Protodefluorinated Selectfluor® promotes aggregative activation of Selectfluor® for efficient C(sp3)−H fluorination reactions

We report herein a simple, yet unexpected approach to dramatically improve the efficiencies of radical fluorination reactions of C(sp3)−H bonds. H−TEDA(BF4)2 is readily generated as a byproduct during fluorination reactions with Selectfluor®, the world’s most popular organic fluorination reagent. However, H−TEDA(BF4)2 to date is overlooked and discarded as waste, despite comprising 95% of the M.W. of Selectfluor®. We demonstrate that the addition of H−TEDA(BF4)2 at the start of fluorination reactions markedly increases their rates, outcompeting side reactions to access higher overall yields of fluorinated products. Showcasing the generality of the phenomenon, the performance additive enhances both photochemical/photocatalytic and thermal radical fluorination reactions by decreasing a discovered induction period in the former and by increasing the rate in the latter. Detailed mechanistic investigations reveal the key importance of aggregation changes in Selectfluor® and H−TEDA(BF4)2 to fill gaps of understanding in how radical C(sp3)−H fluorination reactions work. This study exemplifies how an overlooked reaction waste product can be upcycled for a high value-added application.