Ortho Palladation of the Phenethylamines of Biological Relevance l-Tyrosine Methyl Ester and Homoveratrylamine. Reactivity of the Palladacycles toward CO and Isocyanides. Synthesis of the Natural Alkaloid Corydaldine

Palladacycles derived from l-tyrosine methyl ester, (<i>S</i>)-[Pd<sub>2</sub>{<i>C</i>,<i>N</i>-C<sub>6</sub>H<sub>3</sub>CH<sub>2</sub>CH­(CO<sub>2</sub>Me)­NH<sub>2</sub>-2,(OH)-4}<sub>2</sub>(μ-Br)<sub>2</sub>] (<b>1a-Br</b>), and homoveratrylamine, [Pd<sub>2</sub>{<i>C</i>,<i>N</i>-C<sub>6</sub>H<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>NH<sub>2</sub>-6,(OMe)<sub>2</sub>-3,4}<sub>2</sub>(μ-Br)<sub>2</sub>] (<b>1b-Br</b>), can be easily prepared in good yield by reacting Pd­(OAc)<sub>2</sub>, the corresponding ammonium triflate, and NaBr. Under the same conditions, the reaction of Pd­(OAc)<sub>2</sub> with the free amine affords a low yield of the corresponding acetato complex <b>1a-OAc</b> or <b>1b-OAc</b> (the latter only detected in solution). In our hands, the previously reported palladation at the C2 position of homoveratrylamine with Pd­(OAc)<sub>2</sub> is not observed. Instead, a complex mixture is obtained, mainly containing [Pd­(OAc)<sub>2</sub>{NH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>C<sub>6</sub>H<sub>3</sub>(OMe)<sub>2</sub>-3,4}<sub>2</sub>] and minor amounts of <b>1b-OAc</b>, which reacts with NaBr to afford a new mixture from which [PdBr<sub>2</sub>{NH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>C<sub>6</sub>H<sub>3</sub>(OMe)<sub>2</sub>-3,4}<sub>2</sub>] can be isolated and characterized. These and other adducts can be isolated from Pd­(OAc)<sub>2</sub>, homoveratrylamine, and various ligands (PPh<sub>3</sub> and Br<sup>–</sup>). 6-Bromohomoveratrylamine reacts with Pd­(dba)<sub>2</sub> in the presence of tmeda to give the complex [Pd­{<i>C</i>,<i>N</i>-C<sub>6</sub>H<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>NH<sub>2</sub>-6,(OMe)<sub>2</sub>-3,4}­(tmeda)]­Br. Reactions of complexes <b>1</b> with acetylacetonato or neutral (PR<sub>3</sub>) ligands give products resulting from substitution or bridge-splitting reactions. While <b>1a-Br</b> reacts with XyNC (1:2 molar ratio) to give (<i>S</i>)-[Pd­{<i>C</i>,<i>N</i>-C<sub>6</sub>H<sub>3</sub>CH<sub>2</sub>CH­(CO<sub>2</sub>Me)­NH<sub>2</sub>-2,(OH)-4}­Br­(CNXy)], <b>1b-Br</b> gives [Pd­{<i>C</i>,<i>N</i>-C­(NXy)-C<sub>6</sub>H<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>NH<sub>2</sub>-6,(OMe)<sub>2</sub>-3,4}­Br­(CNXy)]. (<i>S</i>)-7-Hydroxy-3-(methoxycarbonyl)-3,4-dihydroisoquinolin-1­(2<i>H</i>)-one and 6,7-dimethoxy-3,4-dihydroisoquinolin-1­(2<i>H</i>)-one (corydaldine) have been synthesized through the stoichiometric carbonylation of palladacycles <b>1a-Br</b> and <b>1b-Br</b>. The crystal structures of a solvento intermediate in the ortho-metalation reaction of the triflate derivative of l-tyrosine methyl ester and four other complexes have been determined by X-ray diffraction studies.