Tricomponent Decarboxysulfonylative Cross-coupling Facilitates Direct Construction of Aryl Sulfones and Reveals a Mechanistic Dualism in the Acridine/Copper Photocatalytic System

Dual catalytic systems involving
photocatalytic activation and
transition metal-catalyzed steps have enabled innovative approaches
to the construction of carbon–carbon and carbon–heteroatom
bonds. However, the mechanistic complexity of the dual catalytic processes
presents multiple challenges for understanding of the roles of divergent
catalytic species that can impede the development of future synthetic
methods. Here, we report a dual catalytic process that enables the
previously inaccessible, broad-scope, direct conversion of carboxylic
acids to aromatic sulfonescentrally important carbonyl group
bioisosteric replacements and synthetic intermediatesby a
tricomponent decarboxysulfonylative cross-coupling with aryl halides.
Detailed mechanistic and computational studies revealed the roles
of the copper catalysts, bases, and halide anions in channeling the
acridine/copper system via a distinct dual catalytic manifold. In
contrast to the halide-free decarboxylative conjugate addition that
involves cooperative dual catalysis via low-valent copper species,
the halide counteranions divert the decarboxysulfonylative cross-coupling
with aryl halides through a two-phase, orthogonal relay catalytic
manifold, comprising a kinetically coupled (via antithetical inhibitory
and activating roles of the base in the two catalytic cycles), mechanistically
discrete sequence of a photoinduced, acridine-catalyzed decarboxylative
process and a thermal copper-catalyzed arylative coupling. The study
underscores the importance of non-innocent roles of counteranions
and key redox steps at the interface of catalytic cycles for enabling
previously inaccessible dual catalytic transformations.