Although the transition metal-catalyzed radical fluorine
atom transfer
(FAT) strategy has emerged as a powerful tool for the construction
of C–F bonds, to our knowledge, this approach has rarely been
applied to the formation of S–F bonds. Here, we report that
4-methoxypyridine 1-oxide can serve as an inexpensive and simple yet
effective ligand and thus promote the transformation of the copper-mediated
challengeable radical FAT to sulfonyl radicals, paving the way for
the assembly of an FSO2 group. Based on this concept, three
Cu(I)-catalyzed protocols involving site-selective intra- and intermolecular
fluorosulfonylation of inert C(sp3)–H bonds and
1,2-aminofluorosulfonylation of inactivated alkenes have been developed,
enabling the preparation of C(sp3)-rich aliphatic sulfonyl
fluorides that cannot be easily synthesized by known methods. These
practical and operationally simple methods result in high functional
group tolerance under mild conditions and can be applied to the modification
of bioactive derivatives and preparation of highly valued molecules.
Detailed mechanistic studies indicate the unique role of the 4-methoxypyridine
1-oxide ligand in facilitating the formation of such rare radical
FATs via an outer-sphere pathway.