Synthesis of Gem‐difluorocyclobutane‐fused Indolines Via Ruthenium‐Catalyzed Defluorinative Annulation of Trifluoromethyl Carbenoids with 2‐Alkenylanilines

A ruthenium-catalyzed defluorinative annulation of 2-alkenylanilines with alpha-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. alpha-Trifluoromethyl-alpha-diazo reagents serve as gem-difluorinated C2 subunits by cleaving one C-F bond.