein, we report the use of cyclopropenium sulfides as strong and soft Lewis base catalysts for electrophilic selenylation of phenols. The catalytic protocol was also found to be useful for the late-stage modification of tyrosine peptides. Mechanistic studies indicate that the catalyst can activate the amide-type electrophilic reagents by effective site isolation of the counteranion via nonclassical hydrogen bonds.