Synthesis of gem‐Difluorocyclobutane‐Fused Indolines via Ruthenium‐Catalyzed Defluorinative Annulation of Trifluoromethyl Carbenoids with 2‐Alkenylanilines

Abstract A ruthenium‐catalyzed defluorinative annulation of 2‐alkenylanilines with α‐trifluoromethyl diazoester or diazoketones is described. The reaction has broad substrate scope, affording a range of gem ‐difluorocyclobutane‐fused indolines in moderate to good yields with cis ‐configuration. Mechanistic investigations indicate that the reaction proceeds through a sequential N−H insertion/C−F bond cleavage/[2+2] cycloadditon process. α‐Trifluoromethyl‐α‐diazo reagents serve as gem ‐difluorinated C2 subunits by cleaving one C−F bond.