Green synthesis of pyranopyrazoles via biocatalytic one-pot Knoevenagel condensation–Michael-type addition–heterocyclization cascade in non-aqueous media

Research on Chemical Intermediates - An efficient, green and facile route for the one-pot four-component synthesis of pyranopyrazole derivatives through the condensation of the aromatic aldehydes,...     

Recent advances in the application of nanoparticles in the selective reduction of carbon–carbon double bonds

Herein, we present recent advances in the application of metal nanoparticles in the selective hydrogenation of C–C double bonds. The review focuses on reduction methods of alkenes, arenes, and aromatic heterocycles, which were classified according to transition metals used as catalysts. The majority of described systems concern direct hydrogenation, which is of particular importance to industrial processes. Nonetheless, interesting transfer hydrogenation protocols were also developed, which may be incredibly convenient for laboratory purposes. Some of the methods are distinguished with excellent chemoselectivity making them the perfect tool for the synthesis of compounds containing reducible functional groups. Apart from noble metals, the application of earth-abundant ones as catalysts was a subject of studies, and the related methods were highlighted.     

Microwave-promoted efficient synthesis of spiroindenotetrahydropyridine derivatives via a catalyst- and solvent-free pseudo one-pot five-component tandem Knoevenagel/aza-Diels–Alder reaction

A microwave-assisted, one-pot pseudo five-component reaction strategy has been developed for the synthesis of some novel spiroindenotetrahydropyridine derivatives from 1,3-indanedione, an aromatic aldehyde, and ammonium acetate under catalyst- and solvent-free conditions via tandem Knoevenagel/aza-Diels–Alder reaction.     

Overcoming acid–base copolymer neutralization using mesoporous carbon and its catalytic activity in the tandem deacetalization–Knoevenagel condensation reaction

Research on Chemical Intermediates - Acid–base copolymer materials are of considerable interest because of their fundamental implications for acid–base bifunctional catalysis...     

Facile access to C-N bonds via unexpected side reactions of Knoevenagel condensation and their application in high-efficiency organic solar cells

The construction of C-N bonds is of great importance in the fields of biology, medicine, chemistry and materials science. Here,the replacement of organic base from pyridine to piperidine in the Knoevenagel condensation process unexpectedly yields a series of novel organic molecules containing C-N bonds. Interestingly, the synthesis method does not require any external transition-metals catalysis, and photo-/electro-catalysis. Additionally, when the new compound 1b is added as a third component t...     

Asymmetric bioreduction of activated carbon–carbon double bonds using Shewanella yellow enzyme (SYE-4) as novel enoate reductase

Shewanella yellow enzyme (SYE-4), a novel recombinant enoate reductase, was screened against a variety of different substrates bearing an activated double bond, such as unsaturated cyclic ketones, diesters, and substituted imides. Dimethyl- and ethyl esters of 2-methylmaleic acid were selectively reduced to (R)-configured succinic acid derivatives and various N-substituted maleimides furnished the desired (R)-products in up to >99% enantiomeric excess. Naturally occurring (+)-carvone was selectively reduced to (?)-cis-dihydrocarvone and (?)-carvone was converted to the diastereomeric product, respectively. Overall SYE-4 proved to be a useful biocatalyst for the selective reduction of activated CC double bonds and complements the pool of synthetic valuable enoate reductases.     

Determination of isoflavones in rat serum using liquid chromatography–tandem mass spectrometry with a highly efficient core–shell column

Consumption and nutritional supplementation of soy and soy-based products have been linked to health benefits such as lower cholesterol and triglyceride levels, and decreased incidence of cardiovascular disease and diabetes. In this study, we have developed a sensitive, specific, and robust method using high-performance liquid chromatography–tandem mass spectrometry (HPLC-MS/MS) for determination of serum isoflavones. A new highly efficient pentafluorophenyl phase core–shell column was first used to separate all isoflavones within 3 min, a separation time which is comparable to ultra-pressure liquid chromatography (UPLC) and micro-HPLC. A two-enzyme hydrolysis system with sulfatase and β-glucuronidase has also been developed to improve the efficiency of deconjugation of conjugated isoflavones in serum. The corresponding conjugated isoflavones were used to evaluate recoveries. In addition to duplicates, the method of standard addition was also applied in sample analysis for quality control. The developed method was applied to the analysis of 32 serum samples and was shown to be specific, sensitive and reproducible.     

Facile synthesis of highly substituted 2-pyrone derivatives via a tandem Knoevenagel condensation/lactonization reaction of β-formyl-esters and 1,3-cyclohexadiones

A mild and efficient tandem process for the synthesis of new highly substituted 2-pyrones starting from commercially available 2-arylacetic acids has been developed. The synthesis is based on the Knoevenagel condensation of 1,3-cyclohexadiones with various β-formyl-esters, followed by lactonization in the presence of nano ZnO (20 mol %). Moderate to high yields and readily available cheap starting materials are the key features of the present method.     

The total synthesis of (−)-aplysin via a lithiation–borylation–propenylation sequence

A concise, highly enantioselective synthesis of sesquiterpene natural products (?)-debromoaplysin and (?)-aplysin has been completed. The key steps included lithiation–borylation of a secondary benzylic carbamate to give a tertiary boronic ester followed by propenylation which installed the quaternary stereocenter with complete enantioselectivity. Subsequent RCM followed by deprotection and in situ cyclization led to debromoaplysin with good diastereoselectivity from which the target compound was prepared in just eight overall steps.     

An efficient synthesis of 3,4-dihydropyridone via a tandem olefin isomerization–ring-closing metathesis reaction

Novel 3,4-dihydropyridones were efficiently prepared via a tandem olefin isomerization–ring-closing metathesis reaction catalyzed by the second-generation Grubbs catalyst. The products were further functionalized at the 5-position, providing an interesting structural motif to be evaluated in medicinal chemistry.     

The highly chemoselective transfer hydrogenation of the carbon–carbon double bond of conjugated nitroalkenes by a rhodium complex

Chemoselective transfer hydrogenation of conjugated nitroalkenes catalyzed by [RhCl₂Cp¹]₂–diamine complex (Cp¹=η⁵-C₅Me₅) using HCOOH/Et₃N (5:2) (TEAF) as a hydrogen source was realized. A variety of nitrostyrenes, β-methyl nitrostyrenes, and 3-methyl-4-nitro-5-alkenyl-isoxazoles were reduced smoothly in good to excellent yields in short reaction time. Other functional groups are inert under the reaction conditions.     

An efficient synthesis of β-acylureas via a three-component, one-pot synthesis using TCS/ZnCl2

A simple and efficient one-pot, three-component synthesis of new trisubstituted ureas containing diastereotopic protons is achieved via the reaction of aromatic aldehydes, aromatic ketones, and dimethyl cyanamide using a TCS/ZnCl₂ reagent mixture at room temperature.     

Knoevenagel condensation in aqueous media promoted by 2,2′-bipyridinium dihydrogen phosphate as a green efficient catalyst

Research on Chemical Intermediates - A 2,2′-Bipyridine-based ionic compound named 2,2′-bipyridinium dihydrogen phosphate was synthesized by addition of phosphoric acid to a solution of...     

Highly efficient one-pot synthesis of α-aminophosphonates using nanoporous AlSBA-15 catalyst in a three-component system

Research on Chemical Intermediates - Nanoporous AlSBA-15 catalysts with different nSi/nAl ratios (41, 129, and 210) were synthesized using a hydrothermal method. These catalysts were characterized...     

Molecular iodine: a highly efficient catalyst in the synthesis of quinolines via Friedländer annulation

A mild and efficient route for the synthesis of quinolines and polycyclic quinolines via Friedl?nder annulation, utilizing molecular iodine (1 mol%) as a new catalyst, is described.     

Total synthesis and assignment of the absolute stereochemistry of xanthoangelol J: development of a highly efficient method for Claisen–Schmidt condensation

The first total synthesis of cancer chemopreventive terpenyl hydroxychalcone xanthoangelol J isolated from Angelica keiskei was accomplished with asymmetric epoxidation, aromatic C-alkylation and Claisen–Schmidt condensation via enol mode as key steps. The crucial Claisen–Schmidt condensation has been accomplished by a novel green method using KHSO₄–SiO₂ as a recyclable catalyst under microwave activation. The absolute configuration of the molecule was also determined.     

Stereoselective reduction of endocyclic carbon–nitrogen double bond: application to the synthesis of biomolecules

Recent advances in the stereoselective synthesis of nitrogen containing heterocyclic compounds using the reduction of endocyclic double carbon–nitrogen bond are surveyed.     

A quantum chemical study of aluminum–carbon bonds in three-coordinate aluminum compounds

The spatial and electronic structures of three-coordinate aluminum molecules with Al–C bonds are calculated using the GAMESS-Firefly program package at DFT and HF levels of theory. By NBO and AIM methods the main characteristics of Al–C bonds in these molecules are determined. It is shown that by their topological characteristics the Al–C bonds can be characterized as weakened intermediate bonds close to the bonds between closed shell atoms.     

Experimental estimation of axial–vertical flow permeability through a packed bed of granular activated carbon

Journal of Thermal Analysis and Calorimetry - Flow through packed beds of granular materials, and for instance, granular activated carbon (GAC), is of great importance and has various applications...     

Facile one-pot synthesis of tetrahydroisoquinolines from amino acids via hypochlorite-mediated decarboxylation and Pictet–Spengler condensation

A convenient method for oxidative decarboxylation of α-amino acids is presented. The aldehyde products may be isolated or converted to tetrahydroisoquinolines by addition of dopamine via Pictet–Spengler reaction. Racemic products are generated by phosphate buffer >300 mM to maximize regioselectivity. (S)-Enantiomer products are generated by norcoclaurine synthase reaction in maleic acid buffer to minimize chemical background reaction.