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 InI3 as co-catalyst resulted in the same chemo- and enantioselectivity and even higher activity than the benchmark system based on NaBArF Moreover, InI3 safe to handle and cheap, thus providing a simple and practical protocol for an efficient hydrovinylation reaction. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)