Stereoretentive regio‐ and enantioselective allylation of isoxazolinones by a planar chiral palladacycle catalyst

Abstract

The catalytic allylic substitution is one of the most important tools in asymmetric synthesis to form C-C bonds in an enantioselective way. While high efficiency was previously accomplished in terms of enantio‐ and regiocontrol using different catalyst types, a strong general limitation is a very pronounced preference for the formation of allylic substitution products with (E)-configured C=C double bonds. Herein, we report that with a planar chiral palladacycle catalyst a diastereospecific reaction outcome is achieved using isoxazolinones and allylic imidates as substrates, thus maintaining the C=C double bond geometry of the allylic substrates in the highly enantioenriched products. DFT calculations show that the reactions proceed via an SN2 mechanism and not via π‐allyl Pd complexes. Crucial for the high control is the stabilization of the allylic fragment in the SN2 transition state by π‐interactions with the phenyl substituents of the pentaphenylferrocenyl catalyst core.