The
combination of photoredox catalysis with the Wolff–Kishner
(WK) reaction allows the difunctionalization of carbonyl groups by
a radical-carbanion relay sequence (photo-Wolff–Kishner reaction).
Photoredox initiated radical addition to N-sulfonylhydrazones
yields α-functionalized carbanions following the WK-type mechanism.
With sulfur-centered radicals, the carbanions are further functionalized
by reaction with electrophiles including CO2 and aldehydes,
whereas CF3 radical addition furnishes a wide range of gem-difluoroalkenes through β-fluoride elimination
of the generated α-CF3 carbanions. More than 80 substrate
examples demonstrate the broad applicability of this reaction sequence.
A series of investigations including radical inhibition, deuterium
labeling, fluorescence quenching, cyclic voltammetry, and control
experiments support the proposed radical-carbanion relay mechanism.
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