Transition Metal-Catalyzed Cross-Couplings of Benzylic Sulfone Derivatives

Enantiospecific cross-coupling of cyclic alkyl sulfones

Methods to form carbon-carbon bonds efficiently and with control of stereochemistry are critical for the construction of complex molecules. Cross-coupling reactions are among the most efficient and widely used reactions to construct molecules, with reactions enabling the retention or installation of chirality as recent additions to this powerful toolbox. Sulfones are robust, accessible organic electrophiles that have many attractive features as cross-coupling partners; however, since the first example of their use in 1979, there have been no examples of their use in enantioselective, enantiospecific or entantioconvergent cross-couplings. The high acidity of sulfones makes it unclear whether this transformation is even possible outside tertiary systems. Here we report the enantiospecific cross-coupling of cyclic sulfones and Grignard reagents. Up to 99% chirality transfer is observed despite the strong basicity of the Grignard components. In situ monitoring reveals that the cross-coupling is kinetically competitive with competing deprotonation, resulting in a highly enantioselective transformation.

Desulfonylative Functionalization of Organosulfones via Inert (Hetero)Aryl C(sp2)-SO2 Bond Cleavage

As "chemical chameleons," organosulfones have been widely applied in various desulfonylative functionalization reactions. However, the desulfonylative functionalization of (hetero)arylsulfones through the cleavage of inert C(sp2)-SO2 bonds remains a challenging and underexplored task. Over the past twenty years, the use of (hetero)arylsulfones as arylation reagents has gradually gained attention in diverse cross-coupling reactions under specific catalytic conditions, especially in transition metal-catalysis and photocatalysis chemistry. In this review, we discuss the representative accomplishments and mechanistic insights achieved in desulfonylative reactions of inactive C(sp2)-SO2 bonds in (hetero)arylsulfones, including: (i) transition-metal-catalyzed desulfonylative cross-coupling reactions and (ii) photo-/electrocatalytic radical desulfonylative coupling reactions. We anticipate that this review will provide an overall perspective in this area to a general audience of researchers and stimulate further innovative strategies for desulfonylative functionalization of inert arylsulfones.

Efficient Functionalization of Organosulfones via Photoredox Catalysis: Direct Incorporation of α-Carbonyl Alkyl Side Chains into α-Allyl-β-Ketosulfones

A novel and efficient method for functionalizing organosulfones has been established, utilizing a visible-light-driven intermolecular radical cascade cyclization of α-allyl-β-ketosulfones. This process employs fac-Ir(ppy)3 as the photoredox catalyst and α-carbonyl alkyl bromide as the oxidizing agent. Via this approach, the substrates experience intermolecular addition of α-carbonyl alkyl radicals to the alkene bonds, initiating a sequence of C-C bond formations that culminate in the production of organosulfone derivatives. Notably, this technique features gentle reaction conditions and an exceptional compatibility with a wide array of functional groups, making it a versatile and valuable addition to the field of organic synthesis.

Electrochemical desulfurative formation of C-N bonds through selective activation of inert C(sp3)-S bonds

In this study, we introduce an efficient, metal-free electrocatalytic desulfurative protocol for forming C-N bonds by selectively activating inert C(sp3)-S bonds of alkyl thioethers. This method offers a straightforward and environmentally friendly approach for modification of heterocyclic compounds from readily accessible thioethers. Preliminary mechanistic investigations suggest that the reaction proceeds via a carbocation intermediate. Furthermore, successful synthesis on a 10-gram scale was achieved in a continuous flow electrochemical reactor.

Unveiling Pre-Transmetalation Intermediates in Base-Free Suzuki-Miyaura Cross-Couplings: A Computational Study

The pre-transmetalation intermediates are critically important in Suzuki-Miyaura cross-coupling (SMC) reactions and have become a hot spot of the current research. However, the pre-transmetalation intermediates under base-free conditions have not been clear. Herein, a comprehensive theoretical study is performed on the base-free Pd-catalyzed desulfonative SMC reaction. The fragile coordination feature and the acceleration role of the RuPhos chelate ligand are revealed. The hydrogen-bond complex between the Pd-F complex and aryl boronic acid is identified as an important pre-transmetalation intermediate, which increases the energy span to 32.5 kcal/mol. The controlling factor for the formation of the hydrogen-bond complexes is attributed to the electronegativities of halogen atoms in the metal halide complexes. What is more, other reported SMC reaction systems involving metal halide complexes and aryl boronic acids are reconsidered and suggest that the hydrogen-bond complexes widely exist as stable pre-transmetalation intermediates with influencing the catalytic activities. The earth-abundant Ni-catalyzed desulfonative SMC reaction is further designed and predicted to have a higher activity than the original Pd-catalyzed SMC reaction.

Cobalt-Catalyzed Reductive Cross-Coupling To Construct Csp3-Csp3 Bonds via Csp3-S and Csp3-X Bonds Activation

A cross-electrophilic coupling of benzyl sulfonium salts with alkyl halides forming Csp3-Csp3 bonds is described by using a Co-based catalytic system. The activation of the stable Csp3-S bond of benzyl sulfonium salts under mild reaction conditions leads to various functionalized alkyl derivatives. Preliminary mechanistic studies suggest the involvement of alkyl radicals formed from both alkyl halides and benzyl sulfoniums through a single electron transfer.

Nickel-Catalyzed Cross-Coupling Reaction of Aryl Methyl Sulfides with Aryl Bromides

A nickel-catalyzed cross-coupling reaction of aryl methyl sulfides with aryl bromides has been developed to access biaryls in yields of up to 86%. The reactions proceeded well using Ni(COD)2 as catalyst with the ligand BINAP (2,2'-bis(diphenylphosphanyl)-1,1'-binaphthalene) in the presence of magnesium. The method has a broad scope of substrates and is scalable. The wide availability of commercially available aryl bromides and the absence of preparation and preparation of organometallic reagents make the reaction of high application value.

Synthesis of triarylmethanes by silyl radical-mediated cross-coupling of aryl fluorides and arylmethanes

Although the cross-couplings of aryl halides with diarylmethanes are mostly achieved by transition-metal catalysis, aryl fluorides are rarely used as coupling partners owing to the high inertness of C-F bonds. Herein, we describe the efficient silylboronate-mediated cross-coupling reaction of aryl fluorides with arylalkanes under transition-metal-free, room-temperature conditions. The combination of silylboronate and KO ^t Bu is critical for driving a radical process via the cleavage of C-F and C-H bonds in two appropriate coupling precursors, resulting in a cross-coupling product. This practical cross-coupling protocol is applicable to a wide variety of aryl fluorides with a C(sp²)-F bond. This method can be extended to other coupling partners with a C(sp³)-H bond, including diarylmethanes, diarylethanes, and monoarylalkanes. Many di- and triarylalkanes with tertiary or quaternary carbon centers can be obtained easily in moderate to high yields. We believe that the developed silylboronate-mediated cross-coupling method is a valuable contribution to C-F and C-H activation chemistry.

Beyond classical sulfone chemistry: metal- and photocatalytic approaches for C-S bond functionalization of sulfones

The exceptional versatility of sulfones has been extensively exploited in organic synthesis across several decades. Since the first demonstration in 2005 that sulfones can participate in Pd-catalysed Suzuki-Miyaura type reactions, tremendous advances in catalytic desulfitative functionalizations have opened a new area of research with burgeoning activity in recent years. This emerging field is displaying sulfone derivatives as a new class of substrates enabling catalytic C-C and C-X bond construction. In this review, we will discuss new facets of sulfone reactivity toward further expanding the flexibility of C-S bonds, with an emphasis on key mechanistic features. The inherent challenges confronting the development of these strategies will be presented, along with the potential application of this chemistry for the synthesis of natural products. Taken together, this knowledge should stimulate impactful improvements on the use of sulfones in catalytic desulfitative C-C and C-X bond formation. A main goal of this article is to bring this technology to the mainstream catalysis practice and to serve as inspiration for new perspectives in catalytic transformations.

Thianthrenium-Enabled Sulfonylation via Electron Donor-Acceptor Complex Photoactivation

Sulfone-containing compounds are prevalent building blocks in pharmaceuticals and other biomolecules, and they serve as key intermediates in the synthesis of complex scaffolds. During the past decade, several methods have been developed to access sulfones. These strategies, however, require the use of strong reaction conditions, limiting their substrate scope. Recently, visible light-mediated transformations have emerged as novel platforms to access unprecedented structural motifs. This report demonstrates a thianthrenium-enabled sulfonylation via intra-complex charge transfer to generate transient aryl- and persistent sulfonyl radicals that undergo selective coupling to generate alkyl- and (hetero)aryl sulfones under ambient conditions. Importantly, this strategy allows retention of halide handles, presenting a complementary approach to transition metal-mediated photoredox couplings. Furthermore, this sulfonylation allows high functional group tolerance and is amenable to late-stage functionalization of complex biomolecules. Mechanistic investigations support the intermediacy of electron donor-acceptor (EDA) complexes.

Nucleophilic strategies to construct –CF2– linkages using borazine-CF2Ar reagents

Using nucleophilic, boron-based –CF2Ar reagents, we demonstrate three methods to form C–CF bonds: (1) nucleophilic aromatic substitution, (2) palladium catalyzed cross-coupling, and (3) nucleophilic substitution.

Redox-active alkylsulfones as precursors for alkyl radicals under photoredox catalysis

Visible-light photoredox catalytic method for the generation of alkyl radicals using redox-active alkylsulfones to form a new C–C bond is reported.