Difunctionalization Reactions Research Articles

Revisiting the Baddeley Reaction: Access to Functionalized Decalins by Charge‐Promoted Alkane Functionalization

C–H functionalization of purely aliphatic substrates is a challenging endeavor, as the absence of directing groups generally thwarts attempts at regiocontrol. This is particularly true for difunctionalization reactions, where the control of relative stereochemistry poses an additional obstacle. The Baddeley reaction of decalins, despite suffering from strong limitations with regard to yield and generality, stands as one of only few known transformations capable of regio‐ and stereocontrol in aliphatic C–H functionalization. Herein, we report a regio‐ and diastereoselective method for the double functionalization of decalins enabling access to a novel, unreported regioisomer in synthetically useful yields. This method was also successfully applied to a range of other alkane substrates, enabling a straightforward synthesis of keto alcohols from the simplest alkane building blocks.

Revisiting the Baddeley Reaction: Access to Functionalized Decalins by Charge-Promoted Alkane Functionalization.

C-H functionalization of purely aliphatic substrates is a challenging endeavor, as the absence of directing groups generally thwarts attempts at regiocontrol. This is particularly true for difunctionalization reactions, where the control of relative stereochemistry poses an additional obstacle. The Baddeley reaction of decalins, despite suffering from strong limitations with regard to yield and generality, stands as one of only few known transformations capable of regio- and stereocontrol in aliphatic C-H functionalization. Herein, we report a regio- and diastereoselective method for the double functionalization of decalins enabling access to a novel, unreported regioisomer in synthetically useful yields. This method was also successfully applied to a range of other alkane substrates, enabling a straightforward synthesis of keto alcohols from the simplest alkane building blocks.

Aminosulfonylation of Rhodium Carbene via Ylide Formation and 1,4-Sulfonyl Rearrangement.

We report here the use of pyridin-2-yl benzenesulfonates as sulfonylation reagents in a difunctionalization reaction based on oxy-pyridinium ylide chemistry, providing an effective protocol for the installation of both a sulfonyl group and a pyridone moiety into one molecule. Density functional theory (DFT) calculations disclose that the reaction process might proceed through sequential metal-bound ylide formation, keto-enol tautomerism, and the migratory rearrangement of the sulfonyl group.

Cyano-Fluorosulfonylation of Unactivated Alkenes by Photoredox and Copper Dual Catalysis.

Both fluorosulfonyl and cyano groups are important structural motifs in bioactive molecules. Herein, we report a new difunctionalization reaction of alkenes based on fluorosulfonyl radicals, which allows for the introduction of the fluorosulfonyl and cyano groups into unactivated alkenes in one step. This transformation is enabled by merging photoredox and copper catalysis, featuring visible light catalysis, mild conditions, and good functional group tolerance. Further transformation of products via SuFEx reactions is also demonstrated.

Photoredox-catalyzed difunctionalization of alkenes through C[sbnd]N coupling and multicomponent radical/polar crossover

We reported an alkyl-thianthrenium salts (TTs) involved three-component radical alkene difunctionalization reaction. Alkylation of anilines has been realized via this mild method. An oxidative radical/polar crossover may be involved in the strategy, which realizing the combination of polar chemistry and radical chemistry. A variety of anilines, primary alkyl-substituted TTs, secondary alkyl-substituted TTs and olefins could be accessed in medium to good yield. Our work provides a valuable approach to producing diverse functionalized aniline derivatives.

Paired Electrolysis Enables Reductive Heck Coupling of Unactivated (Hetero)Aryl Halides and Alkenes.

The formation of carbon-carbon (C-C) bonds is a cornerstone of organic synthesis. Among various methods to construct Csp2-Csp3 bonds, the reductive Heck reaction between (hetero)aryl halides and alkenes stands out due to its potential efficiency and broad substrate availability. However, traditional reductive Heck reactions are limited by the use of precious metal catalysts and/or limited aryl halide and alkene compatibility. Here, we present an electrochemically mediated, metal- and catalyst-free reductive Heck reaction that tolerates both unactivated (hetero)aryl halides and diverse alkenes such as vinyl boronates and silanes. Detailed electrochemical and deuterium-labeling studies support that this transformation likely proceeds through a paired electrolysis pathway, in which acid generated by the oxidation of N,N-diisopropylethylamine (DIPEA) at the anode intercepts an alkyl carbanion formed after radical-polar crossover at the cathode. As such, this approach offers a sustainable method for the construction of Csp2-Csp3 bonds from (hetero)aryl halides and alkenes, paving the way for the development of other electrochemically mediated olefin difunctionalization reactions.

Paired Electrolysis Enables Reductive Heck Coupling of Unactivated (Hetero)Aryl Halides and Alkenes

AbstractThe formation of carbon‐carbon (C−C) bonds is a cornerstone of organic synthesis. Among various methods to construct Csp2−Csp3 bonds, the reductive Heck reaction between (hetero)aryl halides and alkenes stands out due to its potential efficiency and broad substrate availability. However, traditional reductive Heck reactions are limited by the use of precious metal catalysts and/or limited aryl halide and alkene compatibility. Here, we present an electrochemically mediated, metal‐ and catalyst‐free reductive Heck reaction that tolerates both unactivated (hetero)aryl halides and diverse alkenes such as vinyl boronates and silanes. Detailed electrochemical and deuterium‐labeling studies support that this transformation likely proceeds through a paired electrolysis pathway, in which acid generated by the oxidation of N,N‐diisopropylethylamine (DIPEA) at the anode intercepts an alkyl carbanion formed after radical‐polar crossover at the cathode. As such, this approach offers a sustainable method for the construction of Csp2−Csp3 bonds from (hetero)aryl halides and alkenes, paving the way for the development of other electrochemically mediated olefin difunctionalization reactions.

Photo-/Electrocatalytic Difunctionalization of Alkenes Enabled by C-H Radical Functionalization.

The difunctionalization of alkenes represents a powerful tool to incorporate two functional groups into the alkene bones for increasing molecular complexity and has been widely utilizations in chemical synthesis. Upon the catalysis of the green, sustainable, mild photo-/electrochemistry technologies, much attentions have been attracted to the development of new tactics for the transformations of the important alkene and alkane feedstocks driven by C-H radical functionalization. Herein, we summarize recent advances in the photo-/electrocatalytic difunctionalization of alkenes enabled by C-H radical functionalization. We detailedly discuss the substrate scope and the mechanisms of the photo-/electrocatalytic alkene difunctionalization reactions by selecting impressive synthetic examples, which are divided into four sections based on the final terminated step, including oxidative radical-polar crossover coupling, reductive radical-polar crossover coupling, radical-radical coupling, and transition-metal-catalyzed coupling.

Rapid Synthesis of Highly Substituted 1,6-Naphthyridines Via Heteroaryl Ditriflates.

We report the discovery of a convenient and efficient method for the synthesis of highly substituted 1,6-naphthyridines. A tandem nitrile hydration/cyclization procedure was developed to access 1,6-naphthyridine-5,7-diones under mild conditions. Subsequently, we have found that ditriflation of these intermediates provides 1,6-naphthyridine-5,7-ditriflates which are bench-stable but highly reactive intermediates that can be engaged in one-pot difunctionalization reactions leading to diverse drug-like products in rapid fashion.

Programmed alternating current optimization of Cu-catalyzed C-H bond transformations.

Direct current (DC) electrosynthesis, which has undergone optimization over the past century, plays a pivotal role in a variety of industrial processes. Alternating current (AC) electrosynthesis, characterized by polarity reversal and periodic fluctuations, may be advantageous for multiple chemical reactions, but apparatus, principles, and application scenarios remain underdeveloped. In this work, we introduce a protocol for programmed AC (pAC) electrosynthesis that systematically adjusts currents, frequencies, and duty ratios. The application of representative pAC waveforms facilitates copper-catalyzed carbon-hydrogen bond cleavage in cross-coupling and difunctionalization reactions that exhibit suboptimal performance under DC and chemical oxidation conditions. Moreover, observing catalyst dynamic variation under diverse waveform applications provides mechanistic insight.

Ligand control of regioselectivity in palladium-catalyzed heteroannulation reactions of 1,3-Dienes

Olefin carbofunctionalization reactions are indispensable tools for constructing diverse, functionalized scaffolds from simple starting materials. However, achieving precise control over regioselectivity in intermolecular reactions remains a formidable challenge. Here, we demonstrate that using PAd2nBu as a ligand enables regioselective heteroannulation of o-bromoanilines with branched 1,3-dienes through ligand control. This approach provides regiodivergent access to 3-substituted indolines, showcasing excellent regioselectivity and reactivity across a range of functionalized substrates. To gain further insights into the origin of selectivity control, we employ a data-driven strategy, developing a linear regression model using calculated parameters for phosphorus ligands. This model identifies four key parameters governing regioselectivity in this transformation, paving the way for future methodology development. Additionally, density functional theory calculations elucidate key selectivity-determining transition structures along the reaction pathway, corroborating our experimental observations and establishing a solid foundation for future advancements in regioselective olefin difunctionalization reactions.

Radical Cyclization-Initiated Difunctionalization Reactions of Alkenes and Alkynes.

Radical reactions are powerful in the synthesis of diverse molecular scaffolds bearing functional groups. In previous review articles, we have presented 1,2-difunctionalizations, remote 1,3-, 1,4-, 1,5-, 1,6- and 1,7-difunctionalizations, and addition followed by cyclization reactions. Presented in this paper is radical cyclization followed by the second functionalization reaction. The second functionalization could be realized by atom transfer reactions, radical or transition metal-assisted coupling reactions, and reactions with neutral molecules, cationic and anionic species.

Multicomponent Heteroarylphosphorothiolation of Alkenes for Accessing β‐Phosphorothiolated Quinoxalinones

AbstractHerein, we present a (NH4)2S2O8 mediated difunctionalization reaction of aryl alkenes with quinoxalinones and P(O)SH compounds. This method enables the synthesis of various phosphorothioate‐containing quinoxalin‐2(1H)‐one derivatives (46 examples) in 37–79% yields. The reaction is compatible with a range of functional groups and is easily adaptable to large‐scale synthesis. Preliminary studies suggest the involvement of phosphorothioate radicals in these transformations.

Synthesis of Biindene Derivatives via Pd-Catalyzed Alkene Difunctionalization Reactions.

The palladium-catalyzed cross-coupling of 2-allylphenyl triflate and related electrophiles with substituted indenes affords biindene derivatives in moderate to good yields with high selectivity for thermodynamically preferred alkene isomers. The transformations involve alkene nucleopalladation with indenyl anions, and we also demonstrate that 2-allylphenyl triflates can be transformed to indenes under similar conditions. The scope of this transformation, along with the mechanism of formation of both indene and biindene products, is described.

Photoinduced fluoroalkylation-peroxidation of alkenes enabled by ligand-to-iron charge transfer mediated decarboxylation.

We report here a photoinduced iron-catalyzed fluoroalkylation-peroxidation of activated and/or unactivated alkenes with fluoroalkyl carboxylic acids and hydroperoxide. The ligand-to-iron charge transfer strategy effectively overcomes the high redox potential of the fluoroalkyl carboxylic acids, facilitating the difunctionalization reaction to occur smoothly under mild reaction conditions. The late-stage functionalization of drug and natural product derivatives was also demonstrated.

Visible-light-induced redox-neutral difunctionalization of alkenes and alkynes.

The twelve principles of green chemistry illuminate the pathway in the direction of sustainable and eco-friendly synthesis, marking a fundamental shift in synthetic organic chemistry paradigms. In this realm, harnessing the power of visible light for the difunctionalization of various skeletons without employing any external oxidant or reductant, specifically termed as redox-neutral difunctionalization, has attracted tremendous interest from synthetic organic chemists due to its low cost, easy availability and environmentally friendly nature in contrast to traditional metal-catalyzed difunctionalizations. This review presents an overview of recent updates on visible-light-induced redox-neutral difunctionalization reactions with literature coverage up to May 2024.

Visible Light‐Induced EDA‐Complex Triggered Annulative Difunctionalization via Olefin‐Olefin Coupling and Radical Truce‐Smiles Rearrangement

AbstractAn EDA complex comprising N‐allyl bromodifluoroacetamides and tertiary alkyl amine was exploited to facilitate annulative difunctionalization reaction under visible‐light irradiation. This external photocatalyst‐free methodology garners olefin‐olefin coupling featuring a radical Truce‐Smiles rearrangement and produced long‐chain functionalized gem‐difluoropyrrolidones from N‐substituted methacryloyl sulfonamides, while simple N‐aryl methacrylamides furnished pyrrolidinone‐oxindole hybrid lactams in high yields. Mechanistic investigations substantiate a combined reaction mechanism, involving charge‐transfer EDA complex‐based radical cascade, alongside an α‐aminoalkyl radical‐triggered XAT process, exhibiting a quantum yield value of 1.48.

Photoinduced Single‐Electron Reduction of Alkenes.

AbstractAlkenes serve as versatile building blocks in organic synthesis. However, the challenge of achieving single‐electron reduction of alkenes persists. In recent years, photocatalysis has emerged as a promising and efficient tool for accomplishing the single‐electron reduction of alkenes. Given the potential benefits that can be derived from photoinduced single‐electron reduction of alkenes, including the development of potent catalytic systems to enable diverse alkene difunctionalization reactions, it is necessary to provide a conceptual understanding of this emerging field. Hence, we present an overview of current synthetic techniques for photoinduced single‐electron reduction of alkenes.

Visible-Light-Enabled Radical Alkynylborylation of Activated Alkenes

AbstractA photoredox-catalyzed protocol for performing radical difunctionalization of alkenes using N-heterocyclic carbene (NHC) boranes and alkynyl bromines is described. The alkynylborylation difunctionalization reaction involves photoredox generation of boryl radical, with subsequent radical addition to the double bond followed by the capture of alkynyl bromide to form a C–C bond. This method features mild reaction conditions, remarkable chemoselectivity, broad substrate scope and good to excellent yields (up to 89%). The modification of coumarin derivatives indicates that this approach can provide a useful route for the synthesis of complex alkynylborylated products.

Cobalt‐Catalyzed Difunctionalization of Styrenes via Ligand Relay Catalysis†

Comprehensive SummaryHere, we report a cobalt‐catalyzed sequential dehydrogenative Heck silylation/hydroamination of styrenes with hydrosilane and diazo compound to access 1‐amino‐2‐silyl compounds with excellent regioselectivity. This difunctionalization reaction could undergo smoothly using 1 mol% catalyst loading with good functional group tolerance. Not only di‐ and tri‐substituted hydrosilanes, but also alkoxysilane is suitable, which does explore the scope of the family of 1‐amino‐2‐silyl compounds. The ligand relay phenomenon between neutral tridentate NNN ligand and anionic NNN ligand is observed for the first time via absorption spectral analysis in this one‐pot, two‐step transformations. The primary mechanism has been proposed based on the control experiments.