Synthesis of 3-Fluoro 3-Substituted 2-Oxindoles by Deacylative Alkylation

The fluorination of 3-acetyl-2-oxindole with N-fluorobenzenesulfonimide under Lewis acid catalysis using Mg(ClO4)2 (30 mol%) in EtOAc at r.t. giving the starting compound 3-acetyl-3-fluoro-2-oxindole in 89% yield. This compound is submitted to base-promoted deacylative alkylation (DaA) for the in situ generation of 3-fluoro-2-oxindole enolate under very mild reaction conditions using Triton B (1 equiv.) as base in THF at r.t. and alkyl halides and Michael acceptors as electrophilic reagents. The corresponding 3-alkylated 3-fluoro-2-oxindoles are obtained in good to very high yields. In addition, the palladium-catalyzed deacylative allylation is carried out with allylic alcohols using LiOtBu as base and 6 mol% of Pd(OAc)2 and dppp at r.t. in toluene, giving the resulting 3-allylated 3-fluoro-2-oxindoles in good yields.We gratefully acknowledge financial support from the Spanish Ministerio de Economía y Competitividad (MINECO) (projects CTQ2013-43446-P and CTQ2014-51912-REDC), the Spanish Ministerio de Economía, Industria y Competitividad, Agencia Estatal de Investigación (AEI) and Fondo Europeo de Desarrollo Regional (FEDER, EU) (projects CTQ2016-76782-P and CTQ2016-81797-REDC), the Generalitat Valenciana (PROMETEOII/2014/017) and the University of Alicante. A. O.-M. thanks MINECO for a predoctoral fellowship