Synthesis Of 3-Fluoro-2-Hetarylindoles And 3,3-Difluoro-2-Hetarylindolines Through Lewis Acid-Catalyzed Formation Of 3,3-Difluoroindolium Ions

Synthesis of 3-fluoro-2-hetarylindoles through addition of hetarenes to 3,3-difluoroindolium ions generated in situ by Zn(OTf)(2)-catalyzed oxazolidine ring opening is described. Indoles, pyrroles and alkyl-substituted furans can be used as hetaryl nucleophiles to afford a range of 3-fluoro-2-hetarylindole products 6 in 56-95% yields. A diverse array of 3,3-difluorinated 2-hetarylindolines 7 can also be synthesized in 43-84% yields by a tandem sequential process that involves hetarene nucleophilic addition, HF elimination and fluorocyclization reactions. Our study by H-1 NMR and UV/Vis spectroscopy reveals that 3,3-difluorinated 2-hetarylindolines possess interesting substituent-dependent acidochromic properties. UV absorption and fluorescence spectra of selected compounds 6 and 7 are also studied.