Current Organic Chemistry - Volume 24, Issue 1, 2020

This review is a compilation of the green synthetic methods used in the synthesis of coumarin derivatives. Coumarins are a class of compounds with a pronounced wide range of biological activities, which have found their application in medicine, pharmacology, cosmetics and food industry. Their biological activity and potential application are highly dependent on their structure. Therefore, many researchers have been performing the synthesis of coumarin derivatives on a daily basis. High demands for their synthesis often result in an increased generation of different waste chemicals. In order to minimize the utilization and generation of toxic organic substances, green synthetic methods are applied in this manner. These methods are getting more attention in the last few decades. Green chemistry methods cover a wide range of methods, including the application of ultrasound and microwaves, ionic liquids and deep eutectic solvents, solvent-free synthesis, mechanosynthesis and multicomponent reactions. All typical condensation reactions for coumarin synthesis like Knoevenagel, Perkin, Kostanecki-Robinson, Pechmann and Reformansky reactions, have been successfully performed using these green synthetic methods. According to the authors mentioned in this review, not only these methods reduce the utilization and generation of toxic chemicals, but they can also enhance the reaction performance in terms of product yields, purity, energy consumption and post-synthetic procedures when compared to the conventional methods. Due to the significance of coumarins as biologically active systems and the recent demands of reducing toxic solvents, catalysts and energy consumption, this review provides a first full literature overview on the application of green synthetic methods in the coumarin synthesis. It covers a literature search over the period from 1995-2019. The importance of this work is its comprehensive literature survey on a specific class of heterocyclic compounds, and those researchers working on the coumarin synthesis can find very useful information on the green synthetic approaches to their synthesis. There are some reviews on the coumarin synthesis, but most of them cover only specific reactions on coumarin synthesis and none of them the whole range of green chemistry methods.

The present review provides an overview of visible light-mediated environment- friendly approaches over the past decade for the formation of carbon-carbon and carbon-heteroatom framework. This area has recently emerged as a versatile, environmentally benign and green platform for the development of a highly sustainable synthetic methodology. According to the recent advancements, visible light has come to the forefront in synthetic organic chemistry as a powerful green strategy for the activation of small molecules.

During the past several decades, hypervalent iodine reagents have been widely used in various organic transformations. Specifically, these exclusive classes of reagents have been extensively used for the construction of carbon-carbon bonds. This review aims to cover all the reactions involving the construction of carbon-carbon bonds mediated by hypervalent iodine reagents, providing references and highlights for synthetic chemists who are interested in hypervalent iodine chemistry.

Flavonoids are one of the most common secondary metabolites occurring in plants. Their activity in the Central Nervous System (CNS) including sedative, anxiolytic, anti-convulsive, anti-depressant and neuro-protective actions is well known and documented. The most popular methods for detection, identification and structural elucidation of flavonoids are these based on Nuclear Magnetic Resonance (NMR) and mass spectrometry (MS). NMR allows rapid, high throughput analysis of crude extracts and also gives stereochemical details about identified substances. However, these methods are expensive and less sensitive than MS-based techniques. Combining High Performance Liquid Chromatography (HPLC) with MS detection gives the most powerful tool for analysis of flavonoids occurring in plants. There is a lot of different approaches to use LC/MS based techniques for identification of flavonoids and this short review shows the most important.

Bryophytes, phylogenetically placed between algae and pteridophytes, are divided into three classes, mosses, liverworts, and hornworts. The traditional system of medicine throughout the world has been utilizing this group of plants to treat various ailments. One of the outstanding features of these spore-forming plants is their chemistry, especially that of the liverworts. Liverworts and other bryophytes have yielded a rich array of secondary metabolites. Many of these compounds are characterized by unprecedented structures, and some have not been found in any other plants, fungi, or marine organisms. Among the bryophytes, the chemical constituents of liverworts and their biological activity have been studied in the most detail. In this review, we demonstrate the chemistry of the liverworts, mosses, and hornworts, and also neuroprotective activity of dimeric herbertane- type sesquiterpenoids, mastigophorenes and secoaromadendrane-type sesquiterpenoids, marchantin-type cyclic bisbibenzyls with muscle-relaxant activity, or ent-longipinane-type sesquiterpenoids with acetylcholinesterase inhibitory activity, among others.