Design, Synthesis, and Stereochemical Evaluation of a Novel Chiral Amine–Palladacycle

Abstract

AbstractA novel chiral palladacycle containing ortho‐metallated (±)‐1‐(3,6‐dimethylnaphthalen‐2‐yl)‐N,N‐dimethylethylaminewas designed and synthesized by a multi‐step synthesis by using 2,7‐dimethylnaphthalene as the starting material. The structure and palladacycle ring conformation of the triphenylphosphane derivative was investigated by X‐ray structural analysis in the solid state and by 2D ROESY NMR spectroscopy in solution. Through a designed intramolecular steric interaction, the five‐membered naphthylamine chelate can be locked into a fixed conformation, both in the solid state and in solution. The racemic cyclopalladated complex could be efficiently resolved through the formation of its (S)‐prolinato and (S)‐alaninato derivatives. The structure and absolute configuration of the two optically resolved palladium complexes were determined by X‐ray diffraction. Both the (R,R) and (S,S)‐di‐μ‐chlorido dimeric palladium complexes containing the resolved amine ligand was obtained chemoselectively by treating the corresponding prolinato and alaninato derivatives with 1 M hydrochloric acid. Despite the severe interchelate steric constraint within these new organopalladium complexes, the bulky monodentate ligand 3,4‐dimethyl‐1‐phenylphosphole (dmpp) was able to split the chlorido bridges regiospecifically in the position trans to the NMe2 group. With the new palladacycle used as the chiral template, the stereoselectivity of Diels–Alder cycloaddition between dmpp and ethyl vinyl ketone significantly improves relative to that of other analogue complexes.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)