- Preparation and characterisation of amorphous mesoporous aluminophosphate and metal aluminophosphate as an efficient heterogeneous catalyst for transesterification reaction
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Preparation, characterisation of pure aluminophosphate and aluminophosphate modified with different transition metals (V, Fe, Co Ni & Cu) and their catalytic activity in mono/dibenzyl substituted malonates synthesis are explained. The materials were prepared by the coprecipitation method in the absence of any structure-directing species and characterized for their composition, crystalline nature, total surface acidity, specific surface area pore diameter and pore volume by different techniques. Catalytic activity of the materials was investigated in transesterification of diethylmalonate with benzyl alcohol in liquid phase. Pure aluminophosphate resulted only in benzyl ethylmalonate whereas the incorporation of transition metals favored the formation of both benzyl ethylmalonate and dibenzylmalonate. Catalytic activity parallels the surface acidity and mesoporosity of the catalysts. The effect of the molar ratio of reactants, amount of catalyst, and reaction time on the conversion of diethyl malonate and transester yield has been studied. The highest activity of iron aluminophosphate is attributed to its mesoporous nature with uniform pore size distribution, higher surface acidity and surface area. Further, the scope and generality of iron aluminophosphate as a catalyst in the transesterification was studied using various aliphatic, alicyclic and aromatic alcohols. The catalysts could be recycled by retaining most of its initial activity.
- Vijayasankar,Nagaraju
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- Design of sulphate modified solid acid catalysts for transesterification of diethyl malonate with benzyl alcohol
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Sulphate ion modified multiwalled carbon nanotubes (S-CNTs), mesoporous carbon (S-MC), zirconia (S-ZrO2), alumina (S-Al2O3) and silica (S-SiO2) were prepared by wet impregnation technique. The physico-chemical properties of the prepared materials were inv
- Minchitha,Hareesh,Venkatesh,Shanty,Nagaraju,Kathyayini
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- Enantioselective iridium-catalyzed allylic alkylation of racemic branched alkyl-substituted allylic acetates with malonates
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The regio- and enantioselective allylic substitution of branched alkyl-substituted allylic acetates employing malonates has been achieved through a process that calls for Krische's πallyliridium C,O-benzoate catalyst. The protocol reported herein can be applied to a diverse set of branched alkyl substrates that are generally not well tolerated in the other two types of Ir-catalyzed allylation.
- Zhang, Tian-Yuan,Deng, Yi,Wei, Kun,Yang, Yu-Rong
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supporting information
p. 1086 - 1089
(2021/02/06)
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- O-Benzylation of Carboxylic Acids Using 2,4,6-Tris(benzyloxy)-1,3,5-triazine (TriBOT) under Acidic or Thermal Conditions
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Two methods for the synthesis of benzyl esters from carboxylic acids using the O-benzylating reagent 2,4,6-tris(benzyloxy)-1,3,5-triazine (TriBOT) have been developed. The reactions were conducted either in the presence of a catalytic amount of TfOH at room temperature (acidic conditions) or in the absence of TfOH at 180-230 C (thermal conditions). Interestingly, the O-benzylation of hydroxy carboxylic acids under the two conditions afforded different products: The dibenzylated product under acidic conditions and the hydroxy ester under thermal conditions. In addition to these results, other evidence indicated that the former reaction proceeds through an SN1-type mechanism, and the latter by an SN2-type mechanism. Two methods for the O-benzylation of carboxylic acids using TriBOT have been developed under either acidic or thermal conditions. The O-benzylation of hydroxy carboxylic acids afforded the dibenzylated product under acidic conditions and the hydroxy ester under thermal conditions. The former reaction proceeds through an SN1-type mechanism and the latter by an SN2-type mechanism.
- Yamada, Kohei,Yoshida, Saki,Fujita, Hikaru,Kitamura, Masanori,Kunishima, Munetaka
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p. 7997 - 8002
(2015/12/24)
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- Synthesis of coumarin-3-carboxylic esters via FeCl3-catalyzed multicomponent reaction of salicylaldehydes, Meldrum's acid and alcohols
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A FeCl3-catalyzed multicomponent reaction was developed for the facile synthesis of coumarin-3-carboxylic ester derivatives in a highly atom-economic and environmentally friendly way. Using simple and cheaply available salicylaldehydes, Meldrum's acid and alcohols as the starting materials, the method needs no extra additives and features wide substrate scope, good functional group tolerance and mild reaction conditions.
- He, Xinwei,Shang, Yongjia,Zhou, Yao,Yu, Zhiyu,Han, Guang,Jin, Wenjing,Chen, Jiaojiao
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p. 863 - 868
(2015/01/30)
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- Transesterification of diethyl malonate with benzyl alcohol catalyzed by modified zirconia: Kinetic study
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Zirconia and its modified forms such as 10%Mo(VI)/ZrO2, 10%V(V)/ZrO2, 10%W(VI)/ZrO2 and SO4 2-/ZrO2 were prepared and characterized for their physico-chemical properties such as BET for surface area, NH3-TPD and n-butylamine back titration method for total surface acidity, PXRD technique for crystallinity and ICP-OES technique for elemental analysis. These materials were used as catalysts in liquid phase transesterification reaction of diethyl malonate (DEM) with benzyl alcohol (BA). Optimization of reaction conditions such as reaction time, reaction temperature, weight of the catalyst and molar ratio of reactants were carried out to obtain highest possible transester yield. Dibenzyl malonate (DBM) and benzyl ethyl malonate (BEM) were obtained as major products. Highest total transester yield of (88%) was obtained in the presence of 0.75 g of SZ catalyst at a molar ratio of DEM: BA = 1:3, reaction temperature of 393 K and reaction time 5 h. Kinetic studies were carried out to find out the rate of the reaction and energy of activation values for zirconia catalysts, in order to identify a facile catalyst system for this reaction. A possible reaction mechanism was proposed based on the kinetic data and it was observed that Eley-Rideal mechanism fits well for this reaction. Reactivation and reusability studies of the catalysts were also taken up.
- Thimmaraju,Mohamed Shamshuddin,Pratap,Venkatesh
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- Catalytic asymmetric conjugate allylation of coumarins
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A catalytic asymmetric conjugate allylation was successfully developed to synthesize potential pharmacologically active 4-allyl-2-oxochroman skeletons. A dual activation strategy was employed by using N,N′-dioxide-Yb(OTf) 3 to activate coumarins and using (CuOTf)2?C 7H8 to activate tetraallyltin via transmetalation, respectively. Good yields and enantioselectivities were obtained under mild conditions.
- Kuang, Yulong,Liu, Xiaohua,Chang, Lu,Wang, Min,Lin, Lili,Feng, Xiaoming
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supporting information; experimental part
p. 3814 - 3817
(2011/09/15)
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- Surface properties and the catalytic activity of amorphous iron aluminophosphates: Effect of fe loading
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Iron aluminophosphates (FeAlP) with different percentage of iron were synthesized and characterized for their surface and bulk properties. The catalytic activity was determined in the transesterification of diethyl malonate with benzyl alcohol. Benzyl ethylmalonate and dibenzyl malonate were obtained as the only products. FeAlP with 0.025 mole % of iron was found to be distinctly different in its textural and catalytic properties. Formation of diester was found to be favored by the acid sites of intermediate strength. The presence of hydrated alumina and the polycondensed phosphates in the materials reduced the catalytic activity of iron aluminophosphates in transesterification reaction.
- Vijayasankar,Aniz,Nagaraju
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body text
p. 131 - 136
(2010/09/09)
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- Synthesis of thienamycin-like 2-iso-oxacephems with optional stereochemistry
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All four trans-stereoisomers of 7-(1-hydroxyethyl)-2-iso-oxacephem-4-carboxylic acids, which are the 2-iso-oxacephem analogues of Thienamycin, have been synthesized. (αR,6R,7R)- and (αS,6S,7S)-7-(1-hydroxyethyl)-3-methyl-2-iso-oxacephem-4-carboxylic acids have been prepared starting from l- and d-threonine, the configuration at the α-position was inverted by using Mitsunobu reactions providing the (αS,6R,7R)- and (αR,6S,7S)-diastereomers of the compounds above. A synthetic route to the cis-annelated analogues was also worked out.
- Santa, Zsuzsanna,Nagy, Jozsef,Nyitrai, Jozsef
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p. 3111 - 3127
(2007/10/03)
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- Solubilizing agents for active or functional organic compounds
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An active or functional organic compound is solubilized in a diaryl organic compound having a polar or polarizable functional group therein, as a solvent, cosolvent or additive, to form a composition thereof. Representative active or functional organic compounds include those present in personal care products, e.g., sunscreens containing UVA/UVB absorbing compounds, such as avobenzone, benzophenone-3, and 4-methylbenzylidene camphor. Such compositions also show increased SPF, UVA/UVB absorbance ratio, and critical wavelength performance properties.
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- Synthesis of caffeic acid esters
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A new method for the preparation of caffeic acid esters was investigated. Ten caffeic acid esters were prepared by condensation of protocatechualdehyde with malonic acid mono-esters in moderate yield. Malonic acid mono-esters were prepared from the corresponding malonate di-esters. The conformations of compounds are trans (E) form.
- Xia, Chun-Nian,Hu, Wei-Xiao
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p. 332 - 334
(2007/10/03)
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- Process for preparing malonic esters
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Malonic esters of the general formula where R is C1-10-alkyl, C3-10-alkenyl or aryl-C1-4-alkyl, are prepared by reacting an alkali metal salt of malonic acid with a halide of the general formula R—X (II), where R is as defined above and X is chlorine, bromine or iodine, in the presence of water and a phase-transfer catalyst.
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- Synthesis and decarboxylation of Δ2-cephem-4,4-dicarboxylic acids
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Penicillin V was converted in 14 steps into Δ2-cephems having hydrogen at C-3, hydrogen or methyl at C-2, and two methoxycarbonyl, two benzyloxycarbonyl, or one methoxycarbonyl and one benzyloxycarbonyl substituent at C-4. Deprotection of these Δ2-cephem-4,4-dicarboxylic acid esters by alkaline hydrolysis (in the case of methyl esters) or hydrogenolysis (in the case of benzyl esters) led in all cases to rapid decarboxylation of the Δ2-cephem-4,4-dicarboxylic acid or Δ2-cephem-4,4-dicarboxylic acid monoester. With hydrogen at C-2, hydrolysis of the dimethyl ester with 1 equiv of base produced a Δ2-cephem. With 2 equiv of base, and with all compounds having methyl at C-2, hydrolysis or hydrogenolysis afforded 4α-substituted-Δ2-cephems. In contrast, simpler benzyl or methyl acetamidomalonates could be deprotected without difficulty to afford stable malonic acids. Reasons for the differences in ease of decarboxylation were examined using semiempirical (AM1) and ab initio (3-21G) molecular orbital calculations. The decarboxylation barriers of unionized cephem or acetamido malonic acids were found to be high (35-40 kcal mol-1). Although the monoanion of acetamidomalonic acid retained a high barrier, the epimeric monoanions of a Δ2-cephem malonic acid decarboxylated with barriers of only 2 kcal mol-1.
- Wolfe,Ro,Kim,Shi
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p. 1238 - 1258
(2007/10/03)
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- One-Pot synthesis of 5-Alkylthio-3H-1,2-dithiole-3-thiones: Advantages and scopes
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The reaction of dialkyl malonate esters with P2S5/S8 in boiling xylene in the presence of 2-mercaptobenzothiazole/ZnO as catalyst produces 5-alkylthio-3H-1,2-dithiole-3-thiones as major identifiable product. Moderate yields were obtained with malonate esters of primary alcohols. The reaction fails with malonate esters of secondary alcohols. Regarding the substituent in position two, dialkyl malonates with groups such as CH3, Ph, CH2Ph, OCH3 and Cl afford the corresponding 4-substituted derivatives whereas with Br and NO2 do not give the expected products. Some mechanistic evidences are described.
- Aimar,De Rossi
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p. 1749 - 1755
(2007/10/03)
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- Normal and abnormal heme biosynthesis. 2.1 Synthesis and metabolism of type-III pentacarboxylic porphyrinogens: Further experimental evidence for the enzymic clockwise decarboxylation of uroporphyrinogen-III
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Uroporphyrinogen decarboxylase catalyses the sequential decarboxylation of uroporphyrinogen-III (1) to give coproporphyrinogen-III (2), a precursor to the hemes and chlorophylls. This involves the decarboxylation of four nonequivalent acetate side chains to produce methyl units and in principle could take place by 24 different pathways involving up to 14 intermediary porphyrinogens. In the past, seemingly contradictory data have been presented that either support an ordered 'clockwise' decarboxylation pathway or a random decarboxylation process. Four pentacarboxylate porphyrinogens might be involved immediately before the formation of 2, and these compounds have been synthesized as the corresponding porphyrin pentamethyl esters via tripyrrene and a,c-biladiene intermediates. Hydrolysis of the methyl esters and reduction with 3% sodium amalgam gave the required porphyrinogens, and these were incubated with crude enzyme preparations derived from chicken red cell hemolysates. One of these pentacarboxylate porphyrinogens. (5dab) consistently proved to be a much better substrate than the other three, providing new support for the 'clockwise' pathway for coproporphyrinogen-III formation.
- Lash, Timothy D.,Mani, Ukti N.,Lyons, Elizabeth A.,Thientanavanich, Pornlert,Jones, Marjorie A.
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p. 478 - 487
(2007/10/03)
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- A MILD, RAPID AND CONVENIENT ESTERIFICATION OF HALF ESTERS OF MALONIC ACID
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A new method for the esterification of half esters of malonic acid with chloroformates is described.The reaction proceeds via the mixed anhydride followed by spontaneous decarboxylation.
- Gutman, Arie L.,Boltanski, Aviv
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p. 1573 - 1576
(2007/10/02)
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- A GENERAL ROUTE TOWARD 2-OXO-, 2-THIOXO- AND 2-IMINOPENAMS AND THEIR CONVERSION INTO 2-ALKOXY-, 2-ALKYLTHIO- AND 2-AMINOPENEMS
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A convenient methodology is described which allows the preparation of 2-oxo-, 2-thioxo- and 2-iminopenams from a single precursor readily prepared from penicillin G.These penams have been converted into the corresponding 2-heterosubstituted penems.
- Cossement, Marc,Marchand-Brynaert, Jacqueline,Bogdan, Sophie,Ghosez, Leon
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p. 2563 - 2566
(2007/10/02)
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