The Synthesis Of NFSI Analogues And Enantioselective Fluorination Of Oxindoles

This paper focuses on the enantioselective fluorination reactions of oxindoles with structurally modified N-fluorobenzenesulfonimides (NFSIs). More than ten modified N-fluorobenzenesulfonimides (NFSIs) were synthesized by the reaction between N-fluoro benzenesulfonamide and benzenesulfonyl chloride.6a was chosen as starting substrate. Catalysts, reaction solvents, temperature and amount of catalyst were then screened using NFSI as fluorinating reagents. Yield up to 90% and ee up to 98% were obtained in diethyl ether at 0℃ in the presence of 0.5 mol% c-4.NFSI analogues (4a-4m) were applied in the enantioselective fluorination reactions of oxindoles under the optimized reaction conditions to investigate the influence of o, m, p substituents. It is shown that the novel NFSI analogue bearing F groups at the para-position (4b) leads to ee up to 98%.Then under the optimized reaction conditions using 4b as fluorinating reagents, a series of oxindole substrates (6a-6o) were screened. Excellent yield above 90% and enantioselectivity above 99% were achieved for most examples.