Cycloadditions that involve more than six π electrons are termed higher-order cycloadditions and are an excellent tool for solving complex synthetic challenges, as they provide direct access to polycyclic scaffolds that contain medium-sized rings. They have interesting synthetic potential for the discovery of new bioactive molecules and in natural product synthesis. It is peculiar that stereocontrolled [8+2] and [6+4] cycloadditions have been largely neglected for the past 50 years. Here we demonstrate a cross-dienamine activation of 2-cyclopentenone and the unprecedented endocyclic linear-dienamine activation of 2-cyclohexenones and 2-cycloheptenones. These dienamine intermediates undergo aminocatalytic stereoselective [8+2], [6+4] and formal [4+2] cycloadditions with various heptafulvenes. The periselectivities of the cycloadditions are controlled based on the ring size of the 2-cycloalkenones and the substitution patterns of the heptafulvenes. The chiral products obtained undergo various chemical and photochemical single-step transformations that give access to other classes of all-carbon polycyclic scaffolds.
Selective conversion of 5-hydroxymethylfurfural (HMF) to liquid fuels is an important step in the valorization of carbohydrates. Although not paid much attention to in the scientific community, we discovered an enormous impact of the HMF purity on the product selectivity during its hydroconversion in the presence of Ru/C. The presence of dimethyl sulfoxide (DMSO) showed the most dramatic effect on the aromatic hydrogenation activity, with almost full selectivity for either 2,5dimethylfuran (DMF) or 2,5-dimethyltetrahydrofuran (DMTHF). The sulfur to surface ruthenium molar ratio predicts the selectivity outcome. A similar selective poisoning effect of DMSO was observed while using 2,5-bis(hydroxymethyl)furan (BHMF) as feedstock. These findings provide an approach to modify the selectivity of HMF conversion using the Ru/C catalyst and draw attention to the utmost importance of biobased reagent purity for catalytic studies to avoid erroneous conclusions about catalyst properties.
A general organocatalytic cross‐dienamine activation strategy to produce chiral multifunctionalized norcamphor compounds having a large diversity in substitution pattern is presented. The strategy is based on a Diels–Alder reaction of an amino‐activated cyclopentenone reacting with most common classes of electron‐deficient olefins, such as nitro‐, ester‐, amide‐, and cyano‐substituted olefins, chalcones, conjugated malononitriles, CF3‐substituted enones, and fumarates. The corresponding norcamphor derivatives are formed in good yield, excellent enantioselectivities, and with complete diastereoselectivity. Furthermore, it is demonstrated that quaternary stereocenters and spiro norcamphor compounds can be formed with high stereoselectivity. The present development provides a simple, direct, and efficient approach for the preparation of important norcamphor scaffolds.
Until now, the oil shale kukersite has been used mainly for energy and oil production. To broaden the possible applications of oil shales, the wet air oxidation of kukersite (an organic-rich sedimentary rock from Estonia) was studied. Kukersite was oxidized with an oxygen-rich gas in water at temperatures up to 200 °C and pressures up to 60 bar. The efficiency of this batch process was evaluated from organic matter conversion, from the amount of solubilized organics obtained, and from the rate of dicarboxylic acid (DCA) formation. The effect of several reaction parameters—pressure, temperature, time, acid/base additives, substrate concentration, the origin of a substrate and its organic matter content, and so forth—was measured. A conversion of 91% in total organic carbon was achieved at 175 °C with 40 bar of the 1:1 oxygen/nitrogen mixture in 3 h without the presence of any additives. Under basic conditions, high yields (up to 50%) of dissolved organic matter were obtained with 8% of DCA; the best results are obtained with K 2 CO 3 and KOH. The highest DCA outcome (12%) within the 3 h reaction time was obtained in the presence of acetic acid. It was found that temperatures higher than 185 °C, pressures over 30 bar of pO 2 , and long reaction times in the acidic media caused a considerable decrease in the DCA outcome. It was also found that the same process can be applied to shales of different origins, although with lower DCA yields.
A general organocatalytic cross-dienamine activation strategy to produce chiral multifunctionalized norcamphor compounds having a large diversity in substitution pattern is presented. The strategy is based on a Diels-Alder reaction of an amino-activated cyclopentenone reacting with most common classes of electron-deficient olefins, such as nitro-, ester-, amide-, and cyano-substituted olefins, chalcones, conjugated malononitriles, CF3-substituted enones, and fumarates. The corresponding norcamphor derivatives are formed in good yield, excellent enantioselectivities, and with complete diastereoselectivity. Furthermore, it is demonstrated that quaternary stereocenters and spiro norcamphor compounds can be formed with high stereoselectivity. The present development provides a simple, direct, and efficient approach for the preparation of important norcamphor scaffolds.
The reactivity of the aliphatic dicarboxylic acids (DCAs) mixtures in conditions similar to industrial wet air oxidation (WAO) process conditions has been investigated. DCAs have potential to be separated during WAO of highly polymerized organic matter (e.g., organic waste, biomass, kerogen in oil shale) before transforming to final oxidation products (CO 2 and water). However, a shortage of information about the DCAs stability in such processes restricts this application. The influence of oxygen pressure, temperature, pH, various metal salts, and radical generating organic compounds on DCAs possible transformation was established. High stability of DCAs (C4−C10) was shown at 175 °C with 40 bar of oxygen mixture in wide pH range. The increase in the DCA decomposition with the formation of lower chain DCAs was found to be inevitable in the presence of alkali and homogeneous iron or copper salts in nonbuffered solutions. The relationship between organic co-oxidants, such as malonic acid and resorcinols, and the stability of DCAs was studied. Of them, 5-methylresorcinol was the most efficacious in increasing oxidation of DCAs, and retention values of less than 10% were observed.
Reductive amination plays a paramount role in the synthesis of amines. It is often proposed as a more ecofriendly synthesis process than the traditional S N 2-type reactions of amines as it avoids toxic alkylation reagents such as alkyl halides. This work demonstrates the versatility of the reductive amination reaction via the synthesis of hydroxychloroquine (HCQ), one of the most renowned pharmaceuticals during this coronavirus pandemic. The novel green synthesis strategy is based on three consecutive reductive amination reactions conducted in a one-pot system, avoiding intermediary purification steps. Furthermore, a biobased C 2 platform molecule, glycolaldehyde, was selected as a starting reagent. The newly developed reductive amination pathway was appraised using the CHEM21 Green Metric toolkit and compared with the commercially operating method.
Sustainable bisphenol A (BPA) substitutes should be safe and renewable to abolish the environmental burden of BPA’s endocrine disruption and petrochemical origin. Suitable alternatives preferably also retain the rigid and stiff methylenediphenol (MDP) scaffold to emulate the hallmark performance of BPA-based polymers. Here, we report a holistic solution to sustainable BPA substitutes made from abundant lignin-derivable o-methoxyphenols that display low-to-undetectable xeno-estrogenic activity while preserving the MDP scaffold. More specifically, we propose an innovative zeolite-catalyzed synthesis towards the similar albeit safer methylenediguaiacol (MDG) scaffold via Brønsted acid-catalyzed alkylation of guaiacol with different p-alkenylguaiacols yielding various so-called bisguaiacols. Zeolite catalysis favors regioselectivity and prompts higher rate and chemoselectivity for entropic reasons thanks to active site pocket confinement. Exploiting the intrinsic handles present in o-methoxyphenols not only simplifies and ameliorates classic bisphenol chemistry, but also enables to design out xeno-estrogenic activity. Successful direct reaction of a crude lignin oil extract, as produced by reductive catalytic fractionation, highlights the feasibility and robustness of this route as a downstream process for future wood biorefineries. Last but not least, pure p,p’-bisguaiacols are polymerized into high-molecular weight thermoplastic and thermosetting polymers with promising thermo-physical properties. Overall, this work elucidates that renewability should not merely serve as a goal (renewable carbon), but also as a means (safer chemicals), thereby transcending the scope of renewability.
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