- Iodine-catalyzed synthesis of β-uramino crotonic esters as well as oxidative esterification of carboxylic acids in choline chloride/urea: a desirable alternative to organic solvents
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Abstract: Iodine-mediated selective synthesis of β-uramino crotonic esters was achieved via the reaction of β-dicarbonyls and urea at room temperature. Choline chloride/urea mixture, as an eco-friendly, cheap, non-toxic, and recyclable deep eutectic solvent (DES), was employed as sustainable media as well as reagent at the same time in these transformations. Some derivatives of β-uramino crotonic esters were synthesized with good to high yields without a tedious work-up. The process could be done to synthesize the above-mentioned compounds in gram scale. Moreover, oxidative cross-esterification of carboxylic acids with alkyl benzenes was carried out in the above-mentioned DES by the employment of tetrabutylammonium iodide (TBAI) as the catalyst and tert-butyl hydroperoxide (TBHP) as the oxidant at 80?°C. DES/TBAI system was reused up to five consecutive times. Graphic abstract: Iodine-catalyzed C–N and C–O bond formation in choline chloride/urea as a green solvent under the mild reaction conditions. Providing the clean procedure toward synthesis of β-uramino crotonic esters and benzylic esters.[Figure not available: see fulltext.].
- Moayyed, Mohammadesmaeil,Saberi, Dariush
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p. 445 - 455
(2020/09/07)
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- Highly Efficient Synthesis of Substituted 3,4-Dihydropyrimidin-2-(1H)-ones (DHPMs) Catalyzed by Hf(OTf)4: Mechanistic insights into reaction pathways under metal Lewis acid catalysis and solvent-free conditions
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In our studies on the catalytic activity of Group IVB transition metal Lewis acids, Hf(OTf)4 was identified as a highly potent catalyst for”one-pot, three-component” Biginelli reaction. More importantly, it was found that solvent-free conditions, in contrast to solvent-based conditions, could dramatically promote the Hf(OTf)4-catalyzed formation of 3,4-dihydro-pyrimidin-2-(1H)-ones. To provide a mechanistic explanation, we closely examined the catalytic effects of Hf(OTf)4 on all three potential reaction pathways in both “sequential bimolecular condensations” and “one-pot, three-component” manners. The experimental results showed that the synergistic effects of solvent-free conditions and Hf(OTf)4 catalysis not only drastically accelerate Biginelli reaction by enhancing the imine route and activating the enamine route but also avoid the formation of Knoevenagel adduct, which may lead to an undesired byproduct. In addition, 1H-MMR tracing of the H-D exchange reaction of methyl acetoacetate in MeOH-d4 indicated that Hf(IV) cation may significantly accelerate ketone-enol tautomerization and activate the β-ketone moiety, thereby contributing to the overall reaction rate.
- Kong, Rui,Han, Shuai-Bo,Wei, Jing-Ying,Peng, Xiao-Chong,Xie, Zhen-Biao,Gong, Shan-Shan,Sun, Qi
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- N-Donor ligand activation of titanocene for the Biginelli reaction via the imine mechanism
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The remarkable activation of stable titanocene dichloride (Cp2TiCl2) was achieved using N-donor ligand urea in an alcoholic solvent, leading to the formation of a Ti(iv) species [(MeO)2Ti(NHCONH2)]+,
- Zheng, Shaohua,Jian, Yajun,Xu, Shan,Wu, Ya,Sun, Huaming,Zhang, Guofang,Zhang, Weiqiang,Gao, Ziwei
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p. 8657 - 8661
(2018/03/08)
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- An improved procedure of Miyashita protocol for the preparation of ureidomethylene derivatives of 1,3-dicarbonyl compounds
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A facile method has been developed for the synthesis of ureidomethylene derivatives by the condensation of 1,3-dicarbonyl compounds, urea and trimethylorthoformate in presence of Zn(OTf)2 under solvent-free conditions. A variety of 1,3-dicarbon
- Majee,Kundu,Santra,Hajra
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p. 124 - 126
(2014/02/14)
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- Microwave synthesis of β-uramino crotonic ester and its derivatives
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The new and rapid synthesis of β-uramino crotonic ester and its derivatives involves the condensation of ethyl acetoacetate and urea, thiourea and 1,3-dimethyl urea in presence of ethanol. These compounds are important intermediates for the synthesis of 6-methyl pyrimidinedione derivatives, which are biologically active compounds used in medicinal and pharmaceutical chemistry. The structure of the synthesized compounds has been elucidated with spectral analysis: UV, FTIR and GC-MS.
- Ehsan, Shahana,Khan, Bushra
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experimental part
p. 3202 - 3204
(2012/02/03)
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- Antimony(III) chloride-catalysed Biginelli reaction: a versatile method for the synthesis of dihydropyrimidinones through a different reaction mechanism
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Antimony(III) chloride (20 mol %) in refluxing acetonitrile efficiently catalyses the synthesis of dihydropyrimidinones (50-90% yields) by the Biginelli reaction of aromatic aldehydes, acetoacetate esters and urea. This reaction proceeds through 3-ureido-crotonates followed by cyclisation with an aromatic aldehyde to the dihydropyrimidinone.
- Cepanec, Ivica,Litvi?, Mladen,Filipan-Litvi?, Mirela,Grüngold, Ivana
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p. 11822 - 11827
(2008/03/13)
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