Divergent Reaction Pathways of Homologous and Isosteric Propargyl Amides in Sequential Ru/Pd-Catalyzed Annulations for the Synthesis of Heterocycles

Cu-catalyzed three-component coupling of imines with benzoyl chloride and terminal arylalkynes followed by enyne ring-closing metathesis (RCM) and Heck cyclization afforded medicinally relevant benzoindolines, cyclopropane-fused indenopyridines, pyrroloquinolines, or 1,7-tetrahydrophenanthrolines via divergent cyclization pathways. Unexpectedly, the Pd-catalyzed cyclization of heterocyclic dienes proceeded via regiodivergent 5-exo or 6-endo pathways depending on the ring size (n = 1, 2) or the presence of isosteric groups (CH vs N). A one pot protocol for the enyne-RCM/Heck annulation featuring a sequential addition of the Ru and Pd catalysts was developed maximizing the synthetic efficiency.