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

Abstract

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.

Visible-light acridinium-based organophotoredox catalysis in late-stage synthetic applications

“…Larionov et al 54 reported a visible light-induced, dual catalytic, direct decarboxysulfonylative cross-coupling of carboxylic acids with aryl halides. This reaction includes tricomponent decarboxysulfonylative cross-coupling of carboxylic acid 31 with aryl iodide 33 occurs readily in the dual catalytic system of acridine photocatalyst and diamine ligated copper( i ) triflate, with DABCO or potassium metabisulfite 32 that results sulfone 34 with 91% yield ( Scheme 20 ).…”

Free Carboxylic Acids: The Trend of Radical Decarboxylative Functionalization

“…During the past few years, the group of Larionov led the revival of acridine photocatalysts, an old but underexploited type of catalyst, [45] for decarboxylation through proton‐coupled electron transfer (PCET) [46] . Combined with copper catalysis, they were able to achieve decarboxylative conjugate addition to Michael acceptors, [47] amination with free aryl amines (Chan–Lam type reaction), [48] amidosulfonation with O ‐benzoylhydroxylamines in the presence of immobilized SO 2 , [49] and sulfonylative coupling with aryl halides [50] . Metal‐free decarboxylative sulfinylation was also made possible with in situ generated sulfinyl sulfones (Scheme 17).…”

Decarboxylative Triazolation Enables Direct Construction of Triazoles from Carboxylic Acids

“…We hypothesized that such a tricomponent direct decarboxylative triazolation could be accomplished by a triple catalytic process that entails direct decarboxylative azidation and subsequent cycloaddition with alkynes. However, the combination of the two processes into one multicatalytic process is challenging because of the mismatch between the oxidatively mediated azidation and the oxidant-intolerant Cu I -catalyzed cycloaddition that is instead diverted to a Glaser-type alkyne dimerization. − Additionally, an efficient photocatalytic system would be needed that can both facilitate direct decarboxylation of difficult-to-oxidize carboxylic acids to bypass the typically required preactivation to more reactive carboxylic acid derivatives − and also be compatible with the organoazide- and triazole-forming catalytic cycles. Importantly, the successful development of direct, tricomponent conversion of carboxylic acids to triazoles necessitates a broad-scope, direct decarboxylative azidation of carboxylic acids that is tolerant to oxidation-sensitive processes and is mediated by a simple inorganic azide source.…”