Electrochemical C-H Phosphonylation of Indole with Phosphine Enabled by Chemoselective C-P Bond Cleavage.

Given the significance of phosphonylated heterocycles, new phosphonylation pathways have been intensively pursued ever since. Herein, the electrochemical C3-C-H phosphonylation of indole with trivalent phosphine was accomplished, enabled by sequential electro-oxidations and chemoselective C-P bond cleavage. This strategy provides a new reaction mode and facile access to install phosphonylated indoles by circumventing the drawbacks of pentavalent phosphine oxides, which are frequently used in classical methods. When electrons are employed as traceless oxidants, the protocol is endowed with operational simplicity, mild reaction conditions, excellent regioselectivity, and broad functional group tolerance, especially allowing for the facile preparation of rarely accessed unsymmetrical phosphine oxides. Mechanistically, well-designed sequential electro-oxidations and chemoselective C-P cleavage are involved in the process.