Mechanistic Dichotomy in Enantioselective Pd‐Catalyzed Alkylation of Pyrroles With Diazoesters

A palladium‐catalyzed enantioselective CH alkylation of pyrroles with diazoesters using axially chiral bipyridine‐ N , N ′‐dioxide ligands is reported. The transformation provides direct access to enantioenriched pyrrole derivatives under mild conditions and expands the limited repertoire of asymmetric Pd‐catalyzed pyrrole functionalization. Crucially, comparative studies reveal that bipyridine‐ N , N ′‐dioxide and bipyridine ligands operate through fundamentally different catalytic manifolds. Kinetic analysis, reactivity experiments, and product distribution studies indicate that N ‐oxide ligands divert the reaction from a conventional metal‐carbene‐initiated pathway to a mechanism involving electrophilic CH metalation followed by carbene transfer and protonation. These findings demonstrate that subtle ligand modification can alter the mechanistic pathway in Pd‐catalyzed reactions of diazo compounds, paving the way to mechanistically informed strategies for asymmetric CH functionalization of electron‐rich heterocycles.