Co(III)‐Catalyzed Regioselective C−H Dienylation of Indolines and Indoles with Allenyl Carbinol Acetates

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Herein, we present a Co(III)‐catalyzed regioselective C7‐H dienylation of indolines at room temperature employing allenyl carbinol acetate as an efficient dienylating reagent. The reaction proceeds via C−H activation, regioselective 2,1‐migratory insertion of the allene followed by β‐acetate elimination, resulting in a diverse array of C7‐dienylated indolines. The methodology was further extended to C2‐H dienylation of indoles, affording either branched or linear dienes, contingent on the nature of the substituent present at the allenylic carbon. In addition, hydroarylation of allenes was also successfully achieved with tri‐substituted allenes, which was elusive so far under cobalt catalysis.