Antimycobacterial activity: A facile three-component [3+2]-cycloaddition for the regioselective synthesis of highly functionalised dispiropyrrolidines

Electron-rich benzofulvenes as effective dipolarophiles in copper(i)-catalyzed asymmetric 1,3-dipolar cycloaddition of azomethine ylides

A series of benzofulvenes without any electron-withdrawing substituents were employed as 2π-type dipolarophiles for the first time to participate in Cu(i)-catalyzed asymmetric 1,3-dipolar cycloaddition (1,3-DC) reactions of azomethine ylides. An intrinsic non-benzenoid aromatic characteristic from benzofulvenes serves as a key driving force for activation of the electron-rich benzofulvenes. Utilizing the current methodology, a wide range of multi-substituted chiral spiro-pyrrolidine derivatives containing two contiguous all-carbon quaternary centers were formed in good yield with exclusive chemo-/regioselectivity and high to excellent stereoselectivity. Computational mechanistic studies elucidate the origin of the stereochemical outcome and the chemoselectivity, in which the thermostability of these cycloaddition products is the major factor.

Azomethine Ylides-Versatile Synthons for Pyrrolidinyl-Heterocyclic Compounds

Azomethine ylides are nitrogen-based three-atom components commonly used in [3+2]-cycloaddition reactions with various unsaturated 2π-electron components. These reactions are highly regio- and stereoselective and have attracted the attention of organic chemists with respect to the construction of diverse heterocycles potentially bearing four new contiguous stereogenic centers. This review article complies the most important [3+2]-cycloaddition reactions of azomethine ylides with various olefinic, unsaturated 2π-electron components (acyclic, alicyclic, heterocyclic, and exocyclic ones) reported over the past two decades.

[3+2] regioselective annulation reaction of 2-arylidene-1,3-indandiones towards synthesis of spirocyclopentenes: understanding the mechanism of γ-attack vs. α-attack using DFT studies

A regioselective [3+2] cyclisation reaction between 2-arylidene-1,3-indanedione and ethyl 2,3-butadienoate catalysed by triphenylphosphine has been demonstrated to synthesize functionalised spirocyclic cyclopentenes. The reaction tolerated various electron-rich and electron-deficient aryl substituted 2-arylidene-1,3-indanediones with high to excellent chemical yields (up to 99%) and moderate to good regioselectivity (up to 5 : 1). DFT studies have also been carried out to understand the regioselective nature of this reaction. The results of Frontier molecular orbital calculations and the activation energy (E a) favour the formation of compound 3avia γ-attack compared to that of 4avia α-attack.

Organocatalytic synthesis of enantiopure spiro acenaphthyl-pyrrolizidine/pyrrolidines: justifying the regioselectivity based on a distortion/interaction model

An efficient organocatalytic [3 + 2] reaction with Schreiner's thiourea organocatalyst for the synthesis of a small library of novel enantiopure stable spiroacenaphthyl-pyrrolidines/pyrrolizidines with high regio- and diastereoselectivity (up to 99%) is described for the first time. These chiral compounds were synthesized by a three-component 1,3-dipolar cycloaddition of (E)-1-(2-oxoacenaphthylen-1(2H)-ylidene) pyrrolidin-1-ium-2-ide as a dipolar and (S)-cinnamoyl/crotonoyl oxazolidinone as a dipolarophile. The absolute configuration of cycloadducts was confirmed by X-ray diffraction analysis. The origin of catalyst reactivity and regio- and stereoselectivity was investigated through DFT calculations. DFT calculations showed that the regioselectivity was controlled by the distortion (deformation) of reactants and Schreiner's thiourea acts as a LUMO-lowering catalyst.

Multicomponent synthesis of spiropyrrolidine analogues derived from vinylindole/indazole by a 1,3-dipolar cycloaddition reaction

A new series of spiropyrrolidine compounds containing indole/indazole moieties as side chains have been accomplished via a one-pot multicomponent synthesis. The method uses the 1,3-dipolar cycloaddition reaction between N-alkylvinylindole/indazole and azomethine ylides, prepared in situ from cyclic/acyclic amino acids. The 1,3-dipolar cycloaddition proceeds efficiently under thermal conditions to afford the regio- and stereospecific cyclic adducts.

Molecular Structure and Photoinduced Intramolecular Hydrogen Bonding in 2-Pyrrolylmethylidene Cycloalkanones

The structures of pyrrolylmethylidene derivatives of 2,3-dihydro-1H-inden-1-one (3), 3,4-dihydro-naphthalen-1(2H)-one (4), and cycloalkanones (5-7) were studied for the first time in the solid state and solution by NMR, IR, and UV spectroscopies supported by DFT quantum mechanical calculations. It was shown that all studied compounds except cycloheptanone derivative 7 both in crystal and in solution exist in the form of dimers where single E or E,E configuration with respect to the exocyclic C═C bond is stabilized by intermolecular hydrogen bonds N-H···O═C. UV irradiation at a wavelength of 365 nm of MeCN or DMSO solutions of 3-6 results, depending on the exposition time and solvent, partial to complete isomerization to the Z or Z,E isomers (in the case of 6, also the Z,Z isomer). The NMR and IR spectroscopy data show the existence of a strong intramolecular hydrogen bond N-H···O═C in the Z moieties of isomerized compounds. The studied compounds are protonated by trifluoroacetic acid at the carbonyl oxygen, in spite of the reverse order of basicity and nucleophilicity of the carbonyl group and the pyrrole ring. Investigation of the behavior of compound 6 with respect to acetate and fluoride anions allows one to consider it as a potential fluoride sensor.

Construction of spirocycles containing highly substituted pyrroli-dine and 1-indanone motifs with spiro quaternary stereogenic centers via 1,3-dipolar cycloaddition of 2-alkylidene-1-indanone and azomethine ylides promoted by simple imidazolium salts

The 1,3-dipolar cycloaddition of 2-alkylidene-1-indanone with azomethine ylides has been successfully developed promoted by simple imidazolium salts to construct a variety of spirocycles, containing highly substituted pyrrolidines, in excellent yields (up to 99%).

Highly stereoselective construction of novel dispirooxindole–imidazolidines via self-1,3-dipolar cyclization of ketimines

Self-1,3-dipolar [3 + 2]-cycloaddition of ketimines was successfully realized for the first time and the unprecedented dispirooxindole–imidazolidines were synthesized.

Facile, regio- and diastereoselective synthesis of spiro-pyrrolidine and pyrrolizine derivatives and evaluation of their antiproliferative activities

A number of novel spiro-pyrrolidines/pyrrolizines derivatives were synthesized through [3+2]-cycloaddition of azomethine ylides with 3,5-bis[(E)-arylmethylidene]tetrahydro-4(1H)-pyridinones 2a–n. Azomethine ylides were generated in situ from the reaction of 1H-indole-2,3-dione (isatin, 3) with N-methylglycine (sarcosine), phenylglycine, or proline. All compounds (50 μM) were evaluated for their antiproliferative activity against human breast carcinoma (MDA-MB-231), leukemia lymphoblastic (CCRF-CEM), and ovarian carcinoma (SK-OV-3) cells. N-α-Phenyl substituted spiro-pyrrolidine derivatives (5a–n) showed higher antiproliferative activity in MDA-MB-231 than other cancer cell lines. Among spiro-pyrrolizines 6a–n, a number of derivatives including 6a–c and 6i–m showed a comparable activity with doxorubicin in all three cell lines. Among all compounds in three classes, 6a, 6b, and 6m, were found to be the most potent derivatives showing 64%, 87%, and 74% antiproliferative activity in MDA-MB-231, SK-OV-3, and CCRF-CEM cells, respectively. Compound 6b showed an IC₅₀ value of 3.6 μM in CCRF-CEM cells. These data suggest the potential antiproliferative activity of spiro-pyrrolidines/pyrrolizines.