Current Organic Chemistry - Volume 22, Issue 1, 2018

Background: In recent years, there has been a growing interest in the environmental relevance of the presence of several pharmaceutical compounds and their metabolites in water. To avoid further accumulation of these compounds and their metabolites in the aquatic environment, several research groups are investigating chemical and photochemical methods that could be applied in their destruction and subsequent removal from natural and wastewater. Objective & Method: Different chemical advanced oxidation processes are being developed to destroy organic pollutants in water. Most of these methods are based on the production of HO• radicals that are known to be highly reactive and strong oxidizing agents. In aqueous chemical processes, these radicals can be generated using a variety of reagents and under different reaction conditions such as O3, H2O2/UV, TiO2/UV, O3/UV, H2O2/Fe2+, H2O2/Fe2+/UV and O3/Fe2+/Cu2+/UV. This review is a survey on recent advances in the application of different chemical advanced oxidation processes to mineralize pharmaceuticals. Paracetamol was selected as a model compound since its structure is the main component or metabolite of several anesthetic and analgesic compounds. The degradation of paracetamol by different advanced oxidation methods has been investigated by a combination of techniques (TOC, UV-Vis, IR, HPLC and GC-MS) in order to determine the optimal reaction conditions, kinetics, intermediate and product compounds generated. Conclusion: Understanding the basic concepts about reaction conditions, intermediates and mechanistic details on mineralization of paracetamol will be quite useful for future applications of several techniques in the removal of this and other structurally related pharmaceutical and aromatic compounds from water.

Heliannuols are a unique class of Benzoxacyclic Allelopathic Sesquiterpenes obtained from sunflowers. Allelopathy has been a keen point of interest for researchers and represents a novel but unexplored “Methodology of self-defense mechanism”. Heliannuols exhibit a varied structural pattern of five to eight fused benzoxacycles. Isolation as well as synthesis of eleven members of this group namely heliannuol A to heliannuol L has already been reported. Helianane was initially thought to be a unique member of this group containing an eight-membered benzoxocane framework. The Ring closing Metathesis (RCM) has been explored to a great extent amongst the synthetic intrigues undertaken towards this category of natural products. Recent synthetic approaches and structural studies have demanded for an amendment of helianane to curcudiol, and a tetrahydrobenzofuran ring framework for heliannuol G and H rather the earlier predicted benzoxocane ring system. Albeit, it is perceived that the underlying unexplored directions regarding the structural anomaly have been highlighted in this review. The review explains exciting synthetic intrigues, bioactivity and structural amendment and the probable perplexity of this class of novel benzoxacyclic sesquiterpenes.

Background and Methods: Ratiometric fluorescent probes can provide more precise measurement results than intensity-based fluorescent probes. Carbon dots are convenient platforms to construct ratiometric fluorescent probes. Carbon dots-based ratiometric fluorescent probes can be constructed by carbon dots and other fluorophores' simple mixing or by connecting them via covalent bonds or non-covalent bonds. Otherwise, dual-emission carbon dots can also be taken as the ratiometric fluorescent probes. Carbon dots are reference signals, energy donors, response signals and the double emission matrixes in ratiometric probes. Conclusion: The development of carbon dots-based ratiometric fluorescent probes in recent five years is reviewed in this study which emphasizes their photoluminscene properties, detection mechanisms and applications.

Background: Microwave irradiation has emerged as a useful synthetic strategy for chemists and drug developers due to enhanced yields, regioselectivity, and faster reaction times. One area of importance in its practice has been the design of spiro compounds, which possess great interest on account of their natural occurrence and medicinal capabilities. The increasingly large number of these scaffolds and unlimited amount of methodologies utilized in their preparation have made them good candidates for the microwave assisted approach. Conclusion: Therefore, this review emphasizes the use of microwave irradiation in the synthesis of spiro heterocyclic compounds.

Background: Azole-fused pyrimidinones have been synthesized and tested for biological activities. The present copper-catalyzed version will be attempted as an alternative synthetic method for such N-fused hybrid structures. Objective: This research aims to develop a new synthetic method of azole-fused pyrimidinones from β-bromo-α,β-unsaturated amides and azoles (benzimidazole, imidazole and pyrazole). Method: β-Bromo-α,β-unsaturated amides react with azoles in DMF at 100°C for 1 h in the presence of a catalytic amount of copper powder and base under microwave irradiation. Result: β-Bromo-α,β-unsaturated amides are coupled and cyclized with azoles to give the corresponding azolefused pyrimidinones in moderate to good yields via tandem intermolecular C-N coupling and C-N formative cyclization by C-H activation. Conclusion: This work provides a new method for synthesizing N-fused hybrid scaffolds such as benzimidazo[ 1,2-a]pyrimidin-2-ones, imidazo[1,2-a]pyrimidinones and pyrazolo[1,5-a]pyrimidinones from readily available starting compounds.

Background: Molybdophosphoric acid (PMo) is used in heterogeneous catalysis. The incorporation of vanadium in the primary structure and a transition metal in the secondary structure of PMo improves the oxidative and acidity capacity. 4- Dihydropyrimidin-2-(1H)-thiones/-ones (DHPMs) derivatives are relevant because of their biological activities. The development of ecofriendly procedures, such as multicomponent reactions, to prepare DHPMs is an important challenge for organic chemistry. Objective: Study the effect of adding transition metal counterions to 11-molybdo-1- vanadophosphoric acid (PMoV) on its catalytic activity for the synthesis of bioactive DHPMs derivatives. Method: Transition metal-doped heteropolyacid catalysts (PMoV, FePMoV, and CuPMoV) were prepared and characterized by Fourier transform infrared spectroscopy, 31P nuclear magnetic resonance, and diffuse reflectance spectroscopy. The acid properties were determined by potentiometric titration. A series of bioactive DHPMs derivatives, such as monastrol, were synthesized by a one-pot procedure using the catalysts under solvent-free conditions. Results: The incorporation of V, Fe and Cu in the primary or secondary structure of PMo improved the catalytic activity of the materials. The proposed DHPMs synthesis required short reaction time (1 h) and a temperature of 80°C. A correlation between the yields of monastrol and the acid strength or the number of acid sites of the catalysts was observed, namely, FePMoV>CuPMoV>PMoV>PMo. The FePMoV catalyst was easily recycled and reused without appreciable loss of activity. Conclusion: The described method is a simple, clean and environmentally friendly alternative for the preparation of 22 bioactive substituted DHPMs with very good yields and high selectivity.