Divergent Syntheses of Indoles and Quinolines Involving N1-C2-C3 Bond Formation through Two Distinct Pd Catalyses

Abstract

Pd-catalyzed annulative couplings of 2-alkenylanilines with aldehydes using alcohols as both the solvent and hydrogen source have been developed. These domino processes allow divergent syntheses of two significant N-heterocycles, indoles and quinolines, from the same substrate by tuning reaction parameters, which seems to invoke two distinct mechanisms. The nature of the ligand and alcoholic solvent had a profound influence on the selectivity and efficiency of these protocols. Particularly noteworthy is that indole formation was achieved by overcoming two significant challenges, regioselective hydropalladation of alkenes and subsequent reactions between the resulting Csp(3)-Pd species and less reactive imines.