[3 + 2] Cycloaddition Reaction of in Situ Formed Azaoxyallyl Cations with Aldehydes: An Approach to Oxazolidin-4-ones

α-Halocarbonyls as a Valuable Functionalized Tertiary Alkyl Source

This review introduces the synthetic organic chemical value of α-bromocarbonyl compounds with tertiary carbons. This α-bromocarbonyl compound with a tertiary carbon has been used primarily only as a radical initiator in atom transfer radical polymerization (ATRP) reactions. However, with the recent development of photo-radical reactions (around 2010), research on the use of α-bromocarbonyl compounds as tertiary alkyl radical precursors became popular (around 2012). As more examples were reported, α-bromocarbonyl compounds were studied not only as radicals but also for their applications in organometallic and ionic reactions. That is, α-bromocarbonyl compounds act as nucleophiles as well as electrophiles. The carbonyl group of α-bromocarbonyl compounds is also attractive because it allows the skeleton to be converted after the reaction, and it is being applied to total synthesis. In our survey until 2022, α-bromocarbonyl compounds can be used to perform a full range of reactions necessary for organic synthesis, including multi-component reactions, cross-coupling, substitution, cyclization, rearrangement, stereospecific reactions, asymmetric reactions. α-Bromocarbonyl compounds have created a new trend in tertiary alkylation, which until then had limited reaction patterns in organic synthesis. This review focuses on how α-bromocarbonyl compounds can be used in synthetic organic chemistry.

HIV-1 Tat-Mediated Human Müller Glial Cell Senescence Involves Endoplasmic Reticulum Stress and Dysregulated Autophagy

Antiretroviral treatments have notably extended the lives of individuals with HIV and reduced the occurrence of comorbidities, including ocular manifestations. The involvement of endoplasmic reticulum (ER) stress in HIV-1 pathogenesis raises questions about its correlation with cellular senescence or its role in initiating senescent traits. This study investigated how ER stress and dysregulated autophagy impact cellular senescence triggered by HIV-1 Tat in the MIO-M1 cell line (human Müller glial cells). Cells exposed to HIV-1 Tat exhibited increased vimentin expression combined with markers of ER stress (BiP, p-eIF2α), autophagy (LC3, Beclin-1, p62), and the senescence marker p21 compared to control cells. Western blotting and staining techniques like SA-β-gal were employed to examine these markers. Additionally, treatments with ER stress inhibitor 4-PBA before HIV-1 Tat exposure led to a decreased expression of ER stress, senescence, and autophagy markers. Conversely, pre-treatment with the autophagy inhibitor 3-MA resulted in reduced autophagy and senescence markers but did not alter ER stress markers compared to control cells. The findings suggest a link between ER stress, dysregulated autophagy, and the initiation of a senescence phenotype in MIO-M1 cells induced by HIV-1 Tat exposure.

Base-Promoted Formal (3 + 2) Cycloaddition of α-Halohydroxamates with Electron-Deficient Alkenyl-iminoindolines To Synthesize Spiro-indolinepyrrolidinones

Construction of pyrrolidinyl-spiroindoles with easily available starting materials has attracted considerable attention from the synthesis community and is in great demand. Here, we describe a base-promoted formal (3 + 2) cycloaddition of α-halohydroxamates with alkenyl-iminoindolines. The present methodology features mild reaction conditions and a broad substrate scope with up to 99% yield and excellent diastereoselectivity. The versatility of this approach is demonstrated through valuable synthetic transformations. Preliminary mechanistic studies shed light on the mechanism of this cycloaddition process.

A concise approach to 2-pyrrolin-5-one scaffold construction from α-halohydroxamates and β-keto compounds

A concise approach to the construction of the 2-pyrrolin-5-one scaffold was developed via a one-pot reaction with formal [3 + 2] annulation/elimination between β-keto nitrile/β-keto ester and unsubstituted α-halohydroxamates. This reaction features mild conditions, easy handling, broad substrate scope and good yields. Remarkably, the products could be readily converted into potentially bioactive alkylidenepyrrolinones, pyrroles, pyran-fused pyrrole heterocycles and other useful compounds, exhibiting versatile synthetic potential.

Expedient (3+3)-annulation of in situ generated azaoxyallyl cations with diaziridines

Efficient annulation of in situ formed azaoxyallyl cations using a base has been accomplished with diaziridines to provide 1,2,4-triazines at room temperature. The substrate scope, scale up, functional group tolerance and transition-metal free reaction conditions are the important practical features.

HFIP in Organic Synthesis

1,1,1,3,3,3-Hexafluoroisopropanol (HFIP) is a polar, strongly hydrogen bond-donating solvent that has found numerous uses in organic synthesis due to its ability to stabilize ionic species, transfer protons, and engage in a range of other intermolecular interactions. The use of this solvent has exponentially increased in the past decade and has become a solvent of choice in some areas, such as C-H functionalization chemistry. In this review, following a brief history of HFIP in organic synthesis and an overview of its physical properties, literature examples of organic reactions using HFIP as a solvent or an additive are presented, emphasizing the effect of solvent of each reaction.

Synthesis of spirocyclic oxazole derivatives from 2-arylidene cycloalkanones and α-halohydroxamates

Herein we disclose a facile route to spirocyclic oxazole derivatives via [3 + 2] cycloaddition reactions between 2-arylidene cycloalkanones and azaoxyallyl cations that formed in situ from α-halohydroxamates in the presence of base. This methodology was shown to lead to an efficient formation of a series of functionalized spirocyclic oxazole derivatives in good to excellent yields.

Base-Promoted Formal [3 + 2] Cycloaddition of α-Halohydroxamates with Carbon Disulfide to Synthesize Polysubstituted Rhodanines

A concise and practical strategy via potassium-carbonate-mediated [3 + 2]-cycloaddition reaction of α-halohydroxamates with the common solvent carbon disulfide for the synthesis of functionalized rhodanine derivatives in good to excellent yields is developed. The present methodology features a wide substrate scope as well as good functional group tolerance. The potential synthetic utility of this protocol is demonstrated by synthesis of a series of natural product derivatives containing rhodamine skeletons.

(3 + 2) cycloaddition of 2-alkoxynaphthalenes with azaoxyallyl cations: access to benzo[e]indolones

A route to functionalized benzo[e]indolones has been reported via (3 + 2) cycloaddition of in situ generated azaoxyallyl cations with alkoxynaphthalene followed by aryl C–O bond cleavage. The intermediate adduct has been isolated and characterized.

Synthesis, Characterization of Spirocyclic λ3 -Iodanes and Their Application to Prepare 4,1-Benzoxazepine-2,5-diones and 1,3-Diynes

Herein, a [3+2] cycloaddition of aza-oxyallylic cations with ethynylbenziodoxolones for synthesis of new λ³ -iodanes containing spirocyclic 4-oxazolidinone has been developed. This cyclic λ³ -iodanes display stability in air and excellent solubility in organic solvent. Using them as substrate, both the 4,1-benzoxazepine-2,5-diones and symmetrical 1,3-diynes derivatives were afforded in high yield under copper(I)-catalyzed conditions.

Diastereoselective [3 + 1] Cyclization Reaction of Oxindolyl Azaoxyallyl Cations with Sulfur Ylides: Assembly of 3,3'-Spiro[β-lactam]-oxindoles

Oxindoles and β-lactams are attractive structural motifs because of their unique biological importance. However, the fusion of the two moieties featuring 3,3'-spirocyclic scaffolds is a challenging task in organic synthesis. Herein we designed a novel type of oxindole-based azaoxyallyl cation synthons, which could readily participate in the [3 + 1] cyclization with sulfur ylides. With this protocol, a collection of 3,3-spiro[β-lactam]-oxindoles were facilely produced in up to 94% yield with perfect diastereoselectivity.

Synthesis of 1,4-diazepinone derivatives via a domino aza-Michael/SN2 cyclization of 1-azadienes with α-halogenoacetamides

A novel cyclization of α-halogenoacetamides with 1-azadienes has been developed for the efficient preparation of monocyclic 1,4-diazepinones in one step under transition metal-free conditions. Various α-halogenoacetamides and 1-azadienes are well tolerated and give the desired products in good to excellent yields. This cyclization also demonstrates potential synthetic utility on a gram-scale and further transformation.

The Fascinating Chemistry of α-Haloamides

The aim of this review is to highlight the rich chemistry of α-haloamides originally mainly used to discover new C-N, C-O and C-S bond forming reactions, and later widely employed in C-C cross-coupling reactions with C(sp3), C(sp2) and C(sp) coupling partners. Radical-mediated transformations of α-haloamides bearing a suitable located unsaturated bond has proven to be a straightforward alternative to access diverse cyclic compounds by means of either radical initiators, transition metal redox catalysis or visible light photoredox catalysis. On the other hand, cycloadditions with α-halohydroxamate-based azaoxyallyl cations have garnered significant attention. Moreover, in view of the important role in life and materials science of difluoroalkylated compounds, a wide range of catalysts has been developed for the efficient incorporation of difluoroacetamido moieties into activated as well as unactivated substrates.

Transition metal-free synthesis of α-aryl ketones via oxyallyl cation capture with arylboronic acids

α-Arylated ketones were accessed via oxyallyl cation capture with arylboronic acids in good yields with broad substrate tolerance.

[8+3]-Cycloaddition of Tropones with Azaoxyallyl Cations

Although azaoxyallyl cations are widely used as 1,3-dipoles for various cycloaddition reactions leading to nitrogen-containing heterocycles, their application in higher-order cycloaddition reaction remains scarce. Herein, we present the [8+3]-cycloaddition reaction of tropones with in situ generated azaoxyallyl cations allowing the one-step construction of cycloheptatriene-fused 1,4-oxazinones in moderate to good yields. This base-promoted new carbon-oxygen and carbon-nitrogen bond-forming reaction takes place under mild conditions in the absence of transition metal catalysts.

Facile synthesis of 1,2,4,5-tetrahydro-1,4-benzodiazepin-3-ones via cyclization of N-alkoxy α-halogenoacetamides with N-(2-chloromethyl)aryl amides

A facile and efficient cyclization of N-alkoxy α-halogenoacetamides with N-(2-chloromethyl)aryl amides has been achieved for rapid access to 1,2,4,5-tetrahydro-1,4-benzodiazepine-3-one derivatives (up to 95% yield). The intriguing features of this intermolecular cyclization include its mild reaction conditions and easy handling for scalable synthesis.

One-Step Assembly of Functionalized Morpholinones and 1,4-Oxazepane-3-ones via [3 + 3]- and [3 + 4]-Annulation of Aza-Oxyallyl Cation and Amphoteric Compounds

A new [3 + 3]- and [3 + 4]-annulation strategy involving azaoxyallyl cation and [1,m]-amphoteric compounds (m = 3,4) is presented. This concise method enables easy assembly of functionalized saturated N-heterocycles, comprised of six-and seven-membered rings and is of high significance in the context of drug discovery approaches. This reaction also represents a new trapping modality of the azaoxyallyl cation with amphoteric agents of different chain lengths that consist of a heteroatom nucleophilic site and a π-electrophilic site.

A newly designed heterodiene and its application to construct six-membered heterocycles containing an N-O bond

A new type of zwitterionic nitrosoalkene generated in situ from dehydrohalogenation of α-halo-N-alkylhydroxamic acids was designed. [4+2] cycloadditions of this heterodiene to olefins provide a facile route to construct six-membered heterocycles containing an N-O bond and a new protocol for 1,2-syn carbohydroxylate alkenes with a hydroxyl and acetamide group. DFT calculations support a concerted cycloaddition pathway and the solvent HFIP can stabilize the transition state through H-bonding interaction.

[3 + 2]-Cycloaddition of Azaoxyallyl Cations with 1,2-Benzisoxazoles: A Rapid Entry to Oxazolines

A novel and efficient [3 + 2] cycloaddition reaction of azaoxyallyl cations and 1,2-benzisoxazoles to give oxazoline derivatives has been developed. The transformation provides a rapid entry to functionalized oxazoline scaffolds under mild and transition-metal-free conditions, which will greatly expand the reaction types of heterocycle chemistry and pave the way for syntheses of bioactive compounds.

[3 + 2]-Annulation of Azaoxyallyl Cations and Thiocarbonyls for the Assembly of Thiazolidin-4-ones

A base-promoted, efficient [3 + 2] annulation between azaoxyallyl cations and thiocarbonyls is reported for flexible access to highly functionalized thiazolidin-4-one derivatives in good to excellent yields. An intriguing feature of this method is the metal or Lewis acid free late-stage entry of distinct set of functional groups at C2 of thiazolidin-4-ones via substitution of a latent amino functional group. Overall, this approach constitutes a general platform for convenient access to this medicinally important scaffold.

α-Halogenoacetamides: versatile and efficient tools for the synthesis of complex aza-heterocycles

This review presents the use of α-alkyl- and α-alkoxy-halogenoacetamides as powerful partners for domino and 1,3-dipolar cycloaddition reactions resulting in a ring closure.

Sodium carbonate promoted [3 + 2] annulation of α-halohydroxamates and isocyanates

A new [3 + 2] annulation of readily available α-halohydroxamates and isocyanates has been developed. This protocol allows a rapid assembly of various hydantoins in good to high yields as well as a broad substrate scope and good functional group tolerance.

Metal- and Oxidant-Free Modular Approach To Access N-Alkoxy Oxindoles via Aryne Annulation

An unprecedented metal- and oxidant-free (intermolecular) approach to access N-alkoxy oxindoles via [3 + 2] cycloadition of in situ generated electrophilic species viz. aryne and (putative) aza-oxyallyl cation is reported. This approach is amenable to both C3-unsubstituted as well as C3-substituted oxindoles. A one-pot manipulation further makes this reaction highly practical. The versatility of this approach was demonstrated through valuable synthetic transformations.

[3 + 3] Cycloaddition of Azides with in Situ Formed Azaoxyallyl Cations To Synthesize 1,2,3,4-Tetrazines

A formal [3 + 3] cycloaddition reaction between azides and in situ formed azaoxyallyl cations has been realized. This reaction provided an efficient and practical pathway to synthesize 1,2,3,4-tetrazines in good yields under mild conditions. Biologically active molecules could also be well compatible, highlighting the potential value of this reaction.

Synthesis of 2-Aminoimidazolones and Imidazolones by (3 + 2) Annulation of Azaoxyallyl Cations

The first examples of (3 + 2) annulations between azaoxyallyl cations and cyanamides and nitriles to give the corresponding 2-aminoimidazolones and imidazolones are reported. On the basis of the isolation of unexpected imidate products with certain substrates, it is proposed that the reaction proceeds via fast kinetic O-alkylation followed by rearrangement to the thermodynamically favored 2-aminoimidazolones and imidazolones. The method was applied to the formal synthesis of the antihypertensive drug irbesartan.

Advances in heterocycle synthesis via [3+m]-cycloaddition reactions involving an azaoxyallyl cation as the key intermediate

This feature article highlights recent advances in heterocycle synthesis via [3+m]-cycloaddition reactions involving an azaoxyallyl cation as the key intermediate.

The synthesis of multi-substituted pyrrolidinones via a direct [3 + 2] cycloaddition of azaoxyallyl cations with aromatic ethylenes

A novel [3 + 2] cycloaddition reaction of azaoxyallyl cations and aromatic ethylenes has been developed to afford multi-substituted pyrrolidinones in moderate to good yields.

Base-mediated [2 + 4] cycloadditions of in situ formed azaoxyallyl cations with N-(2-chloromethyl)aryl amides

A base-mediated [2 + 4] annulation of in situ formed azaoxyallyl cations with in situ generated aza-oQMs has been realized.