Current Organocatalysis - Volume 9, Issue 1, 2022

Organocatalysis was established to be a wide-applicable approach from its inception and rediscovery in the year 2000, where proline was used as a catalyst in aldol condensation and soon after the successful emergence of iminium catalysed reactions in organic synthesis. Development of new potential catalytic systems is always an important as well as an uphill task for scientists and researchers. The fundamental organic synthesis majorly deals with metal based catalysts, whereas there is a constant surge of developing metal free reaction condition to make the reactions environmental friendly. For the synthesis of complex organic molecules, reduction and oxidation reactions are always needed and there are plenty of catalysts available for these reactions. Organocatalysts are also developed and applied for these two elementary reactions. This review focuses on some of the latest developments and applications of organocatalysts in oxidation and reduction reactions in fundamental organic synthesis.

Ascorbic acid, also known as Vitamin C, is the most important vitamin observed in diverse food. Ascorbic acid has various applications in several fields. Studies have depicted that in organic synthesis, it can be used as a mediator or substrate. The derivatives of ascorbic acid have been found to possess numerous biological activities. In this review, we report the important derivatives of ascorbic acid, which have significant biological activities. Various studies are considered in this review to prove its wide range of availability.

Green chemistry is also referred to as sustainable technology, which involves the design, synthesis, processing and the use of chemical substances by reducing or eliminating the chemical hazards. This strategy focuses on atom economy, use of safer solvents or chemicals, use of raw materials from renewable resources, consumption of energy and decomposition of the chemical substances to non-toxic material which are eco-friendly. So, this technology is utilized for the sustainable development of novel heterocyclic scaffold like pyrimidine derivatives. Pyrimidine is a six membered heterocyclic aromatic compound with two nitrogen atoms at positions 1 and 3 in the ring system. Among the other heterocyclic compounds, pyrimidine derivatives play a major role due to their diverse promising biological activities, such as antimicrobial, antifungal, anti-viral, anti- tubercular, anti-diabetic, anti-hypertensive, anticancer, anthelmintic, antioxidant, anti-epileptic, antipsychotic, anti-anxiety, antimalarial, antihistaminic, anti-parkinsonian, analgesic and anti-inflammatory etc. The various green methods used for the synthesis of pyrimidine derivatives include microwave assisted synthesis, ultrasound induced synthesis, ball milling technique, grinding technique and photo-catalysis. These processes enhance the rate of the reaction that leads to high selectivity with improved product yields as compared to the conventional synthetic methods. This review is focused on the green synthesis of biologically active pyrimidine derivatives.

Background: Soil is an ultimate source of all types of nutrients, which have both biological and non-biological importance. Studies are being carried out to isolate the various type of micro- organism from soil which has much more importance. So in the present study, amylase-producing bacteria have been isolated from various soil samples. Aim: The isolation, identification, and estimation of various microbial strains for α-amylase enzyme production and then the inhibition of the growth of these microbial stains. Methods: The bacterial strains were isolated and then identified by various microbiological methods, including Gram’s staining method followed by several biochemical methods such as litmus test, Gelatin test and Urea agar media, and by viable cells. Results: Altogether, three microbial strains were identified from the soil samples in the concerned study. The concerned strains include- Shigella, Proteus and Bacillus, respectively. The concerned microbial strains were then analyzed for the amount of amylase enzyme, and it had been found that Bacillus sp produce much more amount of amylase followed by Shigella sp, and lesser amylase enzyme- producing activity was found in Proteus sp. The isolated bacteria were then analysed for inhibition of their growth by water and ethanolic extracts of Cuminum cyminuni. Among the extracts, it had been found that water extracts exhibited more inhibiting capacity than ethanolic extracts. The study also revealed that among the bacterial strains, the Shigella sp got much more affected by the concerned plant extracts followed by Proteus sp and the least inhibition was observed against the Bacillus sp. Conclusion: As per the above study, it is being concluded that - three amylase-producing bacteria viz Shigella, proteus, bacillus sp were isolated from the soil samples. These isolated microbial strains could be used for the decomposition of cholesterol levels in humans in addition to other microbial activity. These isolated bacterial could sometimes be averse, so their growth could be stopped by various biological and chemical substances like Gentamicin and by various Plant extracts viz, Cuminum cyminuni Plant.

Aims: Synthesis of 11H-indeno[1,2-b]quinoxalin-11-ones as well as 6H-indeno[ 1,2-b]pyrido[3,2-e]pyrazin-6-one derivatives under greener conditions. Background: Quinoxaline and related skeletons are very common in naturally occurring bioactive compounds. Objective: Design a facile, green and organo-catalyzed method for the synthesis of 11H-indeno[ 1,2-b]quinoxalin-11-ones as well as 6H-indeno[1,2-b]pyrido[3,2-e]pyrazin-6-one derivatives. Methods: Both the scaffolds were synthesized via the condensation of ninhydrin and o-phenylenediamines or pyridine-2,3-diamines respectively by using a catalytic amount of mandelic acid as an efficient, commercially available, low cost, organo-catalyst in aqueous ethanol at room temperature. Results: Mild reaction conditions, use of metal-free organocatalyst, non-toxic solvent, ambient temperature, and no column chromatographic separation are some of the notable advantages of our developed protocol. Conclusion: In conclusion, we have developed a simple, mild, facile and efficient method for the synthesis of structurally diverse 11H-indeno[1,2-b]quinoxalin-11-one derivatives via the condensation reactions of ninhydrin and various substituted benzene-1,2-diamines using a catalytic amount of mandelic acid as a commercially available metal-free organo-catalyst in aqueous ethanol at room temperature. Under the same optimized reaction conditions, synthesis of 6H-indeno[ 1,2-b]pyrido[3,2-e]pyrazin-6-one derivatives was also accomplished with excellent yields by using pyridine-2,3-diamines instead of o-phenylenediamine.

Aims: In search of a ligand-free, recyclable, selective, and stable catalytic system, we engineered both Pd/GO and Pd/rGO composites and tested them as catalysts for Heck and Suzuki reactions in [bmim] NTf2 ionic liquid medium. Background: Various reports and reviews have been published on exploring the application of ionic liquids as a reaction medium for different organic transformations. Recently, graphene-supported Pt nanoparticles have immobilized with the 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene bis(trifluoromethylsulfonyl) imide ionic liquid [MTBD][bmsi] and further tested to study the oxygen reduction reaction. Surprisingly, [MTBD][bmsi] immobilized system was found highly active towards electrocatalytic reaction. Objective: In various reports, palladium nanoparticles were immobilized with Graphene Oxide (GO) or with reduced graphene oxide (rGO), and these two types of graphene were further tested as a catalyst for different coupling reactions such as Suzuki-Miyaura, Heck, and Suzuki reaction. Both Pd/GO and Pd/rGO were found attractive concerning catalyst specific property, i.e., high surface area, and because of that, graphene immobilized palladium was found to be similar to other commercially available palladium catalysts (e.g., Pd on charcoal), but collectively, both hybrid materials (Pd/GO and Pd/rGO) possess various drawbacks, like high catalyst loading, catalyst leaching (via agglomeration of Pd metals into the clusters) during the recycling test (especially in case of Pd/GO), limited substrate scope, and the requirement of polar solvents, etc. Methods: All the chemicals were purchased from Sigma Aldrich, Acros, or Fluka. NMR spectra were recorded on a standard Bruker 300WB spectrometer with an Avance console at 300 and 75 MHz for ¹H and ¹³C NMR, respectively. Pd/O and Pd/rGO were synthesized as per the reported procedure. The residue was purified by Flash Chromatography (FC) with hexane/ethyl acetate. The detailed ¹H and ¹³C NMR of each Heck and Suzuki reaction product were found similar to the reported analytical data. 1-butyl-3-methylimidazolium bis (trifluoromethyl sulfonyl) imide ([bmim]NTf2) was synthesized as per the reported procedure. Results and Conclusion: We have successfully developed a highly efficient ligand-free method for Heck and Suzuki reaction, using Pd/rGO catalysts in an ionic liquid medium which afforded the coupling products with excellent yield. One of the major advantages of the proposed protocol is that the catalyst system can be easily re-usable without the loss of catalytic activity, thereby multiplying catalyst turnover. Another advantage is that the reaction proceeds without phosphine ligands, which are expensive, toxic, and contaminants of the product. The green nature of ionic liquid and the simplicity of its operation make the present Heck and Suzuki reactions more attractive.

Background: Presently worldwide manufacturing of formic acid follows the permutation of methanol and carbon monoxide in presence of a strong base. But due to the use of toxic CO molecule and easy availability of CO2 molecule in the atmosphere, most of the research has been shifted from the conventional method of formic acid synthesis to direct hydrogenation of CO2 gas using different homogenous and heterogeneous catalysts. Objective: To develop reaction protocol to achieve easy CO2 hydrogenation to formic acid using Ionic liquid reaction medium. Methods: We used the sol-gel method followed by calcination (over 250°C for 5 hours) to synthesize two types of ruthenium metal-doped TiO2 nanoparticles (with and without ionic liquids), namely Ru@TiO2@IL and Ru@TiO2. We are reporting the application NR2 (R= CH3) containing imidazolium- based ionic liquids not only to achieve a good reaction rate but also to get agglomeration free ruthenium metal-doped TiO2 nanoparticles along with easy product isolation due to the presence of NR2 (R= CH3) functionality in ionic liquid structure. We synthesized various NR2 (R= CH3) functionalized ionic liquids such as 1-Butyl-3-methylimidazolium Chloride, 1,3-di(N,Ndimethylaminoethyl)- 2-methylimidazolium trifluoromethanesulfonate ([DAMI][TfO]), 1,3-di(N,Ndimethylaminoethyl)- 2-methylimidazolium bis (trifluoromethylsulfonyl) imide ([DAMI][NTf2]) and 1-butyl-3-methylimidazolium chloride ionic liquids which were synthesized as per the reported procedure. Results: We easily developed two types of Ru metal-doped TiO2 nanoparticles using the sol-gel method. After calcination, both Ru@TiO2@IL (3.2 wt% Ru), and Ru@TiO2 (1.7 wt% Ru) materials were characterized by XRD, FTIR, TEM, ICP-AES, EDS, and XANES analysis. After understanding the correct structural arrangement of Ru metal over TiO2 support, we utilized both Ru@TiO2@IL (3.2 wt% Ru) and Ru@TiO2 (1.7 wt% Ru) the materials as a catalyst for direct hydrogenation of CO2 in the presence of water and functionalized [DAMI] [TfO] ionic liquid. Conclusion: Here we demonstrated the preparation and characterization of TiO2 supported Ru nanoparticles with and without ionic liquid. After understanding the correct morphology and physiochemical analysis of Ru@TiO2@IL (3.2 wt% Ru), and Ru@TiO2 (1.7 wt% Ru) catalysts, we examined their application in CO2 reduction and formic acid synthesis. During the optimization, we also noticed the significant effect of functionalized [DAMI] [TfO] ionic liquid and water to improve the formic acid yield. Lastly, we also checked the stability of the catalyst by recycling the same till the 7^th run.

Aims: A green route for the oxidation of alcohols to corresponding carbonyl compounds in room temperature ionic liquid ([CEMIM]BH4) was developed using hydrogen peroxide as the oxygen source. In aqueous solution at room temperature, 0.2 mol% of ([CEMIM]BH4) showed excellent catalytic properties for selective oxidation of aromatic and aliphatic alcohols. Background: One of the vital reactions in organic synthesis is the oxidation of alcohols to carbonyl compounds. In particular, the conversion of primary alcohols to aldehydes has been utilized in a variety of applications as they are used as intermediates in fine chemicals mostly in the perfume industry. Objective: In the present work, we have reported an effective green route for the selective oxidation of alcohols to the carbonyl compounds using peroxide in an ionic liquid 1-carboxyethyl- 3-methyl-imidazolium tetrahydroborate ([CEMIM]BH4). Methods: A mixture of alcohol (2 mmol), ([CEMIM]BH4) (0.2 mol%), and H2O2 (2 mmol) were stirred thoroughly with the help of a magnetic stirrer for 10 min at ambient temperature. Results: The catalytic activity of ([CEMIM]BH4) is very effective, which reflect its good solvating nature during oxidation. Conclusion: In conclusion, the series of described experiments represents a useful method for the oxidation of primary and secondary alcohols to carbonyl compounds at room temperature. The catalyst can be easily prepared and is therefore extremely cost-effective. The rapid reaction time for the substrates shows that a large number of materials may be screened in parallel over a short period of time.

Background: The synthesis of 5-arylation uracil nucleosides is an imperative challenge, especially for the method of Suzuki reaction using N-unprotected uracil as materials, which holds the potential to enhance the yield. Objective: The objective of this study was to find a more efficient catalyst to increase the yield of aryluracils and aryluridines. Methods: We first constructed the Phosphanamine-Grafted Cellulose (PAGC) from cellulose material. Then the nanocatalyst PAGC/Pd(0) was prepared through heating and reducing the mixture of PAGC and Pa(OAc)2. Results: When using this nanocatalyst to catalyze the Suzuki reaction of 5-iodouracil or 5-iodouridine and aryl heterocyclic boronic acids, the arylation yields have been significantly improved. Conclusion: This means that the resultant nanocatalyst exhibits a remarkable catalytic efficacy for Suzuki arylation of 5-iodouracil and 5-iodouridine.