Diazo Reagents Research Articles

Chemo- and diastereoselective four-component reactions with Rh carbynoids

Multi-component reactions (MCRs) provide an efficient method for constructing multiple chemical bonds by combining three or more starting materials in a single operational step, enabling rapid and cost-effective synthesis of structurally diverse compounds. Although carbynoids (R-C:+) have shown potential for the development of selective MCRs due to their unique carbene and carbocation characteristics, their application in four-component reactions (4CRs) has been constrained by challenges in chemoselectivity. Herein, we provide a general solution to the challenges of chemoselective 4CR, using halo diazo reagents as carbynoid precursors, followed by reacting with pyrazoles, alcohols and imines sequentially. This approach allows the simultaneous construction of three different C(sp3)-N, C(sp3)-O, and C(sp3)-C(sp3) bonds on the same carbon. The success of this protocol mainly depends on precise control of chemical kinetics. Detailed experimental studies elucidate that the generation rate of aza-Rh(II)-carbene is faster than oxy-Rh(II)-carbene.

5-Diazo Dihydrouracils: Preparation and Some Transformations.

An approach to a new type of diazo reagents─diazo dihydrouracils─has been developed, and various transformations of the obtained diazo heterocycles have been studied, demonstrating their high synthetic potential for obtaining structurally diverse derivatives based on the privileged dihydrouracil scaffold. The X-H insertion reactions provide high yields of a variety of 5-substituted dihydrouracils. Cyclopropanation and 1,3-dipolar cycloaddition reactions involving a carbonyl ylide intermediate have been carried out to give spiro-annulated derivatives. The limitations of the modification methods with respect to the nature of substituents on the nitrogen atoms of the diazo heterocycle have been outlined.

Modular Synthesis of Azines Bearing a Guanidine Core from N-Heterocyclic Carbene (NHC)-Derived Selenoureas and Diazo Reagents.

N-Heterocyclic carbene (NHC)-derived selenoureas comprise a fundamentally important class of NHC derivatives, with key applications in coordination chemistry and the determination of NHC electronic properties. Considering the broad reactivity of chalcogen-containing compounds, it is surprising to note that the use of NHC-derived selenoureas as organic synthons remains essentially unexplored. The present contribution introduces a novel, straightforward transformation leading to azines bearing a guanidine moiety, through the reaction of a wide range of NHC-derived selenoureas with commercially available diazo compounds, in the presence of triphenylphosphine. This transformation offers a new approach to such products, having biological, materials chemistry, and organic synthesis applications. The guanidine-bearing azines are obtained in excellent yields, with all manipulations taking place in air. A reaction mechanism is proposed, based on both experimental mechanistic findings and density functional theory (DFT) calculations. A one-pot, multicomponent transesterification reaction between selenoureas, α-diazoesters, alcohols, and triphenylphosphine was also developed, providing highly functionalized azines.

Regioselective Synthesis of Multisubstituted Fluoropyrazoles via Silver‐Catalyzed One‐Pot Cyclization Reaction of Diazo Reagents with Fluoronitroalkenes

AbstractA silver‐catalyzed regioselective one‐pot cyclization reaction of diazo reagents with fluoronitroalkenes was developed. This transformation presents a method for accessing a series of 4‐aryl‐3‐fluoropyrazoles that are substituted with various groups such as trifluoromethyl, carboxylic ester, nitrile, and phosphonate ester. Further synthetic transformations offered the corresponding fluorinated and trifluoromethylated analogues of two fungicide compounds.

Pd‐Catalyzed [3+6+3+6] Macrocyclizations of Aryl α‐Diazo‐β‐Ketoesters

AbstractThanks to Pd(II)‐catalysis, an efficient synthesis of unsaturated macrocycles is achieved by [3+6+3+6] condensation of cyclic ethers with aryl α‐diazo‐β‐ketoesters. The presence of the electron‐rich aryl ester moieties forbids the use of dirhodium complexes as these diazo decomposition catalysts provoke unforeseen intermolecular Csp2−H insertion reactions that derail the targeted reactivity. However, with Pd(acac)2, using high concentration conditions (1 M), a variety of 18‐membered macrocycles (16 examples) is afforded with both aryl and alkyl diazo reagents. Catalyst selection for either electrophilic aromatic substitution (Rh) or ylide (Pd) pathways are explained by computational approaches.

Unique Reactivity of Triazolyl Diazoacetates under Photochemical Conditions.

Under light irradiation, aryldiazo acetates can generate either singlet or triplet carbenes depending on the reaction conditions, but heteroaryl diazo compounds have remained underexplored in this context. Herein, we found that triazolyl diazoacetates exhibit higher reactivity than their aryl counterparts. They even react with dichloromethane (DCM), a common, inert solvent, for photoreactions involving diazo reagents, giving halogenated products. Theoretical studies show that all reactions involve carbenes but progress via different pathways depending on the solvent used.

Photo-cycloaddition reactions of vinyldiazo compounds

Heterocyclic rings are important structural scaffolds encountered in both natural and synthetic compounds, and their biological activity often depends on these motifs. They are predominantly accessible via cycloaddition reactions, realized by either thermal, photochemical, or catalytic means. Various starting materials are utilized for this purpose, and, among them, diazo compounds are often encountered, especially vinyldiazo compounds that give access to donor-acceptor cyclopropenes which engage in [2+n] cycloaddition reactions. Herein, we describe the development of photochemical processes that produce diverse heterocyclic scaffolds from multisubstituted oximidovinyldiazo compounds. High chemoselectivity, good functional group tolerance, and excellent scalability characterize this methodology, thus predisposing it for broader applications. Experimental and computational studies reveal that under light irradiation these diazo reagents selectively transform into cyclopropenes which engage in cycloaddition reactions with various dipoles, while under thermal conditions the formation of pyrazole from vinyldiazo compounds is favored.

Iron(II) Phthalocyanine-Catalyzed Homodimerization and Tandem Diamination of Diazo Compounds with Primary Amines: Access to Construct Substituted 2,3-Diaminosuccinonitriles in One-Pot.

We herein first report the homodimerization and tandem diamination of diazo compounds with primary amines catalyzed by the iron(II) phthalocyanine (PcFe(II)), which can construct one C-C bond and two C-N bonds within 20 min in one-pot. Compared to the traditional metal-catalyzed N-H insertion reaction between amines with diazo reagents, the developed reaction almost does not generate the N-H insertion product, but the homodimerization/tandem diamination product. The proposed mechanism studies indicate that primary amines play a crucial role in the homocoupling of diazo compounds via dimerization of iron(III)-acetonitrile radical generated from the reaction between diazoacetonitrile with PcFe(II) coordinated by bis(amines); the β-hydride elimination is involved, and then, the attack of primary amines toward the carbon atoms on the formed C-C bond is followed. Moreover, this novel reaction can be used to effectively prepare substituted 2,3-diaminosuccinonitriles with high yields and even up to >99:1 d.r., encouragingly these products contain both 1,2-diamines and succinonitrile motifs, which are two classes of important organic compounds with significant applications in many yields. This reaction is also suitable for the gram-scale preparation of 2,3-bis(phenylamino)succinonitrile (2a) with a yield of 84%. Therefore, the developed reaction represents a new type of transformation.

Selective Synthesis of Tetrahydro Oxepines by Cu‐Catalyzed Condensations of Diazomalonates and gem‐Dialkyl Vinyl Oxetanes

AbstractThanks to an unprecedented gem‐dialkyl substituent effect, an efficient synthesis of tetrahydro oxepine derivatives is achieved by ring expansion of vinyl oxetanes using acceptor(−acceptor) diazo reagents under Cu(II)‐catalysis. A large scope of 2‐vinyl oxetanes and either diazo mono or diester reagents give access to a series of functionalized oxepines.

Synthesis of Hypervalent Iodine Diazo Compounds and Their Application in Organic Synthesis.

Diazomethyl-substituted iodine(III) compounds with electron-withdrawing groups (EWG) connected to diazo methyl center were a type of donor-acceptor diazo compounds with potential reaction abilities similar to ordinary diazo compounds. Although several diazomethyl-substituted iodine(III) compounds were synthesized and used in the nucleophilic substitution reactions as early as 1994, the synthesis and application of new iodine(III) diazo compounds have only been reported to a certain extent in recent years. In the presence of rhodium catalyst, photocatalyst, or nucleophiles, diazomethyl-substituted iodine(III) compounds can be converted into rhodium-carbenes, diazomethyl radicals, ester radicals or nucleophilic intermediates, which can be used as key intermediates for the formation of chemical bonds. The aim of this review is to give an overview of diazomethyl-substituted iodine(III) compounds in organic synthesis.

Regioselective [3 + 2] cycloaddition of diazo reagents and internal alkynes: Accessing regiosomers of highly substituted trifluoromethylpyrazoles

We herein descript a metal-free and highly regioselective [3 + 2] cycloaddition reaction between diazo compounds and internal alkynes, accessing to a series of trifluoromethylated pyrazoles. Using different combination of starting materails, both regioisomers can be obtained under this protocal. The developed cycloaddition reaction provides a valuable tool for future medicinal chemistry research on highly substituted trifluoromethyl pyrazoles.

New, Scalable Process for the Preparation of 5-Acetyl-1H-pyrazole-3-carboxylic Acid, a Key Intermediate of Darolutamide

AbstractA new, efficient process for the synthesis of 5-acetyl-1H-pyrazole-3-carboxylic acid, a versatile building block and the key intermediate of darolutamide, using diethyl pyrazole-3,5-dicarboxylate as the starting material is described. Contrary to the synthetic routes known from the literature, this procedure does not employ explosive diazo reagents, moreover it is simple and safe, thereby suitable for scale-up.

Photoredox-Catalyzed Cascade sp2 C-H Bond Functionalization to Construct Substituted Acridine with Diarylamine and Hypervalent Iodine(III) Reagents.

A photocatalyzed cascade double C-C formation via sp2 C-H bond activation of diarylamines with hypervalent iodine diazo reagents was developed. A variety of diarylamines and hypervalent iodine(III) reagents were tolerated well, and a range of substituted acridines with yields ranging from moderate to excellent was provided efficiently. The protocol introduces diazo groups onto diarylamines and enables subsequent late-stage assembly point functionalization with the diazonium structure, forming two new C-C bonds in a sequential fashion.

Cobalt-catalyzed esterification-peroxidation of α-diazoesters: access to α-acyloxy esters

A cobalt-catalyzed three-component reaction of carboxylic acids, diazo reagents andtert-butyl hydroperoxide was realized, which afforded a straightforward synthesis of α-acyloxy esters in good yields.

Carbene-Controlled Regioselective Functionalization of Linear Alkanes under Silver Catalysis.

Control of the regioselectivity in the functionalization of C-H bonds of linear alkanes C2H2n+2 via carbene transfer from diazo compounds is restricted to the use of rhodium-based catalysts, which govern the reaction outcome employing donor-acceptor diazo reagents. At variance with that catalyst-controlled strategy, we present an alternative approach in which employing the appropriate silver complexes containing trispyrazolylborate ligands as catalysts with large differences in their steric and electronic properties, the regioselection is mainly governed by the diazo reagent, which leads to the functionalization of primary or secondary sites of linear alkanes (lacking any activating or directing groups). Donor-acceptor aryl diazoacetates exclusively provide the functionalization of the secondary sites of hexane or pentane, whereas acceptor ethyl diazoacetate leads to an unprecedented level of primary functionalization.

Expanding the Strain‐Promoted 1,3‐Dipolar Cycloaddition Arsenal for a More Selective Bioorthogonal Labeling in Living Cells

AbstractThe advent of bioorthogonal chemistry, more importantly the strain‐promoted 1,3‐dipolar cycloaddition of cyclooctynes with azides to give stable triazoles, has opened new avenues for the study of biomolecules in their native environment. While much effort has been focused on improving the kinetics of these reactions, very little attention has been given to their bioselectivity. In this review, we will take you on our journey that led us to develop new cyclooctyne probes with enhanced physical attributes, including water solubility, cell‐surface labeling selectivity and fluorogenic capabilities. We then went on to expand the bioorthogonal chemistry toolbox by focusing on the development of new chemical reporters. Here you will read about our work investigating the use of other 1,3‐dipoles, including nitrile oxides and diazo reagents, for the labeling of biomolecules, and more recently highly biostable sydnones that can be exploited to selectively influence glycan‐processing enzymes.

Radical Reactions Enabled By Porphyrinoids

“ Look deep into nature , and then you will understand everything better.” Albert Einstein Porphyrinoids, also known as the pigments of life, are a class of naturally occurring organic dyes. They play key roles in crucial processes that support life - oxygen transport (hem), electron transport (cytochrome c), photosynthesis (chlorophyll a), and synthesis of DNA (vitamin B12). Vitamin B12 - a co-factor in many catalytic processes. Following nature, we have been exploiting the potential of this compound in catalysis.Vitamin B12 - catalysis has been successfully translated into the laboratory and used in a small collection of reactions.[1-2] The advantage of using vitamin B12 as a catalyst lays in the complete stability of the central cobalt ion and by the definition it is nontoxic. It has also been well documented that the reaction mechanism usually follows a radical pathway, bringing a new dimension to this already interesting field.[2] Along this line, we have developed new vitamin B12-catalyzed reactions involving reduction of Co(III) to Co(I) or Co(II) and subsequent reactions with electrophiles or radicals. Vitamin B12 derivative unusually catalyzes a new olefinic sp2 C-H alkylation reaction with diazo reagents as a carbene source,[3], acylation of activated olefins, alkylation of strained molecules.[4-6] These key findings emphasize the unique feature of vitamin B12 as a catalyst to achieve something unachievable with other methodologies or to find a greener approach.

Catalytic Asymmetric Syntheses of Alkylidenecyclopropanes from Allenoates with Donor-Acceptor and Diacceptor Diazo Reagents.

The first diastereo- and enantioselective cyclopropanation reactions of electron-deficient allenes with donor-acceptor and diacceptor diazo reagents are described. The desired enantioenriched alkylidenecyclopropanes (ACPs) were obtained in high yields with high diastereo- and enantioselectivities in the presence of Rh2 ((S)-TCPTAD)4 or Rh2 ((R)-BTPCP)4 catalysts (up to 95 % yield, >95 : 5 d.r. and 99 : 1 e.r.). This methodology gave a direct access to ACPs bearing multiple electron-deficient substituents and allows to further expand the availability of ACPs chemistry. Interestingly, during the examination of the scope of this reaction, the asymmetric intramolecular C-H insertion reaction into tert-butyl group was observed as a side reaction with up to 94 : 6 e.r.

Catalytic Enantioselective Synthesis of Functionalized Cyclopropanes from α-Substituted Allyl Sulfones with Donor-Acceptor or Diacceptor Diazo Reagents.

The catalytic asymmetric synthesis of highly functionalized cyclopropanes from α-substituted allyl sulfones and silanes is reported. The reaction, using α-aryl diazoacetates or diacceptor diazo reagents, catalyzed by a chiral rhodium complex (Rh2 ((S)-BTPCP)4 ), furnished the corresponding cyclopropanes in moderate to high yields (27-97 %), high diastereoselectivities (68 : 32 to 20 : 1 d.r.) and moderate to excellent ee (40-99 %). This methodology offers a privileged access to an underexplored class of enantioenriched cyclopropanes with a high level of functionality, an asset for further post-functionalization and their incorporation into more complex structure.

Modular Synthesis of Cyclopropane-Fused N-Heterocycles Enabled by Underexplored Diazo Reagents.

Cyclopropane-fused N-heterocycles are featured in various biologically active compounds and represent attractive scaffolds in medicinal chemistry. However, synthesis routes to access structurally and functionally diverse cyclopropane-fused N-heterocycles remain underexplored. Leveraging novel α-diazo acylating agents, we report a general approach for the direct and modular synthesis of cyclopropane-fused lactams from unsaturated amines. The operationally simple transformation, which proceeds through successive acylation, (3+2) cycloaddition and fragmentation, tolerates a broad range of functional groups and yields a wide spectrum of complex molecular scaffolds, including fused, bridged and spiro ring systems. We demonstrate the utility of this transformation in the concise syntheses of therapeutic agents milnaciprane and amitifadine.