Current Green Chemistry (v.3, #3)

Meet Our Editorial Board Member by Kenta Arai (193-193).

Background: 1,3-Dipolar azide-alkyne cycloaddition (AAC) reaction, often referred to as click reaction, is an expeditious and robust protocol for the construction of triazole derivatives. In most cases, the reaction is catalyzed by a copper catalyst.

Methods: Non-conventional microwave heating has been used for the reaction showing ample advantages over the conventional thermal heating.

Conclusion: This article has presented an overview on the recent advances in the area of microwave- induced AAC reactions in the presence of both homogeneous and heterogeneous copper catalysts, besides a few examples of Ru-catalyzed as well as metal-free AAC reactions.

Background: Recently, ZnTiO3 nanopowder has become an important class of highly stable, environmentally benign, reusable and heterogeneous catalyst.

Method: It has been prepared by means of a sustainable sol-gel method and thoroughly characterized by XRD, SEM and HRTEM analysis.

Result: The dual nature of catalyst displays an imperative role towards quick transformation of amines, formaldehyde and 1- or 2-naphthol to respective [1,3]-oxazine derivatives with good yields (70-92 %) in eco-friendly water medium at room temperature (25-30 °C) under stirring condition.

Sulfamic Acid-catalyzed One-pot Multicomponent Synthesis of 5-phenyl-2- thioxo-1,2,3,5-tetrahydro-4H-pyrimido[4,5-d][1,3]thiazolo[3,2-a]pyrimidin- 4-ones by Sunetra Jadhav, Ajinkya Patravale, Reshma Patil, Digambar Kumbhar, Vishram Karande, Dattatray Chandam, Madhukar Deshmukh (227-234).
Background: A straightforward protocol for the one-pot synthesis of a series of novel thiazolopyrimidine derivatives has been developed.

Method: In which multicomponent reaction between thiobarbituric acid, 2-aminothiozole and several substituted aldehydes using sulfamic acid (20 mol%) as a heterogeneous and easily recoverable catalyst in ethanol under reflux condition.

Conclusion: This method has several advantages like greener synthetic approach, good to excellent yield (82-91%), cost-effectiveness, easy work-up and atom-economic procedure.

Background: Catalyst-free nucleophilic substitution between hydroxylactam and thiol was developed for the construction of N (acyl), S-acetal skeletons.

Methods: The new protocol provides a series of isoindolo-β-carboline-derived N (acyl), S-acetals in high yields.

Result: The methodology has many advantages, such as catalyst-free, mild reaction conditions, simple operations, high atom-economy, and water as by-product and so on. The reaction mechanism was also discussed.

A Solvent-free Method for Synthesis of Dihydroangelicins using Microwaves by Diego M. Ruiz, Juan C. Autino, Gustavo P. Romanelli (242-247).
Background: Dihydrofurocoumarins are a large family of compounds, among them, dihydroangelicins and dihydropsoralens, are present in various plant species with varied biological activity. Several strategies have been developed for synthesizing these compounds and various catalysts have been used for this purpose.

Methods: In this work, we report the synthesis of 8,9-dihydrofuran [2, 3-h] coumarins using allyloxycoumarin cycloaddition in sustainable conditions: absence of solvents, application of microwave radiation, and insoluble acid catalysis by means of heteropolyacids with Preyssler structure, [H14(NaP5MoW29O110)].

Conclusion: With these conditions, and testing sustainability by means of Eco-Scale and E-factor, we replace the use of solvents and mineral acids having a great impact on the environment with a solid, easily recoverable heteropolyacid.

Background: Molecular hybridization (MH) is currently well-practiced in the rational drug design and has offered notable success in developing various lead candidates. With the proven pharmaceutical potentials of 4H-pyrans and indoles, the present work has been conceived to unit these two potent structural motifs within one molecular architecture by introducing a new protocol that satisfies several green chemistry aspects.

Method: The aim of this present work is to develop a facile and eco-friendly protocol for the synthesis of biologically relevant diversely substituted 2-amino-3-cyano-4-(3-indolyl)-4H-chromenes at ambient conditions. Characterizations of the synthesized compounds have been performed using analytical and spectral tools.

Results: A practical method for the facile one-pot synthesis of a series of pharmaceutically interesting functionalized 2-amino-4-(indol-3-yl)-4H-chromene-3-carbonitriles has been developed from the sequential Knoevenagel-cyclocondensation and Michael addition between salicylaldehydes, malononitrile and indoles in aqueous ethanol at room temperature based on commercially available trisodium citrate dihydrate as an inexpensive and eco-friendly catalyst.

Conclusion: We have developed a simple, energy-efficient and eco-friendly method for easy access to such heterocycles of promising interest from a one-pot multicomponent reaction. The mild reaction conditions at room temperature, good to excellent yields, operational simplicity, absence of tedious separation procedures, clean reaction profiles, reusability of the reaction media, energy efficiency, high atom economy, as well as the use of inexpensive and environmentally benign catalyst are the key advantages of the present method.

Green Synthetic Routes to Pharmaceutical Drugs by Patricia G. Ferreira, Caroline D. Nicoletti, Fernando de C. da Silva, Vitor F. Ferreira (259-276).
Background: Pharmaceutical companies produce synthetic drugs in complex multiple-step processes, but due to this high complexity, they generate a large amount of waste and consume high amounts of water and energy. The criticism of environmental agencies around the world has led to demands for changes in these processes.

Methods: With advances in new green reaction conditions and new manufacturing processes, these industries have lowered their impact on the environment. This paper addresses how pharmaceutical companies have developed alternative routes for some drugs within the precepts of green chemistry.