Enantioselective Fluorination of 2‐Oxindoles by Structure‐Micro‐Tuned N ‐Fluorobenzenesulfonamides

We describe our attempts to fine‐tune the reactivity and selectivity of N ‐fluorobenzenesulfonamide in fluorination reactions by changing the substituents on its phenyl rings. A series of N ‐fluorobenzenesulfonamides bearing substituents at the ortho , meta , and para positions were prepared, and were used in the enantioselective fluorination of 2‐oxindoles catalysed by chiral palladium complexes. Fluorinating reagents 1b , 1c , 1d , 1e , 1h , 1i , and 1j gave similar results to 1a , while 1f , 1g , and 1n gave worse yields and selectivities. Under mild reaction conditions, a series of 3‐fluoro‐2‐oxindoles were obtained in excellent yields (up to 98 %) and enantioselectivities (up to 99 % ee ) using N ‐fluoro‐4,4′‐difluoro‐benzenesulfonamide as the fluorination agent.