Nickel‐Catalyzed Mizoroki–Heck‐ versus Michael‐Type Addition of Organoboronic Acids to α,β‐Unsaturated Alkenes through Fine‐Tuning of Ligands

Abstract Various arylboronic acids reacted with activated alkenes in the presence of [Ni(dppe)Br 2 ], ZnCl 2 , and H 2 O in CH 3 CN at 80 °C to give the corresponding Mizoroki–Heck‐type addition products in good to excellent yields. Furthermore, 1 equivalent of the hydrogenation product of the activated alkene was also produced. By tuning the ligands of the nickel complexes and the reaction conditions, Michael‐type addition was achieved in a very selective manner. Thus, various p‐ and o‐ substituted arylboronic acids or alkenylboronic acid reacted smoothly with activated alkenes in CH 3 CN at 80 °C for 12 h catalyzed by Ni(acac) 2 , P( o ‐anisyl) 3 , and K 2 CO 3 to give the corresponding Michael‐type addition products in excellent yields. However, for m‐ substituted arylboronic acids, the yields of Michael‐type addition products are very low. The cause of this unusual meta ‐substitution effect is not clear. By altering the solvent or phosphine ligand, the product yields for m‐ substituted arylboronic acids were greatly improved. In contrast to previous results in the literature, the present catalytic reactions required water for Mizoroki–Heck‐type products and dry reaction conditions for Michael‐type addition products. Possible mechanistic pathways for both addition reactions are proposed.