1,3-Dipolar Cycloaddition of Nitrile Imine with Carbon Dioxide: Access to 1,3,4-Oxadiazole-2(3H)-ones

Research Progress on the Reaction of Carbon Dioxide with Hydrazones and Their Derivatives

CO2, an abundant and renewable C1 source, presents significant potential for applications in organic synthesis. Hydrazones, recognized for their distinctive properties, exhibit high versatility in synthetic chemistry, facilitating numerous chemical transformations. Given their crucial roles in organic synthesis, the combination of CO2 with hydrazones has garnered increasing research interest. This review provides a comprehensive summary of recent progress in reactions involving CO2 and hydrazones or their derivatives. These include the coupling of amines and N-tosylhydrazones with CO2, the umpolung-mediated carboxylation of hydrazones/N-tosylhydrazones with CO2, the cyclization of hydrazones with CO2, and lactamization reactions incorporating N-tosylhydrazones and CO2. These transformations utilize the diverse reactivity of hydrazones and their derivatives to capture and convert CO2, generating valuable organic compounds with both academic and practical relevance. Additionally, the review examines the mechanisms underlying these reactions, offering critical insights for advancing research in this area.

Silver-mediated formal [4π + 2σ] cycloaddition reactions of bicyclobutanes with nitrile imines: access to 2,3-diazobicyclo[3.1.1]heptenes

Despite recent advances in the synthesis of aza-bicyclo[3.1.1]heptanes (aza-BCHeps, which have an sp3-hybridized nitrogen atom) and azabicyclo[3.1.1]heptenes (aza-BCHepes, which have an sp2-hybridized nitrogen atom), which are bioisosteres of pyridine, construction of 2,3-diazobicyclo[3.1.1]heptenes (2,3-diazo-BCHepes), which have both sp2- and sp3-hybridized nitrogen atoms, has yet to be achieved. Herein, we disclose a method for silver-enabled formal [4π + 2σ] cycloaddition reactions between bicyclobutanes and nitrile imines (generated from hydrazonyl chlorides) to furnish a diverse array of 2,3-diazo-BCHepes, which feature both sp2- and sp3-hybridized nitrogen atoms embedded in a BCHepe framework. These compounds have the potential to serve as bioisosteres of both pyridines and pyridazines. Owing to the presence of the sp3-hybridized nitrogen, 2,3-diazo-BCHepes can be expected to exhibit geometries similar to those of aza-BCHepes and much better solubility. We demonstrated the synthetic utility of our method by carrying out a scaled-up reaction and diverse postcatalytic transformations.

Silane-promoted cycloaddition of thiobenzhydrazides with carbon dioxide toward 1,3,4-thiadiazol-2(3H)-ones

Herein, we developed a silane-promoted cycloaddition of thiobenzhydrazides with carbon dioxide leading to 1,3,4-thiadiazol-2(3H)-ones. This procedure involves sequential N-silylation and fixation of carbon dioxide toward a hydrazine formyl intermediate, followed by intramolecular nucleophilic cyclization and aromatization. A series of functional groups are well-tolerated under this procedure. As such, it represents a facile and efficient pathway for utilizing carbon dioxide in the construction of value-added heterocyclic frameworks.

Copper-Catalyzed Oxidative Synthesis of 3-Aryl-5-fluoroalkyl-1,3,4-oxadiazol-2(3H)-ones Using Perfluorocarboxylic Anhydride as a Reagent

A copper-catalyzed oxidative annulation of sydnones with perfluorocarboxylic anhydride for the synthesis of 3-aryl-5-fluoroalkyl-1,3,4-oxadiazol-2(3H)-ones is developed. A diverse array of 3-aryl-5-fluoroalkyl-1,3,4-oxadiazol-2(3H)-ones are prepared with good yields (>73 examples, yields up to 95%). The synthetic utility of the developed protocol was demonstrated by gram-scale synthesis, and the synthetic transformation to 1,2,4-triazol-3-one products. A mechanistic study suggests that the reaction proceeds via the extrusion of carbon dioxide to generate the hydrazide intermediate, which then undergoes intramolecular cyclization and oxidation.

Eco-friendly approaches to 1,3,4-oxadiazole derivatives: A comprehensive review of green synthetic strategies

This review article offers an environmentally benign synthesis of 1,3,4-oxadiazole derivatives, with a focus on sustainable methodologies that have minimal impact on the environment. These derivatives, known for their diverse applications, have conventionally been associated with synthesis methods that utilize hazardous reagents and produce significant waste, thereby raising environmental concerns. The green synthesis of 1,3,4-oxadiazole derivatives employs renewable substrates, nontoxic catalysts, and mild reaction conditions, aiming to minimize the environmental impact. Innovative techniques such as catalyst-based, catalyst-free, electrochemical synthesis, green-solvent-mediated synthesis, grinding, microwave-mediated synthesis, and photosynthesis are implemented, providing benefits in terms of scalability, cost-effectiveness, and ease of purification. This review emphasizes the significance of sustainable methodologies in the synthesis of 1,3,4-oxadiazole and boots for continued exploration in this research domain.

Nitrile Imines as Peptide and Oligonucleotide Photo-Cross-Linkers in Gas-Phase Ions

Nitrile imines produced by photodissociation of 2,5-diaryltetrazoles undergo cross-linking reactions with amide groups in peptide-tetrazole (tet-peptide) conjugates and a tet-peptide-dinucleotide complex. Tetrazole photodissociation in gas-phase ions is efficient, achieving ca. 50% conversion with 2 laser pulses at 250 nm. The formation of cross-links was detected by CID-MS3 that showed structure-significant dissociations by loss of side-chain groups and internal peptide segments. The structure and composition of cross-linking products were established by a combination of UV-vis action spectroscopy and cyclic ion mobility mass spectrometry (c-IMS). The experimental absorption bands were found to match the bands calculated for vibronic absorption spectra of nitrile imines and cross-linked hydrazone isomers. The calculated collision cross sections (CCSth) for these ions were related to the matching experimental CCSexp from multipass c-IMS measurements. Loss of N2 from tet-peptide conjugates was calculated to be a mildly endothermic reaction with ΔH0 = 80 kJ mol-1 in the gas phase. The excess energy in the photolytically formed nitrile imine is thought to drive endothermic proton transfer, followed by exothermic cyclization to a sterically accessible peptide amide group. The exothermic nitrile imine reaction with peptide amides is promoted by proton transfer and may involve an initial [3 + 2] cycloaddition followed by cleavage of the oxadiazole intermediate. Nucleophilic groups, such as cysteine thiol, did not compete with the amide cyclization. Nitrile imine cross-linking to 2'-deoxycytidylguanosine was found to be >80% efficient and highly specific in targeting guanine. The further potential for exploring nitrile-imine cross-linking for biomolecular structure analysis is discussed.

Synthesis and Reactivity of a Zinc Diazoalkyl Complex: [3+2] Cycloaddition Reaction with Carbon Monoxide

This work reports the synthesis, characterization, and reactivity of the first example of a well-defined zinc α-diazoalkyl complex. Treatment of zinc(I)-zinc(I) bonded compound L2 Zn2 [L=CH3 C(2,6-i Pr2 C6 H3 N)CHC(CH3 )(NCH2 CH2 PPh2 )] or zinc(II) hydride LZnH with trimethylsilyldiazomethane affords zinc diazoalkyl complex LZnC(N2 )SiMe3 . This complex liberates N2 in the presence of a nickel catalyst to form an α-zincated phosphorus ylide by reacting with the pendant phosphine. It selectively undergoes formal [3+2] cycloaddition with CO2 or CO to form the corresponding product with a five-membered heterocyclic core. Notably, the use of CO in such a [3+2] cycloaddition reaction is unprecedented, reflecting a novel CO reaction mode.

Amide Bond Formation via the Rearrangement of Nitrile Imines Derived from N-2-Nitrophenyl Hydrazonyl Bromides

We report how the rearrangement of highly reactive nitrile imines derived from N-2-nitrophenyl hydrazonyl bromides can be harnessed for the facile construction of amide bonds. This amidation reaction was found to be widely applicable to the synthesis of primary, secondary, and tertiary amides and was used as the key step in the synthesis of the lipid-lowering agent bezafibrate. The orthogonality and functional group tolerance of this approach was exemplified by the N-acylation of unprotected amino acids.

Synthesis of spiro[4.4]thiadiazole derivatives via double 1,3-dipolar cycloaddition of hydrazonyl chlorides with carbon disulfide

An operationally simple and convenient synthesis method toward a series of diverse spiro[4.4]thiadiazole derivatives via double [3 + 2] 1,3-dipolar cycloaddition of nitrilimines generated in situ from hydrazonyl chlorides with carbon disulfide has been achieved under mild reaction conditions.

Synthesis of 3H-1,2,4-Triazol-3-ones via NiCl2-Promoted Cascade Annulation of Hydrazonoyl Chlorides and Sodium Cyanate

A nickel-promoted cascade annulation reaction for the facile synthesis of 3H-1,2,4-triazol-3-ones from readily available hydrazonoyl chlorides and sodium cyanate has been developed. The transformation occurs through a cascade nickel-promoted intermolecular nucleophilic addition-elimination process, intramolecular nucleophilic addition, and a hydrogen-transfer sequence. The method has been successfully applied for the construction of the core skeleton of the angiotensin II antagonist.

How the Lewis Base F- Catalyzes the 1,3-Dipolar Cycloaddition between Carbon Dioxide and Nitrilimines

The mechanism of the Lewis base F- catalyzed 1,3-dipolar cycloaddition between CO2 and nitrilimines is interrogated using DFT calculations. F- activates the nitrilimine, not CO2 as proposed in the literature, and imparts a significant rate enhancement for the cycloaddition. The origin of this catalysis is in the strength of the primary orbital interactions between the reactants. The Lewis base activated nitrilimine-F- has high-lying filled FMOs. The smaller FMO-LUMO gap promotes a rapid nucleophilic attack and overall cycloaddition with CO2.

Palladium-Catalyzed Cascade Carbonylative Synthesis of 1,2,4-Triazol-3-ones from Hydrazonoyl Chlorides and NaN3

A palladium-catalyzed three-component carbonylative reaction for the synthesis of 3H-1,2,4-triazol-3-ones from hydrazonoyl chlorides and NaN₃ has been achieved. The reaction presumably proceeds through a cascade carbonylation, acyl azide formation, Curtius rearrangement, and intramolecular nucleophilic addition sequence. A wide variety of structurally diverse 3H-1,2,4-triazol-3-ones were constructed in moderate to excellent yields. Benzene-1,3,5-triyl triformate (TFBen) was applied as a solid and convenient CO surrogate.

Understanding the 1,3-Dipolar Cycloadditions of Allenes

We have quantum chemically studied the reactivity, site-, and regioselectivity of the 1,3-dipolar cycloaddition between methyl azide and various allenes, including the archetypal allene propadiene, heteroallenes, and cyclic allenes, by using density functional theory (DFT). The 1,3-dipolar cycloaddition reactivity of linear (hetero)allenes decreases as the number of heteroatoms in the allene increases, and formation of the 1,5-adduct is, in all cases, favored over the 1,4-adduct. Both effects find their origin in the strength of the primary orbital interactions. The cycloaddition reactivity of cyclic allenes was also investigated, and the increased predistortion of allenes, that results upon cyclization, leads to systematically lower activation barriers not due to the expected variations in the strain energy, but instead from the differences in the interaction energy. The geometric predistortion of cyclic allenes enhances the reactivity compared to linear allenes through a unique mechanism that involves a smaller HOMO-LUMO gap, which manifests as more stabilizing orbital interactions.

A synthesis of N-(1H-pyrazol-5-yl)-1,3,4-thiadiazol-2(3H)-imines from nitrile imines and Erlenmeyer thioazlactones

Erlenmeyer thioazlactones are reacted with hydrazonoyl chlorides in the presence of Et₃N to afford functionalized N-(1H-pyrazol-5-yl)-1,3,4-thiadiazol-2(3H)-imines in excellent yields. This strategy is based on a domino double 1,3-dipolar cycloaddition reaction of nitrile imines to Erlenmeyer thioazlactones, followed by the elimination of carbon monoxide and phenylmethanthiol from the initially formed cycloadducts. This method provides fast access to a variety of structurally diverse N-(1H-pyrazol-5-yl)-1,3,4-thiadiazol-2(3H)-imines. The structure of a typical product was established by X-ray crystallography.

One-pot synthesis of 1,3,4-oxadiazol-2(3H)-ones with CO2 as a C1 synthon promoted by hypoiodite

A convenient and efficient route has been developed to synthesize 1,3,4-oxadiazol-2(3H)-ones from CO₂, hydrazines and aryl or aliphatic aldehydes. Promoted by hypoiodite (IO^-) generated in situ from KI and oxidant TBHP, the one-pot synthesis could proceed smoothly to afford the desired products in moderate to high yields. Mechanism studies revealed that nitrile imine was an important intermediate in this transformation. Notably, a commercial herbicide Oxadiazon could be successfully synthesized by this route.

Recent Advances in the Chemical Fixation of Carbon Dioxide: A Green Route to Carbonylated Heterocycle Synthesis

Carbon dioxide produced by human activities is one of the main contributions responsible for the greenhouse effect, which is modifying the Earth’s climate. Therefore, post-combustion CO2 capture and its conversion into high value-added chemicals are integral parts of today’s green industry. On the other hand, carbon dioxide is a ubiquitous, cheap, abundant, non-toxic, non-flammable and renewable C1 source. Among CO2 usages, this review aims to summarize and discuss the advances in the reaction of CO2, in the synthesis of cyclic carbonates, carbamates, and ureas appeared in the literature since 2017.

[3 + 2] Cycloaddition of para-Quinone Methides with Nitrile Imines: Approach to Spiro-pyrazoline-cyclohexadienones

[3 + 2] cycloaddition of para-quinone methides with nitrile imines under mild conditions has been achieved. The corresponding spiro-pyrazoline-cyclohexadienone products were constructed in good to excellent yields (up to 97% yield) with high regioselectivity. This straightforward protocol exhibits good functional group tolerance and scalability and provides the spiro-pyrazoline-cyclohexadienones.

Direct Carboxylation of Electron-Rich Heteroarenes Promoted by LiO-tBu with CsF and [18]Crown-6

We herein demonstrate that the combination of LiO-tBu, CsF, and [18]crown-6 efficiently promotes the direct C-H carboxylation of electron-rich heteroarenes (benzothiophene, thiophene, benzofuran, and furan derivatives). A variety of functional groups, including methyl, methoxy, halo, cyano, amide, and keto moieties, are compatible with this system. The reaction proceeds via the formation of a tert-butyl carbonate species.

1,3-Dipolar cycloaddition of nitrones to oxa(aza)bicyclic alkenes

A new 1,3-dipolar cycloaddition of oxa(aza)bicyclic alkenes with nitrones has been developed without any catalyst and additive under mild conditions. The proposed concerted mechanism is investigated by DFT calculations of the reaction pathways.

KI-catalyzed reactions of aryl hydrazines with α-oxocarboxylic acids in the presence of CO2: access to 1,3,4-oxadiazol-2(3H)-ones

A novel KI-catalyzed synthesis of 1,3,4-oxadiazol-2(3H)-ones from aryl hydrazines, α-oxocarboxylic acids and CO₂ was reported.

Recent advances in nucleophile-triggered CO2-incorporated cyclization leading to heterocycles

CO₂, as a sustainable, feasible, abundant one-carbon synthon, has been utilized in carboxylative cyclization, carbonylative cyclization, and reductive cyclization.

A metal-free and mild approach to 1,3,4-oxadiazol-2(3H)-ones via oxidative C–C bond cleavage using molecular oxygen

A metal-free aerobic oxidative C–C bond cleavage reaction for the synthesis of 1,3,4-oxadiazol-2(3H)-ones is described.

1,3-Dipolar [3 + 3] cycloaddition of α-halohydroxamate-based azaoxyallyl cations with hydrazonoyl chloride-derived nitrile imines

Promoted by Et₃N, the 1,3-dipolar [3 + 3] cycloaddition of α-halohydroxamate-based azaoxyallylcations with hydrazonoyl chloride-derived nitrile imines occurred efficiently, and furnished desired products in acceptable chemical yields.