Heterogeneous synthesis of glycerol carbonate from glycerol and dimethyl carbonate catalyzed by LiCl/CaO

In this article, a CaO-based catalyst was prepared by impregnating chloride salts on CaO to develop a highly efficient heterogeneous catalyst for the synthesis of glycerol carbonate (GC) from glycerol and dimethyl carbonate. LiCl/CaO exhibited a high catalytic activity under moderate reaction conditions. The effects of the LiCl loadings, the amount of catalyst and the calcination temperature on the catalytic activity were investigated. The highest yield of 94.19% glycerol carbonate was obtained at 65 °C on CaO loaded with 10% LiCl after 1 h, and the catalyst had high stability in reusing work. Scanning electron microscopy (SEM), X-ray diffraction (XRD), BET, CO₂-TPD, XPS and thermalgravity (TG) were used to characterize the prepared catalyst. It was found that the high catalytic activity of CaO after modification with LiCl is associated with the structural aspects and the amount of basicity of the catalyst. The Li₂O₂ species, which is a strong basic site that is formed by the substitution of the Ca²⁺ in CaO lattice by Li⁺, has great activity for transesterification.     

Reactive sensing of gold (III) by coumarin tethered fluorescent probe through alkyne activation

A novel strategy, involving anchoring and un-anchoring of coumarin based fluorophore, has been established for the selective detection of Au³⁺ species. Selective sensing of Gold (Au³⁺) was triggered due to alkynophilicity of gold ions to create lateral fluorescence of a latent fluorophore. The 4-methyl-2-oxo-2H-chromen-7-yl 2-(2-phenylethynyl) benzoate (CEB) probe was synthesized by reacting 7-hydroxy-4-methylcoumarin with iodo-benzoic acid. CEB probe has an absorption at 300 nm and 335 nm which decreases gradually and new absorption appeared at 406 nm due to Au³⁺ promoted ester hydrolysis selectively over other metal ions with great sensitivity, which accompanies a turn on fluorescence change produced by 7-hydroxy coumarin. The principle behind this sensing strategy is activation of triple bond induced uniquely by Au⁺³ ions leading to cascade and delivers active fluorophore. The sensing mechanism was proposed and supported by ¹H NMR, MS and TD-DFT experiments. The density functional theory (DFT) and time dependent density functional theory (TD-DFT) theoretical results of the CEB-probe and Au³⁺ reaction is in good agreement with the experimental results. Additionally, probe could be well incorporated onto the test strips for effective detection of Au^3+.     

Iodine-catalyzed direct allylation of chiral oxazolidinones by the amide-aldehyde-alkene condensation

An iodine-catalyzed direct allylation of chiral oxazolidinones with aldehydes and alkenes has been developed. The reaction proceeds, without use of any bases or metals, directly converted the 3-chiral oxazolidinones into N-allylated oxazolidinones. Additionally, the 3-chiral allylamine skeleton was constructed and the diastereomers were isolated by simple column chromatography.     

The unusual physicochemical properties of azulene and azulene-based compounds

Azulene, an isomer of naphthalene, has become one of hot chemical structures in the research field of functional materials, due to its anti-Kasha’s rule emissions and unusual physicochemical properties (e.g., photophysical, electrochemical, and photoelectrochemical properties). In the past, the synthesis of azulene-based compounds is relatively inconvenient. Recently, there have been more and more reports about the synthesis strategies of the azulene-based compounds for finely tuning the physicochemical properties. In this article, we introduce several synthetic methods for kinds of azulene-based compounds which has unusual physicochemical properties. With these convenient methods and unique physicochemical properties, azulene-based compounds can be applied into many fields such as specific bioimaging, advanced molecular switches, organic field-effect transistor (OFET), organic light emitting diode (OLED), solar cells, and so forth. And these properties are also summarized here.     

Synthesis of both enantiomers of the docosahexaenoic acid ester of 13-hydroxyoctadecadienoic acid (13-DHAHLA)

Recently, several different classes of endogenous lipids have been reported that display antidiabetic and anti-inflammatory effects. Due to their minute presence in human samples, access to synthetic material of each enantiomer becomes necessary for exact structural elucidation and extensive biological evaluation. Herein we report the multi-milligram synthesis of both enantiomers of the docosahexaenoic acid ester of 13-hydroxyoctadecadienoic acid (13-DHAHLA) from commercially available starting materials.     

Studies towards the stereoselective total synthesis of Gliomasolide A

The first synthetic approach towards the Gliomasolide A is described in 15 linear steps with 4% overall yield. The key steps in this approach are RCM protocol for the construction of 14-member macrolide, a Sharpless kinetic resolution, Keck and Brown’s allylations for the installation of desired stereocenters.     

Abnormal Beckmann rearrangement of steroidal α-chlorocyclobutanone oximes: the fragmentation-substitution reaction

α,α-Dichlorocyclobutanones of various substitution patterns, readily available by the thermal cycloaddition of dichloroketene to steroid olefins, were selectively dehalogenated and further transformed to α-chlorocyclobutanone oximes. In contrast to the Beckmann rearrangement of the α-unsubstituted oximes, α-chlorocyclobutanone oximes, on treatment with thionyl chloride in benzene, gave normal and abnormal reaction products. In all reactions studied, the Beckmann fragmentation-substitution was the major process. The rearrangement of α-chlorocyclobutanone oximes is the key step of the novel method for geminal functionalization of carbonyl carbon atom in ketones and regioselective vicinal functionalization of unsymmetrical olefins. The regiochemistry observed in the rearrangements is supported by semiempirical calculations (AM1).     

Simple and rapid p-methoxybenzylation of hydroxy and amide groups at room temperature by NaOt-Bu and DMSO

The p-methoxybenzylation of hydroxy and amide groups by p-methoxybenzyl chloride utilizing NaOt-Bu in DMSO is described. p-Methoxybenzylation of sterically hindered menthol using NaOt-Bu in DMSO proceeded faster than the commonly used methods which use NaH in THF or DMF for p-methoxybenzylation of hydroxy and amide groups. The described method was applicable for sterically hindered substrates at room temperature without adding any activating reagents such as tetrabutylammonium iodide.     

Synergic effect of hydrogen bonding and dipole repulsion in the ring-closing metathesis of N-homoallyl-2-(hydroxymethyl)acrylamides

This study reveals that the Ru-catalyzed ring-closing metathesis of N-homoallyl-2-(hydroxymethyl)acrylamides is promoted by substrate-catalyst hydrogen bonding as well as dipole repulsion between the electron-rich side-chain and the carbonyl group, providing clues for designing effective synthetic routes towards 5,6-dihydro-2(1H)-pyridinones.     

An efficient Darzens reaction promoted by 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)

An efficient DBU promoted Darzens reaction utilising α-haloketones containing an enolizable α′-hydrogen is reported. This method diastereoselectively afforded the corresponding α,β-epoxy ketones good to excellent yields in an one-pot reaction without using any transition metals or additives. Furthermore, haloketones without an α′-hydrogen are also applicable in this reaction.     

Microwave promoted oxazole synthesis: cyclocondensation cascade of oximes and acyl chlorides

Microwave irradiation promotes the rapid O,N-acylation-cyclodehydration cascade reaction of oximes and acid chlorides to give oxazoles.     

Synthesis of 6-hydroxymethyl-5,6-dihydro-4H-1,2-oxazines by one-pot-cyclization of dilithiated oximes with epibromohydrin

6-Hydroxymethyl-5,6-dihydro-4H-1,2-oxazines were regioselectively prepared by one-pot cyclization of dilithiated oximes with epibromohydrin.     

Chemical modification of oximes with N-protected amino acids

The modification of oximes, including 5α-steroids, with N-protected amino acids, in solution phase, using benzotriazole methodology is reported.     

Step by step and one-pot syntheses of 5-hydroxy-5-(polyfluoroalkyl)isoxazol-4(5H)-one oximes

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Synthesis of coumarins by Pt-catalyzed hydroarylation of propiolic acids with phenols

Synthesis of coumarins from phenols and propiolic acids was examined by using a Pt catalyst such as PtCl₂/AgOTf, K₂PtCl₄/AgOTf, and K₂PtCl₄/AgOAc. Propiolic acid reacted even with less reactive phenols in trifluoroacetic acid to give coumarins and dihydrocoumarins. In the case of substituted propiolic acids, phenylpropiolic acid and 2-octynoic acid, the reactions proceeded selectively to afford coumarins in good to high yields.     

Palladium catalyzed annulation of benzylamines and arynes via C–H activation to construct 5,6-dihydrophenanthridine derivatives

An efficient and versatile strategy employing palladium catalyst to synthesize 5,6-dihydrophenanthridine derivatives by annulation of benzylamines and arynes through C–H activation has been reported. This is promising one pot methodology which includes the use of Kobayashi's aryne precursor to construct plethora of 5,6-dihydrophenanthridine derivatives in moderate to good yield.     

Synthesis of chiral titanium-containing phosphinoamide ligands for enantioselective heterobimetallic catalysis

The synthesis of six chiral titanium-containing phosphinoamide ligands is discussed. These ligands assemble chiral heterobimetallic Pd–Ti complexes, enable enantioselective intramolecular allylic aminations with hindered amine nucleophiles and achieve selectivity up to 53% ee. Mechanistic studies demonstrate the reversibility of the enantio-determining C–N bond forming step, which leads to a gradual increase in the % ee of the reaction over time. These results represent a rare example of enantioselective heterobimetallic catalysis and suggest that these new ligands could find broad application in enantioselective transition metal catalysis.     

Synthesis of chiral quaternary fluorinated cyclic sulfamidates via palladium-catalyzed arylation with arylboronic acids

An enantioselective palladium-catalyzed arylation of fluorinated cyclic N-sulfonyl ketimines with arylboronic acids is described. This methodology provides an efficient and convenient route to chiral quaternary fluorinated cyclic sulfamidates in high yields with up to 99% ee.     

The preparation and properties of polyimide films modified by octa(aminopropylsilsesquioxane)

A number of polyimide films incorporated with different amounts of octa(aminopropylsilsesquioxane) (POSS-NH₂) were prepared from 1,2,4,5-Benzenetetracarboxylic anhydride, 4,4′-Oxydianiline and POSS-NH₂. The structure and properties of the hybrid polyimide films were characterized and evaluated. It is found that, compared with pure polyimide without POSS-NH₂, the thermal stabilities and electrical capabilities of hybrid polyimide films are improved. Meanwhile, the incorporation of POSS-NH₂ also brings improvement in the flexibility of polyimide films.     

An efficient Pd(II)-(2-aminonicotinaldehyde) complex as complementary catalyst for the Suzuki-Miyaura coupling in water

An efficient new Pd(II)-(2-aminonicotinaldehyde)-catalyzed Suzuki-Miyaura coupling of the aryl halides (Br, Cl and I) and organoboronic acids at moderate temperature in water is described. Low catalyst loading, easy accessibility, being an air-stable catalyst, functional group compatibility, and water as the reaction medium are some of the key features of this synthetic method. This protocol is also applicable for gram scale.