PPh ₃ -Catalyzed Remote Aminofluorination Reactions: Regioselective Access to γ- and ε-Fluoroamines Containing Oxindole

Remote aminofluorinations as a powerful strategy to synthesize 1,<i>n</i>-fluoroamines (<i>n</i> > 2) are of great significance and highly challenging. Herein, a remote 1,5-aminofluorination of spirovinylcyclopropyl oxindoles and <i>N</i>-fluorobenzenesulfonimide (NFSI) was achieved by using PPh₃ as a catalyst, affording ε-fluoroamines containing oxindole (up to 60% yield, all >20:1 <i>E</i>:<i>Z</i>). As opposed to the traditional choice, TMSCN was used as an additive, which makes the reaction a dramatic shift to the 1,3-aminofluorination of spirovinylcyclopropyl oxindoles, and γ-fluoroamines containing oxindole were obtained with high diastereoselectivity and high yield (up to 99%). Based on experimental results and high-resolution mass spectrometry experiments, a plausible reaction mechanism is proposed.