Nickel-Catalyzed Electroreductive Homocoupling of α-Allenyl Electrophiles Provides Direct and Selective Access to [4]-Dendralenes

A direct and regioselective route to symmetrical [4]-dendralenes has been developed based on nickel-catalyzed electroreductive homocoupling of α-allenyl electrophiles. The methodology offers the first electrochemical approach to dendralenes and a rare example of nickel-mediated activation of α-allenyl electrophiles. Under mild conditions in an undivided cell, a broad range of α-, β-, and δ-substituted allenyl acetates undergo efficient dimerization to furnish diversely substituted cross-conjugated tetraenes in moderate to good yields. Aryl-substituted substrates display particularly high stereocontrol, generally affording the corresponding dendralenes with excellent preference for the (E,E)-diastereomer. This work introduces a complementary reductive disconnection for [4]-dendralene synthesis and reveals a previously unexplored dimerization manifold of α-allenyl electrophiles.