Ruthenium(II)-Catalyzed C–H Activation/Annulation of 5-Phenyl-pyrroline-2-carboxylates with Alkynes: Synthesis of 2,3-Diphenylspiro-[indene-1,2′pyrrolidine]carboxylate Derivatives

While saturated nitrogen heterocycles are privileged scaffolds, their streamlined catalytic synthesis with unsymmetrical substitution patterns remains a daunting challenge. Herein, we report the ruthenium(II)-catalyzed synthesis of spiro[indene-proline] derivatives via C-H activation/annulation of 5-phenyl-pyrroline-2-carboxylates with alkynes. The protocol utilized imine coordination, resulting in high reaction yields with a wide range of functional group tolerance, scalability, and scaffold diversity. This annulation was successful even with various biologically active pharmacophores. The reaction featured a reversible C-H metalation step and suggested the possibility of a base-assisted internal electrophilic substitution pathway.