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Organic Synthesis
Published in Suresh C. Ameta, Rakshit Ameta, Garima Ameta, Sonochemistry, 2018
Chetna Ameta, Arpit Kumar Pathak, P. B. Punjabi
An aldol condensation is a condensation reaction in organic chemistry in which an enol or an enolate ion reacts with a carbonyl compound to form a P-hydroxyaldehyde or P-hydroxyketone, followed by dehydration to give a conjugated enone. Aldol condensations are important in organic synthesis, because they provide a smooth way to form carbon-carbon bonds (Carey and Sundberg, 1993). These reactions are usually catalysed by strong acids or bases, and a variety of different Lewis acids have been evaluated in this reaction (Reeves, 1966). Unfortunately, the presence of a strong acid or base promotes the reverse reaction (Hathaway, 1987) and this leads to the self-condensation of the reacting materials to give the corresponding byproducts in low yields (Nakano et al., 1987).
Enolate Anions and Condensation Reactions
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
Yes! It is also possible for an ester enolate anion to react with another ester. Just as the enolate anions of aldehydes and ketones react with other aldehydes and ketones in the aldol condensation, ester enolates react with a variety of carbonyl derivatives. What is the product when ethyl propanoate is reacted with 1. LDA, THF, -78°C; 2. ethyl propanoate?
Retrosynthesis of undescribed sesquiterpene lactone
Published in Binoy K. Saikia, Advances in Applied Chemistry and Industrial Catalysis, 2022
Lujie Pu, Jingsong Chen, Weichen Tang, Jiawei Li, Haozhe Xu
As we know, hydrogens at the a-carbon of carbonyl compounds are somewhat acidic. (SCRIBD, https://www.scribd.com) When an a-proton is removed, a conjugate-base anion is formed at the a-carbon which is called an enolate ion involved in the formation of enol. Consequently, breaking the carbon-carbon single bond attached to a seven-membered ring can be retrosynthetic hydrolyzed to two carbonyl compounds as shown in Figure 3.
Synthesis of bioactive heterocycles using reusable heterogeneous catalyst HClO4–SiO2 under solvent-free conditions
Published in Green Chemistry Letters and Reviews, 2018
Leimajam Vartima Chanu, Thokchom Prasanta Singh, Laishram Ronibala Devi, Okram Mukherjee Singh
On the basis of the results obtained by the control experiments, tentative mechanisms of the chromenes and dihydropyrimidine synthesis have been shown below (Scheme 2). Initially, the condensation product of β-oxodithioester 1a and o-hydroxybenzaldehyde 2a, activated by HClO4–SiO2, generates an enolate A, which facilitates in subsequent intramolecular aldol condensation to give phenyl(2-thioxo-2H-chromen-3-yl)methanone 3a. The mechanism of Biginelli reaction has been discussed in various experimental and theoretical reports, and has been a topic of much debate. A plausible mechanism for the synthesis of 5-methylmercaptothiocarbonyl-4-aryl-3,4-dihydropyrimidin-2(1H)-ones 4a is presented in (Scheme 2). For dihydropyrimidines, the first step in this reaction, the acid-catalyzed formation of an acyl imine intermediate A formed by reaction of the aldehyde with urea, is the key rate-limiting step. Interception of the iminium ion by β-oxodithioester 1a produces an open-chain ureide B that subsequently cyclizes to the dihydropyrimidinone 4a.