Recent advances in the synthesis of highly substituted imidazolidines

Imidazolidine is a saturated heterocycle with a cyclic aminal core that can be found in natural products and biologically active molecules. Additionally, these heterocyclic compounds have been utilized as chiral ligands, N-heterocyclic carbene precursors, and catalysts in organic synthesis. This review is an attempt to compile the literature of various synthetic procedures of highly substituted imidazolidines, chiral imidazolidines with high diastereoselectivities and enantioselectivities, bis-imidazolidines, and spiro-imidazolidines, as well as their pharmacological properties during the period from 1949 to 2023.

Catalytic asymmetric synthesis of 1,2-diamines

The asymmetric catalytic synthesis of 1,2-diamines has received considerable interest, especially in the last ten years, due to their presence in biologically active compounds and their applications for the development of synthetic building blocks, chiral ligands and organocatalysts. Synthetic strategies based on C-N bond-forming reactions involve mainly (a) ring opening of aziridines and azabenzonorbornadienes, (b) hydroamination of allylic amines, (c) hydroamination of enamines and (d) diamination of olefins. In the case of C-C bond-forming reactions are included (a) the aza-Mannich reaction of imino esters, imino nitriles, azlactones, isocyano acetates, and isothiocyanates with imines, (b) the aza-Henry reaction of nitroalkanes with imines, (c) imine-imine coupling reactions, and (d) reductive coupling of enamines with imines, and (e) [3+2] cycloaddition with imines. C-H bond forming reactions include hydrogenation of CN bonds and C-H amination reactions. Other catalytic methods include desymmetrization reactions of meso-diamines.

Organocatalytic Asymmetric [4 + 2]-Cycloadditions of 2-Aminophenyl Enones with Isatin-Derived Ketimines: Diastereo- and Enantioselective Synthesis of Spirooxindole-Tetrahydroquinazolines

A novel method for the enantioselective synthesis of spiro N,N-heterocyclic oxindoles has been developed, employing asymmetric [4 + 2]-cycloadditions of 2-aminophenyl enones with isatin-derived ketimines. This method employs an organocatalytic approach, utilizing a bifunctional squaramide-based catalyst. It enables the precise synthesis of chiral spirooxindole-tetrahydroquinazolines with intricate structures, featuring chiral quaternary centers. This process achieves remarkable results, including high yields and exceptional levels of enantioselectivity and diastereoselectivity (up to 96% yield, 95% ee, and >20:1 dr).

Organocatalytic Asymmetric [3 + 2]-Annulations of γ-Sulfonamido/γ-Hydroxy-α,β-Unsaturated Ketones with Cyclic N-Sulfimines: Synthesis of Chiral Polyheterotricyclic Imidazolidines and Oxazolidines

The first organocatalytic asymmetric [3 + 2]-annulation of γ-sulfonamido-α,β-unsaturated ketones with cyclic N-sulfimines has been developed, and enantioenriched functionalized polyheterotricyclic imidazolidines were obtained in good yields and with excellent enantioselectivities. This approach was also extended to the asymmetric [3 + 2]-annulation of γ-hydroxy-α,β-unsaturated ketones, affording enantioenriched polyheterotricyclic oxazolidines. In addition, base-catalyzed [3 + 2]-annulations of γ-sulfonamido/γ-hydroxy-α,β-unsaturated ketones with cyclic N-sulfimines were re-investigated under mild reaction conditions for the synthesis of racemic polyheterotricyclic imidazolidines and oxazolidines with excellent diastereoselectivities.

Enantioselective [3+2] Cycloaddition of Donor-Acceptor Aziridines and Imines to Construct 2,5-trans-Imidazolidines

An enantioselective [3+2] cycloaddition of donor-acceptor aziridines with N-aryl protected imines was developed with a Ni(ClO₄ )₂  ⋅ 6H₂ O/N,N'-dioxide catalyst system, providing a broad range of chiral trans-substituted imidazolidine compounds with good yields and excellent enantioselectivities (up to 99 % yield, up to 98 % ee). Control experiments indicated that the products could offer excellent diastereoselectivities with the control of chiral Ni(II)-N,N'-dioxide complex and the interaction of the substrates. The possible catalytic process was proposed to rationalize the stereocontrol.

Direct Observation of the Dynamics of Ylide Solvation by Hydrogen-bond Donors Using Time-Resolved Infrared Spectroscopy

The photoexcitation of α-diazocarbonyl compounds produces singlet carbene intermediates that react with nucleophilic solvent molecules to form ylides. The zwitterionic nature of these newly formed ylides induces rapid changes in their interactions with the surrounding solvent. Here, ultrafast time-resolved infrared absorption spectroscopy is used to study the ylide-forming reactions of singlet carbene intermediates from the 270 nm photoexcitation of ethyl diazoacetate in various solvents and the changes in the subsequent ylide-solvent interactions. The results provide direct spectroscopic observation of the competition between ylide formation and C-H insertion in reactions of the singlet carbene with nucleophilic solvent molecules. We further report the specific solvation dynamics of the tetrahydrofuran (THF)-derived ylide (with a characteristic IR absorption band at 1636 cm-1) by various hydrogen-bond donors and the coordination by lithium cations. Hydrogen-bonded ylide bands shift to a lower wavenumber by -19 cm-1 for interactions with ethanol, -14 cm-1 for chloroform, -10 cm-1 for dichloromethane, -9 cm-1 for acetonitrile or cyclohexane, and -16 cm-1 for Li+ coordination, allowing the time evolution of the ylide-solvent interactions to be tracked. The hydrogen-bonded ylide bands grow with rate coefficients that are close to the diffusional limit. We further characterize the specific interactions of ethanol with the THF-derived ylide using quantum chemical (MP2) calculations and DFT-based atom-centered density matrix propagation trajectories, which show preferential coordination to the α-carbonyl group. This coordination alters the hybridization character of the ylidic carbon atom, with the greatest change toward sp2 character found for lithium-ion coordination.

An overview of the applications of chiral phosphoric acid organocatalysts in enantioselective additions to CO and CN bonds

Since 2004, chiral phosphoric acids (CPAs) have emerged as highyl efficient organocatalysts, providing excellent results in a wide reaction scope. In this review, the applications of CPA for enantioselective additions to CO and CN bonds are covered.

Regio- and stereoselective synthesis and evaluation of densely functionalized bispiro[oxindole-isoxazole-indandione] hybrids as anticancer agents

This is the combination of three key pharmacophores through bispiro quaternary carbon atoms and evaluation of their anticancer activity.

Construction of Spirooxindole Analogues Engrafted with Indole and Pyrazole Scaffolds as Acetylcholinesterase Inhibitors

Twenty-five new hits of spirooxindole analogs 8a-y engrafted with indole and pyrazole scaffolds were designed and constructed via a [3+2]cycloaddition (32CA) reaction starting from three components: new chalcone-based indole and pyrazole scaffolds 5a-d, substituted isatins 6a-c, and secondary amines 7a-d. The potency of the compounds were assessed in modulating cholinesterase (AChE) activity using Ellman's method. Compounds 8i and 8y showed the strongest acetylcholine esterase inhibition (AChEI) with IC50 values of 24.1 and 27.8 μM, respectively. Molecular docking was used to study their interaction with the active site of hAChE.

Organocatalytic Asymmetric Synthesis of Spirooxindole Embedded Oxazolidines

The first organocatalytic asymmetric synthesis of spirooxindole embedded oxazolidines has been developed via a domino reaction involving hemiaminal formation, followed by an unprecedented aza-Michael reaction between isatin derived N-Boc ketimines and γ-hydroxy enones. A quinine derived bifunctional squaramide catalyst was found to be efficient for this reaction, and the products were obtained in good diastereoselectivity and with high enantioselectivity.

Cu(I)-Catalyzed asymmetric exo-selective synthesis of substituted pyrrolidines via a 1,3-dipolar cycloaddition reaction

An (R)-DM-BINAP/Cu(CH3CN)4BF4 complex catalyzed exo-selective asymmetric 1,3-dipolar cycloaddition (1,3-DCA) reaction of imino esters with α,β-unsaturated pyrazoleamides has been developed. A series of highly functionalized pyrrolidines with multiple stereogenic centers were obtained with good yields and diastereoselectivities and excellent enantioselectivities (up to 99% ee).

A sequential Ugi–Smiles/transition-metal-free endo-dig Conia–ene cyclization: the selective synthesis of saccharin substituted 2,5-dihydropyrroles

A convenient, transition-metal-free access to a series of unprecedented saccharin substituted 2,5-dihydropyrroles is reported.

An organocatalytic enantioselective ring-reorganization domino sequence of methyleneindolinones with 2-aminomalonates

Novel organocatalytic enantioselective ring-reorganization domino sequence was developed to efficiently construct polycyclic pyrrolo[3,4-c]quinolinones in high yields (up to 92%) and stereoselectivity (up to >99% ee, >20 : 1 dr).

Recent advances in organocatalytic asymmetric multicomponent cascade reactions for enantioselective synthesis of spirooxindoles

Catalytic asymmetric MCCRs for enantioselective synthesis of spirooxindoles by using chiral phosphoric acids, amines, bifunctional thiourea/squaramides and metal-based reagents as catalysts.

Copper-catalyzed regioselective [3+2] annulation of malonate-tethered acyl oximes with isatins

A copper-catalyzed regioselective [3+2] annulation of malonate-tethered acyl oximes with isatins was developed, affording valuable 2,3-dihydrooxazole-spirooxindoles in moderate to good yields with excellent diastereoselectivity.

Diastereodivergent synthesis of dispiroheterocyclic structures comprising pyrrolidinyloxindole and imidazothiazolotriazine moieties

Highly diastereoselective methods for the synthesis of two different diastereomers of polynuclear dispiroheterocyclic compounds with five chiral centers comprising pyrrolidinyloxindole and imidazothiazolotriazine moieties (dispiro[imidazo[4,5-e]thiazolo[2,3-c]-1,2,4-triazine-7,3'-pyrrolidine-2',3''-indoles]) have been developed on the basis of a dipolar cycloaddition of azomethine ylides to benzylidene derivatives of imidazothiazolotriazines and an alkali-induced rearrangement of the thiazolotriazine fragment. The different sequence of the cycloaddition and rearrangement stages allows us to perform the targeted synthesis of two diastereomerically pure products from the same starting compounds.

1,3-Dipolar cycloaddition of isatin N,N'-cyclic azomethine imines with α,β-unsaturated aldehydes catalyzed by DBU in water

A simple and green procedure was established by [3 + 3] cycloaddition reaction of isatin derived cyclic imine 1,3-dipoles with α,β-unsaturated aldehydes, giving the desired spiro heterocyclic oxindoles with aza-quaternary centers in good yields and diastereoselectivities. It should be noted that water can be employed as a suitable solvent for the improvement of diastereoselectivity.

A simple and green procedure was established by [3 + 3] cycloaddition reaction of isatin derived cyclic imine 1,3-dipoles with α,β-unsaturated aldehydes, giving spirooxindoles with aza-quaternary center in good yields and diastereoselectivities.

Catalytic asymmetric synthesis of diazabicyclo[3.1.0]hexanes by 1,3-dipolar cycloaddition of azomethine ylides with azirines

Substituted 1,3-diazabicyclo[3.1.0]hexanes with two contiguous quaternary stereocentres are readily prepared by catalytic asymmetric [3+2] cycloaddition of α-substituted iminoesters with azirines. High diastereoselectivities and enantioselectivities (up to 98% ee) are achieved using Cu^I/(R)-Fesulphos as the catalytic system.

Design, Synthesis and Antimicrobial Study of Novel 1-(1,3-benzothiazol-2- yl)-3-chloro-4H-spiro[azetidine-2,3'-indole]-2',4(1'H)-diones Through Ketene– imine Cycloaddition Reaction

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The present study deals with the synthesis of novel 1-(1,3-benzothiazol-2-yl)-3-chloro-4Hspiro[ azetidine-2,3'-indole]-2',4(1'H)-dione derivatives from the reaction of 3-(1,3-benzothiazol-2- ylimino)-1,3-dihydro-2H-indol-2-one derivatives with chloroacetyl chloride in the presence of triethylamine (TEA). The mechanism involved simple acid or base catalysed reaction through the formation of Schiff base followed by cyclisation via ketene–imine cycloaddition reaction. All synthesized compounds were characterized by FT-IR, 1H-NMR, 13C-NMR, and elemental analysis. The antimicrobial activities of the synthesized derivatives 5a-5g were examined via Micro Broth Dilution method against bacterial strains Bacillius subtilis, Staphylcoccus aureus, E. coli, P. aeruginosa, and fungal strain Candida albicans for determining MIC values. Ampicillin, chloramphenicol, and griseofulvin were used as standard drugs.

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The MIC values for antimicrobial activity of synthesized compounds were examined using Micro Broth Dilution method. Compounds 5a, 5b, and 5c were found effective against E. coli (MTCC 442) and P.aeruginosa (MTCC 441) and all compounds showed moderate to excellent activity against Streptococcus aureus (MTCC 96) and Bacillius subtilis (MTCC 441). Regarding the antifungal screening, compounds 5a, 5b, and 5c exhibited excellent activity against Candida albicans MTCC 227. 1-(1,3-benzothiazol-2-yl)-3-chloro-4H-spiro[azetidine-2,3'-indole]-2',4(1'H)-dione derivatives may be used as potential lead molecules as effective antimicrobial agents.

Chemodivergent synthesis of functionalized methanodibenzo[b,f][1,5]diazocin-13-ylmethanones and tetrahydroquinolines via solvent-dependent AB2 and A2B2 multicomponent annulation reactions

A solvent-dependent chemodivergent approach was developed for the synthesis of 6,12-methanodibenzo[b,f][1,5]diazocin-13-ylmethanones and 2,3,4-trisubstituted 1,2,3,4-tetrahydroquinolines involving two distinct AB₂ and A₂B₂ multicomponent processes.

Cyclocondensation of coumarin-3-thioformates with 3-hydroxyoxindoles and 3-aminooxindoles for the synthesis of spiro-fused pentaheterocyclic compounds

A range of spiro-fused pentaheterocyclic compounds including spiro-butyrolactoneoxindole[3,4-c]coumarins and spiro-butyrolactamoxindole[3,4-c]coumarins were smoothly obtained via tandem Michael addition-lactonization/lactamization process.

Divergent syntheses of spirooxindoles from oxindole-embedded four-membered synthon via cycloaddition reactions

The construction of five and six membered heterocycle fused spirooxindoles was achieved via the [4 + 1] and formal [4 + 2] cycloadditions between our rationally designed four-membered synthons and pyridinium methylides and α-bromoacetophenones, respectively.

Enantioselective construction of 3-substituted 3-amino-2-oxindoles containing an N,N-ketal skeleton via organocatalyzed aza-addition of isatin imines

The first example of organocatalytic chemo-, regio- and enantioselective aza-Mannich reactions of triazoles and arylamines, respectively, with isatin-derived imines has been achieved in the presence of double hydrogen bonding organocatalysts, affording the valuable optically active 3-substituted 3-amino-2-oxindoles featuring N,N-ketal structural motifs in high yields. This strategy was featured by low catalyst loading, mild conditions, broad substrate scope, and high efficiency and selectivity.

Direct access to spirobiisoxazoline via the double 1,3-dipolar cycloaddition of nitrile oxide with allenoate

The double [3 + 2]-cycloadditions between nitrile oxides and allenoates have been achieved. In the presence of DABCO combined with Et₃N, 2-substituted buta-2,3-dienoates reacted with oxime chlorides to afford spirobiisoxazolines in 55-90% yields via the double 1,3-dipolar cycloaddition. Notably, the construction of double isoxazoline moieties and two chiral centers including a spiro carbon center was achieved.

Design and synthesis of new substituted spirooxindoles as potential inhibitors of the MDM2-p53 interaction

The designed compounds, 4a-p, were synthesized using a simple and smooth method with an asymmetric 1,3-dipolar reaction as the key step. The chemical structures for all synthesized compounds were elucidated and confirmed by spectral analysis. The molecular complexity and the absolute stereochemistry of 4b and 4e designed analogs were determined by X-ray crystallographic analysis. The anticancer activities of the synthesized compounds were tested against colon (HCT-116), prostate (PC-3), and hepatocellular (HepG-2) cancer cell lines. Molecular modeling revealed that the compound 4d binds through hydrophobic-hydrophobic interactions with the essential amino acids (LEU: 57, GLY: 58, ILE: 61, and HIS: 96) in the p53-binding cleft, as a standard p53-MDM2 inhibitor (6SJ). The mechanism underlying the anticancer activity of compound 4d was further evaluated, and the study showed that compound 4d inhibited colony formation, cell migration, arrested cancer cell growth at G2/M, and induced apoptosis through intrinsic and extrinsic pathways. Transactivation of p53 was confirmed by flow cytometry, where compound 4d increased the level of activated p53 and induced mRNA levels of cell cycle inhibitor, p21.