Cyclopalladation of Schiff Bases from Methyl Esters of α-Amino Acids. Unexpected Activation of the O-Me Bond with Formation of a Bianionic Tridentate Metallacycle

The action of palladium acetate on imines from methyl esters of the alpha-amino acids glycine, alanine, valine, and tyrosine is herein described. The reactivity of the new metallacycles obtained with phosphines and amines is also described, as well as the synthesis of isoquinolinium salts by insertion of diphenylacetylene into the Pd-C bond. Besides this, the unexpected activation of the Me-O bond of the ester group of the amino acid fragment is also reported, in a process that affords new cyclopalladated derivatives having the metalated molecule as a dianionic (C,N,O) ligand.