Engaging Isatins in Multicomponent Reactions (MCRs) - Easy Access to Structural Diversity

Direct synthesis of N-functionalized indoles through isomerization of azomethine ylides

An unexpected isomerization of azomethine ylides generated in situ from isatin with indoline-2-carboxylic acid has been disclosed, providing direct access to N-functionalized indole scaffolds. This protocol has good functional group tolerance and provides various 3-(1H-indol-1-yl)indolin-2-one derivatives in moderate to high yields simply by using alcohol as the solvent, with no additional additive being required.

Highly Diastereoselective Multicomponent Synthesis of Spirocyclopropyl Oxindoles Enabled by Rare-Earth Metal Salts

The synthesis of polysubstituted spirocyclopropyl oxindoles using a series of rare-earth metal (REM) salts is reported. REMs, in particular Sc(OTf)₃, allowed access to the target compounds by a multicomponent reaction with high diastereoselectivity (≤94:6:0:0). Density functional theory calculations on the model reaction are consistent with the observed selectivity and revealed that the special coordinating capabilities and the oxophilicity of the metal are key factors in inducing the formation of one main diastereoisomer.

Organocatalysed one-pot three component synthesis of 3,3'-disubstituted oxindoles featuring an all-carbon quaternary center and spiro[2H-pyran-3,4'-indoline]

A simple and efficient methodology for the one-pot synthesis of 3,3'-disubstituted oxindoles featuring an all-carbon quaternary center has been demonstrated through l-proline catalysed three-component reaction based on sequential Knoevenagel condensation/Michael addition and also one-pot synthesis of spiro[2H-pyran-3,4'-indoline] through consecutive Knoevenagel condensation/Michael addition/reduction/cyclization reactions from readily available isatin derivatives, malononitrile, and ketones. The present methodology presents several advantages, including simple reaction set-up, short reaction times, and easy to work-up. Also, this strategy offers broad substrate scope with excellent yields and high atom economy, under mild reaction conditions.

Recent Advances on Direct Functionalization of Indoles in Aqueous Media

Indoles and their derivatives have dominated a significant proportion of nitrogen-containing heterocyclic compounds and play an essential role in synthetic and medicinal chemistry, pesticides, and advanced materials. Compared with conventional synthetic strategies, direct functionalization of indoles provides straightforward access to construct diverse indole scaffolds. As we enter an era emphasizing green and sustainable chemistry, utilizing environment-friendly solvents represented by water demonstrates great potential in synthesizing valuable indole derivatives. This review aims to depict the critical aspects of aqueous-mediated indoles functionalization over the past decade and discusses the future challenges and prospects in this fast-growing field. For the convenience of readers, this review is classified into three parts according to the bonding modes (C-C, C-N, and C-S bonds), which focus on the diversity of indole derivatives, the prominent role of water in the chemical process, and the types of catalyst systems and mechanisms. We hope this review can promote the sustainable development of the direct functionalization of indoles and their derivatives and the discovery of novel and practical organic methods in aqueous phase.

3D-Printing of Capsule Devices as Compartmentalization Tools for Supported Reagents in the Search of Antiproliferative Isatins

The application of high throughput synthesis methodologies in the generation of active pharmaceutical ingredients (APIs) currently requires the use of automated and easily scalable systems, easy dispensing of supported reagents in solution phase organic synthesis (SPOS), and elimination of purification and extraction steps. The recyclability and recoverability of supported reagents and/or catalysts in a rapid and individualized manner is a challenge in the pharmaceutical industry. This objective can be achieved through a suitable compartmentalization of these pulverulent reagents in suitable devices for it. This work deals with the use of customized polypropylene permeable-capsule devices manufactured by 3D printing, using the fused deposition modeling (FDM) technique, adaptable to any type of flask or reactor. The capsules fabricated in this work were easily loaded "in one step" with polymeric reagents for use as scavengers of isocyanides in the work-up process of Ugi multicomponent reactions or as compartmentalized and reusable catalysts in copper-catalyzed cycloadditions (CuAAC) or Heck palladium catalyzed cross-coupling reactions (PCCCRs). The reaction products are different series of diversely substituted isatins, which were tested in cancerous cervical HeLa and murine 3T3 Balb fibroblast cells, obtaining potent antiproliferative activity. This work demonstrates the applicability of 3D printing in chemical processes to obtain anticancer APIs.

The preparation of polyvinyl imidazole-functionalized magnetic biochar decorated by silver nanoparticles as an efficient catalyst for the synthesis of spiro-2-Amino-4H-pyran compounds

The silver nanoparticle was synthesized by developing poly (1-vinylimidazole) on the surface of magnetized biochar (the stem and roots of Spear Thistle) (biochar/Fe₃O₄/PVIm/Ag). This nanocomposite was characterized by Fourier-transformed infrared spectroscopy (FTIR), powder X-ray diffraction (XRD), vibrating sample magnetometer (VSM), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), and transmission electron microscopy (TEM). The SEM and TEM images of the nanocatalyst, biochar/Fe₃O₄/PVIm/Ag-NPs, confirmed the observation of microscopic sheets of biochar. The catalytic activity of these Ag NPs was tested via multicomponent reaction plus reusing to successful formation of 2-amino-4H-pyran and functionalized spirochromen derivatives. The prepared nanocatalyst was easily separated by an external magnet and reused in repeating coupling reaction cycles four times without remarkable activity loss. The catalyst showed great efficiency and reusability, thus making it an ideal candidate for catalytic purposes in several organic transformations.

Multicomponent Synthesis of Spiro-dihydropyridine Oxindoles via Cascade Spiro-cyclization of Knoevenagel/Aza-Michael Adducts

An efficient, straightforward, and one-pot synthesis of biologically relevant spiro-dihydropyridine oxindoles was described via readily available isatin, malononitrile, allenoate, and amines. The metal/organocatalyst-free, Et₃N-mediated reaction proceeds via cascade spiro-cyclization of in situ generated Knoevenagel/aza-Michael adducts. The reaction has great flexibility over electron-rich and electron-poor substituents affording desired products in good to excellent yields. We have also demonstrated the selected spiro-dihydropyridines for late-stage diversification into new spiro-dihydropyridine hybrids of pharmaceutical relevance.

Four-Component Cyclization of Naphthol/Thionaphthol/Naphthylamine, Formaldehyde, and DBU in Water

A practical and environmentally benign cascade multicomponent condensation of naphthol/thionaphthol/naphthylamine, formaldehyde, and DBU in water without any catalysts has been achieved. A wide variety of dihydrooxazine, dihydrothiazine, and tetrahydrobenzoquinazoline derivatives N-substituted with a tether bearing a caprolactam unit were afforded in moderate to good yields. The advantages of being cost-effective, metal-free, and easily handled and the use of water as medium made this protocol conform with the principle of green synthesis.

Chitosan-EDTA-Cellulose network as a green, recyclable and multifunctional biopolymeric organocatalyst for the one-pot synthesis of 2-amino-4H-pyran derivatives

In this research, cellulose grafted to chitosan by EDTA (Cs-EDTA-Cell) bio-based material is reported and characterized by a series of various methods and techniques such as FTIR, DRS-UV–Vis, TGA, FESEM, XRD and EDX analysis. In fact, the Cs-EDTA-Cell network is more thermally stable than pristine cellulose or chitosan. There is a plenty of both acidic and basic sites on the surface of this bio-based and biodegradable network, as a multifunctional organocatalyst, to proceed three-component synthesis of 2-amino-4H-pyran derivatives at room temperature in EtOH. The Cs-EDTA-Cell nanocatalyst can be easily recovered from the reaction mixture by using filtration and reused for at least five times without significant decrease in its catalytic activity. In general, the Cs-EDTA-Cell network, as a heterogeneous catalyst, demonstrated excellent catalytic activity in an environmentally-benign solvent to afford desired products in short reaction times and required simple experimental and work-up procedure compared to many protocols using similar catalytic systems.

Ugi Reaction Synthesis of Oxindole-Lactam Hybrids as Selective Butyrylcholinesterase Inhibitors

Molecular hybridization is a valuable approach in drug discovery. Combining it with multicomponent reactions is highly desirable, since structurally diverse libraries can be attained efficiently in an eco-friendly manner. In this work, isatin is used as the key building block for the Ugi 4-center 3-component reaction synthesis of oxindole-lactam hybrids, under catalyst-free conditions. The resulting oxindole-β-lactam and oxindole-γ-lactam hybrids were evaluated for their potential to inhibit relevant central nervous system targets, namely cholinesterases and monoamine oxidases. Druglikeness evaluation was also performed, and compounds 4eca and 5dab exhibited great potential as selective butyrylcholinesterase inhibitors, at the low micromolar range, with an interesting predictive pharmacokinetic profile. Our findings herein reported suggest oxindole-lactam hybrids as new potential agents for the treatment of Alzheimer's disease.

Petasis adducts of tryptanthrin – synthesis, biological activity evaluation and druglikeness assessment

The first example of a tryptanthrin-based Petasis multicomponent reaction is reported, with one of the new derivatives showing moderate fungicidal activity.