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

The six-membered C,N-palladacycle [Pd(C,N-C6H4CH2CMe2NH2-2)(mu-Cl)](2) (A) derived from phentermine reacts with norbornadiene to give a di- or tetranuclear 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 toward 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-methylphenethylamine 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.