Solvent-Regulated Coupling of 2‑Alkynylbenzaldehydes with Cyclic Amines: Selective Synthesis of Fused N‑Heterocycles and Functionalized Naphthalene Derivatives

An efficient synthesis of 1,2,3,4-tetrahydrobenzo­[g]­quinoline derivatives through PdCl2-catalyzed, TBHP-promoted, and toluene-mediated dehydrogenation/[4+2] cycloaddition of saturated cyclic amines with 2-alkynylbenzaldehydes was developed. On the contrary, when the reaction medium was changed from toluene to DMSO/H2O, another class of important compounds, naphthyl chain amines, formed via a dehydrogenation–intermolecular condensation–C–N bond cleavage–intramolecular condensation pathway, was obtained with good selectivity.