Organocatalytic asymmetric hydroarylation of o-hydroxyl styrenes via remote activation of phenylhydrazones

The first catalytic asymmetric styrene hydroarylation reaction has been established via the enantioselective Friedel-Crafts alkylations of phenylhydrazones with o-hydroxyl styrenes under the catalysis of a chiral phosphoric acid as an organocatalyst, leading to the construction of a chiral 1,1-diarylethane scaffold with high enantioselectivity (up to 89% ee). The investigation on the activation mode suggested that the two reactants, o-hydroxyl styrenes and phenylhydrazones, were simultaneously activated by the catalyst via multiple hydrogen-bonds. The remote activation of the hydrazone functionality by a dual hydrogen-bonding interaction with the catalyst contributed greatly to the hydroarylation reaction of the o-hydroxyl styrenes. (C) 2014 Elsevier Ltd. All rights reserved.