Azide Source Research Articles

Electrochemical C-H Azidation and Diazidation of Anilines for the Synthesis of Aryl Azides and Diazides.

The increasing importance and need in many aspects have driven the rapid development of synthetic studies toward aryl azides. In this paper, electrochemical C-H azidation and diazidation of anilines have been developed using TMSN3 as an azide source. A range of functional groups can be tolerated under the optimized reaction conditions.

Azidoindolines—From Synthesis to Application: A Review

Azide-containing compounds, organic azides, showcases a variety of reactivities, making them highly convenient and chameleonic intermediates. An indoline derivative has been proven to be of great significance in drug discovery due to its sp3-rich property. In this context, it is interesting to perform such vigorous azidation on medicinal-relevant indoles/indolines, resulting in the production of sp3-rich azidoindolines. The potential biological activity, in combination with the sp3-rich indoline bearing the azido moiety, makes azidoindolines an attractive synthetic target for medicinal and synthetic chemists. This review describes recent advances in the synthesis and application of azidoindolines: (1) iodine-mediated azidations, (2) metal-catalyzed azidations, (3) electrochemical azidations, (4) photochemical azidations, (5) azidation using a combination of an oxidant and an azide source, and (6) nucleophilic azidation.

Palladium‐Catalyzed/Mn(OAc)3‐Mediated 1,2‐Diazidation and 1,2‐Acetoxy/Hydroxylation of N‐Allyl Sulfonamides

AbstractPalladium‐catalyzed conditions for diazidation or acetoxy/hydroxylation of N‐allyl sulfonamides by using Pd(OAc)2 as the catalyst combined with Mn(OAc)3 ⋅ 2H2O have been developed. The 1,2‐diazidation reaction of the carbon‐carbon double bond occurs in mild conditions (i. e. NaN3 as azide source in THF at room temperature), whereas the 1,2‐acetoxy/hydroxylation requires an excess of Mn(OAc)3 ⋅ 2H2O. The well‐known ability of this reagent to act through single‐electron transfer (SET) makes plausible a radical mechanism involving high valent palladium complexes.

Benzylic C(sp3)−H Azidation: Copper vs Iron Catalysis

AbstractThe generation of benzylic radicals through hydrogen atom abstraction (HAT) has been a recent research focus and various C(sp3)−H bond functionalization protocols have been developed relying on this elementary step. We report herein copper‐ and iron‐catalyzed C(sp3)−H benzylic azidation reactions using mCPBA and NFSI as oxidant, respectively, and TMSN3 as azide source. The reaction is thought to be initiated via intermolecular abstraction of benzylic hydrogen by the in situ generated heteroatom‐centered radicals. The Fe(OTf)3‐catalyzed azidation protocol displays good chemoselectivity as it takes place preferentially at the secondary and tertiary benzylic C(sp3)−H bonds over the primary benzylic and tertiary aliphatic carbons. Efforts on the development of catalytic enantioselective processes are also documented.

Simple, catalytic C(sp3)-H azidation using the C-H donor as the limiting reagent.

C-N bonds play a critical role in pharmaceutical, agrochemical, and materials sciences, necessitating ever-better methods to forge this linkage. Here we report a simple procedure for direct C(sp3)-H azidation using iron or manganese catalysis and a nucleophilic azide source. All reagents are commercially available, the experimental procedure is simple, and we can use the C-H donor substrate as the limiting reagent, a challenge for many C-H azidation methods. Preliminary experiments are consistent with a hydrogen atom transfer (HAT)/radical ligand transfer (RLT) radical cascade mechanism and a wide variety of substrates can be azidated in moderate to high yields.

Iron-Catalyzed Synthesis of α-Azido α-Amino Esters via the Alkylazidation of Alkenes.

An iron-catalyzed alkylazidation of dehydroamino acids using peroxides as alkyl radical precursors is described. Non-natural azidated amino esters bearing an α-alkyl chain could be obtained in 18-94% yields using TMSN3 as an azide source. The obtained α-alkyl-α-azide α-amino esters could be further functionalized through cycloaddition or azide reduction with amide couplings to afford aminal-type peptides, α-triazolo amino acids, and tetrahydro-triazolopyridine, showing the great versatility of this now easily accessible class of amino acids.

Synthesis of Quinoxalines through Cu-electrocatalytic Azidation/Annulation Cascade at Low Catalyst Loading.

A Cu-electrocatalytic azidation of N-aryl enamines and subsequent denitrogenative annulation for the construction of quinoxaline frameworks is reported. Only 0.5 mol % of copper(II) chloride was employed for this cascade transformation displaying excellent functional-group compatibility even with complex bioactive scaffolds. The efficient electro-oxidative protocol enables the use of NaN3 as the cheapest azide source. Detailed mechanistic experiments, cyclic voltammetry, and spectroscopic studies provided strong evidence for a dual role of the Cu catalyst in azidyl and iminyl radical generation steps.

Azido-difluoromethylthiolation of Alkenes with TMSN3 and PhSO2SCF2H.

An oxidative azido-difluoromethylthiolation of alkenes by employing TMSN3 as the azide source and PhSO2SCF2H as the difluoromethylthiolation reagent is reported. The present method is characterized by good functional group tolerance, broad substrate scope, and short reaction time, thereby providing an efficient access to synthetically useful β-difluoromethylthiolated azides. Mechanistic studies indicate a radical pathway involved in the reaction.

An eco‐friendly synthesis of 5‐aminotetrazoles using trichloroisocyanuric acid as desulfurization agent of thioureas

AbstractA novel procedure for the preparation of various 5‐aminotetrazoles derivatives was achieved using trichloroisocyanuric acid as a desulfurizing agent of thioureas and trimethylsilyl azide in ethyl acetate at room temperature. This methodology provided substituted 5‐aminotetrazoles through a more sustainable reaction using an affordable, safe, stable, and easily handled N‐halo reagent, a safer azide source, and an environmentally friendly solvent.

Cobalt-catalyzed regioselective hydroazidation of 1-aryl-1,3-dienes: facile access to allylic azides

A new cobalt-catalyzed hydroazidation of 1-aryl-1,3-dienes by using TMSN3 as a nucleophilic azide source under mild conditions has been reported, leading to the synthesis of a wide range of allylic azides with moderate to good yields.

Nonheme Iron(III) Azide and Iron(III) Isothiocyanate Complexes: Radical Rebound Reactivity, Selectivity, and Catalysis.

The new nonheme iron complexes FeII(BNPAPh2O)(N3) (1), FeIII(BNPAPh2O)(OH)(N3) (2), FeII(BNPAPh2O)(OH) (3), FeIII(BNPAPh2O)(OH)(NCS) (4), FeII(BNPAPh2O)(NCS) (5), FeIII(BNPAPh2O)(NCS)2 (6), and FeIII(BNPAPh2O)(N3)2 (7) (BNPAPh2O = 2-(bis((6-(neopentylamino)pyridin-2-yl) methyl)amino)-1,1-diphenylethanolate) were synthesized and characterized by single crystal X-ray diffraction (XRD), as well as by 1H NMR, 57Fe Mössbauer, and ATR-IR spectroscopies. Complex 2 was reacted with a series of carbon radicals, ArX3C· (ArX = p-X-C6H4), analogous to the proposed radical rebound step for nonheme iron hydroxylases and halogenases. The results show that for ArX3C· (X = Cl, H, tBu), only OH· transfer occurs to give ArX3COH. However, when X = OMe, a mixture of alcohol (ArX3COH) (30%) and azide (ArX3CN3) (40%) products was obtained. These data indicate that the rebound selectivity is influenced by the electron-rich nature of the carbon radicals for the azide complex. Reaction of 2 with Ph3C· in the presence of Sc3+ or H+ reverses the selectivity, giving only the azide product. In contrast to the mixed selectivity seen for 2, the reactivity of cis-FeIII(OH)(NCS) with the X = OMe radical derivative leads only to hydroxylation. Catalytic azidation was achieved with 1 as catalyst, λ3-azidoiodane as oxidant and azide source, and Ph3CH as test substrate, giving Ph3CN3 in 84% (TON = 8). These studies show that hydroxylation is favored over azidation for nonheme iron(III) complexes, but the nature of the carbon radical can alter this selectivity. If an OH· transfer pathway can be avoided, the FeIII(N3) complexes are capable of mediating both stoichiometric and catalytic azidation.

Synthesis of carbamoyl azides via the Lossen rearrangement utilizing diphenyl phosphorazidate

A novel method was developed for the synthesis of carbamoyl azides from hydroxamic acids via the Lossen rearrangement using diphenyl phosphorazidate, which acts as both the activator and azide source to produce the azides via an isocyanate intermediate. Using this method, various hydroxamic acids were converted into the corresponding carbamoyl azides, enabling their preparation without the use of highly explosive reagents.

Decatungstate-photocatalysed C(sp3)-H azidation.

C-H Azidation is an increasingly important tool for bioconjugation, materials chemistry, and the synthesis of nitrogen-containing natural products. While several approaches have been developed, these often require exotic and energetic reagents, expensive photocatalysts, or both. Here we report a simple and general C-H azidation reaction using earth-abundant tetra-n-butylammonium decatungstate as a photocatalyst and commercial p-acetamidobenzenesulfonyl azide (p-ABSA) as the azide source. This system can azidate a variety of unactivated C(sp3)-H bonds in moderate to good yields and excellent turnover numbers. Preliminary mechanistic experiments implicate a radical mechanism proceeding VIA photo-hydrogen atom transfer (photo-HAT).

Metal-free oxoammonium salt-mediated C(sp3)-H oxidative Ugi-azide multicomponent reaction.

In this work, an efficient oxidative C(sp3)-H Ugi-azide multicomponent reaction of cyclic benzylic amines to the corresponding α-tetrazolo compounds using a TEMPO salt as mild hydride abstractor-type oxidant is reported. This simple one-pot approach allows the direct functionalization of N-heterocycles such as tetrahydroisoquinolines with a variety of isocyanides and NaN3 as a practical azide source. The reaction proceeds at room temperature and without the need of acid additives, allowing for the use of sensitive substrates, while minimizing isocyanide polymerization to provide the desired heterocycle-tetrazole products in synthetically useful yields (up to 99%).

Synthesis of new bile acid-fused tetrazoles using the Schmidt reaction.

A practical and high-yielding Schmidt reaction for the synthesis of fused tetrazoles from bile acid precursors was developed. Mild reaction conditions using TMSN3 instead of hydrazoic acid as an azide source produced good yields of the desired tetrazoles. These conditions could be applied to other steroidal precursors. Additionally, an improved methodology for the synthesis of different ketone and enone precursors from cholic acid, deoxycholic acid, and chenodeoxycholic acid was established. Newly obtained tetrazole derivatives were characterized by NMR and X-ray diffraction spectroscopy. In a number of cases, preliminary antiproliferative tests of new compounds showed strong and selective activity towards certain tumor cell lines.

Copper‐Catalyzed Decarboxylative Cycloaddition of Alkynyl Carboxylic Acids and Sodium Azide with Epoxides and Ethers

AbstractCopper‐catalyzed decarboxylative cycloaddition of alkynyl carboxylic acids and sodium azide with structurally different epoxides and ethers has been reported for the regioselective synthesis of 1,4‐disubstituted‐1,2,3‐triazoles. These one‐pot transformations are likely to proceed through a mechanism that involves an in situ generated organic azide intermediate, a decarboxylative formation of copper‐alkyne component, and a ring closure to form triazole product. The present three‐component protocols offer several advantages including using economic, bench stable and safe azide source, simple and convenient experimental procedures, high product yields, excellent regioselectivity, wide substrate scope and good functional group tolerance, which could promote their potential synthetic applications in many related areas.

Amidinate Supporting Ligands Influence Molecularity in Formation of Uranium Nitrides.

Uranium nitride complexes are attractive targets for chemists as molecular models for the bonding, reactivity, and magnetic properties of next-generation nuclear fuels, but these molecules are uncommon and can be difficult to isolate due to their high reactivity. Here, we describe the synthesis of three new multinuclear uranium nitride complexes, [U(BCMA)2]2(μ-N)(μ-κ1:κ1-BCMA) (7), [(U(BIMA)2)2(μ-N)(μ-NiPr)(K2(μ-η3:η3-CH2CHNiPr)]2 (8), and [U(BIMA)2]2(μ-N)(μ-κ1:κ1-BIMA) (9) (BCMA = N,N-bis(cyclohexyl)methylamidinate, BIMA = N,N-bis(iso-propyl)methylamidinate), from U(III) and U(IV) amidinate precursors. By varying the amidinate ligand substituents and azide source, we were able to influence the composition and size of these nitride complexes. 15N isotopic labeling experiments confirmed the bridging nitride moieties in 7-9 were formed via two-electron reduction of azide. The tetra-uranium cluster 8 was isolated in 99% yield via reductive cleavage of the amidinate ligands; this unusual molecule contains nitrogen-based ligands with formal 1-, 2-, and 3- charges. Additionally, chemical oxidation of the U(IV) precursor U(N3)(BCMA)3 yielded the cationic U(V) species [U(N3)(BCMA)3][OTf]. Magnetic susceptibility measurements confirmed a U(IV) oxidation state for the uranium centers in the three nitride-bridged complexes and provided a comparison of magnetic behavior in the structurally related U(III)-U(IV)-U(V) series U(BCMA)3, U(N3)(BCMA)3, and [U(N3)(BCMA)3][OTf]. At 240 K, the magnetic moments in this series decreased with increasing oxidation state, i.e., U(III) > U(IV) > U(V); this trend follows the decreasing number of 5f valence electrons along this series.

Manganese-catalyzed Electro-oxidative Azidation-annulation Cascade to Access Oxindoles and Quinolinones.

An environmentally benign and proficient electro-oxidative tandem azidation-radical cyclization strategy is reported. Manganese-catalyzed electrochemical reaction in an undivided cell at room temperature and the use of NaN3 as the cheapest azide source are the key features of this protocol. Using this approach, a series of oxindole and quinolinone derivatives are synthesized in high yields. The synthesized azide functionality was efficiently converted to various valuable derivatives.

The Introduction of the Radical Cascade Reaction into Polymer Chemistry: A One-Step Strategy for Synchronized Polymerization and Modification.

SummaryPolymerization and modification play central roles in polymer chemistry and are generally implemented in two steps, which suffer from the time-consuming two-step strategy and present considerable challenge for complete modification. By introducing the radical cascade reaction (RCR) into polymer chemistry, a one-step strategy is demonstrated to achieve synchronized polymerization and complete modification in situ. Attributed to the cascade feature of iron-catalyzed three-component alkene carboazidation RCR exhibiting carbon-carbon bond formation and carbon-azide bond formation with extremely high efficiency and selectivity in one step, radical cascade polymerization therefore enables the in situ synchronized polymerization through continuous carbon-carbon bond formation and complete modification through carbon-azide bond formation simultaneously. This results in a series of α, β, and γ poly(amino acid) precursors. This result not only expands the methodology library of polymerization, but also the possibility for polymer science to achieve functional polymers with tailored chemical functionality from in situ polymerization.

Intramolecular Aminoazidation of Unactivated Terminal Alkenes by Palladium-Catalyzed Reactions with Hydrogen Peroxide as the Oxidant.

The palladium-catalyzed aminoazidation of aminoalkenes yielding azidomethyl-substituted nitrogen-containing heterocycles was developed. The procedure requires oxidative conditions and occurs at room temperature in the presence of hydrogen peroxide and NaN3 as the azide source. These conditions provide selective exo-cyclization/azidation of the carbon-carbon double bond, furnishing a versatile approach toward five-, six-, and seven-membered heterocyclic rings.