Visible-Light Photocatalyzed C3–H Alkylation of 2<i>H</i>-Indazoles/Indoles with Sulfoxonium Ylides via Diversified Mechanistic Pathways
Altman Yuzhu Peng, Yujing Wang, Kaifeng Wang, Qing Sun, Xiaoguang Bao
Abstract
Herein, the C3–H alkylation of 2 H -indazoles and indoles with sulfoxonium ylides is developed under visible-light photocatalysis. This protocol employs easily accessible reagents, and a wide range of 2 H -indazoles, indoles, and sulfoxonium ylides are suitable for this reaction to afford the desired products under benign conditions. Synergistic experimental and computational studies suggest that the sulfoxonium ylides involving C3–H alkylation of 2 H -indazoles and indoles under visible-light photocatalysis could proceed via different mechanistic pathways. For the C3-alkylation of 2 H -indazoles, a triplet energy transfer mechanistic pathway of 2 H -indazoles is proposed for quenching the excited photocatalyst. Subsequently, the formed excited triplet state of 2 H -indazoles could undergo radical attack on the C═S moiety of sulfoxonium ylides. After the dissociation of DMSO and 1,2-H migration, the final product of C3-alkylation of 2 H -indazoles could be yielded. However, such a mechanistic pathway is not applicable for indoles. Instead, sulfoxonium ylides could be converted to a C-centered radical in the presence of KH 2 PO 4 under visible-light photoredox conditions. The formed C-centered radical can attack the C3-site of indoles and thus lead to the C3-alkylation product of indoles.