Claisen-Schmidt condensation reaction on BaO-ZrO2 mixed oxides

A series of BaO-ZrO₂ mixed oxides has been prepared by the sol-gel method. Crystalline structures were observed by XRD in the mixed oxides. High selectivity to chalcone and benzoic acid as by-products was obtained by performing the acetophenone-benzaldehyde condensation reaction. For both reactions a basic heterogeneous catalytic mechanism was suggested.     

Graphene-supported ZnO nanoparticles: An efficient heterogeneous catalyst for the Claisen-Schmidt condensation reaction without additional base

ZnO nanoparticles supported on reduced graphene oxide (ZnO/RGO) were prepared by the hydrothermal method and characterized by TEM, XPS, XRD, and Raman spectroscopy. As a green catalyst, ZnO/RGO was applied to the Claisen-Schmidt condensation reaction of aryl aldehydes and aryl ketones under microwave irradiation. Therein, chalcone products could be efficiently synthesized and easily separated from the heterogeneous catalysis system. The catalyst could be recycled four times without significant loss of catalytic activity.     

Z-Selective intramolecular Horner-Wadsworth-Emmons reaction for the synthesis of macrocyclic alkenes

The Z-selective intramolecular Horner-Wadsworth-Emmons reaction of the substrates 7-12 (RO)₂P(O)CHR′CO₂Et (R′ = (CH₂)_nCHO) (R = Ph or o-tBuC₆H₄) gives the 13-18-membered cyclic alkenes selectively (up to Z:E = 97:3) in good yields using NaH in THF under high dilution conditions.     

The Horner-Wadsworth-Emmons reaction in the synthesis of macrocyclic peptides: the Trp-His-Gly-Arg derived macrocycle of moroidin

The Trp-His-Gly-Arg derived macrocycle 4 of moroidin 1 containing the unusual tryptophan C-2 histidine N-1 link has been synthesised in protected form. The key steps are displacement of a 2-chloroindole with a histidine derived nucleophile, a Horner-Wadsworth-Emmons reaction followed by asymmetric hydrogenation to establish the tryptophan side chain, and incorporation of the Gly-Arg dipeptide by peptide coupling.     

Temperature effects on stereocontrol in the Horner-Wadsworth-Emmons condensation of alpha-phosphono lactones

The Horner-Wadsworth-Emmons condensation of some alpha-phosphono lactones has been examined for conditions that impact product stereochemistry. The temperature employed to quench the reaction was found to be a major factor. For example, after the diethyl phosphonate derivative of gamma-butyrolactone was treated with potassium hexamethyldisilazane, 18-crown-6, and propionaldehyde at -78 degrees C in THF, an aliquot transferred to a flask at approximately 30 degrees C gave almost exclusively the Z-olefin product, while one allowed to warm to room temperature over several hours greatly favored the E-olefin.     

Synthetic application of fluorinated vinamidinium salts: Synthesis of fluorinated 1,3-butadienylphosphonates by the reaction with Horner-Wadsworth-Emmons reagents

The reaction of β-fluoro vinamidinium salt 1 with Horner-Wadsworth-Emmons reagents (HWE) such as diethyl(ethoxycarbonyl)methylphosphonate (2a), diethyl(methoxycarbonyl)methylphosphonate (2b), diethyl-2-oxopropylphosphonate (2c), diethyl benzylphosphonate (2d), tetraethyl methylenediphosphonate (2e) and diethyl cyanomethylphosphonate (2f) under basic conditions gave the fluorinated 1,3-butadienylphosphonates 3 in moderate to good yields. The phosphonates 3 could be hydrolyzed with a 10% HCl aqueous solution to afford the corresponding γ-(diethylphosphono)-α-fluoro-α,β-unsaturated aldehydes 7 in good yields. The treatment of the phosphonate 3c with an NH₃ aqueous solution at 70 °C produced the pyridine derivative 8 in 60% yield.     

Reinvestigation of the condensation of 2-hydrazinobenzothiazole with ethyl acetoacetate

The reaction of 2-hydrazinobenzothiazole (1) with ethyl acetoacetate has twice been reported to yield a fused triazepinobenzothiazolone, namely, 3-methyl[1,2,4]triazepino[3,4-b]benzothiazol-5(4H)-one (4). We have repeated this work and reassigned the reaction product as 2-(2-benzothiazolyl)-1,2-dihydro-5-methyl-3H-pyrazol-3-one (5) on the basis of X-ray crystallography.     

Stereoselective synthesis of tetrasubstituted (Z)-alkenes from aryl alkyl ketones utilizing the Horner-Wadsworth-Emmons reaction

Tetrasubstituted (Z)-alkenes were readily prepared through the Horner-Wadsworth-Emmons reactions of methyl 2-[bis(2,2,2-trifluoroethyl)phosphono]propionate with aryl alkyl ketones by employing Sn(OSO(2)CF(3))(2) and N-ethylpiperidine.     

The Claisen-Schmidt reaction with heterocyclic analogs of o-hydroxyacetphenone

Claisen-Schmidt condensation of 4-hydroxy-3-acetyl-6-methylpyrid-2-one, and its N-methyl and N-phenyl derivatives with aromatic aldehydes is investigated, and it is shown that the products of this reaction are 3-cinnamoyl and not 6-styryl derivatives.     

A general stereoselective method for the synthesis of cyclopropanecarboxylates. A new version of the homologous Horner-Wadsworth-Emmons reaction

The synthesis of alpha-, beta- and gamma-substituted alpha-phosphono-gamma-lactones was accomplished using different ring closure and ring homologation strategies. It was found that the lactones could be selectively transformed into the corresponding ethyl cyclopropanecarboxylates by treatment with sodium ethoxide in boiling THF. The reported reaction provides an attractive alternative to the classical homologous Horner-Wadsworth-Emmons approach to the construction of cyclopropanes with electron-withdrawing functionalities.     

A new chemical access for 3′-acetyl-4′-hydroxychalcones using borontrifluoride-etherate via a regioselective Claisen-Schmidt condensation and its application in the synthesis of chalcone hybrids

A new chemical access has been developed for the synthesis of 3′-acetyl-4′-hydroxychalcones from 1-(5-acetyl-2-hydroxy-phenyl)-ethanone and various substituted benzaldehydes via a regioselective Claisen-Schmidt condensation using borontrifluoride-etherate (BF₃·OEt₂) at room temperature, in good to excellent yields within 12-24 h. Application of this methodology has also been demonstrated in the synthesis of chalcone hybrids.     

A novel pyridine-based three-component condensation reaction: synthesis of highly substituted quinolizines

Reaction of the zwitterions generated from pyridine or pyridine derivatives and dialkyl acetylenedicarboxylate with electron-deficient tetracyanoethylene lead to highly substituted quinolizines without using any catalyst or activation.     

Base-catalyzed cross coupling of secondary alcohols and aryl-aldehydes with concomitant oxidation of alcohols to ketones: An alternative route for synthesis of the Claisen-Schmidt condensation products

Base-catalyzed C–C cross coupling of secondary alcohols and aryl-aldehydes was achieved, when an alcoholic solution of an aryl-aldehyde was stirred under reflux for 45 h in the presence of a catalytic (20 mol%) amount of K₂CO₃. The consistent formation of α,α′-bis-(benzylidene) alkanones was obtained in moderate to good yields using various secondary alcohols and substituted aryl-aldehydes. Herein, α,α′-bis-(benzylidene)alkanones, which are the classical products of Claisen-Schmidt (cross aldol) condensation, have been synthesized via an alternative strategy using secondary alcohols. Bis-(benzylidene) alkanones are an integral part of various drug regimes and the production of bis-(benzylidene) alkanones without using any precious metal is a major outcome of the present reaction.     

Mn-MOF@Pi composite: synthesis,characterisation and an efficient catalyst for the Knoevenagel condensation reaction

We have synthesised new Mn-MOF@Pi composite by encapsulation of piperidine in desolvated Mn-MOF and investigated its catalytic performance in Knoevenagel condensation reaction. The newly developed composite is compatible with various aromatic aldehydes and converting them to the desired Knoevenagel condensation products in good yields and selectivity. Furthermore, composite Mn-MOF@Pi is reusable and shows good catalytic activity than native MOF.     

Silica sulfuric acid-catalyzed Claisen-Schmidt condensation of 1,3,4 trisubstituted pyrrole 2,5 dione to chalcones

A series of 11 chalcones was synthesized from 1-(4-acetylphenyl)-3,4-dibromo-1H-pyrrole-2,5-dione with various substituted benzaldehyde under solvent-free conditions using silica-sulphuric acid as a catalyst. The yields of chalcones are more than 90 %. All the compounds were characterized by physical, spectroscopic, and elemental analysis.     

Applications of Knoevenagel condensation reaction in the total synthesis of natural products

Monatshefte für Chemie - Chemical Monthly - The Knoevenagel condensation reaction is a prominent organic reaction commonly being utilized in the total synthesis of natural and biologically...     

A facile method for the stereoselective Horner-Wadsworth-Emmons reaction of aryl alkyl ketones

Excellent Z or E selectivity was observed in the Horner-Wadsworth-Emmons (HWE) reactions of methyl bis(2,2,2-trifluoroethyl)phosphonoacetate or ethyl 2-fluoro-2-diethylphosphonoacetate with aryl alkyl ketones bearing substituents on an aromatic moiety employing Sn(OSO2CF3)2 in the presence of N-ethylpiperidine.     

Microwave-assisted four-component, one-pot condensation reaction: an efficient synthesis of annulated pyridines

A one-pot, effective synthesis of pyridines by a modified Kr?hnke procedure is described. Polysubstituted annulated pyridines were synthesized in high yields by four-component, one-pot cyclocondensation reactions of N-phenacylpyridinium bromide, aromatic aldehydes, acetophenones or cyclic ketones in the presence of ammonium acetate and acetic acid, assisted by microwave irradiation. In this procedure, cyclic ketones with two alpha-CH(2) groups yield annulated pyridines with additional alpha-benzylidene groups, which are derived in situ from double aldol condensation of cyclic ketones with two moles of aromatic aldehydes.