Electrochemical Cobalt-catalyzed Cyclotrimerization of Alkynes to 1,2,4-Substituted Arenes

The transition-metal-catalyzed [2 + 2 + 2] cyclotrimerization of alkynes is one of the most straightforward routes for constructing six-membered ring motifs. Although this strategy possesses high atom/step economy and readily available substrates, the catalyst cycling is the key problem. Herein, we disclosed a facile and efficient cobalt-catalyzed cyclotrimerization of alkynes through electrochemical tools. Both terminal and internal alkynes were tolerated under the mild reaction conditions, affording the 1,2,4-trisubstituted and hexasubstituted benzenes with high regioselectivity. Electrochemical redox accurately tuned the valence of Co species to cycle the catalyst smoothly during the whole reaction.