A New Family of Nucleophiles for Photoinduced, Copper-Catalyzed Cross-Couplings via Single-Electron Transfer: Reactions of Thiols with Aryl Halides Under Mild Conditions (O °C)

Building
on the known photophysical properties of well-defined
copper–carbazolide complexes, we have recently described photoinduced,
copper-catalyzed N-arylations and N-alkylations of carbazoles. Until
now, there have been no examples of the use of other families of heteroatom
nucleophiles in such photoinduced processes. Herein, we report a versatile
photoinduced, copper-catalyzed method for coupling aryl thiols with
aryl halides, wherein a single set of reaction conditions, using inexpensive
CuI as a precatalyst without the need for an added ligand, is effective
for a wide range of coupling partners. As far as we are aware, copper-catalyzed
C–S cross-couplings at 0 °C have not previously been achieved,
which renders our observation of efficient reaction of an unactivated
aryl iodide at −40 °C especially striking. Mechanistic
investigations are consistent with these photoinduced C–S cross-couplings
following a SET/radical pathway for C–X bond cleavage (via
a Cu­(I)–thiolate), which contrasts with nonphotoinduced, copper-catalyzed
processes wherein a concerted mechanism is believed to occur.