A large number of stereoselective methods for benzylic and homobenzylic functionalization have been developed based on this property.
[3] The chromium(0) activates the side chain of the arene, facilitating dissociation of a benzylic proton, leaving group, or nucleophilic addition to the homobenzylic position of styrenes.
Further transformations of the resulting conformationally restricted, benzylic anion or cation involve the approach of reagents exo to the chromium fragment.
Thus, benzylic functionalization reactions of planar chiral chromium arene complexes are highly diastereoselective.
[1] Removal of the chromium fragment to afford the metal-free functionalized aromatic compound is possible photolytically[4] or with an oxidant.
[1] Benzylic cations of chromium arene complexes are conformationally stable, and undergo only exo attack to afford SN1 products stereospecifically, with retention of configuration.