Synthesis of 2‐Fluoroindoles Via the Base‐Free Nucleophilic 5‐Endo‐Trig Cyclization of o‐Amido‐β,β‐Difluoro‐α‐Silylstyrenes

Upon heating in the presence of molecular sieves 4A, β,β‐difluoro‐α‐silylstyrenes bearing an ortho ‐amido group readily underwent nucleophilic 5‐ endo ‐ trig cyclization, affording 2‐fluoro‐3‐silylindoles in high yields. The silicon‐ and fluorine‐stabilized zwitterionic intermediates formed during an addition–elimination process likely promoted nucleophilic vinylic substitution (S N V) in a 5‐ endo ‐ trig fashion even under base‐free conditions. Furthermore, the silyl group in the formed 2‐fluoro‐3‐silylindoles was employed for further transformation.