A new valorization strategy for selected plant-based waste materials has been put forward. We have shown that avocado peels (fruit waste) and green leaves of Japanese knotweed (plant waste) are good ...sources of free xanthophylls such as antheraxanthin (9 mg/100 g dry weight) and lutein (106 mg/100 g dry weight), respectively, which can be converted into xanthophyll esters, a process inspired by nature to regulate the physicochemical properties of these bioactive species such as solubility and chemical stability. To this end, we developed the first environmentally friendly and economically viable synthetic platform and critically evaluated it by preparing 55 different xanthophyll esters (combining 5 model xanthophylls with 11 structurally and electronically distinct acid anhydrides). These esters were synthesized using β-pinene as a bio-derived solvent at ambient temperature and pressure with excellent selectivity (median 97%) and finally isolated in high yields (median 81%) and with high purities (median 97%). The integration of this technology with xanthophyll-containing wastes contributes to the zero-waste principle, and new valorization pathways for invasive alien plant species (such as Japanese knotweed) are particularly welcome as they help to control their rapid spread which causes great economic damage and loss of biodiversity around the globe.
The application of activated carbon (Darco KB) for the acceleration and direction of the transformation of various 2H-pyran-2-ones with N-substituted maleimides toward isoindole derivatives through ...the reaction sequence cycloaddition/elimination/dehydrogenation is described. In this reaction, the catalyst mainly influences the dehydrogenation step, which is essential to avoid the formation of bicyclo2.2.2octenes as the other possible products. We found that the combination of Darco KB, as the metal-free catalyst, and decalin, as the solvent in a closed vessel, represents the most successful conditions. A comparison of the effect of various dehydrogenation catalysts and reaction conditions is also presented. In addition, we have proven that the aromatization occurs via a hydrogen transfer from the cyclohexadiene intermediate to the maleimide derivative (therefore producing succinimides). This transfer is facilitated by the active surface of the heterogeneous carbon-based catalyst.
The synthesis and crystal structures of 1-(5-methyl-1H-indol-6-yl)ethan-1-one (7), C11H11NO, and 1-3-(dimethylamino) methyl-5-methyl-1H-indol-6-ylethan-1-one (8), C14H18N2O, are reported. The ...synthesis is based on the Diels-Alder cycloaddition of a substituted 2H-pyran-2-one derivative, followed by an acid-catalyzed cyclization and concomitant deprotection (the last two steps were carried out as a one-pot domino process) yielding substituted indole 7, which was further derivatized via Mannich reaction to the gramine derivative 8. Both structures 7 and 8 were determined on the basis of IR, 1H NMR and mass spectroscopy, as well as by the elemental analysis and melting point determination. According to the single-crystal X-Ray diffraction analysis, the structure 7 has a single unique molecule in the asymmetric unit whereas the structure 8 contains four unique molecules in the asymmetric unit. Molecules 7 are linked via N-H···O hydrogen bonds between the secondary amine group and carbonyl moiety of the acetyl group of adjacent molecules, whereas molecules 8 are linked via N-H···N hydrogen bonds between the secondary and tertiary amine groups of adjacent molecules. Both structures are further stabilized by weak C-H···O, C-H···π and π···π interactions.
In Diels–Alder reactions, 2H-pyran-2-ones as dienes can yield a large variety of cycloadducts with up to four contiguous carbon stereogenic centers. Some of the potentially most useful, however ...difficult to prepare due to their low thermal stability, are the primary CO2-containing oxabicyclo2.2.2octenes, which could be formed as eight distinctive isomers (two sets of regioisomers, each of these composed of four different stereoisomers). A high-pressure synthesis of such products was recently described in a few cases where vinyl-moiety-containing dienophiles were used as synthetic equivalents of acetylene. However, structures of the primary products have been so far only rarely investigated in detail. Herein, we present seven novel single-crystal X-ray diffraction structures of such cycloadducts of both stereoisomeric forms, i.e., endo and exo. Additionally, we present a single-crystal structure of a rare case of a cyclohexadiene system stable at room temperature, obtained as a secondary product upon the retro-hetero-Diels–Alder elimination of CO2 under thermal conditions (microwave irradiation), during this elimination the symmetry is increased and out of eight initially possible isomers of the reactant, this number in the product is decreased to four. In oxabicyclo2.2.2octene compounds, centrosymmetric hydrogen bonding was found to be the predominant motif and diverse supramolecular patterns were observed due to rich variety of C–H⋯O and C–H⋯π interactions.
With the application of a double dienophile 1,1'-(hexane-1,6-diyl)bis(1H-pyrrole-2,5-dione) for a 4+2 cycloaddition with a substituted 2H-pyran-2-one a novel 26-membered tetraaza heteromacrocyclic ...system 3 was prepared via a direct method under solvent-free conditions with microwave irradiation. The macrocycle prepared is composed of two units of the dienophile and two of the diene. The structure of the macrocycle was characterized on the basis of IR, 1H and 13C NMR and mass spectroscopy, as well as by the elemental analysis and melting point determination. With X-ray diffraction of a single crystal of the macrocycle we have determined that the two acetyl groups (attached to the bridging double bond of the bicyclo2.2.2octene fragments) are oriented towards each other (and also towards the inside of the cavity of the macrocycle), therefore, mostly filling it completely.
The cycloaddition of (Z)-1-methoxybut-1-en-3-yne (2) with 5,6-disubstituted 3-acylamino-2H-pyran-2-ones 1 under microwave-irradiation conditions, with classical heating or at high-pressures ...(13–15kbar) affords the benzene derivatives 3 with a strategically positioned 2-methoxyethenyl moiety. In some cases, at high-pressures after long reaction times, 2,2-dimethoxyethyl products 4 were obtained. Adducts 3 and 4 can be cyclized under mild conditions into 1,5,6-trisubstituted indole derivatives 5.
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We describe a three‐step one‐pot metal‐free domino procedure yielding a set of boscalid derivatives, parent compound being a highly important agrochemical agent. The first step of the process ...consists of the Diels–Alder reaction between a substituted 2H‐pyran‐2‐one and styrene derivatives, followed by the elimination of CO2 and aromatization (oxidation). The last step was found to be efficiently promoted by the application of chloranil as the oxidant. Alternatively, activated carbon Darco KB could also act as the dehydrogenation catalyst necessitating a larger excess of the styrene to act as the hydrogen acceptor.
Methyl 2‐benzamido‐4‐(3,4‐dimethoxyphenyl)‐5‐methylbenzoate, C24H23NO5, (Ia), and N‐{5‐benzoyl‐2‐(Z)‐2‐methoxyethenyl‐4‐methylphenyl}benzamide, C24H21NO3, (IIa), were formed via a Diels–Alder ...reaction of appropriately substituted 2H‐pyran‐2‐ones and methyl propiolate or (Z)‐1‐methoxybut‐1‐en‐3‐yne, respectively. Each of these cycloadditions might yield two different regioisomers, but just one was obtained in each case. In (Ia), an intramolecular N—H...O hydrogen bond closes a six‐membered ring. A chain is formed due to aromatic π–π interactions, and a three‐dimensional framework structure is formed by a combination of C—H...O and C—H...π(arene) hydrogen bonds. Compound (IIa) was formed not only regioselectively but also chemoselectively, with just the triple bond reacting and the double bond remaining unchanged. Compound (IIa) crystallizes as N—H...O hydrogen‐bonded dimers stabilized by aromatic π–π interactions. Dimers of (IIa) are connected into a chain by weak C—H...π(arene) interactions.
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