Markovnikov-Selective Radical Addition of S-Nucleophiles to Terminal Alkynes through a Photoredox Process

Direct radical additions to terminal alkynes have been widely employed in organic synthesis, providing credible access to the anti-Markovnikov products. Because of the Kharasch effect, regioselective control for the formation of Markovnikov products still remains a great challenge. Herein, we develop a transition-metal-free, visible light-mediated radical addition of S-nucleophiles to terminal alkynes, furnishing a wide array of a-substituted vinyl sulfones with exclusive Markovnikov regioselectivity. Mechanistic investigations demonstrated that radical/ radical cross-coupling might be the key step in this transformation. This radical Markovnikov addition protocol also provides an opportunity to facilitate the synthesis of other valuable a-substituted vinyl compounds.