Ligand controlled regio‐divergent [2+2+2] cyclotrimerization of alkynes by merging electrochemistry and nickel catalysis

Abstract

Transition metal catalyzed [2+2+2] cycloaddition reactions between three alkynes, a diyne and an alkyne, or a triyne offer a straightforward and typical protocol toward all kinds of polysubstituted benzens. Herein, the synthesis of polysubstituted aromatics through electrochemical nickel catalyzed cyclotrimerization of alkynes is developed. The regio‐divergent cyclotrimerization of terminal alkynes was achieved by judicious choice of ligands. And tributylphosphine, sterically hindered bipyridine or β‐diketone ligands delivered 1,2,4‐ and 1,3,5‐substituted aromatics with high regioselectivities respectively. Besides, the semi‐intermolecular [2+2+2] cycloaddition between diynes and alkynes are also amenable under this catalytic system. This approach operates without metal reductant, exhibits wide functional groups tolerance, ease of scalability and furnishes 75 examples with moderate to good yields, including some biorelevant compounds. Mechanistic experiments and DFT calculation revealed the catalytic pathways of 1,3,5‐ and 1,2,4‐cyclotrimerizations, and the origin of the ligand controlled regioselectivity.