Organocatalytic diastereo- and atropo-selective construction of eight-membered bridged (hetero)biaryls via asymmetric intramolecular [3 + 2] cycloaddition

An unprecedented and straightforward route for the asymmetric construction of privileged atroposelective bridged (hetero)biaryl eight-membered scaffolds has been accomplished through chiral phosphoric acid catalyzed asymmetric intramolecular [3 + 2] cycloaddition of innovative (hetero)biaryl aldehydes with 3-aminooxindole hydrochlorides. A class of eight-membered bridged (hetero)biaryl lactones fused to spiro[pyrrolidine-oxindole] derivatives, possessing both chiral C-C/C-N axes and multiple contiguous stereocenters, were obtained in good yields with excellent enantioselectivities and diastereoselectivities in one step through this direct strategy. In addition, the good scalability and derivatization of the title compounds demonstrated their synthetic utility.

Decarboxylative 1,3-dipolar cycloaddition of amino acids for the synthesis of heterocyclic compounds

The [3 + 2] cycloadditions of stabilized azomethine ylides (AMYs) derived from amino esters are well-established. However, the reactions of semi-stabilized AMYs generated from decarboxylative condensation of α-amino acids with arylaldehydes are much less explored. The [3 + 2] adducts of α-amino acids could be used for a second [3 + 2] cycloaddition as well as for other post-condensation modifications. This article highlights our recent work on the development of α-amino acid-based [3 + 2] cycloaddition reactions of N-H-type AMYs in multicomponent, one-pot, and stepwise reactions for the synthesis of diverse heterocycles related to some bioactive compounds and natural products.

Copper-catalyzed [3 + 2]-cycloaddition of α-halonitroalkenes with azomethine ylides: facile synthesis of multisubstituted pyrrolidines and pyrroles

An efficient route for the synthesis of multifunctionalized pyrrolidines based on copper-catalyzed diastereoselective [3 + 2]-cycloaddition of nitroalkenes with azomethine ylides was developed. Novel fluorinated heterocycles - β-fluoro-β-nitropyrrolidines - were accessed via this method. The products can be prepared in good to excellent yields and with high diastereoselectivity. Subsequent transformations of pyrrolidines including oxidative aromatization into fluorinated pyrrolines and medicinally attractive β-fluoro-NH-pyrroles as well as chemoselective reduction reactions were demonstrated. Application of the developed procedures for the non-fluorinated analogues was demonstrated to lead to various β-substituted pyrrole derivatives.

Asymmetric sequential annulation/aldol process of 4-isothiocyanato pyrazolones and allenones: access to novel spiro[pyrrole-pyrazolones] and spiro[thiopyranopyrrole-pyrazolones]

A catalytic asymmetric sequential annulation/aldol reaction of 4-isothiocyanato pyrazolones and allenyl ketones has been developed, which furnished a series of spiro[pyrrole-pyrazolone] heterocycles and structurally novel spiro[thiopyranopyrrole-pyrazolone] derivatives in good yields with high to excellent enantioselectivities. Notably, parallel resolution of racemic spiro[pyrrole-pyrazolones] was achieved by a catalyst-controlled asymmetric intramolecular vinylogous aldol process. Structure diversity of the product was further enhanced by ready transformations.

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.

Enantioselective [3 + 2] annulation of 4-isothiocyanato pyrazolones and alkynyl ketones under organocatalysis

An asymmetric [3 + 2] annulation reaction of 4-isothiocyanato pyrazolones with alkynyl ketones is developed, providing expeditious access to spiro[pyrroline–pyrazolones].

Coumarin-3-formylpyrazoles as 3-carbon synthons in cyclocondensation for the synthesis of spiro-fused pentacyclic spirooxindoles

Coumarin-3-formylpyrazoles have been synthesized and applied as 3-carbon synthons in reaction with 3-hydroxyoxindoles by using DABCO as the catalyst. A range of structurally diverse spiro-fused pentacyclic spirooxindoles, bearing a spirooxindole-γ-lactone and a 3,4-dihydrocoumarin substructure, could be smoothly obtained in good to excellent yields (up to 99%) with excellent diastereoselectivities (all cases >20 : 1 dr). The asymmetric version of this tandem reaction was preliminarily investigated by using chiral organocatalysts.

Double 1,3-Dipolar Cycloadditions of Two Nonstabilized Azomethine Ylides for Polycyclic Pyrrolidines

Nonstabilized azomethine ylides derived from decarboxylation of oxazolidin-5-ones were used for double 1,3-dipolar cycloadditions in diastereoselective synthesis of pyrrolidine-containing tetracyclic compounds. This is the first example of one-pot and five-component reactions involving two nonstabilized azomethine ylides. Only CO₂ and water were generated as byproducts.

Stereocontrolled [3+2] Cycloaddition of Donor-Acceptor Cyclopropanes to Iminooxindoles: Access to Spiro[oxindole-3,2'-pyrrolidines]

A novel stereocontrolled assembly of spiro[oxindole-3,2'-pyrrolidines] via [3+2]-cycloaddition of donor-acceptor cyclopropanes to electron-poor ketimines, iminooxindoles, was developed. The method allows for efficient employment of common readily available donor-acceptor cyclopropanes, functionalized with ester, keto, nitro, cyano etc. groups, and N-unprotected iminooxindoles. The stereospecificity of the initial S_N2-like imine attack on a cyclopropane molecule together with a high diastereoselectivity of further C-C bond formation facilitate a rapid access to spiro[oxindole-3,2'-pyrrolidines] in their optically active forms. Preliminary in vitro testing of the synthesized compounds against LNCaP (p53+) and PC-3 (p53-) cells revealed good antiproliferative activities and p53-selectivity indices for several compounds that are intriguing in terms of their further investigation as inhibitors of MDM2-p53 interaction.

A regio- and stereocontrolled approach to the synthesis of 4-CF3-substituted spiro[chromeno[3,4-c]pyrrolidine-oxindoles]viareversible [3+2] cycloaddition of azomethine ylides generated from isatins and sarcosine to 3-nitro-2-(trifluoromethyl)-2H-chromenes

The first example of regio- and stereocontrolled synthesis of 4-CF₃-spiro[chromeno[3,4-c]pyrrolidine-oxindoles] with anticancer activity.

Catalytic asymmetric synthesis of spirooxindoles: recent developments

The past four years have witnessed significant developments in the field of the catalytic asymmetric synthesis of spirooxindoles, and this feature article outlines the recent progress in this area, including the contributions of our group. This article is divided into sections according to the size and type of the generated spiro-ring fused at the C3-position of the oxindole core.