[3 + 2] Cycloaddition of Azaoxyallyl Cations with Cyclic Ketones: Access to Spiro-4-oxazolidinones

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.

A concise update on the synthetic transformation of aurones via asymmetric cycloaddition, annulation, and Michael/Mannich reactions

This review provides a comprehensive overview of the significance of aurone cores in organic chemistry, highlighting their crucial role as synthetic intermediates. With their innate electrophilic reactivity and convenient accessibility, aurone cores play a vital role in catalysing the development of novel methodologies and facilitating the creation of intricate compounds. The objective of this review is to present a current and insightful compilation that summarizes the progress in aurone synthetic transformations, focusing on diverse cycloaddition ([3 + 2], [4 + 2], [4 + 3], [10 + 2]) and annulation reactions.

Design and synthesis of novel 1,2,3,4-tetrazines as new anti-leukemia cancer agents

A series of novel 1,2,3,4-tetrazines were designed and synthesized. 1 H-NMR spectroscopy, 13 C NMR spectroscopy, and HRMS were used to determine the structures of this novel compounds. Computational approaches suggested that DHFR is a putative target for the newly synthesized 11 compounds. Extensive molecular dynamics simulations followed by molecular docking simulations were employed to evaluate DHFR as a potential target protein. The anticancer activities of the compounds were evaluated against five different types of leukemia cell lines (Jurkat, Nalm-6, Reh, K562, and Molt-4) and one non-leukemic cell line (Hek293T) by MTT test in vitro and imatinib was used as a control drug. Among these compounds, 3a exhibited the best activity against all the leukemic cell lines, except Reh cell line. For Nalm-6, K562, Jurkat, and Molt-4 cell lines, IC50 values were found to be 15.98, 19.12, 23.15, and 25.80 μM, respectively. Our work focuses on the synthesis of original and novel 1,2,3,4-tetrazine derivatives while contributing to the ongoing effort to discover more potent new antileukemia agents.

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.

Heteroarylation of Congested α-Bromoamides with Imidazo-Heteroarenes and Indolizines via Aza-Oxyallyl Cations: Enroute to Dibenzoazepinone and Zolpidem Analogues

Herein, we report a highly efficient and unprecedented approach for heteroarylation of congested α-bromoamides via electrophilic aromatic substitution of imidazo-heteroarenes and indolizines under mild reaction conditions (room temperature, metal, and oxidant free). The participation of an in situ generated aza-oxyallyl cation as an alkylating agent is the hallmark of this transformation. The method was readily adapted to synthesize novel imidazo-heteroarene-fused dibenzoazepinone architectures of potential medicinal value.

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.

(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.

Switchable and efficient conversion of 2-amido-aryl oxazolines to quinazolin-4(3H)-ones and N-(2-chloroethyl)benzamides

Switchable chemoselective conversion of 2-amido-aryl oxazolines to quinazolin-4(3H)-ones or N-(2-chloroethyl)benzamides is achieved.

A Role for Isatin Azomethine Imines as a Dipolarophile in Cycloaddition Reactions

An unusual [2 + 3] cycloaddition of isatin azomethine imines (AIs) and in situ generated azaoxyallyl cations has been developed. It is the first example where AIs serve as the [C,O] 2-atom synthon in organic synthesis. This work not only reveals a new role of isatin AIs in cycloaddition reaction but also provides an efficient access to unprecedented spiroheterocycle compounds.

BI-OAc-Accelerated C3-H Alkylation of Quinoxalin-2(1H)-ones under Visible-Light Irradiation

An efficient, photoredox-catalyst-free radical alkylation of quinoxalin-2(1H)-ones has been described. This reaction utilizes 4-alkyl-1,4-dihydropyridines (R-DHPs) as alkyl radical precursors and acetoxybenziodoxole (BI-OAc) as an electron acceptor to undergo single-electron transfer with photoexcited R-DHPs. The benign conditions allow for good compatibility in the scope of both quinoxalin-2(1H)-ones and R-DHPs. The synthetic value of the protocol was also demonstrated by the successful functionalization of natural products and drug-based complex molecules.

Hydride Transfer Initiated Redox-Neutral Cascade Cyclizations of Aurones: Facile Access to [6,5] Spirocycles

Reported herein is the hydride transfer initiated redox-neutral cascade cyclizations of aurones, providing a variety of [6,5] spiro-heterocycles in satisfactory yields and good diastereoselectivities.

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.

[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.

Efficient synthesis of spirooxindolyl oxazol-2(5H)-ones via palladium(ii)-catalyzed addition of arylboronic acids to nitriles

A versatile synthesis of spirooxindolyl oxazol-2(5H)-ones via palladium(ii)-catalyzed addition of arylboronic acids to nitriles is described. A wide range of spirooxindolyl oxazol-2(5H)-ones and other spirocyclic frameworks incorporating the oxazol-2(5H)-one unit can be readily prepared in good to high yields under the optimal conditions.

An efficient synthesis of oxazolines via a cascade reaction between azaoxyallyl cations and 1,2-benzisoxazoles

A formal [3 + 2] cycloaddition reaction between the C and O terminals of azaoxyallyl cations formed in situ and 1,2-benzisoxazoles has been realized. This one-pot cycloaddition method provided an effective and practical pathway to synthesize oxazoline in good yields under mild conditions. The title products exhibited unique fluorescence properties.

[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.

Synthesis of 1,4,5,6-tetrahydropyridazines and pyridazines via transition-metal-free (4 + 2) cycloaddition of alkoxyallenes with 1,2-diaza-1,3-dienes

We developed an economical and practical protocol for the synthesis of 1,4,5,6-tetrahydropyridazines. A diverse range of alkoxyallenes and 1,2-diaza-1,3-dienes undergo (4 + 2) cycloaddition to generate the desired products in excellent yields. The high efficiency, wide substrate scope and good functional group tolerance of this process, coupled with operational simplicity, render the method synthetically attractive. The utility of the cycloaddition is also demonstrated by the preparation of various pyridazines from 1,4,5,6-tetrahydropyridazines.

We developed an economical and practical protocol for the synthesis of 1,4,5,6-tetrahydropyridazines and pyridazines via cyclization of alkoxyallenes and 1,2-diaza-1,3-dienes.

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.

[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.

Silver(I)- and Base-Mediated [3 + 3]-Cycloaddition of C,N-Cyclic Azomethine Imines with Aza-oxyallyl Cations

A silver(I) and base-mediated [3 + 3]-cycloaddition reaction of in situ generated C,N-cyclic azomethine imines with in situ formed aza-oxyallyl cations is reported. This one-pot cycloaddition process shows broad substrate scope an excellent functional group tolerance and provides the corresponding biologically important isoquinoline-fused triazines in good to excellent yields.