Current Green Chemistry - Volume 5, Issue 2, 2018

Quinoxaline and azole heterocyclic compounds (thiazoles, imidazoles, oxazoles, etc.) are important compounds from both an academic and industrial points of view. Furthermore, they have a great interest in medicinal chemistry due to their biological and pharmacological activities. The development of environmentally friendly synthetic methodologies that allow access to quinoxaline and azole nucleus is of critical interest to the scientific community. Recently, the research into new reagents that can accomplish a safe and efficient heterocyclic synthesis has grown enormously. The present review summarizes the utilization of N-halo compounds (e.g N-halosuccinimides, trihaloisocyanuric acids, N-halosulfonamides, etc.) as safe reagents for the construction of quinoxalines, thiazoles, oxazoles, imidazoles and related compounds.

2-methyltetrahydrofuran (2-MeTHF) has become a broadly used (biogenic) solvent in organic synthesis, particularly with promising applications in biocatalysis, due to its excellent behaviour and favourable properties. 2-MeTHF may be derived from renewable sources - such as furfural or levulinic acid and its low water solubility facilitates its complete recovery in reactions in aqueous media, reducing wastes and simplifying the recycling and reuse. 2-MeTHF properties typically outperform those of traditional solvents (such as THF), enabling its application in a wide range of chemical and enzymatic synthetic processes. Remarkably, this trend can be observed not only in academia, but also at industrial scale, where companies start to assess 2-MeTHF for the replacement of non-GRAS solvents (Generally Regarded As Safe). Given that increasing importance, this mini-review discusses the recent advances in biocatalysis using 2-MeTHF, with applications for different enzymes (hydrolases, oxidoreductases, lyases, etc.), as well as in innovative combinations such as gas-liquid mixtures (CO2-2-MeTHF expanded phase), in multi-step enzymatic systems, and flow biocatalysis. The combination of 2-MeTHF with the intrinsic sustainability associated with biotransformations creates an attractive synergy.

This study describes a new, simple and efficient process for the preparation of N-(2- hydroxyethyl)-2-oxo-2H-chromene-3-carboxamide, on a multigram scale (0.38 moles), by using ultrasound irradiation as green chemistry method. Optimal conditions and yield (83%) were obtained by using 1.2 molar equivalents of ethanolamine at 675 W for 5.0 hours. This intermediate is very versatile and could be transformed in a wide range of derivatives, which could be employed in different areas, such as inorganic complexes, dyes, pesticides and fluorescent coumarins. In the medicinal chemistry, N-(2-hydroxyethyl)-2-oxo-2H-chromene-3-carboxamide is also very useful because a wide variety of compounds could be synthesized and evaluated with diverse types of diseases. In this context, it can be mentioned N-(2-chloroethyl)-2-oxo-2H-chromene-3-carboxamide, a useful intermediate, which was synthesized in this work in gram scale (0.04 moles) in 80% of yield, that could react with diverse types of nucleophiles.

Oxidation of 2-(substituted thio) quinazolines in THF and aqueous media using stoichiometric amounts of oxone afforded their corresponding 2-(substituted sulfonyl)quinazolines with excellent selectivity (75-94% yield). This versatile synthetic protocol proved efficient with various substituted thio quinazoline compounds as substrates. All the twelve products were characterized by melting range, infrared, 1H-NMR, 13C-NMR and mass spectrometry.

Environmental requirements are becoming of great importance in today´s society since there is an increased interest in the industrial use of renewable resources. For this reason, the objective of the work presented was to examine and compare several natural, commercial or even waste products in diclofenac uptake, using synthetic water solutions in laboratory measurements. Diclofenac belongs to a class of drugs that provides analgesic, antipyretic and anti-inflammatory effects. To date, more than 200 different pharmaceuticals alone have been reported in river waters globally. According to the monitoring provided by the national water authorities and researchers, consumption of pharmaceuticals in the Czech and Slovak Republics are among the highest in Europe. According to our research, the results of the most effective adsorbents in diclofenac uptake from aqueous solutions were products in the following order: Chezacarb, with a capacity nearly 300 mg/g, Peatsorb CB18, with a capacity close to 250 mg/g, the German Silcarbon and the commercial product KlinoCarb, from the company Zeocem, with a capacity of ca. 200 mg/g. The domestic product KlinoCarb, which proved to have sufficiently high adsorption towards diclofenac, including a favourable price, was characterized by 1H-13C CP MAS NMR, Raman spectroscopy, XRD, and moreover, as with the other materials studied, by the SEM and S(BET) methods.

An efficient one-pot three-component reaction of ethyl acetoacetate with hydroxylamine hydrochloride and various aromatic aldehydes containing an electron donating group, was carried out. The current protocol gives diverse 4-arylidene-3-methylisoxazol-5 (4H) -ones providing good to excellent yield of products in an aqueous medium using iodine as a catalyst. This particular cyclocondensation reaction was performed in water, which is an environmentally benign universal solvent having unique properties being clean, efficient, inexpensive, and readily available.