Alcohol-alcohol cross-coupling enabled by SH2 radical sorting

Dehomologative C-C Borylation of Aldehydes and Alcohols via a Rh-Catalyzed Dehydroformylation-Borylation Relay

The dehomologative conversion of linear or α-methyl aldehydes to vinyl boronates is achieved via a one-pot sequence of rhodium-catalyzed transfer dehydroformylation and transfer borylation of the resulting alkenes. Similarly, allylic or aliphatic alcohols are converted to vinyl boronates through a sequence involving, respectively, rhodium-catalyzed isomerization or transfer dehydrogenation to aldehyde intermediates, followed by dehydroformylation-borylation. The vinyl boronates can be further hydrogenated to alkyl boronates using the same rhodium precatalyst, enabling all five catalytic steps with a single catalyst system.

Aryl Acid-Alcohol Cross-Coupling: C(sp3)-C(sp2) Bond Formation from Nontraditional Precursors

Alcohols and aryl carboxylic acids are among the most commercially abundant, synthetically versatile, and operationally convenient building blocks in organic chemistry. Despite their widespread availability, the direct formation of C(sp3)-C(sp2) bonds from these functional groups remains a challenge. Recently, our group developed robust protocols to harness alcohols as alkyl radical precursors, but the activation of aryl acids remains relatively unexplored. Herein, we describe the merger of N-heterocyclic carbene (NHC)-mediated deoxygenation and nickel-mediated decarbonylation of aryl acids toward C(sp3)-C(sp2) bond formation. The utility of this method is demonstrated through the synthesis of a diverse range of aryl-alkyl cross-coupled products and the late-stage functionalization of complex molecules, including drugs, natural products, and biomolecules.

Photocatalyst-Dependent Enantioselectivity in the Light-Driven Deracemization of Cyclic α-Aryl Ketones

We report a photoredox-enabled deracemization of cyclic α-aryl ketones that occurs with high stereoselectivity and yield and proceeds by mechanistically distinct proton transfer reactions. This reaction is jointly mediated by a visible-light photocatalyst and a chiral phosphate base cocatalyst under blue light irradiation. Notably, the extent of deracemization for this reaction exhibits an unexpected dependence on the identity of the photocatalyst and the concentration of a chiral base cocatalyst, wherein the extent of deracemization can be increased by employing photocatalysts with more positive ground-state reduction potentials, raising the concentration of the chiral base cocatalyst, or by a combination of these factors. This effect is attributed to two competing processes, back-electron transfer and deprotonation, which consume the same reaction intermediate, and we propose a kinetic model that rationalizes this behavior. We also demonstrate that the redox properties of the photocatalyst impact the stereoselectivity of the product-forming step, which is the dominant stereoselective step in this transformation. Together, these mechanistic insights facilitate a deeper understanding of the complexity of light-driven deracemization reactions involving reversible electron transfer and suggest approaches by which the stereoselectivity of these processes may be increased.

Generalizing arene C-H alkylations by radical-radical cross-coupling

The efficient and modular diversification of molecular scaffolds, particularly for the synthesis of diverse molecular libraries, remains a notable challenge in drug optimization campaigns1-3. The late-stage introduction of alkyl fragments is especially desirable due to the high sp3 character and structural versatility of these motifs4. Given their prevalence in molecular frameworks, C(sp2)-H bonds serve as attractive targets for diversification, although this process often requires difficult prefunctionalization or lengthy de novo syntheses. Traditionally, direct alkylations of arenes are achieved by using Friedel-Crafts reaction conditions with strong Brønsted or Lewis acids5,6. However, these methods suffer from poor functional group tolerance and low selectivity, limiting their broad implementation in late-stage functionalization and drug optimization campaigns. Here we report the application of a new strategy for the selective coupling of differently hybridized radical species, which we term 'dynamic orbital selection'. This mechanistic model overcomes common limitations of Friedel-Crafts alkylations via the in situ formation of two distinct radical species, which are subsequently differentiated by a copper-based catalyst on the basis of their respective binding properties. As a result, we demonstrate here a general and highly modular reaction for the direct alkylation of native arene C-H bonds using abundant and benign alcohols and carboxylic acids as the alkylating agents. Ultimately, this solution overcomes the synthetic challenges associated with the introduction of complex alkyl groups into highly sophisticated drug scaffolds in a late-stage fashion, thereby granting access to vast new chemical space. Based on the generality of the underlying coupling mechanism, 'dynamic orbital selection' is expected to be a broadly applicable coupling platform for further challenging transformations involving two distinct radical species.

Synergistic LMCT and Ni Catalysis for Methylative Cross-Coupling Using tert-Butanol: Modulating Radical Pathways via Selective Bond Homolysis

Ligand-to-metal charge transfer (LMCT) excitation has emerged as a potent strategy for the selective generation of heteroatom-centered radicals, yet its full potential in modulating open-shell radical pathways remains underexplored. Here, we present a photocatalytic methylative cross-coupling reaction that capitalizes on the synergistic interplay between LMCT and Ni catalysis, enabling the use of tert-butanol as an efficient and benign methylating reagent. The electron-deficient ligand 2,6-ditrifluoromethyl benzoate facilitates Ce(IV)-mediated bond scission of tert-butanol, generating a methyl radical that is subsequently captured by the Ni catalytic cycle to form C-CH3 bonds. Under mild reaction conditions, this strategy affords efficient methylation of sp3 carbons adjacent to carbonyls and sp2 centers, demonstrating broad functional group tolerance and applicability in late-stage functionalization of bioactive molecules. Additionally, trideuteromethylative coupling can be facilely achieved using commercial tert-butanol-d10. This approach circumvents the need for traditional tert-butoxy radical precursors, such as peroxides, while strategically modulating the radical pathway to favor β-scission and suppress unwanted tert-butoxy radical formation in solution. Mechanistic studies reveal that the benzoate ligand plays a crucial role in enabling LMCT excitation and facilitating methyl radical generation, supporting a concerted Ce-OR and β-C-C bond homolysis mechanism, further evidenced by the modulation of regioselectivity in alkoxy radical-mediated β-scission.

Palladium-Catalyzed/Titanium-Promoted Csp3-Csp3 Coupling of Two Alcohols: Generation of an All-Carbon Quaternary Center

Naturally abundant and inexpensive alcohols represent appealing and suitable Csp3 coupling partners in transition metal-catalyzed cross-coupling reactions. A palladium-catalyzed/titanium-promoted Csp3-Csp3 cross coupling between two distinct unprotected alcohols has been accomplished. The reaction features a Pd-catalyzed β-H elimination, enabling the reversal of the electrophilic π-allyl-Pd intermediate into a nucleophilic dienolate and the generation of an all-carbon quaternary center.

Facile, general allylation of unactivated alkyl halides via electrochemically enabled radical-polar crossover

Electrochemically driven carbon-carbon formation is receiving considerable interest in organic synthesis. In this study, we present an electrochemically driven method for the formation of C(sp3)-C(sp3) bonds using readily available allylic carbonates, as well as primary, secondary, and tertiary alkyl bromides as electrophiles. This approach offers a highly selective route for synthesizing a broad range of allylic products with excellent functional group tolerance, all without the need for transition metal catalysts. Remarkably, this method also enables the smooth late-stage functionalization of various natural product- and drug-derived substrates, yielding the corresponding complex allylalkanes.

Development of N-centered radical scavengers that enables photoredox-catalyzed transition-metal-free radical amination of alkyl pinacol boronates

In recent years, amination of alkylboronates through ionic copper catalysis or boron-ate complex 1,2-metalation has been well established, but complementary radical processes remain less studied before. Herein, based on rational design, we develop several imine-type N-centered radical scavengers and apply them to the radical amination of alkylboronates. The reaction proceeds under mild photoredox-catalyzed transition-metal-free conditions and features excellent functional group tolerance. It also enables the preparation of a range of medicinally valuable amine derivatives from complex natural products. Further application of this reagent in C-H amination, deoxygenative amination, decarboxylative amination and three component trifluoromethylative/sulfonylative aminations are also realized. Further mechanistic studies and DFT calculations are conducted to provide detailed evidence for the mechanism.

Alcohol Activation by Benzodithiolylium for Deoxygenative Alkylation Driven by Photocatalytic Energy Transfer

The 1,3-benzodithiolylium (BDT) cation was identified as an efficient hydroxyl-activating reagent for the photocatalytic deoxygenative radical functionalization of alcohols in the absence of any electron transfer process. A series of unprecedented photocatalytic energy transfer (EnT)-driven deoxygenative radical coupling reactions of alcohols with bifunctional oxime carbonates have been developed based on the activation by BDT. Nickel-catalyzed radical sorting followed by C(sp3)─C(sp3) bond construction facilitates the heteroselective cross-coupling of two distinct alkyl radicals originating from parallel radical relays. These reactions allow the versatile synthesis of diverse nitrogen-containing molecules, including amino acid derivatives, imines, nitriles, and pyrrolines, by using ubiquitous alcohols as regiodefined alkyl building blocks.

Enantioselective Alkyl-Acyl Radical Cross-Coupling Enabled by Metallaphotoredox Catalysis

Radical-radical cross-coupling (RCC) offers a promising approach for carbon-carbon bond formation in organic synthesis, particularly for creating complex, three-dimensional molecules. However, achieving both cross- and enantioselectivity in RCC reactions has remained a significant challenge. Here, we report a novel metallaphotoredox platform that enables highly enantioselective decarboxylative coupling of carboxylic acid derivatives with aldehydes. Our strategy leverages independent control over radical generation and subsequent enantioselective bond formation through fine-tuning of a common photocatalyst and a simple chiral bis(oxazoline) nickel catalyst. This redox-neutral protocol requires no exogenous oxidants or reductants and demonstrates broad substrate scope and functional group compatibility in the synthesis of enantioenriched α-aryl and α-amino ketones. The α-amino ketone products can be readily transformed into valuable β-amino alcohols, streamlining access to these important motifs. Furthermore, we showcase the potential of this approach for more challenging enantioselective C(sp3)-C(sp3) alkyl-alkyl RCC reactions. This unified platform for enantioselective alkyl-acyl radical cross-coupling represents a significant advance in asymmetric catalysis and underscores the potential for metallaphotoredox catalysis to exploit new mechanisms to solve long-standing synthetic problems.

Photocatalytic Redox-Neutral and Reductive Deoxygenative Alkylation of Benzyl Alcohols Using N-Acyl Carbamothioates as Radical Precursors

Herein, we report a photocatalytic redox-neutral and reductive deoxygenative alkylation of N-acyl carbamothioates from benzylic alcohols, with substituted Hantzsch esters and allylic sulfones to afford unsymmetrical 1,2-diaryl ethanes and allylarylmethanes, respectively. This protocol facilitates facile deoxyalkylation of primary, secondary, and tertiary benzylic alcohol-derived N-acyl carbamothioates, which features mild reaction conditions, broad functional group tolerance, and the obviation of external S/O trapping reagents as well as transition metal-coupling catalysts.

Heterocoupling Two Similar Benzyl Radicals by Dual Photoredox/Cobalt Catalysis

Transition-metal-regulated radical cross coupling enables the selective bonding of two distinct transient radicals, whereas the catalytic method for sorting two almost identical transient radicals, especially similar benzyl radicals, is still rare. Herein, we show that leveraging dual photoredox/cobalt catalysis can selectively couple two similar benzyl radicals. Using easily accessible methylarenes and phenylacetates (benzyl N-hydroxyphthalimide (NHPI) esters) as benzyl radical sources, a range of unsymmetrical 1,2-diarylethane classes via the 1°-1°, 1°-2°, 1°-3°, 2°-2°, 2°-3° and 3°-3° couplings were obtained with broad functional group tolerance. Besides the photochemical continuous flow synthesis, the one-pot procedure that directly uses phenylacetic acids and NHPI as the starting materials to avoid the pre-preparation of benzyl NHPI esters for the gram-scale synthesis is also feasible and affords good yields, showcasing the synthetic utility of our protocol.

Photoredox-catalyzed deoxygenative radical transformation of alcohols to sulfinamides

Sulfinamides play a crucial role in organic synthesis and pharmaceuticals. In this study, we introduce a highly effective method for the deoxygenative radical addition to N-tritylsulfinylamine, which produces sulfinamides via photoredox catalysis. This method is compatible with a diverse array of functional groups and the resulting sulfonamides were achieved in moderate to high yields. Furthermore, the synthetic applications to access various sulfur(vi)-centered functional groups highlight the practicality of this approach.

Making Mo(0) a Competitive Alternative to Ir(III) in Phosphors and Photocatalysts

Iridium is used in commercial light-emitting devices and in photocatalysis but is among the rarest stable chemical elements. Therefore, replacing iridium(III) in photoactive molecular complexes with abundant metals is of great interest. First-row transition metals generally tend to yield poorer luminescence behavior, and it remains difficult to obtain excited states with redox properties that exceed those of noble-metal-based photocatalysts. Here, we overcome these challenges with a nonprecious second-row transition metal. Tailored coordination spheres for molybdenum(0) lead to photoluminescence quantum yields that rival those of iridium(III) complexes and photochemical reduction reactions not normally achievable with iridium(III) become possible. These developments open new perspectives for replacing noble metals in lighting applications with Earth-abundant metals and for advancing metal-based photocatalysis beyond current limits.

Palladium-Catalyzed Oxidative Allene-Allene Cross-Coupling

Direct cross-coupling reactions between two similar unactivated partners are challenging but constitute a powerful strategy for the creation of new carbon-carbon bonds in organic synthesis. [4]Dendralenes are a class of acyclic branched conjugated oligoenes with great synthetic potential for the rapid generation of structural complexity, yet the chemistry of [4]dendralenes remains an unexplored field due to their limited accessibility. Herein, we report a highly selective palladium-catalyzed oxidative cross-coupling of two allenes with the presence of a directing olefin in one of the allenes, enabling the facile synthesis of a broad range of functionalized [4]dendralenes in a convergent modular manner. Specifically, the selective allenic C-H activation of an allene with an allyl substituent as the assisting group gives rise to a vinylpalladium intermediate, which reacts with a less substituted allene in a carbopalladation, followed by a β-hydride elimination. The reaction sequence leads to a new C(sp2)-C(sp2) bond between two diene units. Remarkably, this protocol provides an unconventional strategy for the site-selective and stereoselective construction of C(vinyl)-C(vinyl) bonds without using any halogenated and organometallics olefin precursors. Furthermore, the practical transformations of the synthesized [4]dendralenes and late-stage modifications of biorelevant molecules demonstrate their potential in the total synthesis of natural products and drug discovery.

N-Heterocyclic carbene (NHC) organocatalysis: from fundamentals to frontiers

N-Heterocyclic carbenes (NHCs) have been used as organocatalysts for a multitude of C-C and C-heteroatom bond-forming reactions. They enable diverse modalities of activating a wide range of structurally distinct substrate classes and allow access to electronically distinct intermediates. The easy tunability of the NHC scaffold contributes to its versatility. Recent years have witnessed a surge of interest in various organocatalytic reactions of NHCs, leading to the forays of NHC catalysis into the relatively newer domains such as reactions involving radical intermediates, atroposelective synthesis, umpolung of electrophiles other than aldehydes, and the use of NHCs as non-covalent templates for enantioinduction. This tutorial review provides an overview of various important structural features and reactivity modes of NHCs and delves deep into some frontiers of NHC-organocatalysis.

Aminoalkylation of Alkenes Enabled by Triple Radical Sorting

The direct synthesis of C(sp3)-rich architectures is a driving force for innovation in synthetic organic chemistry. Such scaffolds impart beneficial properties onto drug molecules that correlate with greater clinical success. Consequently, there is a strong impetus to develop new methods by which to access sp3-rich molecules from commercial feedstocks, such as alkenes. Herein, we report a three-component aminoalkylation reaction that utilizes the principles of triple radical sorting to regioselectively add N-centered and C-centered radicals across alkenes. This process relies upon photoredox catalysis to transform alkyl bromides and reductively activated N-centered radical precursors into high-energy radical species in a redox-neutral fashion. A broad scope of coupling partners is demonstrated, with multiple synthetic applications, including facile syntheses of pharmacophoric substituted N-heterocycles.

Stereoselective Vinylic C-H Addition via Metallaphotoredox Migration

Geometrically defined allylic alcohols with SE, SZ, RE and RZ stereoisomers serve as valuable intermediates in synthetic chemistry, attributed to the stereoselective transformations enabled by the alkenyl and hydroxyl functionalities. When an ideal scenario presents itself with four distinct stereoisomers as potential products, the simultaneous control vicinal stereochemistry in a single step would offer a direct pathway to any desired stereoisomer. Here, we unveil a metallaphotoredox migration strategy to access stereodefined allylic alcohols through vinylic C-H activation with aldehydes. This method harnesses a chiral nickel catalyst in concert with a photocatalyst to enable a 1,4-Ni migration by using readily accessible 2-vinyl iodoarenes as starting materials. The efficacy of this methodology is highlighted by the precise construction of all stereoisomers of allylic alcohols bearing analogous substituents and the efficient synthesis of key intermediates en route to Myristinin family. Experimental and computational studies have shed light on pivotal aspects including the synergy of metal catalysis and photocatalysis, the driving forces behind the migration, and the determination of absolute configuration in the C-H addition process.

Organometallic Photocatalyst-Promoted Synthesis and Modification of Carbohydrates under Photoirradiation

Carbohydrates are natural, renewable, chemical compounds that play crucial roles in biological systems. Thus, efficient and stereoselective glycosylation is an urgent task for the preparation of pure and structurally well-defined carbohydrates. Photoredox catalysis has emerged as a powerful tool in carbohydrate chemistry, providing an alternative for addressing some of the challenges of glycochemistry. Over the last few decades, Ir- and Ru-based organometallic photocatalysts have attracted significant interest because of their high stability, high-energy triplet state, strong visible-light absorption, long luminescence lifetime, and amenability to ligand modification. This review highlights the recent progress in the organometallic photocatalyst-promoted synthesis and modification of carbohydrates under photoirradiation, as well as the related benefits and drawbacks.

Synergistic photobiocatalysis for enantioselective triple-radical sorting

Multicomponent reactions-those where three or more substrates combine into a product-have been highly useful in rapidly building chemical building blocks of increased complexity1, but achieving this enzymatically has remained rare2-5. This limitation primarily arises because an enzyme's active site is not typically set up to address multiple substrates, especially in cases involving multiple radical intermediates6. Recently, chemical catalytic radical sorting has emerged as an enabling strategy for a variety of useful reactions7,8. However, making such processes enantioselective is highly challenging owing to the inherent difficulty in the stereochemical control of radicals9. Here we repurpose a thiamine-dependent enzyme10,11 through directed evolution and combine it with photoredox catalysis to achieve a photobiocatalytic enantioselective three-component radical cross-coupling. This approach combines three readily available starting materials-aldehydes, α-bromo-carbonyls and alkenes-to give access to enantioenriched ketone products. Mechanistic investigations provide insights into how this dual photocatalyst-enzyme system precisely directs the three distinct radicals involved in the transformation, unlocking enzyme reactivity. Our approach has achieved exceptional stereoselectivity, with 24 out of 33 examples achieving ≥97% enantiomeric excess.

Scalable deoxygenative alkynylation of alcohols via flow photochemistry

Internal alkynes are often contained in bioactive pharmaceuticals and crucial intermediates in material sciences, yet their production methods are often limited and challenging, necessitating the development of more efficient and versatile synthetic routes. Here we report a method of deoxygenative alkynylation of alcohols via flow photochemistry. Formation of N-heterocyclic carbene-alcohol adducts undergoes oxidation by a photocatalyst, generating alkyl radicals. These radicals are subsequently trapped by an alkynylation agent, yielding the desired alkyne. Compared to batch reactions, the strategy using flow photochemistry is practical and efficient to complete the reaction in relatively short time with good yields. A wide range of functional groups were tolerated. The broad application of this method for alkyne synthesis in industry settings is anticipated, supported by the potential in late-stage functionalization of biomolecules and gram-scale synthesis.

Iron-Catalyzed Cross-Electrophile Coupling for the Formation of All-Carbon Quaternary Centers

Quaternary carbon centers are desirable targets for drug discovery and complex molecule synthesis, yet the synthesis of these motifs within traditional cross-coupling paradigms remains a significant challenge due to competing β-hydride elimination pathways. In contrast, the bimolecular homolytic substitution (SH2) mechanism offers a unique and attractive alternative pathway. Metal porphyrin complexes have emerged as privileged catalysts owing to their ability to selectively form primary metal-alkyl complexes, thereby eliminating the challenges associated with tertiary alkyl complexation with a metal center. Herein, we report an iron-catalyzed cross-electrophile coupling of tertiary bromides and primary alkyl electrophiles for the formation of all-carbon quaternary centers through a biomimetic SH2 mechanism.

Electroinduced Reductive and Dearomative Alkene-Aldehyde Coupling

The direct coupling of alkene feedstocks with aldehydes represents an expedient approach to the generation of new and structurally diverse C(sp3)-hybridized alcohols that are primed for elaboration into privileged architectures. Despite their abundance, current disconnection strategies enabling the direct coupling of carbon-carbon π-bonds and aldehydes remain challenging because contemporary methods are often limited by substrate or functional group tolerance and compatibility in complex molecular environments. Here, we report a coupling between simple alkenes, heteroarenes and unactivated aliphatic aldehydes via an electrochemically induced reductive activation of C-C π-bonds. The cornerstone of this approach is the discovery of rapid alternating polarity (rAP) electrolysis to access and direct highly reactive radical anion intermediates derived from conjugated alkenes and heterocyclic compounds. Our developed catalyst-free protocol enables direct access to new and structurally diverse C(sp3)-hybridized alcohol products. This is achieved by the controlled reduction of conjugated alkenes and the C2-C3 π-bond in heteroarenes via an unprecedented reductive dearomative functionalization for heterocyclic compounds. Experimental mechanistic studies demonstrate a kinetically biased single-electron reduction of C-C π-bonds over aldehydes. Application of rAP enables chemoselective generation of olefinic radical anion intermediates and avoids undesired saturative overreduction. Overall, this technology provides a versatile approach to the reductive coupling of olefin and heterocycle feedstocks with aliphatic aldehydes, offering straightforward access to diverse C(sp3)-rich oxygenated scaffolds.

Multicomponent Construction of Tertiary Alkylamines by Photoredox/Nickel-Catalyzed Aminoalkylation of Organohalides

Tertiary alkylamines are privileged structural motifs widely present in natural products, pharmaceutical agents, and bioactive molecules, and their efficient synthesis has been a longstanding goal in organic chemistry. The functionalization of α-amino radicals derived from abundant precursors represents an emerging approach to accessing alkylamines, but application of this strategy to obtain tertiary alkylamines remains challenging. Here, we show that dual photoredox/nickel catalysis enables aminoalkylation of organohalides (sp2- and sp3-hybridized) in combination with secondary alkylamines and aldehydes. The multicomponent process proceeds through selective generation of α-amino radicals from the reduction of in situ-generated iminium ions by photoredox catalysis, followed by nickel-catalyzed cross-coupling to build a wide array of functionally diverse tertiary alkylamines. This strategy could also be extended to unprecedented four-component reactions and their asymmetric variants to deliver enantioenriched α-aryl-substituted γ-amino acid derivatives. Taken together, this work offers a streamlined synthetic route to aliphatic tertiary amines.

Alcohols as Alkyl Electrophiles for Deoxygenative Heck Reaction Enabled by Excited State Pd Catalysis

Here, we present a general method for the photoinduced Pd-catalyzed deoxygenative Heck reaction of vinyl arenes with ortho-iodophenyl-thionocarbonate derived from alcohols. Mechanistic studies reveal that the deoxygenation involves a 5-endo-trig cyclization and fragmentation process, with radical addition identified as the rate-determining step in this transformation. This one-pot procedure demonstrates excellent selectivity for less hindered hydroxyl groups in diols, facilitating late-stage functionalization of complex molecules and scalability to gram-scale synthesis. The protocol highlights significant synthetic potential and can be extended to the cascade 1,1-difunctionalization of isocyanides and the intermolecular radical cascade cyclization of N-arylacrylamides.

Reductive alkyl-alkyl coupling from isolable nickel-alkyl complexes

The selective cross-coupling of two alkyl electrophiles to construct complex molecules remains a challenge in organic synthesis1,2. Known reactions are optimized for specific electrophiles and are not amenable to interchangeably varying electrophilic substrates that are sourced from common alkyl building blocks, such as amines, carboxylic acids and halides3-5. These limitations restrict the types of alkyl substrate that can be modified and, ultimately, the chemical space that can be explored6. Here we report a general solution to these limitations that enables a combinatorial approach to alkyl-alkyl cross-coupling reactions. This methodology relies on the discovery of unusually persistent Ni(alkyl) complexes that can be formed directly by oxidative addition of alkyl halides, redox-active esters or pyridinium salts. The resulting alkyl complexes can be isolated or directly telescoped to couple with a second alkyl electrophile, which represent cross-selective reactions that were previously unknown. The utility of this synthetic capability is showcased in the rapid diversification of amino acids, natural products, pharmaceuticals and drug-like building blocks by various combinations of dehalogenative, decarboxylative or deaminative coupling. In addition to a robust scope, this work provides insights into the organometallic chemistry of synthetically relevant Ni(alkyl) complexes through crystallographic analysis, stereochemical probes and spectroscopic studies.

Catalytic undirected methylation of unactivated C(sp3)-H bonds suitable for complex molecules

In pharmaceutical discovery, the "magic methyl" effect describes a substantial improvement in the pharmacological properties of a drug candidate with the incorporation of methyl groups. Therefore, to expedite the synthesis of methylated drug analogs, late-stage, undirected methylations of C(sp3)-H bonds in complex molecules would be valuable. However, current methods for site-selective methylations are limited to activated C(sp3)-H bonds. Here we describe a site-selective, undirected methylation of unactivated C(sp3)-H bonds, enabled by photochemically activated peroxides and a nickel(II) complex whose turnover is enhanced by an ancillary ligand. The methodology displays compatibility with a wide range of functional groups and a high selectivity for tertiary C-H bonds, making it suitable for the late-stage methylation of complex organic compounds that contain multiple alkyl C-H bonds, such as terpene natural products, peptides, and active pharmaceutical ingredients. Overall, this method provides a synthetic tool to explore the "magic methyl" effect in drug discovery.

Keggin structure heteropolyacid-catalyzed phosphinylation of secondary propargyl alcohols with phosphine oxides to γ-ketophosphine oxides

Phosphotungstic acid with a Keggin structure as an efficient, simple and green catalyst for the phosphinylation of secondary propargyl alcohols with phosphine oxides to afford γ-ketophosphine oxides with up to 88% isolated yield was developed using dimethyl carbonate as a green solvent. Diaryl- or alkylaryl-substituted propargyl alcohols, and diaryl or arylalkylphosphine oxides could tolerate the system, which reduced the catalyst dosage, and avoided the use of multi-components and toxic solvents. More interestingly, phosphotungstic acid exhibited the best activity when 0.58 moles of water were added per mole of HPWA, elevating the yield from 55% to 85%. An 18O labelled product was afforded using trace H218O instead of H2O, indicating the participation of water in the reaction. Besides, our work underscores the importance and effect of a small amount of water, acting to promote the transformation of secondary propargyl alcohols into enones, which should be the real intermediates of the reaction. A mechanism involving a carbocation, Meyer-Schuster rearrangement and Michael addition of enones was proposed.

Strategies and Mechanisms of First-Row Transition Metal-Regulated Radical C-H Functionalization

Radical C-H functionalization represents a useful means of streamlining synthetic routes by avoiding substrate preactivation and allowing access to target molecules in fewer steps. The first-row transition metals (Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) are Earth-abundant and can be employed to regulate radical C-H functionalization. The use of such metals is desirable because of the diverse interaction modes between first-row transition metal complexes and radical species including radical addition to the metal center, radical addition to the ligand of metal complexes, radical substitution of the metal complexes, single-electron transfer between radicals and metal complexes, hydrogen atom transfer between radicals and metal complexes, and noncovalent interaction between the radicals and metal complexes. Such interactions could improve the reactivity, diversity, and selectivity of radical transformations to allow for more challenging radical C-H functionalization reactions. This review examines the achievements in this promising area over the past decade, with a focus on the state-of-the-art while also discussing existing limitations and the enormous potential of high-value radical C-H functionalization regulated by these metals. The aim is to provide the reader with a detailed account of the strategies and mechanisms associated with such functionalization.

Chromium- and Metal-Reductant-Free Asymmetric Nozaki-Hiyama-Kishi (NHK) Reaction Enabled by Metallaphotoredox Catalysis

Chiral allylic alcohols are highly prized in synthetic chemistry due to their versatile reactivity stemming from both alkenyl and hydroxyl functionalities. While the Nozaki-Hiyama-Kishi (NHK) reaction is a widely used method for the synthesis of allylic alcohols, it suffers from drawbacks such as the use of toxic chromium salts, high amounts of metal reductants, and poor enantiocontrol. To address these limitations, we present a novel approach involving a metallaphotoredox-catalyzed asymmetric NHK reaction for the production of chiral allylic alcohols. This method marries alkenyl (pseudo)halides with aldehydes, leveraging a synergistic blend of a chiral nickel catalyst and a photocatalyst. This innovative technique enables both oxidative addition and insertion just using nickel, diverging significantly from the conventional NHK reaction pathway mediated by nickel and chromium salts. The adoption of this methodology holds immense promise for crafting a spectrum of intricate compounds, particularly those of significance in pharmaceuticals. Detailed experimental investigations have shed light on the metallaphotoredox process, further enhancing our understanding and enabling further advancements.

Visible-Light-Mediated Azidation of α-Diazoesters with TMSN3 via Direct Photoexcitation and SH2 Mechanism

A visible light-mediated azidation of α-diazoesters with TMSN3 to synthesize valuable α-azidoesters has been developed. Without using any catalysts and additives, the reaction proceeded smoothly under visible light irradiation at room temperature. A variety of α-diazoesters were successfully converted to the desired α-azidoesters, showing good functional group tolerance. The products could be readily transformed into triazole, α-azidoacid, and α-azidoamide. Mechanistic studies suggested that the reaction is mainly carrying out via direct photoexcitation and SH2 mechanism. This work provides a novel, mild, and practical protocol for synthesizing α-azidoesters.

Development of an Easy-To-Handle Redox Active Group for Alcohols: Catalytic Transformation of Tertiary Alcohols to Nitriles

The generation of radical intermediates via SET-mediated deoxygenation of activated alcohol derivatives is desirable, as alcohols can be utilized in various radical-mediated reactions. Herein, we introduce α-N-phthalimido-oxy isobutyrate (NPIB) as a novel activating group for alcohols. Essentially, it is a more chemically robust alternative to Overman's N-phthalimidoyl oxalate group. The utility of the NPIB group is showcased in the conversion of tertiary alcohols to nitriles under Ir/Cu dual catalysts and in the presence of TMSCN upon blue LED irradiation. With our newly developed NPIB handle, the reactivities of N-hydroxyphthalimide esters derived from carboxylic acids would be achievable with naturally and commercially more abundant alcohol substrates.

Triple Radical Sorting: Aryl-Alkylation of Alkenes

The cross-coupling of aryl bromides with alkenes can provide access to diverse combinatorial chemical space. Two-component couplings between these partners are well-known, but three-component aryl-functionalizations of unactivated alkenes remain underdeveloped. In particular, the aryl-alkylation of unactivated alkenes would allow for rapid construction of molecular complexity and the expedient exploration of a pharmaceutically relevant and C(sp3)-rich structural landscape. Herein, we report a general approach toward the aryl-alkylation of alkenes through a triple radical sorting mechanism. Over the course of the reaction, a high energy aryl radical, a primary radical, and a hindered alkyl radical are simultaneously formed. Through mediation by a nickel-based catalyst, the three radicals are sorted into productive bond-forming pathways toward the efficient aryl-alkylation of alkenes. A wide range of electronically and sterically differentiated alkenes and aryl radical precursors can be used to access complex scaffolds. This method was further applied to the synthesis of highly substituted semisaturated fused heterocycles.