Current Green Chemistry (v.3, #4)

Meet Our Editorial Board Member by Luca Sancineto (277-277).

Visible Light Photocatalyzed Carbon-Heteroatom Bond Formation and Synthesis of Related Compounds by Nirmalya Mukherjee, Pintu Maity, Tubai Ghosh, Subir Panja, Brindaban C. Ranu (279-317).
Background: In this Chapter an overview on visible light photocatalyzed carbonheteroatom bond formations (C-N, C-O, C-P, C-S/Se/Te etc.) and the synthesis of related compounds by environment friendly approach has been reported. We have discussed visible light photocatalyzed C-N bond formation including amination, imination, azidation, and amidation. Construction of C-O and C-P bond have also been studied by photoredox catalysis under visible light irradiation implicating a novel, powerful and green strategy. Visible light photocatalysis is also useful in the formation of C-S/Se/Te bonds avoiding harsh reaction conditions.

Methods: Moreover, using visible light irradiation the synthesis of many important heterocycles such as N-containing heterocycles (pyridine, quinoline, phenanthridine, dibenzo[a,f]quinolizidine and pyrroles etc), O-containing heterocycles (benzocoumarin, tetrahydrofuran and tetrahydropyran ), P-containing heterocycles (benzo[b]phosphole oxide), N-O-containing heterocycles (oxazole, isoxazole benzoxazole etc), N-S-containing heterocycles (thiazole and benzothiazole) and OS- containing heterocycles (oxathiolane) have been demonstrated.

Conclusion: A series of representative reactions and examples have been provided and in specific cases reaction mechanisms have been discussed for better understanding of the reaction.

Recent Progress in Asymmetric Aldol Reactions Under Solvent-free Conditions or in Aqueous Medium by Phatsimo Mokgweetsi, Lame Botlhole, Girija S. Singh (318-327).
The present article aims to review the recent developments in asymmetric aldol reactions under solvent-free conditions or in water. Asymmetric catalysis is undoubtedly the most popular technique for realizing enantioselective synthesis of different target molecules. Prolines and Cinchona alkaloids have emerged as very powerful chiral organocatalysts. There is continuous effort around the globe to develop greener methodologies for organic syntheses. Researchers have made efforts to apply the principles of green chemistry in asymmetric aldol reactions as well. The present review article focuses on the recent development of enantioselective aldol reactions under solvent-free conditions or in water as a green solvent. In many cases, such reactions occur at ambient temperature, thereby offering energy-efficiency in those transformations. L-proline and its derivatives, especially amides, have been observed to play prominent role in catalyzing asymmetric aldol reactions in aqueous medium or under solvent-free conditions. The use of compounds derived from azetidine, L-serine, and morpholine as catalysts in enantioselective aldol reactions in either aqueous medium or under solvent-less condition is also described.

Recent Advances in the Application of Meldrum's Acid in Multicomponent Reactions by Ankita Chaudhary, Pooja Saluja, Jitender M. Khurana (328-345).
Background: The design of environmentally benign protocols complying with the 'Green Chemistry principles' such as energy consumption, atom efficiency and sustainability has evoked immense interest among researchers.

Methods: Multicomponent reactions provide powerful synthetic method for the rapid generation of structurally diverse combinatorial libraries for drug discovery. These reactions avert the need for isolation as well as purification of intermediates, resulting in maximization of yield and reduction of waste, rendering the protocol environmentally benevolent. Meldrum's acid has been used in the design and synthesis of diverse types of heterocyclic compounds and considered as a vital building block in organic synthesis.

Conclusion: This review describes the multicomponent reactions of Meldrum's acid which serves as a starting material for the synthesis of heterocycles like pyrazines, quinolines, chromenes, pyrans, zwitter ions, pyridines, pyrimidines, pyrrolidiones, benzothiazines, benzoxazepines, amides, esters, spiro compounds, acids etc. with array of pharmacological properties.

Background: Polyaniline salts like polyaniline-sulfate (PANI-H2SO4), polyanilinehydrochloride (PANI-HCl), and polyaniline-phosphate (PANI-H3PO4) are swimmingly revealed as heterogeneous polymer supported catalysts for the polymerization of tetrahydrofuran to produce polytetramethylene ether glycol (PTMG).

Method: Polymerization of tetrahydrofuran by ring-opening in acetic anhydride environment using the pint-sized PANI catalyst at room temperature for 2 h resulted in the product, PTMG in the order: PANI-H2SO4 (35%) > PANI-HCl (30%) > PANI-H3PO4 (20%). The molecular weight of PTMG synthesized by PANI-H2SO4, PANI-HCl and PANI-H3PO4 catalysts are found to be 2244, 2034 and 2019 respectively.

Conclusion: These catalysts could be easily handled and reused. This approach gives phylloclade stem leaf-like morphology of highly crystalline polymer. Privileges of this method are reuasble, cheaper, user friendly synthesis, and eco-friendly nature of the catalyst.

Background: A simple and efficient one-pot green synthesis of 1,4-dihydropyridine derivatives and biphenyl derivatives has been reported. The overall conversion was assisted by ultrasound irradiation at ambient temperature (25-30 A°C) in aqueous medium.

Methods: All the products were synthesized in good toexcellent yields.

Conclusion: This study extends the applicability of the synthetic routes prompted by ultrasound irradiation under eco-friendly condition.

Background: A simple and eco-friendly synthetic protocol for synthesizing naphtho[ e]bis[1,3]oxazines in good yields has been developed by using one-pot three-component Mannich-type condensation cyclization reaction of various dihydroxynaphthalenes with primary amines and formaldehyde in water at 80-90°C.

Methods: The chemical structures of synthesized monomers were confirmed by IR, 1H-NMR, mass and elemental analysis.

Result: Some of these compounds exhibited promising processing window for polymerization according to their differential scanning calorimetric analysis.

Triphenyl Phosphite-mediated “Green” Synthesis of Novel Carboxycoumarin Amides by Pramod K. Sharma, Divya Mathur, Shashwat Malhotra, Neha Rana, Brajendra K. Singh, Ashok K. Prasad, Anjani J. Varma, Najam A. Shakil, Balaram Ghosh, Christophe Len, Ramesh C. Kuhad, Francois Jerome, Virinder S. Parmar (366-373).
Background: A library of eleven novel coumarin carboxamides were efficiently synthesized in high yields, by triphenyl phosphite-activated direct condensation of coumarin carboxylic acids and various alkyl amines.

Methods: The procedure has several advantages and addresses key 'Green' chemistry issues, such as one step condensation, no prior activation of coumarin carboxylic acids by toxic chlorinating agents, no toxic by-products are produced and does not involve troublesome/hazardous disposal of the catalyst. The synthesized coumarin carboxamides were examined for their antiinflammatory activity by measuring the effect on tumour necrosis factor-α (TNF-α) induced expression of intercellular adhesion moledule-1 (ICAM-1).

Conclusion: The structure-activity relationship (SAR) studies revealed that N-dodecyl-7- hydroxy-4-methyl-2-oxo-2H-chromene-8-carboxamide (23) exhibited the maximum inhibition (90%) of ICAM-1 expression at an IC50 value of 43 μM.