Lithium Enables Pd-Catalyzed 5<i>-endo-dig</i> Cyclization/Coupling of α-Homopropargyl-β-ketoesters with Aryl Bromides and Triflates

Tight chelation of enolate by lithium alters the selectivity of tandem palladium-catalyzed cyclization/coupling of terminal α-homopropargyl-β-ketoesters with aryl halides. In the presence of LiOH, substituted cyclopentenes are preferentially formed via 5-<i>endo-dig</i> carbocyclization, in contrast to the 6<i>-exo-dig</i> oxocyclization exclusively observed in the absence of a hard, chelating metal center. The disclosed transformation, featuring mild conditions and broad functional group tolerance, can be applied for a variety of (hetero)aryl bromides as well as aryl and vinyl triflates.