Nickel‐Catalyzed Asymmetric Hydrovinylation Using Lewis Acid Activation

A broad range of commercially available Lewis acids were investigated for their ability to activate and regulate nickel catalysts for asymmetric hydrovinylation processes using styrene as model substrate and ligand ( R a , S C , S C )‐ 5 as benchmark system. The colour change during the activation step associated with the halide abstraction furnishes helpful indications to adapt the activation conditions to the pre‐catalyst/Lewis acid system. In general, metal halide Lewis acids led to higher activities and enantioselectivities than the corresponding triflates. In particular, the use of InI 3 as co‐catalyst resulted in the same chemo‐ and enantioselectivity and even higher activity than the benchmark system based onNaBArF. Moreover, InI 3 is safe to handle and cheap, thus providing a simple and practical protocol for an efficient hydrovinylation reaction.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)