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

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 benzazepines
and one isoquinoline, derived from a five-membered palladacycle, have
been determined by X-ray diffraction studies.