Mechanistic Analysis Reveals Key Role of Interchalcogen Multicatalysis in Photo‐Aerobic 3‐Pyrroline Syntheses by Aza‐Wacker Cyclizations

Abstract

AbstractA light‐driven dual and ternary catalytic aza‐Wacker protocol for the construction of 3‐pyrrolines by partially disulfide‐assisted selenium‐π‐acid multicatalysis is reported. A structurally diverse array of sulfonamides possessing homopolar mono‐, di‐ and trisubstituted olefinic double bonds is selectively converted to the corresponding 3‐pyrrolines in up to 95 % isolated yield and with good functional group tolerance. Advanced electrochemical mechanistic investigations of the protocol suggest a dual role of the disulfide co‐catalyst. On the one hand, the disulfide serves as an electron hole shuttle between the excited photoredox catalyst and the selenium co‐catalyst. On the other hand, the sulfur species engages in the final, product releasing step of the catalytic cycle by accelerating the β‐elimination of the selenium moiety, which was found in many cases to lead to considerably improved product yields.