Tetrahedron Green Chem最新文献

Glycols are non-volatile, non-flammable solvents for efficient, facile, and environmentally benign syntheses of various types of symmetric and non-symmetric squaraine dyes, thus providing a viable alternative to conventionally used n-butanol/toluene system.

Ammonia (NH₃) stands as a cornerstone compound across industries, pivotal in agriculture, chemicals, and energy sectors. However, the conventional Haber-Bosch process demands high pressures, temperatures, and fossil fuels, calling for sustainable alternatives. Electrocatalytic Nitrogen Reduction Reactions (E-NRRs) and Photocatalytic Nitrogen Reduction Reactions (Photo-NRRs) present innovative routes, leveraging electricity and direct sunlight to convert nitrogen (N₂) to NH₃ under mild conditions, reducing emissions and softening energy requirements. Catalysts play a strategic role in these approaches, overcoming activation barriers and enhancing efficiency. However, some challenges still need to be addressed. Indeed, noble metals exhibit limits and their scarcity, geopolitical involvement, and often fluctuating costs inhibit large-scale use. Non-noble metals offer promise but require optimization and face durability concerns. Finally, carbon-based catalysts present challenges in optimization and doping. In this scenario, a molecular-based approach, comprising both specific single coordination-based molecules with transition metal centres and either metal centre coordination-based or fully organic multi-dimensional networks originating from direct molecular organic precursors, overcomes these issues while keeping the benefits of the previously mentioned classes of compounds. This mini-review explores the molecular approach to E-NRRs and Photo-NRRs from coordination compounds carrying porphyrins and phthalocyanines as organic ligands to polymeric networks based on coordination compounds between metallic centres and organic ligands (Metal-Organic Frameworks), and to networks of molecular organic units into multi-dimensional structures (Covalent Organic Frameworks). Mechanistic insights into E-NRRs and Photo-NRRs pathways elucidate N₂ conversion to NH₃. A critical comparative evaluation of reported catalysts has been carried out to highlight the limits and the possibilities of each class of compounds. Although challenges persist in terms of stability, cost and complexity of the synthesis, the use of a molecular approach in NRRs represents one of the most promising routes towards the sustainable preparation of ammonia.

A hypervalent iodine-catalyzed phenolic coupling reaction of norbelladine derivatives was examined with a catalytic amount of iodobenzene and meta-chloroperbenzoic acid as the terminal oxidant. The addition of acetic acid dramatically accelerated the reaction rate even at room temperature, and the cyclized products were successfully obtained under mild reaction conditions. The methods were applicable to the racemic total synthesis of oxomaritidine.

Herein we have described the Pd-catalyzed sonochemistry driven by [BMIM]-IL as re-useable solvent to synthesize various carbazole scaffolds from 2,2′-dibromodiphenyl. Diverse primary amines were utilised as coupling partners in the presence of [PAIM][NTf₂], which exhibits an impactful promoter in the IL medium, thereby avoiding the need for hazardous VOC's. The recyclability of ionic liquids highlights the green approach of the reaction. Further, the synthesized carbazole scaffolds were assessed for antimicrobial activity. Compounds 3e and 3g are found to be highly active. The most probable binding sites for these scaffolds were screened through a computer-simulated docking method with targeted protein.

The transformation of biomass derived platform molecules is an interesting approach to produce valuable chemicals from biomass. In addition, process intensification by reducing the number of steps for final chemicals production by performing cascade-type catalytic reactions in one-pot mode is largely desirable in a biorefinery facility. In this review the possibilities of valorization of representative platform molecules such as sugars, itaconic and levulinic acids and furanic aldehydes through one-pot cascade processes using mono and multifunctional heterogeneous catalysts are illustrated through selected examples.

A catalyst-free synthesis of various 2-alkyl or aryl-substituted benzothiazoles and benzimidazoles has been developed at room temperature by simply combining alkyl or arylaldehydes with ortho-phenylenediamines and 2-aminothiophenols, respectively. The synthesis of these widely applicable fused heterocycles is often challenging and requires additives. The advantages of this new benign procedure include: products with nearly quantitative yields, high atom economy and no toxic waste formation, catalyst-free process with no need for catalyst separation and/or recycling, the use of a green and sustainable solvent, ethanol, and mostly room temperature reactions with moderate reaction times to ensure that the protocol is energetically favorable.

Bicyclic ortho-amino carbonitriles (tetrahydronaphthalenes) are crucial in their role to develop other heterocyclic compounds such as dicyanoanilines which can be used in optical electronic (optronic) devices. Tetrahydronaphthalenes can be obtained via the four-component reaction of malononitrile (2 equivalents), a cyclic ketone and an aldehyde. On the other hand, 5,6-substituted-2-amino-3-cyanopyridines (tetrahydroquinolines) have been found to be potent anti-cancer, anti-hypertensive, anti-microbial and anti-inflammatory agents. The synthesis of such compounds is directly linked by the single reactant replacement (SRR) technique because they derive from the combination of malononitrile, a cyclic ketone, an aldehyde and ammonium acetate as a nitrogen source. In this study, the activity of the heterogeneous metal-free catalyst DABCO supported on Amberlyst® 15 was explored in relation to the synthesis of both mentioned scaffolds. To the best of our knowledge, there are no instances in the literature where this has been achieved using the same catalyst, furthermore a novel successful DABCO-Amberlyst®15 catalysed one-pot sequential combination of multicomponent reactions (MCR²) was also reported.

The development of sustainable catalytic processes is the requirement of the future to replace traditional protocols involving hazardous, non-green, non-benign reagents/solvents, and cost ineffectiveness. Metal and mixed metal oxides due to their redox properties make them potential substitutes for conventional homogeneous catalysts. The acidity can be enhanced further by the sulfation process to form sulfated oxides representing a new class of solid acid catalysts. This review is the revisiting of sulfated solid acid catalysts, with major emphasis on understanding, methods, applications, and their role in the syntheses of heterocycles of pharmaceutical importance. The present review also discusses factors affecting the acidity of the catalysts, possibilities of leaching in reaction media, methods of sulfation to arrest leaching, other challenges, and future prospects.