An efficient green approach for the synthesis of novel triazolyl spirocyclic oxindole derivatives via one-pot five component protocol using DBU as catalyst in PEG-400

Dicarbonyl compounds in the synthesis of heterocycles under green conditions

Carbon–carbon and carbon-heteroatom bond forming reactions are strategically employed for the generation of a variety of heterocyclic systems. This class of compounds represents the most general structural unit, present in many natural compounds. They are recognized for their valuable biologically properties and wide range of applications in medicinal, pharmaceutical, and other related fields of chemistry. This is an updated review on the use of dicarbonyl compounds under environmentally friendly conditions to access a series of heterocyclic structures, e.g., quinoxaline, quinazolinones, benzochalcogenazoles, indoles, among others. Synthetic protocols involving copper-catalyzed, multicomponent and cascade reactions, decarboxylative cyclization, recycling of CO2, and electrochemical approaches are presented and discussed.

Recent Developments on Five-Component Reactions

Multicomponent reactions (MCRs) have inherent advantages in pot, atom, and step economy (PASE). This important green synthetic approach has gained increasing attention due to high efficiency, minimal waste, saving resources, and straightforward procedures. Presented in this review article are the recent development on 5-compoment reactions (5CRs) of the following six types: (I) five different molecules A + B + C + D + E; pseudo-5CRs including (II) 2A + B + C + D, (III) 2A + 2B + C, (IV) 3A + B + C, (V) 3A + 2B, and (VI) 4A + B. 5CRs with more than five-reaction centers are also included.

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

Multicomponent reactions (MCRs) are a valuable tool in diversity-oriented synthesis. Its application to privileged structures is gaining relevance in the fields of organic and medicinal chemistry. Isatin, due to its unique reactivity, can undergo different MCRs, affording multiple interesting scaffolds, namely oxindole-derivatives (including spirooxindoles, bis-oxindoles and 3,3-disubstituted oxindoles) and even, under certain conditions, ring-opening reactions occur that leads to other heterocyclic compounds. Over the past few years, new methodologies have been described for the application of this important and easily available starting material in MCRs. In this review, we explore these novelties, displaying them according to the structure of the final products obtained.

Access to molecular complexity. Multicomponent reactions involving five or more components

The evaluation of the significance of a chemical transformation addresses many factors, including such important characteristics as the number of chemical bonds formed in one step, the reaction time, labour intensity, the cost of reactants and catalysts and so on. The amount of waste produced in the reaction has also gained increasing importance in recent years. Multicomponent reactions (MCRs) occupy a special place as a synthetic tool in modern organic chemistry. These reactions allow the synthesis of target products with complex structures, minimizing labour costs. This review summarizes the literature on multicomponent reactions involving five or more components. The data in the review are classified according to the number of reactants participating in the reaction and the types of reactions. It is worth noting that in some cases, these transformations can be a part of a domino process, making this classification difficult, if not impossible. The structural diversity of the reaction products greatly increases with increasing number of components involved in the MCR, which becomes virtually unlimited when using combinations of MCRs. This review highlights the main trends of past decades in the field of MCRs. The last two decades have witnessed an explosive growth in the number of publications in this area of chemistry.

The bibliography includes 309 references.

Expedient synthesis of novel antibacterial hydrazono-4-thiazolidinones under catalysis of a natural-based binary ionic liquid

A library of pyran-2H-one-3-ylmethylidene and chromene-2H-one-3-ylmethylidene derivatives of the titled heterocyclic framework was synthesized from 3-acyl-4-hydroxypyran/chromene-2H-one via sequential reaction with thiosemicarbazide and dialkyl acetylenedicarboxylates. The syntheses were carried out under efficient catalysis of a new binary ionic liquid mixture [L-prolinium chloride][1-methylimidazolium-3-sulfonate] in one pot and solvent-free conditions. Calculations based on density functional theory displayed that the barrier energy for interconversion of the two possible diastereomeric isomers of each product is less than the thermal energy of molecules at room temperature, as only one product can be resolved from a given reaction mixture. This seems to be the case for the previously reported hydrazonothiazolidines. The binary ionic liquid mixture melts at near room temperature and can be considered as a solution of HCl in 1:1 mixture of two zwitterionic species. It proved to be more efficient than its constituents in catalyzing the above synthesis in one-pot operation. Some of the synthesized products have shown pronounced antibacterial activities. The ionic liquid is virtually stable in air and moisture, as can be retrieved several times without appreciable decrease in its catalytic activity.

Synthesis of spiropyrrolidine oxindolesviaAg-catalyzed stereo- and regioselective 1,3-dipolar cycloaddition of indole-based azomethine ylides with chalcones

In excess of 100 new compounds were prepared in moderate to high yields (50–95%) with good to excellent diastereoselectivity (11 : 1 → 20 : 1 dr) by Ag-catalyzed 1,3-dipolar cycloaddition.

"In Water": Organocatalyzed Diastereoselective Multicomponent Reactions toward 2-Azapyrrolizidine Alkaloid Scaffolds

Synthesis of the 2-aza analogues of pyrrolizidine and spirooxindole-2-azapyrrolizidine hybrid, a spiro-tetracyclic scaffold possessing multiple contiguous stereocenters, by an exclusive regio-, chemo-, and diastereoselective multicomponent reaction in water is reported. This logical and didactical tactic has integrated the principles of an ideal organic synthesis, privileged substructure-based diversity-oriented synthesis, and biology-oriented synthesis to access hybrid heterocyclic scaffolds.

Anatase TiO2 Mesocrystals: Green Synthesis, In Situ Conversion to Porous Single Crystals, and Self-Doping Ti3+ for Enhanced Visible Light Driven Photocatalytic Removal of NO

Mesocrystals are of great interest for a wide range of applications owing to their unique structural features and properties. The realization of well-defined metal oxide mesocrystals through a facile and green synthetic approach still remains a great challenge. Here, a novel synthesis strategy is reported for the production of spindle-shaped anatase TiO₂ mesocrystals with a single-crystal-like structure, which was simply achieved through the one-step hydrolysis reaction of TiCl₃ in the green and recyclable media polyethylene glycol (PEG-400) without any additives. Such anatase mesocrystals were constructed from small nanocrystal subunits (≈1.5-4.5 nm in diameter) and formed through oriented aggregation of the nanocrystals pre-formed in the reaction system. Owing to their novel structural characteristics, the as-synthesized anatase mesocrystals could be easily fused in situ into porous single crystals by annealing in air. More significantly, after being annealed in vacuum, Ti³⁺ sites could be easily induced in the anatase crystal lattice, resulting in the formation of Ti³⁺ self-doped anatase mesocrystals. The thus-transformed mesocrystals exhibited enhanced visible light activity towards the photocatalytic oxidation of nitric oxide (NO) to NO₃^- , which could be largely attributed to their intrinsic Ti³⁺ self-doped nature, as well as high crystallinity and high porosity of the mesocrystalline architecture.

Green chemistry oriented multi-component strategy to hybrid heterocycles

An oxindole decorated 4H-chromene scaffold has been synthesized in water under catalyst-free reaction conditions at ambient temperature by integrating the guiding principles of Diversity Oriented Synthesis (DOS) and green chemistry.