Photocatalytic Dehydroformylation of Benzyl Alcohols to Arenes

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Photocatalytic Dehydroformylation of Benzyl Alcohols to Arenes

The combination of photoinduced hydrogen atom transfer (HAT) and cobalt catalysis gives access to a mild dehydroformylation sequence for the defunctionalization of benzyl alcohols to arenes. The transformation proceeds through a stepwise radical pathway, wherein benzylic and acyl radicals are generated as key intermediates. As a result, stable C−C bonds can be cleaved while generating concomitant syngas (CO+H2).


Abstract

In the last decades, many C−C bond-forming reactions have been developed, whereas less attention has been paid to the design of strategies involving C−C bond cleavage. We report a photocatalytic dehydroformylation sequence for the conversion of benzyl alcohols to arenes in a one-pot two-step process. Herein, the initial dehydrogenation of the benzyl alcohols to the corresponding benzaldehydes is combined with an additional decarbonylation step yielding arenes. As a result, a broad range of benzyl alcohols can be easily transformed in short times under mild photocatalytic conditions. The conducted mechanistic studies indicate that our cooperative hydrogen atom transfer (HAT)-cobalt system proceeds through the formation of α-alkoxy- and acyl radicals as key intermediates, involving concomitant syngas (CO+H2) generation.

Vigna unguiculata L. Walp. Leaves as a Source of Phytochemicals of Dietary Interest: Optimization of Ultrasound‐Assisted Extraction and Assessment of Traditional Consumer Habits.

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Vigna unguiculata L. Walp. is an African crop spread worldwide mainly for pulses production. Despite being a neglected and under-utilized food, cowpea leaves are a rich source of phytochemicals and micronutrients. The aim of the work is to characterize the phytochemical composition of cowpea leaves by an optimized ultrasound-assisted extraction (USAE) and to compare raw and boiled leaves.A three-level factorial design (Box-Behnken) was employed for the optimization of the USAE considering three different parameters (% ethanol, drug-to-solvent ratio, and number of cycles). The optimized extracts were characterized by LC-MS/MS. Finally, leaves were boiled at 100 °C for 30 min to simulate traditional cooking procedures and compared to raw leaves. The best extraction condition was EtOH/H2O 1:2 v/v, drug to solvent ratio 1:47 w/v, and 3 extraction cycles. The phytochemicals identified mainly belong to the family of phenolic acids, flavonoids, terpenoids, and alkaloids. Boiled leaves revealed a significant loss of most phytochemicals and a net decrease of their antioxidant activity compared to the raw ones. The results highlight the potential nutraceutical value of cowpea leaves whilst the impoverishment triggered by traditional consumer habits pushes the need to evaluate alternative cooking procedures helpful in the maintenance of their phytochemical properties.

Spatial variation in yield, chemical composition, and phytotoxic activity of Cistus ladanifer essential oils.

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Cistus ladanifer L. (rockrose) is a widespread shrub species of the Mediterranean region with products highly valued by the perfume and cosmetics industry. In this research, the variability in yield, chemical composition and phytotoxic activity of C. ladanifer essential oils collected from 12 plots belonging to four natural populations and settled on two different types of edaphic substrates were evaluated. The essential oils were analyzed by GC-MS. The essential oil content ranged from 0.19 to 0.42 ml/100 g. The volatile profiles were found to be rich in oxygenated sesquiterpenes and oxygenated monoterpenes. PCA analysis clustered the samples into two groups that were mainly attributed to the type of substrate on which the plants grow. Furthermore, CCA and correlation analysis revealed that soil organic matter was the most effective edaphoclimatic driver accounting for these high levels of variation in essential oil yield and composition. Finally, C. ladanifer essential oils showed strong phytotoxic activity on R. sativus seedlings, indicating its potential use as a natural bio-herbicide in agriculture. The results showed that the effect associated to local edaphoclimatic conditions not only impacted on the quality and quantity of the essential oil, but also on the industrial uses derived from its biological activities.

Asymmetric Synthesis of Pantolactone: Recent Advances

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(R)-Pantolactone, an intermediate in the syntheses of Vitamin B5 and coenzyme A, is an important chiral molecule often used as a food additive, chiral auxiliary, and chiral starting material for organic transformations. Enantioenriched pantolactones are predominantly produced by biological fermentation and chemical synthesis approaches. Herein, we present a review of recent developments in the asymmetric synthesis of pantolactone via different methods, and systematically summarize the characteristics and advantageous features of these strategies. Among the strategies discussed herein, the direct asymmetric catalysis of glyoxylate and isobutyraldehyde with small organocatalyst molecules has attracted growing attention owing to its good step-economy, commercially available starting materials, absence of toxic reagents, mild reaction conditions, convenient operation, and low catalyst loading. These characteristics render the direct asymmetric route to pantolactone a particularly attractive procedure. This review provides valuable guidance for the design and synthesis of enantioenriched pantolactone and its analogs.

A new 3‐benzylphthalide from the moss Erythrodontium julaceum

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From the moss Erythrodontium julaceum Paris growing in Vietnam, julacelide, a new 3-benzylphthalide compound, along with methyl orsellinate, ethyl orsellinate, 4-O-methylhaematommic acid, and zeorin, were isolated and structurally elucidated. Their chemical structures were elucidated through extensive 1D and 2D NMR analysis and high-resolution mass spectroscopy as well as through comparisons to the existing literature. Compound 4-O-methylhaematommic acid was a new natural product. The absolute configuration of julacelide was defined using time-dependent density functional theory (TDDFT) calculations. Julacelide was evaluated for alpha-glucosidase inhibition.

Glycolipids from Sargassum filipendula, a Natural Alternative for Overcoming ABC Transporter‐Mediated MDR in Cancer

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Chemotherapy is a widely used strategy to treat cancer, a disease that causes millions of deaths each year. However, its efficacy is reduced by the overexpression of ABC transporters, which are proteins that expel the drugs used in chemotherapy and involved in the multidrug resistance (MDR). Glycolipids have been identified as potential inhibitors of ABC transporters. Algae of the genus Sargassum contain high levels of glycolipids, being a promising therapeutic alternative against the MDR phenotype. Sargassum filipendula glycolipids were obtained by exhaustive maceration with chloroform/methanol, purified by column and thin layer chromatography, and then characterized by FTIR, NMR, and LC-MS. Cell viability by PI labeling and inhibition of ABC transporters were analyzed by flow cytometry. Assessment of resistance reversal was determined by MTT assay. Ten sulfoquinovosylglycerol-type compounds were found, and six of them are reported for the first time. Moiety 4 (GL-4) showed strong and moderate inhibitory activity against ABCC1 and ABCB1 transporters, respectively. Treatment of GL-4 in combination with the antineoplastic drug vincristine sensitized Lucena-1 cell model to drug and reversed the MDR phenotype. This is the first report of glycolipids isolated from S. filipendula capable of inhibiting ABC transporters and thus overcoming acquired drug resistance.

Prebiotic synthesis of 3’,5’ cyclic adenosine and guanosine monophosphates via carbodiimide‐assisted cyclization

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3’,5’ cyclic nucleotides play a fundamental role in modern biochemical processes and have been suggested to play a central role at the origin of terrestrial life. In the current work we suggest that a formamide-based systems chemistry may account for their availability on the early Earth. In particular, we demonstrate that in a liquid formamide environment at elevated temperatures 3’,5’ cyclic nucleotides are obtained in good yield and selectivity upon intramolecular cyclization of 5’ phosphorylated nucleosides in the presence of carbodiimides.

The stability of oxygen‐centered radicals and its response to hydrogen bonding interactions

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The stability of oxygen-centered radicals and its response to hydrogen bonding interactions

The thermodynamic stability of various alkoxy/aryloxy/peroxy radicals, as well as TEMPO and triplet dioxygen has been explored at a variety of theoretical levels. The effects of hydrogen bonding interactions on the stability of oxygen-centered radicals have been probed by addition of a single solvating water molecule.


Abstract

The stability of various alkoxy/aryloxy/peroxy radicals, as well as TEMPO and triplet dioxygen (3O2) has been explored at a variety of theoretical levels. Good correlations between RSEtheor and RSEexp are found for hybrid DFT methods, for compound schemes such as G3B3-D3, and also for DLPNO-CCSD(T) calculations. The effects of hydrogen bonding interactions on the stability of oxygen-centered radicals have been probed by addition of a single solvating water molecule. While this water molecule always acts as a H-bond donor to the oxygen-centered radical itself, it can act as a H-bond donor or acceptor to the respective closed-shell parent.

Study on the Turbulent Vortex Structure Characteristics of a Two‐Layer Impinging Stream Reactor

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Study on the Turbulent Vortex Structure Characteristics of a Two-Layer Impinging Stream Reactor

The intensity of the vortex structure in a two-layer impinging stream reactor was quantitatively analyzed according to the Liutex method. The bound vortex, trapped vortex, and longitudinal vortex in the reactor were studied for the first time. The formation of vortices is related to the velocity field and pressure field. In this paper, the field synergy theory is used to evaluate their synergy.


Abstract

The structure of the turbulent vortex in a two-layer impinging stream reactor was studied by large eddy simulation. The distributions of vortex intensity, turbulent kinetic energy, and shear stress at different Reynolds numbers Re, nozzle spacings L, and nozzle layer spacings are discussed. The relationship between vortex structure and mixing effect in the flow field is revealed. The effects of longitudinal swirls and shear flow characteristics are analyzed. Finally, the field synergy theory is used for evaluation. With increasing Re, the vortex intensity and average shear stress increase. The nozzle spacing and layer spacing affect the mixing effect in the reactor by controlling the change of vortex structure in the flow field. When L/D = 3, where D is the nozzle diameter, the energy loss is the smallest and the mixing effect is the best. The research results provide a theoretical reference for the structural optimization of the impinging stream reactor.