Unusual 1,2-Aryl Migration and Depalladation of Alkylpalladium Intermediates Containing a syn-beta-Hydrogen Atom

Abstract

In general, alkylpalladium intermediates containing a syn beta-hydrogen atom are expected to undergo beta-hydride elimination preferentially. However, this study unveils a new mechanistic mode in a Pd(II)-catalyzed transformation, which leads to a series of both C-N/C-C bond forming and C-C bond forming/cleavage events. It has been demonstrated that a Pd(II)catalyzed oxidative cyclization of stilbenes bearing a pendent nucleophile such as 2-alkenylanilines and 2-alkenylphenyl 1,3-diketones operates through an uncommon Pd-C bond cleavage assisted by a neighboring aryl group and CuCl2-assisted transient Pd oxidation, rather than generally preferred beta-hydride elimination in alkylpalladium intermediates containing a syn beta-hydrogen atom. As a result, 1,2-aryl migration occurs to lead to the unexpected formation of a variety of 3-substituted indoles and 4-aryl-1-naphthols. In addition, selective migration of an aryl group could be achieved from beta,beta-disubstituted alkene substrates through alkylpalladium intermediates deprived of syn beta-hydrogen atom.