A Rational Approach to the Design and Synthesis of Chiral Organopalladium-Amine Complexes

A new chiral auxiliary, (±)-N,N-dimethyl-1-(2,5-dimethylphenyl)ethylamine, was designed and synthesized in two steps from 1-acetyl-2,5-dimethylbenzene. Its cyclopalladated dimeric complex could be efficiently resolved via the formation of (S)-prolinate derivatives. Both hand forms of the complex could be obtained in similar yields. Despite the enormous inter-chelate steric constraints, the bulky monodentate ligand 3,4-dimethyl-l-phenylphosphole (DMPP) is able to coordinate regiospecifically to the orthopalladated 2,5-dimethylbenzylamine unit trans to the NMe2 group. Compared to its naphthylamine analogue, the orthopalladated 2,5-dimethylbenzylamine complex exhibits a significantly higher stereoselectivity in the chiral template promoted asymmetric cycloaddition reaction between DMPP and ethyl vinyl ketone.