Direct C-H bond arylation of (hetero)arenes is a very convenient approach for the synthesis of a wide variety of molecular targets, including compounds of pharmaceutical interest and π-conjugated ...small molecules and polymers. Compared to traditional transition metal-promoted cross-coupling reactions, direct C-H arylations best fit the
Green Chemistry
criteria, particularly in minimization of waste, use of less hazardous chemicals, atom economy, and reduction of unnecessary derivatization steps. Despite the advantages, these reactions still initially suffered from major limitations in terms of sustainable chemistry,
i.e.
, toxic and expensive transition-metal catalysts, toxic and/or hazardous solvents, high temperatures and long reaction times. The increasing attention towards environmentally friendly reaction protocols has boosted studies directed towards the development of sustainable strategies for direct C-H bond arylation of (hetero)arenes. This review offers a critical overview of the research on this topic, focusing on three main aspects: (i) recoverable catalysts; (ii) sustainable solvents; (iii) non-conventional energy sources.
A comprehensive and critical overview of the sustainable strategies for direct C-H bond arylation of (hetero)arenes, based on the use of recoverable catalysts, sustainable solvents and non-conventional energy sources, has been performed.
Direct arylation of 5-octylthieno3,4-cpyrrole-4,6-dione with a series of functionalized aryl iodides via C–H bond activation is demonstrated in a deep eutectic solvent made of choline chloride and ...urea in non-anhydrous conditions and without exclusion of air. This is the first demonstration of a thiophene–aryl coupling via direct arylation in deep eutectic solvents.
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The increasing attention towards environmentally friendly synthetic protocols has boosted studies directed to the development of green and sustainable methods for direct C−H bond arylation of ...(hetero)arenes. In this context, here the infrared (IR) irradiation‐assisted solvent‐free Pd‐catalyzed direct C−H bond arylation of (hetero)arenes was achieved. Several heteroaryl‐aryl coupling reactions were described, also involving heterocycles commonly used as building blocks for the synthesis of organic semiconductors. The reaction tolerated many functional groups on the aromatic nuclei. The IR‐irradiation as the energy source compared favorably with thermal heating and, in combination with solvent‐free conditions, provided an important contribution to the development of protocols fitting with the principles of green chemistry.
No solvent needed: Pd‐catalyzed (hetero)aryl–aryl coupling via C−H bond activation is proven in solvent‐free conditions under IR irradiation as effective and convenient energy source. The reaction efficiently works on several conjugated cores and tolerates several functional groups on aryl iodides used as coupling partners. The protocol opens the way to energy‐effective solvent‐free methods in organic synthesis.
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Direct arylation of thienopyrrolodione, diketopyrrolopyrroles, benzodithiophene derivatives, and fluorinated heteroarenes with functionalized aryl iodides is proven in solvent-free and non-anhydrous ...conditions. The reaction is performed in the presence of air and tolerates several functional groups on both the coupling partners, enabling a convenient synthesis of extended heteroaromatic conjugated molecules.
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Production of value-added compounds from waste materials is of utmost importance for the development of a sustainable society especially regarding their use as catalysts in industrially relevant ...synthetic reactions. Herein, we show the production of laccases from four white-rot fungi, which were grown on agricultural residues, specifically Trametes versicolor 11269, Pleurotus ostreatus 1020, Panus tigrinus 707 and Lentinula edodes SC-495. The produced laccases were tested on a laccase-mediator system (LMS) for the biocatalytic oxidation of the model substrate benzyl alcohol into benzaldehyde. The LMS was carried out in the presence both of tetrahydrofuran as co-solvent and of the mediator 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) due to its high redox potential and its ability to perform the oxidation. Tolerance studies showed that the dialyzed solutions were able to tolerate 1% (99:1 v/v) of co-solvent, whereas a concentration of 10% v/v had a detrimental activity. Performances in the biocatalytic oxidation of laccase solutions from different purification steps were compared. Similar conversion was observed for laccase in dialysis (raw) and gel filtration (GF) product versus commercial T. versicolor laccase. The latter oxidized almost 99% of substrate while the other laccase solutions were able to reach a conversion from 91% for the laccase solution from P. tigrinus 707 after dialysis, to 50% for the laccase solution from P. ostreatus 1020 after gel filtration. This work highlights the potential of unpurified laccase solutions to be used as catalysts in synthetic reactions.
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The complex structure of aminobenzylnaphthols can be easily obtained with the useful Betti reaction. These valuable compounds can give rise to chiral intermediates, that found wide application in ...asymmetric synthesis. 1-(1S)-(4-Fluorophenyl)-((1′S)-1′-naphthalen-1-yl-ethylamino)-methyl-naphthalen-2-ol 1 was treated with triflic anhydride to yield the corresponding (S,S)-triflate 2, which is a valuable intermediate in the future synthesis of aminophosphine, to be used in asymmetric catalysis. Preliminarily structural considerations based upon H(1)-NMR spectroscopy are also reported.
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The Betti reaction of 2-naphthol, benzaldehyde and (S)-1-(4-nitrophenyl)ethylamine without any solvent gave the corresponding aminobenzylnaphthol, that is the ...(S,S)-1-(phenyl((1′-4-nitrophenyl-ethyl)amino)methyl)-2-naphthol, in good yield (56%). The absolute configuration of the title compound was attributed by NMR analysis, a procedure that is reliable if compared with the data obtained by X-ray diffraction experiments.
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The solvent-free Betti reaction of 2-naphthol, 4-nitrobenzaldehyde and (S)-valine methyl ester gave the corresponding aminobenzylnaphthol of the ...(S,S)-2-(((hydroxynaphth-1-yl)(4′-nitrophenyl)methyl)amino)-3-methylbutanoic acid methyl ester in good yield (59%). This product was fully characterized. We observed that the racemization that occurs in some Betti reactions with (S)-valine methyl ester was absent in this reaction, and thus the predominant (S,S)-product was obtained.
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Two aminobenzylnaphthols, which are representative items of the family of compounds synthesized with the Betti reaction, were investigated as antiproliferative agents against adenocarcinoma human ...colorectal (Caco-2) and human neuroblastoma (SH-SY5Y) cell lines, using cisplatin as a positive control. A better antiproliferative activity was recorded after 24 h of incubation for the first tested molecule, whereas the other one was more effective after 72 h of incubation. These results support the hypothesis that both of the tested aminobenzylnaphthols could potentially be endowed with a biological activity.
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