Palladium-Catalyzed Regioselective <i>Syn</i>-Chloropalladation–Olefin Insertion–Oxidative Chlorination Cascade: Synthesis of Dichlorinated Tetrahydroquinolines

Abstract

A palladium catalyzed cascade process involving syn-chloropalladation, intramolecular olefin insertion, and oxidative C-Cl bond formation reactions was demonstrated for the synthesis of dichlorinated tetrahydroquinolines in high yields (up to 93%). The N-propargyl arylamines having a tethered α,β-unsaturated carbonyl moiety underwent a regioselective syn-chloropalladation followed by a Heck-type reaction to deliver the tetrahydroquinoline scaffold. The rare insertion of the second chlorine atom was rationalized comprising a Pd^II/IV catalytic cycle and oxidative cleavage of the C-Pd^II bond.