Direct electrochemical construction of C─O bonds through C(sp3)─H functionalization still remains fundamentally challenging. Here, electrochemical oxidation-induced benzylic and allylic C(sp3)─H etherification has been developed. This protocol not only offers a practical strategy for the construction of C─O bonds using nonsolvent amounts of alcohols but also allows direct electrochemical benzylic and allylic C(sp3)─H functionalization in the absence of transition metal catalysis. A series of alcohols and benzylic and allylic C(sp3)─H compounds were compatible with this transformation. Mechanistically, the generation of aryl radical cation intermediates is the key to this C(sp3)─H etherification, as evidenced by radical probe substrate (cyclopropane ring opening) and electron paramagnetic resonance experiments.

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.

A [4+2] annulation of two different styrenes to construct polysubstituted 1,2-dihydronaphthalenes was achieved. This transformation proceeded smoothly under electrochemical oxidative conditions without metal catalysts and external oxidants. A series of polysubstituted 1,2-dihydronaphthalenes were obtained with high regioselectivity and diastereoselectivity. Moreover, polysubstituded 1,2-dihydronaphthalenes were further transformed to polysubstituted 1,2,3,4-tetrahydronaphthalenes and polysubstituted naphthalenes, which showed great potentials in synthetic application.