Tetrahedron Green Chem最新文献

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.

Benzylic systems such as 9H-xanthenes, 9H-thioxanthenes and 9,10-dihydroacridines can be easily oxidized to the corresponding xanthones, thioxanthones or acridones, respectively, in deep eutectic solvents by a visible blue light-promoted photooxidation procedure carried out using ambient air as oxidant in the presence of riboflavin tetraacetate as a metal-free photocatalyst. The obtained yields are high or almost quantitative, and the reaction media can be recovered and reused. The environmental friendliness of the protocol is demonstrated based on several green metrics.

The coordination complexes [MoO₂(SAP)]₂ [Mo] and [VO(SAP)]₂O [V] (SAP = salicylideneamino-phenolato) were tested as pre-catalysts for oxidation of a biomass-issued substrate, linalool (L). The reaction was studied using different oxidants, TBHP (in water or in decane) or H₂O₂ (in water with/without acetonitrile). Efficient linalool (L) conversions were obtained with selectivity towards two selected products, 2-(5-methyl-5- vinyltetrahydro-furan-2-yl propan-2-ol) (1) and 2,2,6- trimethyl-6-vinyltetrahydro-2H-pyran-3-ol (2) depending on pre-catalysts and oxidant. Green metrics have been calculated and showed the role of organic solvent for the process.

Carboxylation of benzyl chlorides with CO₂ has been developed with photoredox/HAT dual-catalysis. The reaction could be conducted at room temperature with blue LED light source. Potassium formate (HCO₂K) is used as a green reductant and a catalytic amount of sodium thiophenolate (PhSNa) is applied as the HAT reagent. Strongly reductive carbon dioxide radical anion (CO₂^‧–) is produced to promote the cleavage of C–Cl bond.

The adverse effect of carbon dioxide occurred in past decade on environment, led researchers to use CO₂ as a C1 building block for the synthesis of various commodity chemicals. Most of the drug molecules and polymers have back bone of carbon chain which provides great opportunity to researchers, to make use of CO₂ as an abundant and renewable source of carbon. Chemo-catalytic synthesis of industrially important cyclic and open chain carbamate using amino alcohol/alcohol and amine in presence of CO₂ as carbonylating agent has got much more attention in recent years. This review focuses on the literature survey from 1986 to 2022 on carbamate synthesis and provides clear idea about prerequisite active sites in catalyst for the activation of CO₂ which is a major challenge. The details of mechanism proposed for the chemo-catalytic pathway has been discussed in detail in order to understand and design the novel and efficient catalyst system in near future in this demanding research field.

Without a doubt, asymmetric catalysis has been significantly enriched by the introduction of cinchona alkaloid derivatives. Moreover, such methods have been further enabled when used in conjunction with continuous flow systems.

Besides being used in flow chemistry as organocatalysts, they also have been used as ligands or modifiers of metal catalysts. This has generally been accomplished via their immobilization on heterogeneous supports and incorporation into catalysis-enabling reactors or similar systems. In this minireview we look at the impact that cinchona-based catalysts and analogues have had on the field of continuous flow-chemistry during the last two decades or so.

The cooperative activity of two proximal metal ions is well-known to exhibit highly efficient and synergistic catalytic activities in living organisms. Owing to this knowledge, tandem Cu–Zn systems have been widely used to catalyze a diversity of chemical transformations. This report describes the use of CuI and zinc dust as a sustainable tandem catalyst for the preparation of propargylamines via a three-component coupling reaction under neat conditions. This reaction proceeds at low temperature, and produces good yields with a number of aliphatic and aromatic aldehydes. The reactivity of a number of amines and alkynes has also been explored under these reaction conditions, resulting in 33 fully characterized compounds prepared in the process. Among the ketones tested during this study, only cyclohexanone was able to produce the expected product in a decent yield. The catalytic system reported here represents one of the sustainable approaches to the preparation of propargylamines, as it involves the use of naturally abundant metals as a tandem catalyst, at a low temperature and under neat conditions.

Lemon juice has been studied and reported as an efficient catalyst or green medium in organic synthesis. The present digest paper shows the successful and efficient Removal of multiple acid-labile protecting groups using crude lemon juice for the first time. Several drops of lemon juice can rapidly convert some simple liquid acetals to carbonyl compounds. Also, when mixed with ethanol, lemon juice effectively removes cyclic acetals and other protection groups on primary or secondary alcohols. In addition, for the selective Removal of acetonide on diacetone-d-glucose and its derivatives, the yield can reach more than 85%. Lemon juice, combined with ethanol as a solvent, can avoid using hazardous organic or inorganic acids to remove acid-labile protecting groups while being environmentally friendly.