Alkyne Reactions with the Cyclopalladated 8-Methylquinoline Ligand: Synthesis of Novel Heterocyclic Compounds with a Brighehead Nitrogen

Article abstract of DOI:10.1021/jo00033a042

The stepwise reaction of cyclopalladated 8-methylquinoline (compound 1, obtained via intramolecular metalation of 8-methylquinoline by Pd(II)) with 2 equiv of various internal alkynes affords 4H-indolo<2,1,7-cde>quinolizines 3 through simultaneous Pd-mediated C-C and C-N bond formation.This reaction displays a high selectivity provided that the first alkyne reacting with 1 bears two electron-withdrawing substituents such as -CF3 or -CO2Me and that the second alkyne is also substituted by electrophilic substituents.Varying the reaction conditions allowed us to isolate o rganometallic intermediates, whose nature shed some light upon the mechanism of the formation of 3.Several deviations from the synthesis of 3 were encountered when different alkynes were reacted with 1, e.g., with ethyl-3-phenylpropynoate a four-substituted α-pyrone was synthesized through C-O activation of one of the ester functions.