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, (S)-[Pd2{C,N-C6H3CH2CH­(CO2Me)­NH2-2,(OH)-4}2(μ-Br)2]
(1a-Br), and homoveratrylamine, [Pd2{C,N-C6H2CH2CH2NH2-6,(OMe)2-3,4}2(μ-Br)2] (1b-Br), can be easily prepared
in good yield
by reacting Pd­(OAc)2, the corresponding ammonium triflate,
and NaBr. Under the same conditions, the reaction of Pd­(OAc)2 with the free amine affords a low yield of the corresponding acetato
complex 1a-OAc or 1b-OAc (the latter only
detected in solution). In
our hands, the previously reported palladation at the C2 position
of homoveratrylamine with Pd­(OAc)2 is not observed. Instead,
a complex mixture is obtained, mainly containing [Pd­(OAc)2{NH2CH2CH2C6H3(OMe)2-3,4}2] and minor amounts of 1b-OAc, which reacts with NaBr to afford a new mixture from which [PdBr2{NH2CH2CH2C6H3(OMe)2-3,4}2] can be isolated and characterized.
These and other adducts can be isolated from Pd­(OAc)2,
homoveratrylamine, and various ligands (PPh3 and Br–). 6-Bromohomoveratrylamine reacts with Pd­(dba)2 in the presence of tmeda to give the complex [Pd­{C,N-C6H2CH2CH2NH2-6,(OMe)2-3,4}­(tmeda)]­Br.
Reactions of complexes 1 with acetylacetonato or neutral
(PR3) ligands give products resulting from substitution
or bridge-splitting reactions. While 1a-Br reacts with
XyNC (1:2 molar ratio) to give (S)-[Pd­{C,N-C6H3CH2CH­(CO2Me)­NH2-2,(OH)-4}­Br­(CNXy)], 1b-Br gives
[Pd­{C,N-C­(NXy)-C6H2CH2CH2NH2-6,(OMe)2-3,4}­Br­(CNXy)]. (S)-7-Hydroxy-3-(methoxycarbonyl)-3,4-dihydroisoquinolin-1­(2H)-one and 6,7-dimethoxy-3,4-dihydroisoquinolin-1­(2H)-one (corydaldine) have been synthesized through the stoichiometric
carbonylation of palladacycles 1a-Br and 1b-Br. 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.