Norbornadiene as a Building Block for the Synthesis of Linked Benzazocinones and Benzazocinium Salts through Tetranuclear Carbopalladated Intermediates.

Abstract

The six-membered C,N-palladacycle [Pd(C,N-C6H4CH2CMe2NH2-2)(mu-Cl)]2, derived from phentermine, reacts with norbornadiene to give a di- or tetra-nuclear complex arising from the double insertion of the same molecule of the strained alkene into one or two distinct Pd-aryl bonds. The tetranuclear complex has been characterized by X-ray diffraction studies and exhibits a very unusual cisoid geometry in both, the disposition of the C,N-chelate ligands and the position of the palladium centers. The newly formed Pd–alkyl bonds are still reactive towards the insertion of unsaturated molecules and the tetranuclear complex reacts with CO or isocyanides to give double benzazocinones or benzazocinium salts with a cisoid geometry, after depalladation of the corresponding organometallic intermediates, which have been isolated in some cases. When the related palladacycles derived from phenethylamine or N-methyl-phenethylamine are used as starting materials, polymeric compounds are obtained, from which double benzazocinones or benzazocinium salts with a transoid geometry are obtained after CO or RNC insertion and subsequent depalladation. The presence of substituents on the alpha-carbon atom of the chelated amine influences the regiochemistry of the double carbopalladation of the norbornadiene.