Current Organocatalysis - Volume 8, Issue 1, 2021

The synthesis of organoselenium compounds continues to be a very active research area, due to their distinct chemical, physical and biological properties. Selenium-based methods have developed rapidly over the past few years and organoselenium chemistry has become a very powerful tool in the hands of organic chemists. This review describes the synthesis of organocatalysed bioactive selenium scaffolds especially including transition metal-catalysed diaryl selenide synthesis, Cu-catalysed selenium scaffolds, Pd-catalysed selenium scaffolds, asymmetric catalysis, Nickel catalysed selenium scaffolds and Rh-catalysed selenium scaffolds.

Background: Since the discovery of metal-free catalysts or organocatalysts about twenty years ago, a number of small molecules with different structures have been used to accelerate organic transformations. With the development of environmental awareness, to obtain highly efficient scaffolds, scientists have directed their studies towards synthetic methodologies that minimize or preferably eliminate the formation of waste, avoid toxic solvents and reagents and use renewable starting materials as far as possible. Methods: In this connection, the organocatalytic reactions providing efficiency and selectivity for most of the transformations have become an endless topic in organic chemistry since several advantages from both practical and environmental standpoints. Organocatalysts contributing to the transformation of reactants into products with the least possible waste production, have been serving the concept of green chemistry. Results and Conclusion: Organocatalysts have been classified based on their binding capacity to the substrate with covalent or noncovalent interactions involving hydrogen bonding and electrostatic interaction. Diverse types of small organic compounds including proline and its derivatives, phase-transfer catalysts, (thio)urease, phosphoric acids, sulfones, N-oxides, guanidines, cinchona derivatives, aminoindanol, and amino acids have been utilized as hydrogen bonding organocatalysts in different chemical transformations.

Cellulose sulfuric acid has proved its competence as a potential bio-compatible, non-toxic, and inexpensive heterogeneous solid acid catalyst in synthetic organic chemistry. Owing to its remarkable properties, such as non-hygroscopic nature, recyclability, superior catalytic activity and high stability, it has been actively explored as an efficient and biodegradable organocatalyst in diverse chemical transformations of synthetic relevance. This review attempts to summarize a significant advancement and catalytic applications of cellulose sulfuric acid for the synthesis of a plethora of biologically relevant organic molecules.

The use of small organic molecules as organocatalysts in organic synthesis has been intensely studied over the past decade. In this emerging field, considerable studies have led to the introduction of various efficient organocatalyzed synthetic methods of carbon-carbon and carbon- heteroatom bond formations. The use of these organocatalysts also showed environmentally benign reaction conditions compared to the metal-catalyzed transformations. In this review, we paid special attention to the most recent organocatalytic protocols reported for the synthesis of heterocycles. The studies have been outlined, depending on the organocatalysts used as: (i) nitrogen-based molecules as organocatalyst, (ii) NHCs as organocatalyst, and (iii) phosphorus-based molecules as organocatalysts. The discussion intends to reveal the scope as well as the vitality of organocatalysis in the area of heterocycle synthesis.

The recent widespread infection of COVID-19 in the entire world has created a pandemic situation with a serious health challenge to mankind. Numerous incidents of cardiovascular diseases were found among COVID-19 patients with a significantly high morbidity rate. Medication with several anticoagulant or blood thinner drugs are being performed on COVID-19 patients with atrial fibrillation and cardiovascular ailments to minimize the incidence of death. Warfarin is a widely used anticoagulant and cardiovascular drug prescribed as its sodium salt. S-Enantiomer is two to five times more active than R-enantiomer as an anticoagulant. Synthesis of enantiomerically pure warfarin is thus a rational and extremely important task. Organocatalyzed synthetic strategies may be considered as important avenues to produce optically pure warfarin in comparison to biocatalysis and chiral metal complex catalysis. Herein, a comprehensive review of the asymmetric organocatalyzed synthesis of warfarin catalyzed by diamine based organocatalysts, amino acidbased organocatalysts, quinine based organocatalysts, and proline derived organocatalysts in both aqueous and non-aqueous media has been discussed.

This review highlights the application of biopolymers of natural α-amino acids and its derived wild-type peptides employed as organocatalysts for the asymmetric synthesis of various important compounds published by researchers across the globe. The α-amino acid with L-configuration is available commercially in the pure form and plays a crucial role in enantioselective chiral molecule synthesis. Out of twenty natural amino acids, only one secondary amine-containing proline amino acid exhibited revolution in the field of organocatalysis because of its rigid structure and the formation of an imine like transition state during the reaction, which leads to more stereoselectivity. Hence, it is referred to as a simple enzyme in organocatalyst. Chiral enantioselective organic molecule synthesis has been further discussed by employing oligopeptides derived from the natural amino acids as a robust biocatalyst that replaced enzyme catalysts. The di-, tri, tetra-, penta- and oligopeptide derived from the natural amino acids are demonstrated as a potential organocatalyst, whose catalytic activity and mechanistic pathways are reviewed in the present paper. Several choices of organocatalyst are developed to achieve a facile and efficient stereoselective synthesis of many complex natural products with optically pure isomer. Subsequently, the researcher developed green and sustainable heterogeneous catalytic system containing organocatalyst immobilized onto solid inorganic support or porous material for accelerating reaction rate with asymmetric one isomer product through the heterogeneous phase. Further, researchers developed heterogeneous organocatalysts-Metal-Organic Frameworks (MOFs) that emerged as alternative simple and facile heterogeneous catalysts for the bulk production and flow reactor for enantioselective synthesis. This review compiled many outstanding discoveries in organocatalysts derivative of amino acids, peptides and heterogenized-MOFs employed for many organic transformations in research and industrial applications.

Background: Indoles and various indolyl derivatives are very common in naturally occurring biologically active compounds. Many methods are being developed for the synthesis of various bioactive indole derivatives. Objective: Synthesis of biologically promising structurally diverse indole derivatives under mild and environmentally benign conditions. Methods: Synthesis of 3-hydroxy-3-(5-(trifluoromethoxy)-1H-indol-3-yl)indolin-2-one was achieved by the reaction of an equimolar mixture of isatin and 3-(trifluoromethoxy)-1H-indol using 20 mol% of mandelic acid as catalyst in aqueous ethanol at room temperature. Under the same optimized reaction conditions, synthesis of 3-(3-hydroxy-2-oxoindolin-3-yl)chroman-2,4-diones was accomplished via the reactions of substituted isatins and 4-hydroxycoumarin. On the other hand, 2-hydroxy-2-(indol-3-yl)- indene-1,3-diones and 10-hydroxy-10-(5-methoxy-1H-indol-3- yl)phenanthren-9(10H)-one were synthesized from the reactions of indoles and ninhydrin or 9,10-phenanthrenequinone respectively using the same 20 mol% of mandelic acid as an efficient organo-catalyst in aqueous ethanol at room temperature. Results: Mild, safe and clean reaction profiles, energy efficiency, high atom-economy, use of naturally occurring non-toxic organo-catalyst, easy isolation procedure by avoiding column chromatographic purification and gram scale production are some the major advantages of this developed protocol. Conclusion: A simple, straightforward and eco-friendly protocol has been developed for the efficient synthesis of biologically promising novel 3-hydroxy-3-(5-(trifluoromethoxy)-1H-indol- 3-yl)indolin-2- one, 3-(3-hydroxy-2-oxoindolin-3-yl)chroman-2,4-diones, 2-hydroxy-2-(indol-3- yl)-indene-1,3-diones and 10-hydroxy-10-(5-methoxy-1H-indol-3-yl)phenanthren-9(10H)-one using a catalytic amount of mandelic acid in aqueous ethanol at room temperature.