Insertion of Allenes into the Pd–C Bond of Ortho-Palladated Primary Arylamines of Biological Relevance: Phenethylamine, Phentermine, (l)-Phenylalanine Methyl Ester, and (l)-Tryptophan Methyl Ester. Synthesis of Tetrahydro-3-benzazepines and Their Salts

Abstract

The previously reported ortho-metalated complexes [Pd(C,N-ArCH2CRR'NH2-2)(μ-X)]2 derived from phenethylamine (Ar = C6H4, R = R' = H, X = Cl, Br), phentermine (Ar = C6H4, R = R' = Me, X = Cl), (l)-phenylalanine methyl ester (Ar = C6H4, R = H, R' = CO2Me, X = Cl, Br)), and (l)-tryptophan methyl ester (Ar = C8H5N, R = H, R' = CO2Me, X = Cl) react with various allenes to give (1) the corresponding η3-allyl complexes derived from the insertion of one molecule of the allene into the Pd–C bond, the formation of which has been studied by DFT using a model complex, or (2) Pd(0) and the tetrahydro-3-benzazepinium salts, resulting from the decomposition of the above mentioned η3-allyl complexes, containing an exocyclic double bond, which, subsequently, react with a base to afford the corresponding benzazepines. The regiochemistry of these decomposition reactions has been studied and compared with that described for similar processes involving five-membered palladacycles. The crystal structures of the salts of some b...