No abstract

Heterocyclic compounds play a tremendous role in the field of medicinal chemistry due to their association with diverse pharmacological properties. Most of the pharmaceutical drugs used in medicines possess a wide range of heterocyclic nucleus. It was decided basis on literature studies that various synthetic protocols like microwave‐assisted, nanocatalysed, green synthesis, click reaction, and multicomponent routes could be used for the betterment of the purity of products, selectivity, and better yields of the products. We have focused attention on the development of synthetic strategies of the above‐mentioned moieties because N‐, O‐ and S‐ containing heterocyclic compounds have seemed owing to a wide diversity of their biological activities viz. antioxidant, anticancer, anticonvulsant, anti‐inflammatory, neuroprotective, antiproliferative, anti‐obesity, antihyperglycemic, antihypercholesteroler, antiulcer, antidiabetic, antileishmanial, antitrypanosomal, antibiotic, etc. In this review article, an overview of the applications of synthetic protocols for the preparation of five‐membered and six‐membered heterocyclic compounds containing two or more heteroatoms (O, N, S) at different‐different positions along with their different potent and competent candidates against various diseases is presented in last 10–15 years.

The development of new strategies for the production of nitrogen and sulfur-containing heterocycles remains an extremely alluring but challenging proposition. Current progress in the various synthetic methods and biological activities are discussed.

An efficient, environmentally benign and novel method for the synthesis of phenacyl halides as antiplatelet agents has been reported in the presence of nanocatalyst (TiO2) by using N‐halosuccinimides (NXS, X=Cl, Br) as a source of halogen and tert‐Butyl Hydrogen Peroxide (TBHP) under microwave irradiation. Compound 2a showed best in vitro antiplatelet activity with 540 and 480 sec as clotting time in prothrombin time (PT) and activated partial thromboplastin time (APTT) assay respectively. Rest compounds showed good to moderate activity. Structures of all synthesized compounds were elucidated by IR, NMR and Mass spectrometry.

Recently, the use of green methodologies like sonication, use of ionic liquids, etc. attracted the attention of researchers in the field of organic synthesis as they have advantages such as mild reaction conditions, environmentally benign procedures, etc. Herein, this chapter highlights some recyclable ionic liquids (ILs) catalyzed ring closure reactions of chalcones to obtain several heterocyclic rings viz.; pyrazoles, pyrans, pyrimidines under ultrasonification. These reactions have very important features i.e., short routine, high yields, being environmentally friendly, high functional group tolerance, formation of a single product, high atom economy, high yielding, no need for column purification, etc. The various synthesized compounds were prepared in optimized reaction conditions in good to efficient yields. Analytical and spectral (FTIR, 1H, and 13C NMR) techniques were employed for the structural elucidation of the synthesized compounds. The ionic liquids used in the synthesis are recycled and reused several times.

A series of pyrano­[3,2-c]­quinolone derivatives has been synthesized in the presence of taurine (2-aminoethanesulfonic acid) as a green bio-organic catalyst and water as the solvent. The target compounds were synthesized through the three-component reaction between aldehydes, malononitrile/ethylcyanoacetate, and 4-hydroxy-1-methyl-2­(1H)-quinolone. The advantages of this protocol are excellent yields of products, short reaction times, cost efficiency, atom economy, and a simple work-up procedure with no need for extra purification techniques. Moreover, the catalyst can be easily recovered and reused for up to three cycles without losing any significant activity.

An environmentally friendly, economic synthetic protocol was advanced for synthesis of biologically and pharmacologically vital five-and six-membered heterocycles containing nitrogen, sulphur and oxygen as heteroatom. A series of thiazole derivatives was prepared by the reaction of substituted phenacyl halides and phenyl thiourea in the presence of TiO 2 nanoparticles (NPs) as nanocatalyst in DCM. Similarly, another series of six-membered heterocyclic compounds were synthesized by the reaction of phenacyl halides with phenylenediamine, 2-aminophenol, 2-aminobenzenethiol to produce corresponding products (1,4-quinoxaline, benzoxazine, benzothiazine) under catalytic effect of TiO 2 nanocatalyst. Analytical and spectral (FTIR, 1 H and 13 C NMR and SEM) techniques were employed for the structural elucidation of the synthesized compounds.

In recent years, magnetic nanoparticles and nanocomposites play an important role as a nanocatalyst in the creation of a wide range of bioactive heterocycles with extraordinarily high activity and selectivity, low energy consumption, and extended life. Among all heterocycles, many natural products, pharmaceuticals, and bioactive compounds contain pyran scaffolds which have a wide range of uses in biomedical research, industry, and medicine. Additionally, these are also widely used in the synthesis of novel heterocyclic systems as precursors. This study focused on recent advances in the last 5 years in using various magnetic recoverable and recycled nanoparticles and nanocomposites to synthesize pyran derivatives and their pharmacological activity. This article has been classified into three subsections: (i) MNPs‐metal nanocomposite catalyzed reactions, (ii) MNPs‐organic based nanocomposite catalyzed reactions, and (iii) MNPs‐ionic liquid nanocomposite catalyzed reactions and (iv) MNPs‐acid based nanocomposite to describe catalytic efficiency of magnetic nanocomposites for the synthesis of pyran derivatives. A comparative study of nanocomposites and different approaches for green synthesis of pyrans by highlighting the advantages and disadvantages along with catalyst recovery and recyclability has been mentioned, which will help scientists to probe and stimulate the study of these scaffolds.