Synthesis of Water-Tolerant Indium Homoenolate in Aqueous Media and Its Application in the Synthesis of 1,4-Dicarbonyl Compounds via Palladium-Catalyzed Coupling with Acid Chloride

Visible light induced cooperative carbonylation and (hetero)aryl migration: synthesis of multi-carbonyl compounds

Carbonylative transformation represents one of the most straightforward procedures for the synthesis of carbonyl-containing compounds. However, the carbonylative procedure toward 1,4-diketones is still limited which are key moieties with potent applications in various areas. Herein, we report a new strategy for the synthesis of multi-carbonyl compounds containing a 1,4-diketone skeleton through remote heteroaryl migration of traditionally restricted 1,3-migratory substrates utilizing carbon monoxide (CO) as the C1 synthon and diazonium compounds as the starting material.

Cobalt(II)-Catalyzed Synthesis of γ-Diketones from Aryl Alkenes and Its Utilization in the Synthesis of Various Heterocyclic Compounds

An earth-abundant Co(II) salt-catalyzed mild and affordable synthetic route has been developed for the synthesis of industrially relevant 1,4-dicarbonyl compounds (or γ-diketones) via oxidative coupling between aryl alkenes and ketones (both cyclic and acyclic) using TBHP and DBU as the oxidant and base, respectively. 1,4-Dicarbonyl compounds are known to be synthesized using expensive metal catalysts, dual catalysts, or low-cost metal complexes combined with an additive or ligand template, which further needs to be synthesized. Herein, we report the synthesis of 1,4-dicarbonyl compounds using cobalt(II) acetate as a catalyst without any expensive co-catalyst or ligand templates. This methodology has a broad substrate scope with significant yields and good functional group tolerance. Generation of unsymmetrical 1,4-dicarbonyls at room temperature and its versatile synthetic expansion to produce synthetically and biologically valuable heterocyclic compounds are salient features of this novel methodology. In addition, various controlled experiments such as primary kinetic isotope effect study, Hammett analysis with variation of the nature of the substituents on the styrene ring, and theoretical calculations (density functional theory) unravel the mechanistic intricacies involved in this new, simple, and atom-economic methodology.

Development and Applications of Water-Compatible Reactions: A Journey to Be Continued

ConspectusThe pursuit of novel and eco-friendly methods in organic synthesis is gaining prominence, with a strong emphasis on green transformations using renewable and sustainable resources. Among these environmentally conscious approaches, water-compatible reactions stand out for their many advantages. Water, as a solvent, offers unmatched abundance, cost-efficiency, and environmental compatibility compared to organic solvents. Its use eliminates the need for complex protection and deprotection steps for reactive functional groups in multistep synthesis and enables the use of water-soluble substrates like proteins and carbohydrates. Water-compatible reactions also provide opportunities to combine with enzymes, resulting in chemoenzymatic transformations that can increase efficiency. Additionally, these reactions facilitate site-specific modification and the bioconjugation of biomolecules, leading to bioconjugate therapeutics.Over nearly three decades, our research group has been dedicated to developing innovative water-compatible methodologies and concepts. This Account provides a comprehensive overview of our contributions since 1994. Our central strategy revolves around integrating green chemistry principles into our methods, focusing on (i) developing reactions that can operate under mild conditions, including room temperature, atmospheric pressure, and physiological pH; (ii) designing atom-economical reactions that minimize waste production; (iii) replacing toxic and flammable organic solvents with eco-friendly alternatives like water and ethanol; and (iv) reducing reliance on metals or halogenated compounds in specific reactions.In this Account, we detail our achievements in developing efficient methodologies in aqueous media, highlighting their scope, limitations, asymmetric control, and applications for synthesizing complex molecules and functionalizing peptides and proteins. Mechanistic investigations underlying these developments are also discussed when applicable. Furthermore, we offer insights into the reasoning behind our work and address future opportunities and challenges in this area of research. We hope that this Account will inspire continued interest and foster new breakthroughs. By exploring innovative and broadly applicable strategies that expand the water-compatible synthetic toolbox, we aim to pave the way for the truly green and sustainable synthesis of complex molecules and pharmaceuticals.

Photoredox-catalyzed 1,2-oxo-alkylation of vinyl arenes with 1,3-diketones: an approach to 1,4-dicarbonyls via C-C activation

A mild and inexpensive approach to synthesising a series of 1,4-diketones in moderate to excellent yields via 1,2-oxo alkylation has been developed using fluorescein as a photocatalyst and air as an oxidant. The key features include (i) varied substrate scope (39 examples); (ii) good functional group tolerance; (iii) unsymmetrical 1,4-dicarbonyls; (iv) late-stage functionalization of thymol and ibuprofen derivatives; and (v) the synthetic expansion to 5- and 6-membered N-, O- and S-containing heterocycles.

Synthesis of 1,4-ketoaldehydes and 1,4-diketones by Mo-catalyzed oxidative cleavage of cyclobutane-1,2-diols

A new two-step procedure for the synthesis of 1,4-dicarbonyls has been developed involving an efficient and clean Mo-catalyzed oxidative cleavage of cyclobutane-1,2-diols with DMSO, which is used as solvent and oxidant. The required starting glycols were prepared by nucleophilic additions of organolithiums and Grignard reagents to easily available 2-hydroxycyclobutanones.

Cooperative Initiation in a Dinuclear Indium Complex for CO2 Epoxide Copolymerization

Dinuclear indium complexes have been synthesized and characterized. These include neutral and cationic indium complexes supported by a Schiff base ligand bearing a binaphthol linker. The new compounds were investigated for alternating copolymerization of CO₂ and cyclohexene oxide. In particular, the neutral indium chloride complex (±)-[(O_NapN_iN)InCl₂]₂ (4) showed high conversion of cyclohexene oxide and selectivity for poly(cyclohexene carbonate) formation without cocatalysts at 80 °C under various CO₂ pressures (2-30 bar). Importantly, the reactivity of the dinuclear indium chloride complex 4 is drastically different from that of the mononuclear indium chloride complex (±)-(NN_iO_tBu)InCl₂ (5), suggesting a cooperative initiation mechanism involving the two indium centers in 4.

Synthesis of 1,4-diketones via palladium/photo-cocatalyzed dehydrogenative cross-coupling

Herein we report a palladium/TBADT-cocatalyzed dehydrogenative cross-coupling reaction, enabling the synthesis of a variety of 1,4-diketones starting from simple allylic alcohols and aldehydes as the precursors under mild reaction conditions.

Titanium(IV)-Mediated Ring-Opening/Dehydroxylative Cross-Coupling of Diaryl-Substituted Methanols with Cyclopropanol Derivatives

A titanium(IV)-mediated ring-opening/dehydroxylative cross-coupling of diaryl-substituted methanols with a cyclopropanol derivative was developed. The reactions proceeded efficiently to provide synthetically useful γ,γ-diaryl esters in moderate to good yields, which could be applied to the functionalization of complex molecules derived from bioactive fenofibrate and isoxepac and the synthesis of a precursor of Zoloft.

Synthesis of Unsymmetrical 1,4-Dicarbonyl Compounds by Photocatalytic Oxidative Radical Additions

Herein we report a photocatalytic oxidative radical addition reaction for the synthesis of unsymmetrical 1,4-dicarbonyl compounds. This reaction utilizes a desulfurization process to generate electrophilic radicals, which add to α-halogenated alkenes and undergo further oxidation to deliver 1,4-dicarbonyl compounds. This mild and highly efficient method provides a valuable alternative to known strategies.

Copper-Catalyzed Three-Component Reactions of α-Ketoaldehyde, 1,3-Dicarbonyl Compound, and Organic Boronic Acid in Water: A Route to 1,4-Diketones

A novel three-component reaction of α-ketoaldehydes, 1,3-dicarbonyl compounds, and organic boronic acids catalyzed by CuO in water has been developed to give a wide range of products containing 1,3/1,4-diketones. The method has some advantages such as the use of readily available starting materials, wide substrate scopes, excellent yields, gram-scale synthesis, and mild reaction conditions.

Photochemical Synthesis of 1,4-Dicarbonyl Bifluorene Compounds via Oxidative Radical Coupling Using TEMPO as the Oxygen Atom Donor

A visible-light-induced metal-free synthesis of 1,4-dicarbonyl compounds from alkyne-containing aryl iodides via photochemical C-I bond cleavage, intramolecular cyclization, oxidation, and intermolecular radical coupling sequence is reported. TEMPO was employed as the oxygen atom donor in this transformation. This protocol provided a new strategy for the synthesis of 1,4-dicarbonyl bifluorene compounds.

Nickel-catalyzed reductive coupling of homoenolates and their higher homologues with unactivated alkyl bromides

The catalytic generation of homoenolates and their higher homologues has been a long-standing challenge. Like the generation of transition metal enolates, which have been used to great affect in synthesis and medicinal chemistries, homoenolates and their higher homologues have much potential, albeit largely unrealized. Herein, a nickel-catalyzed generation of homoenolates, and their higher homologues, via decarbonylation of readily available cyclic anhydrides has been developed. The utility of nickel-bound homoenolates and their higher homologues is demonstrated by cross-coupling with unactivated alkyl bromides, generating a diverse array of aliphatic acids. A broad range of functional groups is tolerated. Preliminary mechanistic studies demonstrate that: (1) oxidative addition of anhydrides by the catalyst is faster than oxidative addition of alkyl bromides; (2) nickel bound metallocycles are involved in this transformation and (3) the catalyst undergoes a single electron transfer (SET) process with the alkyl bromide.

Indium-mediated difunctionalization of iodoalkyl-tethered unactivated alkenes via an intramolecular cyclization and an ensuing palladium-catalyzed cross-coupling reaction with aryl halides

A cobalt-catalyzed, indium-mediated difunctionalization of iodoalkyl-tethered unactivated alkenes for accessing five-membered cyclic compounds via a cyclization/cross-coupling sequence was developed.

Photocatalytic Radical Aroylation of Unactivated Alkenes: Pathway to β-Functionalized 1,4-, 1,6-, and 1,7-Diketones

We report the development of a photocatalytic strategy for the synthesis of β-functionalized unsymmetrical 1,4-, 1-6 and 1,7-diketones from aroyl chlorides and unactivated alkenes at room temperature. The mild reaction conditions not only tolerate a wide range of functional groups and structural moieties, but also enable migration of a variety of distal groups including (hetero)arenes, nitrile, aldehyde, oxime-derivative, and alkene. The efficiency of chirality transfer, factors that control the distal-group migration, and synthesis of carbo- and heterocycles from the diketones are also described. Mechanistic studies suggest a reaction pathway involving a photocatalytic radical aroylation of unactivated alkenes followed by a distal-group migration, oxidation, and deprotonation to afford the desired diketones.

Iron(0)-Mediated Reformatsky Reaction for the Synthesis of β-Hydroxyl Carbonyl Compounds

An efficient, economical, and practical Reformatsky reaction of α-halo carbonyl compounds with aldehydes/ketones by using cheap and commercial iron(0) powder as reaction mediator is developed. The reactions proceeded effectively in the presence of a catalytic amount of iodine (20 mol %) to afford the synthetically useful β-hydroxyl carbonyl compounds in moderate to good yields.

Visible-light-induced consecutive C-C bond fragmentation and formation for the synthesis of elusive unsymmetric 1,8-dicarbonyl compounds

Synthesis of the valuable unsymmetric 1,8-dicarbonyl compounds remains underexplored currently. Herein, we disclose a new strategy for the synthesis of 1,8-diketones through the coupling of cyclopropanols and cyanohydrins under visible-light irradiation. The protocol features a cascade of intriguing ring opening of cyclopropanols and remote cyano migration. The unfavorable addition of an alkyl radical to an electron-rich alkene is facilitated by the intramolecular cyanohydrin interception. A variety of multiply functionalized 1,8-diketones are furnished in useful yields. The products could be further transformed into other valuable compounds, manifesting the utility of this method.

De novo synthesis of benzofurans via trifluoroacetic acid catalyzed cyclization/oxidative aromatization cascade reaction of 2-hydroxy-1,4-diones

A simple metal-free cyclization/oxidative aromatization reaction starting from 2-hydroxy-1,4-diones for the de novo synthesis of benzofurans was developed.

Metallic salt-catalyzed direct indium insertion into alkyl iodides and their applications in cross-coupling reactions

An efficient method for the synthesis of alkyl indium reagents via an indium(iii) or lead(ii) halide-catalyzed direct insertion of indium into alkyl iodides is developed. NMR and ESI-MS analyses indicated the formation of a mixture of an alkyl indium dihalide (RInX₂) and a dialkyl indium halide (R₂InX).

A general deoxygenation approach for synthesis of ketones from aromatic carboxylic acids and alkenes

The construction of an aryl ketone structural unit by means of catalytic carbon–carbon coupling reactions represents the state-of-the-art in organic chemistry. Herein we achieved the direct deoxygenative ketone synthesis in aqueous solution from readily available aromatic carboxylic acids and alkenes, affording structurally diverse ketones in moderate to good yields. Visible-light photoredox catalysis enables the direct deoxygenation of acids as acyl sources with triphenylphosphine and represents a distinct perspective on activation. The synthetic robustness is supported by the late-stage modification of several pharmaceutical compounds and complex molecules. This ketone synthetic strategy is further applied to the synthesis of the drug zolpidem in three steps with 50% total yield and a concise construction of cyclophane-braced 18–20 membered macrocycloketones. It represents not only the advancement for the streamlined synthesis of aromatic ketones from feedstock chemicals, but also a photoredox radical activation mode beyond the redox potential of carboxylic acids.

Synthesis of aryl ketones can be generally achieved via C–C coupling strategies. Here, the authors show a deoxygenative coupling of carboxylic acids and alkenes enabled by photoredox catalysis and report a wide scope of products, including bioactive and macrocyclic ketones.

Cross-coupling of dissimilar ketone enolates via enolonium species to afford non-symmetrical 1,4-diketones

Due to their closely matched reactivity, the coupling of two dissimilar ketone enolates to form a 1,4-diketone remains a challenge in organic synthesis. We herein report that umpolung of a ketone trimethylsilyl enol ether (1 equiv) to form a discrete enolonium species, followed by addition of as little as 1.2–1.4 equivalents of a second trimethylsilyl enol ether, provides an attractive solution to this problem. A wide array of enolates may be used to form the 1,4-diketone products in 38 to 74% yield. Due to the use of two TMS enol ethers as precursors, an optimization of the cross-coupling should include investigating the order of addition.