Asymmetric 1,3-dipolar cycloadditions of acrylamides

Application of 2-Azabicyclo[2.2.1]Hept-5-En-3-One (Vince Lactam) in Synthetic Organic and Medicinal Chemistry

2-Azabicyclo[2.2.1]hept-5-en-3-one (Vince lactam) is known to be a valuable building block in synthetic organic chemistry and drug research. It is an important precursor to access of some blockbuster antiviral drugs such as Carbovir or Abacavir as well as other carbocyclic neuraminidase inhibitors as antiviral agents. The ring C=C bond of the Vince lactam allows versatile chemical manipulations to create not only functionalized γ-lactams, but also γ-amino acid derivatives with a cyclopentane framework. The aim of the current account is to summarize the chemistry of Vince lactam, its synthetic utility and application in organic and medicinal chemistry over the last decade.

Spectral Assignment in the [3 + 2] Cycloadditions of Methyl (2E)-3-(Acridin-4-yl)-prop-2-enoate and 4-[(E)-2-Phenylethenyl]acridin with Unstable Nitrile N-Oxides

The investigation of cycloaddition reactions involving acridine-based dipolarophiles revealed distinct regioselectivity patterns influenced mainly by the electronic factor. Specifically, the reactions of methyl-(2E)-3-(acridin-4-yl)-prop-2-enoate and 4-[(1E)-2-phenylethenyl]acridine with unstable benzonitrile N-oxides were studied. For methyl-(2E)-3-(acridin-4-yl)-prop-2-enoate, the formation of two regioisomers favoured the 5-(acridin-4-yl)-4,5-dihydro-1,2-oxazole-4-carboxylates, with remarkable exclusivity in the case of 4-methoxybenzonitrile oxide. Conversely, 4-[(1E)-2-phenylethenyl]acridine displayed reversed regioselectivity, favouring products 4-[3-(substituted phenyl)-5-phenyl-4,5-dihydro-1,2-oxazol-4-yl]acridine. Subsequent hydrolysis of isolated methyl 5-(acridin-4-yl)-3-phenyl-4,5-dihydro-1,2-oxazole-4-carboxylates resulted in the production of carboxylic acids, with nearly complete conversion. During NMR measurements of carboxylic acids in CDCl3, decarboxylation was observed, indicating the formation of a new prochiral carbon centre C-4, further confirmed by a noticeable colour change. Overall, this investigation provides valuable insights into regioselectivity in cycloaddition reactions and subsequent transformations, suggesting potential applications across diverse scientific domains.

Azoxy Compounds-From Synthesis to Reagents for Azoxy Group Transfer Reactions

The azoxy functional group is an important structural motif and represents the formally oxidized counterpart of the azo group. Azoxy compounds find numerous applications ranging from pharmaceuticals to functional materials, yet their synthesis remains underdeveloped with a main focus on the formation symmetric azoxy compounds. To overcome challenges in the synthesis of such unsymmetric azoxy compounds, we designed a process employing readily accessible nitroso compounds and iminoiodinanes. This method builds on the use of visible light irradiation to generate a triplet nitrene from iminoiodinanes, which is trapped by nitroso arenes to give access to sulfonyl-protected azoxy compounds with a good substrate scope and functional group tolerance. We further describe two applications of these sulfonyl-protected azoxy compounds as radical precursors in synthesis, where the whole azoxy group can be transferred and employed in C(sp3 )-H functionalization of ethers or 1,2-difunctionalization of vinyl ethers. All of the reactions occurred at room temperature under visible light irradiation without the addition of any photoredox catalysts and additives. Control experiments, mechanism investigations, and DFT studies well explained the observed reactivity.

Theoretical insight into the unexpected initial (3 + 2) cycloaddition reaction of mesitonitrile oxide with 1, 4-diazepine derivatives: A computational study

1,4-Diazepine as an active drug component underlies the potency of most psychotic, anticancer, anticonvulsant, and antibacterial drugs in the market and is, therefore crucial in chemotherapeutic treatment in biomedicine. Proper functionalization of this moiety can afford even more potent drugs. As a result of their therapeutic significance, this study aims at precisely giving a comprehensive computational insight into the unexpected initial reactivity of 1,4-diazepine derivatives and mesitonitrile oxide. The initial reaction between mesitonitrile oxide and 1,4-diazepine derivatives proceeds via a (3 + 2) cycloaddition reaction which leads to the formation of a cycloadduct where the mesitonitrile oxide unexpectedly adds across the imine functionality at the expense of the potential olefinic carbon-carbon double bond. Calculations at the density functional theory (DFT) M06/6-311G (d, p) level of theory indicate that the initial (3 + 2) cycloaddition reaction of mesitonitrile oxide (1,3-dipole) and 1,4-diazepine derivatives (dipolarophile) in all cases proceeds to form the cycloadduct where the 1,3-dipole adds preferentially to the imine functionality at the expense of the potential olefinic carbon-carbon double bond. In light of the parent reaction, the most kinetically favored cycloadductP3A had a rate constant of 5.1 × 10⁶ M^-1s^-1, which is about 12 manifolds faster than the next competing stereoisomer P1A with a rate constant of 4.1 × 10⁵ M^-1s^-1 and about 10²⁴ faster than the most favored cycloadduct P3B with a rate constant of 7.2 × 10^-19 M^-1s^-1 in the unfavored pathway (Path B). Irrespective of the electronic and steric nature of the electron-donating (EDG) and electron-withdrawing (EWG) substituents placed on the dipolarophile, the selectivities of the reaction were maintained. Rationalization of the potential energy surface depicts that the 1,3-dipole adds across the dipolarophile via an asynchronous concerted mechanism. Rationalization of the HOMO-LUMO energies of the mesitonitrile oxide (1,3-dipole) and the 1,4-diazepine derivatives (dipolarophile) depict that the EDG-substituted dipolarophile react as nucleophiles, whereas the dipole reacts as an electrophile. Conversely, the HOMO-LUMO interaction between the EWG-substituted dipolarophile indicates that the EWG-substituted dipolarophile react as electrophiles, whereas the dipole reacts as a nucleophile. The electrophilic parr function at various reactive sites of the dipolarophile shows that the 1,3-dipole preferentially adds across the local centers with the largest electrophilic NBO or Mulliken spin densities which is consistent with the energetic trend observed. The reactivity of the 1,4-diazepine derivatives and the mesitonitrile oxide showed poor stereoselectivity.

One-Bond-Nucleophilicity and -Electrophilicity Parameters: An Efficient Ordering System for 1,3-Dipolar Cycloadditions

Diazoalkanes are ambiphilic 1,3-dipoles that undergo fast Huisgen cycloadditions with both electron-rich and electron-poor dipolarophiles but react slowly with alkenes of low polarity. Frontier molecular orbital (FMO) theory considering the 3-center-4-electron π-system of the propargyl fragment of diazoalkanes is commonly applied to rationalize these reactivity trends. However, we recently found that a change in the mechanism from cycloadditions to azo couplings takes place due to the existence of a previously overlooked lower-lying unoccupied molecular orbital. We now propose an alternative approach to analyze 1,3-dipolar cycloaddition reactions, which relies on the linear free energy relationship lg k₂(20 °C) = s_N(N + E) (eq 1) with two solvent-dependent parameters (N, s_N) to characterize nucleophiles and one parameter (E) for electrophiles. Rate constants for the cycloadditions of diazoalkanes with dipolarophiles were measured and compared with those calculated for the formation of zwitterions by eq 1. The difference between experimental and predicted Gibbs energies of activation is interpreted as the energy of concert, i.e., the stabilization of the transition states by the concerted formation of two new bonds. By linking the plot of lg k₂ vs N for nucleophilic dipolarophiles with that of lg k₂ vs E for electrophilic dipolarophiles, one obtains V-shaped plots which provide absolute rate constants for the stepwise reactions on the borderlines. These plots furthermore predict relative reactivities of dipolarophiles in concerted, highly asynchronous cycloadditions more precisely than the classical correlations of rate constants with FMO energies or ionization potentials. DFT calculations using the SMD solvent model confirm these interpretations.

Stereoselective synthesis of CF3-containing spirocyclic-oxindoles using N-2,2,2-trifluoroethylisatin ketimines: an update

The introduction of fluorine-containing groups into organic molecules either changes or improves the characteristics of the target compounds. On the other hand, spirocyclic-oxindoles featuring C-3 functionalized sp3-hybridized carbon atoms of three-dimensional orthogonally shaped molecules were well recognized in the core structure of varied natural products and synthetic pharmaceutical targets. Consequently, the construction of spirooxindoles by an elegant synthetic approach with efficient stereocontrol has received tremendous interest over the past decades. In this context of the synergic combination of the features associated with fluorine-containing compounds and the synthetic and medicinal efficiency associated with spirooxindoles, the stereodivergent installation of CF3 groups embedded with spirooxindoles is of increasing academic and scientific interest. This mini-review article is dedicated to demonstrating a critical overview of the recent stereoselective synthesis of spirocyclic-oxindoles featuring trifluoromethyl groups by employing the reactivity of N-2,2,2-trifluoroethylisatin ketimines as an efficient and easily prepared synthon, and covers the literature reports from 2020 to date. Besides exploring the advancements accomplished in this area, we also investigate the limitations associated with reaction discovery, mechanistic rationalization, and future applications.

Dipolarophile-Controlled Regioselective 1,3-Dipolar Cycloaddition: A Switchable Divergent Access to Functionalized N-Fused Pyrrolidinyl Spirooxindoles

N-fused pyrrolidinyl spirooxindole belongs to a class of privileged heterocyclic scaffolds and is prevalent in natural alkaloids and synthetic pharmaceutical molecules. To realize the switchable synthesis of divergent N-fused pyrrolidinyl spirooxindoles for further biological activity evaluation via a substrate-controlled strategy, a chemically sustainable, catalysis-free, and dipolarophile-controlled three-component 1,3-dipolar cycloaddition of isatin-derived azomethine ylides with diverse dipolarophiles is described in this work. A total of 40 functionalized N-fused pyrrolidinyl spirooxindoles were synthesized in 76-95% yields with excellent diastereoselectivities (up to >99:1 dr). The scaffolds of these products can be well-controlled by employing different 1,4-enedione derivatives as dipolarophiles in EtOH at room temperature. This study provides an efficient strategy to afford a spectrum of natural-like and potentially bioactive N-fused pyrrolidinyl spirooxindoles.

DABCO-promoted highly diastereo- and regioselective construction of C-3 functionalized spirooxindoles via [3 + 2] cycloaddition of 2-aryl/heteroarylidene-1H-indene-1,3(2H)-diones with N-2,2,2-trifluoroethylisatin ketimines at ambient conditions

The application of 2-aryl/heteroarylidene-1H-indene-1,3(2H)-dione as an activated olefin source in the DABCO-catalyzed [3 + 2] cycloaddition with N-2,2,2-trifluoroethylisatin ketimines has been disclosed. This highly efficient 1,3-dipolar cycloaddition reaction offered a variety of trifluoro methyl group bearing spiro-pyrrolidine linked oxindoles with four consecutive stereocentres in good to excellent yield and excellent diastereoselectivity. The synthetic practicality of the protocol was established by demonstrating the enantioselective construction of spiro-pyrrolidine-oxindoles with two vicinal spiro-quaternary chiral centres in good yield excellent enantioselectivity (>90% ee) by using ultralow loading of quinine as the catalyst at room temperature.

Organocatalytic Enantioselective Formal (4 + 2)-Cycloadditions of Phosphine-Containing Dipoles with Isocyanates

Phosphine-catalyzed enantioselective formal (4 + 2)-cycloadditions of 2-(4H-benzo[d][1,3]oxazin-4-yl)acrylates with isocyanates have been developed for the first time. The initial S_N2' attack of the chiral phosphine organocatalyst on 2-(4H-benzo[d][1,3]oxazin-4-yl)acrylates generated the key phosphine-containing dipolar intermediates, and the subsequent formal cycloaddition with isocyanates furnished a broad scope of 3,4-dihydroquinazolin-2-ones in 60-84% yields with 61-92% ee.

Synthetic and biosynthetic routes to nitrogen-nitrogen bonds

The nitrogen-nitrogen bond is a core feature of diverse functional groups like hydrazines, nitrosamines, diazos, and pyrazoles. Such functional groups are found in >300 known natural products. Such N-N bond-containing functional groups are also found in significant percentage of clinical drugs. Therefore, there is wide interest in synthetic and enzymatic methods to form nitrogen-nitrogen bonds. In this review, we summarize synthetic and biosynthetic approaches to diverse nitrogen-nitrogen-bond-containing functional groups, with a focus on biosynthetic pathways and enzymes.

Synthesis, crystal structure and Hirshfeld surface analysis of dimethyl 3-(3-bromo-phen-yl)-6-methyl-7-oxo-3,5,6,7-tetra-hydro-pyrazolo-[1,2-a]pyrazole-1,2-di-carboxyl-ate

The title compound, C17H17BrN2O5, resulted from the 1,3-dipolar cyclo-addition reaction between dimethyl acetyl-enedi-carboxyl-ate and (3-bromo-benzyl-idene)-4-methyl-5-oxopyrazolidin-2-ium-1-ide in CHCl3. The dihedral angle between the pyrazole rings (all atoms) is 32.91 (10)°; the oxo-pyrazole ring displays an envelope conformation whereas the other pyrazole ring adopts a twisted conformation. The bromo-phenyl ring subtends a dihedral angle of 88.95 (9)° with the mean plane of its attached pyrazole ring. In the crystal, the mol-ecules are linked by C-H⋯O hydrogen bonds and aromatic π-π inter-actions with an inter-centroid distance of 3.8369 (10) Å. The Hirshfeld surface analysis and fingerprint plots reveal that the mol-ecular packing is governed by H⋯H (37.1%), O⋯H/H⋯O (31.3%), Br⋯H/H⋯Br (13.5%) and C⋯H/H⋯C (10.6%) contacts. The energy framework indicates that dispersion energy is the major contributor to the mol-ecular packing.

Diversity-Oriented Synthesis of Highly Functionalized Alicycles across Dipolar Cycloaddition/Metathesis Reaction

This Account gives an insight into the selective functionalization of some readily available commercial cyclodienes across simple chemical transformations into functionalized small-molecular scaffolds. The syntheses involved selective cycloadditions, followed by ring-opening metathesis (ROM) of the resulting azetidin-2-one derivatives or isoxazoline frameworks and selective cross metathesis (CM) by discrimination of the C=C bonds on the alkenylated heterocycles. The CM protocols have been described when investigated under various conditions with the purpose on exploring chemodifferentiation of the olefin bonds and a study on the access of the corresponding functionalized β-lactam or isoxazoline derivatives is presented. Due to the expanding importance of organofluorine chemistry in drug research as well as of the high biological potential of β-lactam derivatives several illustrative examples to the access of some fluorine-containing molecular entities is also presented in this synopsis.

1 Introduction

2 Ring C=C Bond Functionalization of Some Cycloalkene β-Amino Acid Derivatives across Chlorosulfonyl Isocyanate Cycloaddition

3 Ring C=C Bond Functionalization of Some Cycloalkene β-Amino Acid Derivatives across Nitrile Oxide Cycloaddition

4 Ring C=C Bond Functionalization of Some Cycloalkene β-Amino Acid Derivatives across Metathesis

5 Functionalization of sSome Cyclodienes across Nitrile Oxide Cycloaddition

6 Selective Synthesis of Functionalized Alicycles across Ring-Opening Metathesis

7 Selective Synthesis of Functionalized Alicycles through Cross Metathesis

8 Summary and Outlook

9 List of Abbreviations

Chiral Ligands in Hypervalent Iodine Compounds: Synthesis and Structures of Binaphthyl-Based λ3 -Iodanes

Several novel binaphthyl-based chiral hypervalent iodine(III) reagents have been prepared and structurally analysed. Various asymmetric oxidative reactions were applied to evaluate the reactivities and stereoselectivities of those reagents. Moderate to excellent yields were observed; however, very low stereoselectivities were obtained. NMR experiments indicated that these reagents are very easily hydrolysed in either chloroform or DMSO solvents leading to the limited stereoselectivities. It is concluded that the use of chiral ligands is an unsuccessful way to prepare efficient stereoselective iodine(III) reagents.

Investigating the site-, regio-, and stereo-selectivities of the reactions between organic azide and 7-heteronorbornadiene: a DFT mechanistic study

The site-, regio-, and stereo-selectivities of the title reactions have been studied using density functional theory (DFT) at the M06/6-311G(d,p) level of theory. The effects of substituents on both the three-atom component (TAC) and norbornadiene derivatives have been investigated with a focus on the site-selectivity. The reaction of benzylazide with (1S,4R)-2-tosyl-7-oxabicyclo[2.2.1]hepta-2,5-diene and (1R,4S)-2-bromo-3-tosyl-7-oxabicyclo[2.2.1]hepta-2,5-diene proceeds via addition across the substituted olefinic bond of the two norbornadiene derivatives. Substituents on the TAC do not affect the selectivity of the reaction while substituents on the norbornadiene significantly affect the selectivity of the reaction. Benzylazide preferentially adds across the substituted olefinic bond of the norbornadiene derivative when strong electron-withdrawing group (EWGs) and electron-releasing group (ERGs) substituents are on the norbornadiene while weak ERGs and EWGs on the norbornadiene significantly decreases the site-selectivity such that addition across either double is no longer favored over the other. The formation of exo-cycloadducts is generally favored over the endo-cycloadducts. The reaction of benzylazide and norbornadiene derivatives is a highly irreversible exergonic reaction. The direction of electron density flux is dependent on the nature of the substituent on the reactants. Global reactivity indices and Parr function calculations are in good agreement with the activation barriers and the selectivity of the reactions.

20 Years of Forging N-Heterocycles from Acrylamides through Domino/Cascade Reactions

Acrylamides are versatile building blocks that are easily obtained from readily available starting materials. During the last 20 years, these valuable substrates bearing a nucleophilic nitrogen atom and an electrophilic double bond have proven to be efficient domino partners, leading to a wide variety of complex aza-heterocycles of synthetic relevance. In this non-exhaustive review, metal-free and metal-triggered reactions followed by an annulation will be presented; these two approaches allow good modulation of the reactivity of the polyvalent acrylamides.

1 Introduction

2 Metal-Free Annulations

2.1 Domino Reactions Triggered by a Michael Addition

2.2 Domino Reactions Triggered by an Aza-Michael Addition

2.3 Domino Processes Triggered by an Acylation Reaction

2.4 Domino Reactions Triggered by a Baylis–Hillman Reaction

2.5 Cycloadditions and Domino Reactions

2.6 Miscellaneous Domino Reactions

3 Metal-Triggered/Mediated Annulations

3.1 Zinc-Promoted Transformations

3.2 Rhodium-Catalyzed Functionalization/Annulation Cascades

3.3 Cobalt-Catalyzed Functionalization/Annulation Cascades

3.4 Ruthenium-Catalyzed Functionalization/Annulation Cascades

3.5 Iron-Catalyzed Functionalization/Annulation Cascades

3.6 Palladium-Catalyzed Functionalization/Annulation Cascades

3.7 Copper-Catalyzed Transformations

3.8 Transition Metals Acting in Tandem in Domino Processes

4 Radical Cascade Reactions

5 Conclusion

Synthesis and structure-activity relationships of new chiral spiro-β-lactams highly active against HIV-1 and Plasmodium

The synthesis and antimicrobial activity of new spiro-β-lactams is reported. The design of the new molecules was based on the structural modulation of two previously identified lead spiro-penicillanates with dual activity against HIV and Plasmodium. The spiro-β-lactams synthesized were assayed for their in vitro activity against HIV-1, providing relevant structure-activity relationship information. Among the tested compounds, two spirocyclopentenyl-β-lactams were identified as having remarkable nanomolar activity against HIV-1. Additionally, the same molecules showed promising antiplasmodial activity, inhibiting both the hepatic and blood stages of Plasmodium infection.

Asymmetric synthesis of dihydro-1,3-dioxepines by Rh(ii)/Sm(iii) relay catalytic three-component tandem [4 + 3]-cycloaddition

Heterocycles have been widely used in organic synthesis, agrochemical, pharmaceutical and materials science industries. Catalytic three-component ylide formation/cycloaddition enables the assembly of complex heterocycles from simple starting materials in a highly efficient manner. However, asymmetric versions remain a yet-unsolved task. Here, we present a new bimetallic catalytic system for tackling this challenge. A combined system of Rh(ii) salt and chiral N,N'-dioxide-Sm(iii) complex was established for promoting the unprecedented tandem carbonyl ylide formation/asymmetric [4 + 3]-cycloaddition of aldehydes and α-diazoacetates with β,γ-unsaturated α-ketoesters smoothly, affording various chiral 4,5-dihydro-1,3-dioxepines in up to 97% yield, with 99% ee. The utility of the current method was demonstrated by conversion of products to optically active multi-substituted tetrahydrofuran derivatives. A possible reaction mechanism was provided to elucidate the origin of chiral induction based on experimental studies and X-ray structures of catalysts and products.

Oxidize Amines to Nitrile Oxides: One Type of Amine Oxidation and Its Application to Directly Construct Isoxazoles and Isoxazolines

A facile oxidative heterocyclization of commercially available amines and tert-butyl nitrite with alkynes or alkenes leading to isoxazoles or isoxazolines is described. The unprecedented strategy of the oxidation of an amine directly to a nitrile oxide was used in this cyclization process. This reaction is highly efficient, regiospecific, operationally simple, mild, and tolerant of a variety of functional groups. Control experiments support a nitrile oxide intermediate mechanism for this novel class of oxidative cyclization reactions. Moreover, synthetic applications toward bioactive molecular skeletons and the late-stage modification of drugs were realized.

(3 + 2) cycloaddition reaction of 7-isopropylidenebenzonorbornadiene and diazomethane derivatives: A theoretical study

The ability to synthesize targeted molecules hinges on detailed mechanistic insight of the reaction. The 1,3-dipolar cycloaddition reaction between diazomethane derivatives and 7-isopropylidenebenzonorbornadiene have been extensively studied using density functional theory (DFT) at the M06-2X/6-311G(d,p) level of theory in order to delineate the peri-, regio-, and stereo-selectivities of the reaction. The diazomethane is shown to periselectively add across the endocyclic olefinic bond of the 7-isopropylidenebenzonorbornadiene and stereoselectively in the exo fashion, yielding the exo-cycloadduct as the major product, with a rate constant of 3.83 × 10⁴ s^-1. The endo approach of this periselective path is the closest competing pathway with a rate constant of 8.78 × 10¹ s^-1. Neither electron-donating groups (R = methyl, ethyl, amine, cyclopropyl) nor electron-withdrawing groups (R = cyano, nitro, carbonyl) on the diazomethane alters the peri- and stereo-selectivity of the reaction. However, the substituents do have an effect on whether the addition follow normal or inverse electron demand mechanisms. EDGs favor a normal electron demand mechanism while EWGs favor an inverse electron demand 1,3-dipolar cycloaddition reaction. While EDGs-substituted diazomethane derivatives behave as nucleophiles in reactions with 7-isopropylidenebenzonorbornadiene, EWGs-substituted diazomethane derivatives behave as electrophiles. The 1,3-dipole adds across the dipolarophile via a concerted asynchronous mechanism, but a stepwise diradical mechanism has been ruled out. The selectivities observed in the title reaction are kinetically controlled. Analysis of the nucleophilic Parr function (P_K^-) at the different reaction sites in the dipolarophile indicates that the diazomethane adds across the atomic centers with highest NBO and Mulliken atomic spin densities.

Predicting Absolute Rate Constants for Huisgen Reactions of Unsaturated Iminium Ions with Diazoalkanes

The kinetics and stereochemistry of the reactions of iminium ions derived from cinnamaldehydes and MacMillan's imidazolidinones with diphenyldiazomethane and aryldiazomethanes were investigated experimentally and with DFT calculations. The reactions of diphenyldiazomethane with iminium ions derived from MacMillan's second-generation catalysts gave 3-aryl-2,2-diphenylcyclopropanecarbaldehydes with yields >90 % and enantiomeric ratios of ≥90:10. Predominantly 2:1 products were obtained from the corresponding reactions with monoaryldiazomethanes. The measured rate constants are in good agreement with the rate constants derived from the one-center nucleophilicity parameters N and sN of diazomethanes and the one-center electrophilicity parameters E of iminium ions as well as with quantum chemically calculated activation energies.

Copper-Catalyzed Asymmetric Reaction of Alkenyl Diynes with Styrenes by Formal [3 + 2] Cycloaddition via Cu-Containing All-Carbon 1,3-Dipoles: Access to Chiral Pyrrole-Fused Bridged [2.2.1] Skeletons

The generation of metal-containing 1,3-dipoles from metal carbenes represents a significant advance in 1,3-dipolar cycloaddition reactions. However, these transformations have so far been limited to reactions based on diazo compounds or triazoles as precursors. Herein, we disclose a copper-catalyzed enantioselective reaction of alkenyl N-propargyl ynamides with styrene derivatives by formal [3 + 2] cycloaddition via Cu-containing all-carbon 1,3-dipoles, which constitutes a novel way for the generation of metal-containing 1,3-dipoles via metal carbenes. This protocol allows the practical and atom-economical synthesis of valuable chiral pyrrole-fused bridged [2.2.1] skeletons in moderate to good yields (up to 90% yield) with excellent diastereoselectivities (dr > 50/1) and generally excellent enantioselectivities (up to >99% ee).

Regio- and stereoselective synthesis of spiropyrrolidine-oxindole and bis-spiropyrrolizidine-oxindole grafted macrocycles through [3 + 2] cycloaddition of azomethine ylides

A convenient and efficient method for the regioselective macrocyclization of triazole bridged spiropyrrolidine-oxindole, and bis-spiropyrrolizidine-oxindole derivatives was accomplished through intra and self-intermolecular [3 + 2] cycloaddition of azomethine ylides. The chalcone isatin precursors 9a-i required for the click reaction were obtained from the reaction of N-alkylazidoisatin 4 and propargyloxy chalcone 8a-i which in turn were obtained by the aldol condensation of propargyloxy salicylaldehyde 6 and substituted methyl ketones 7a-i. The regio- and stereochemical outcome of the cycloadducts were assigned based on 2D NMR and confirmed by single crystal XRD analysis. High efficiency, mild reaction conditions, high regio- and stereoselectivity, atom economy and operational simplicity are the exemplary advantages of the employed macrocyclization procedure.

Catalytic Asymmetric Formal [3+2] Cycloaddition of Azoalkenes with 3-Vinylindoles: Synthesis of 2,3-Dihydropyrroles

Chiral phosphoric acid-catalyzed highly enantioselective formal [3 + 2] cycloaddition reaction of azoalkenes with 3-vinylindoles has been established. Under mild conditions, the projected cycloaddition proceeded smoothly, affording a variety of 2,3-dihydropyrroles in high yields and excellent enantioselectivities, and also in a diastereospecific manner. As opposed to the common 4-atom synthons in the previous literature reports, azoalkenes served as 3-atom synthons. Besides, the observed selectivity was supported by primary theoretical calculation. The unique chemistry of azoalkenes disclosed herein will empower asymmetric synthesis of nitrogen-containing ring structural motifs in a broader context.

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Chiral phosphoric acid catalyzed formal [3 + 2] cycloaddition reaction

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2,3-Dihydropyrroles were enantioselectively synthesized

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Azoalkenes served as 3-atom synthons

Peri-, Chemo-, Regio-, Stereo- and Enantio-Selectivities of 1,3-dipolar cycloaddition reaction of C,N-Disubstituted nitrones with disubstituted 4-methylene-1,3-oxazol-5(4H)- one: A quantum mechanical study

The peri-, chemo-, regio-, stereo- and enantio-selectivities of 1,3-dipolar cycloaddition reaction of C,N-disubstituted nitrones with disubstituted 4-methylene-1,3-oxazol-5(4H)-one have been studied using density functional theory (DFT) at the M06-2X/6-311G (d,p) level of theory. The 1,3-dipole preferentially adds chemo-selectively across the olefinic bond in a (3 + 2) fashion forming the corresponding spirocycloadduct. The titled reaction occurs with poor enantio- and stereo-selectivities, but a high degree of regio-selectivity is observed for the addition of the 1,3-dipole across the dipolarophile. Electron-withdrawing groups on the dipolarophile significantly reduce the activation barriers while electron-donating groups on the dipolarophile increase the activation barriers. Analysis of the HOMO and LUMO energies of the two reacting species indicates that the 1,3-dipole reacts as a nucleophile while the dipolarophile reacts as the electrophile. Investigation of the electrophilic Parr function (P_K⁺) at the various reaction centers in the dipolarophile indicates that the 1,3-dipole selectively adds across the atomic species with the largest electrophilic Mulliken and NBO atomic spin densities which is in accordance with the energetic trends observed.

Pd-Catalyzed asymmetric [5 + 2] cycloaddition of vinylethylene carbonates and cyclic imines: access to N-fused 1,3-oxazepines

A facile route to access enantioenriched N-fused 1,3-oxazepines via Pd-catalyzed asymmetric [5 + 2] cycloaddition of vinylethylene carbonates and cyclic imines has been developed.