Self-Sustaining Fluorination of Active Methylene Compounds and High-Yielding Fluorination of Highly Basic Aryl and Alkenyl Lithium Species with a Sterically Hindered N-Fluorosulfonamide Reagent.

Fluorination of carbanions is pivotal for the synthesis of fluorinated compounds, but the current N-F fluorinating agents have significant drawbacks due to many reactive locations that surround the reactive N-F site. By developing a sterically hindered N-fluorosulfonamide reagent, namely N-fluoro-N-(tert-butyl)-tert-butanesulfonamide (NFBB), we discovered a conceptually novel base-catalyzed, self-sustaining fluorination of active methylene compounds and achieved the high-yielding fluorination of the hitherto difficult highly basic (hetero)aryl and alkenyl lithium species. In the former, the mild and high yield fluorination of active methylene compounds exhibited wide functional group tolerance and its novel catalytic fluorination-deprotonation cycle mechanism was demonstrated by deuterium-tracing experiments. In the latter, NFBB reacted with a variety of highly basic (hetero)aryl and alkenyl lithium species to provide the desired fluoro (hetero)arenes and alkenes in unprecedented high or quantitative yields.