Rajesh H. Vekariya

Recent advances in the synthesis of quinolines: a review

Quinolines have become important compounds because of their variety of applications in medicinal, synthetic organic chemistry as well as in the field of industrial chemistry. In recent years there are greater societal expectations that chemists should produce greener and more sustainable chemical processes. This review article gives information about the green and clean syntheses using alternative reaction methods for the synthesis of quinoline derivatives. The article includes synthesis by microwave, using clay or some other catalyst which could be recycled and reused, one-pot reaction, solvent-free reaction conditions, using ionic liquids, ultrasound promoted synthesis and photocatalytic synthesis (UV radiation).

Recent Advances in the Synthesis of Coumarin Derivatives via Knoevenagel Condensation: A Review

Abstract The synthesis of coumarins through Knoevenagel condensation is one of the most important processes in synthetic organic chemistry and medicinal chemistry. Compounds including a coumarin (2-oxo-2H-1-benzopyran) backbone have a wide range of application in the pharmaceutical field. Thus, many methodologies have been developed for the synthesis of this important class of compounds. However, some methods are always associated with toxic and corrosive catalysts, longer reaction time, poor yield, less purity, and by-products along with the desired product. Furthermore, some of these processes are not efficient and environmentally friendly. Therefore, mild, efficient, and environmentally friendly protocols have been developed recently by many scientists for the synthesis of coumarin derivatives via Knoevenagel condensation with good yield and purity. In this review, we have summarized various methods for the synthesis of coumarins via Knoevenagel condensation. GRAPHICAL ABSTRACT

Recent advances in the synthesis of 2-substituted benzothiazoles: a review

Benzothiazole can serve as unique and versatile scaffolds, especially in synthetic and pharmaceutical chemistry because of their potent and significant pharmacological activities. This important class of derivatives possess numerous pharmacological activities like antitumor, antimicrobial, anti-inflammatory, anticonvulsant, antidiabetic activities and so on. Many scientists have developed a wide range of methodologies for the synthesis of the 2-substituted benzothiazole nucleus and its derivatives using different types of catalysts to improve the selectivity, purity and yield of the products. Thus, the present review article focuses mainly on the different kind of reactions involved in synthesis of the 2-substituted benzothiazole nucleus and its derivatives.

Sulfonic Acid–Functionalized Silica (SiO2-Pr-SO3H) as a Solid and a Heterogeneous Catalyst in Green Organic Synthesis: Recent Advances

Abstract The application of sulfonic acid–functionalized silica (SBA-Pr-SO3H) as a catalyst in organic synthesis has become an efficient and green strategy for the selective construction of organic motifs. Therefore, the great efforts have been made by scientists to replace the conventional acid catalysts by sulfonic acid–functionalized silica used as solid, heterogeneous catalyst in various organic transformations. The sustainable advantage of sulfonic acid–functionalized silica is that it can be recovered and reused several times without loss of its efficiency. In this tutorial review, we attempt to give an overview about the use of sulfonic acid–functionalized silica as a catalyst in the synthesis of various organic compounds having industrial as well as pharmaceutical applications. GRAPHICAL ABSTRACT

Sulfonated polyethylene glycol (PEG-OSO3H) as a polymer supported biodegradable and recyclable catalyst in green organic synthesis: recent advances

The objective of this review is to summarize some of the recent advances in a sulfuric acid-modified polyethylene glycol 6000 (PEG-OSO3H) as a stable, recyclable and bio-degradable polymeric catalyst in organic synthesis. PEG-OSO3H is a highly efficient and eco-friendly catalyst, which catalyzed various organic reactions and could be recovered and reused several times without significant loss of its activity. In this review, preparation and application of PEG-OSO3H in organic synthesis are investigated.

Selective Nitration of Phenolic Compounds by Green Synthetic Approaches

Abstract Aromatic nitration is one of the most important unit processes in synthetic organic chemistry and in the chemical industry. Particularly, nitrophenols are important precursors for the production of dyestuffs, pharmaceuticals, agrochemicals, explosives, plastics, and other industrially important products. Many commercial processes are available for the production of these important nitro precursors, but some processes are commonly lead to mixtures of regioisomers and are not environmentally friendly. Thus, in recent years many scientists have been developed new methodologies to improve selectivity and yield of the products. In this review, we summarize recent advances in the synthesis of nitrophenols by green chemistry approaches. GRAPHICAL ABSTRACT

Melamine trisulfonic acid (MTSA): an efficient and recyclable heterogeneous catalyst in green organic synthesis

Melamine trisulfonic acid (MTSA) as a highly efficient heterogeneous solid acid catalyst catalyzes various organic transformations. The great efforts have been made by many scientists to utilize MTSA as a green catalyst for the preparations of N- and O-containing heterocyclic compounds, for the protections of alcohol, phenols, amines and aldehydes and ketones, for the acetylation of alcohols and phenols and for the N-formylation of amines. The superior advantage of this heterogeneous catalyst is that it can be recovered and reused several times without the loss of their efficiency. In this review, preparation and applications of MTSA in organic synthesis are investigated.

A green and one-pot synthesis of a library of 1,4-dihydropyrano[2,3-c]-pyrazole-5-carbonitrile derivatives using thiourea dioxide (TUD) as an efficient and reusable organocatalyst

The efficacy of thiourea dioxide (TUD) as an efficient, inexpensive, and readily accessible organocatalyst for the synthesis of 1,4-dihydropyrano[2,3-c]-pyrazole-5-carbonitrile derivatives via a four-component reaction of ethyl acetoacetate, hydrazine hydrate, aryl aldehydes, and malononitrile is described. Upon completion of the reaction, the product was isolated by filtration, and the remaining aqueous TUD solution could be reused several times with consistent catalytic activity. High yields, simple work-up process, avoiding the use of organic solvents, short reaction time, and recyclable catalyst are the superior advantages of the present protocol.Graphical Abstract

Ceric Ammonium Nitrate (CAN)–Catalyzed Multicomponent Reactions: An Efficient Catalyst for Green Organic Synthesis

Abstract Multicomponent reactions (MCRs) consist of two or more synthetic steps carried out without isolation of any intermediate, which reduces time and saves money, energy, and raw materials. The development of MCRs in the presence of ceric ammonium nitrate (CAN) is an efficient approach that meets with requirements of sustainable chemistry. The aim of this review is to highlight the interactive effect of the combined use of MCRs and CAN for the development of new ecofavorable methodologies for synthetic organic chemistry. There are many advantages to the use of CAN as a catalyst in organic synthesis, including the very small amount of this catalyst needed to complete reactions in most cases, lower costs, ecofriendly nature, ease of handling, nontoxicity, and high reactivity. GRAPHICAL ABSTRACT

Silica-supported polyphosphoric acid (PPA-SiO2): An efficient and reusable heterogeneous catalyst for ecofriendly organic synthesis

ABSTRACT This review discusses the advances in the use of silica-supported polyphosphoric acid (PPA-SiO2) as a green and reusable heterogeneous catalyst in the preparation of various organic compounds and pharmaceutical intermediates. PPA-SiO2 could be recovered and reused several times without significant loss of their efficiency. In this review, we attempt to give an overview of the applications of PPA-SiO2 as a catalyst in condensation, cyclization, and addition reactions for the preparation of various organic compounds. GRAPHICAL ABSTRACT