- Solvent free protection of carbonyl group under microwave irradiation
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Protection of aldehydes and ketones as acetals or dioxolanes catalysed by PTSA or KSF clay was readily achieved from orthoformates, 1,2-ethanediol or 2,2-dimethyl-1,3-dioxolane without solvent under microwave irradiation.
- Perio, Bertrand,Dozias, Marie-Joelle,Jacquault, Patrick,Hamelin, Jack
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- Trifluoroacetylation of unsymmetrical ketone acetals. A convenient route to obtain alkyl side chain trifluoromethylated heterocycles
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A convenient method to obtain β-alkyl-β-methoxyvinyl trifluoromethyl ketones [CF3COCHC(OMe)R, where R = Et, n-Pr, i-Pr, i-Bu, t-Bu, -(CH2)2OMe] from the regiospecific acylation of kinetic enol ether generated in situ is reported. The unsymmetrical ketone dimethyl acetals react with trifluoroacetic anhydride in the presence of pyridine using dry chloroform as solvent with a temperature range of 25-60°C. These acetals [R-C(OMe)2Me] are obtained from the reaction of alkyl methyl ketones with trimethyl orthoformate in the presence of p-toluenesulfonic acid as catalyst in pure methanol as solvent. The new acetylated enol ethers proved to be versatile building blocks for the construction of interesting alkyl trifluoromethyl substituted heterocycles. Thus, examples of isoxazoline, pyrazoline, pyrazole and pyrimidinone have been obtained in good yields (62-79%).
- Bonacorso, Helio G.,Martins, Marcos A.P.,Bittencourt, Sandra R.T.,Lourega, Rogerio V.,Zanatta, Nilo,Flores, Alex F.C.
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- Photocatalytic Reductive Formation of α-Tertiary Ethers from Ketals
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A general photocatalytic reductive strategy for the construction of unsymmetrical α-tertiary dialkyl ethers is reported. By merging Lewis acid-mediated ketal activation and visible-light photocatalytic reduction, in situ-generated α-alkoxy radicals were found to engage in addition reactions with a variety of olefinic partners. Good reaction efficiency is demonstrated with a range of ketals of aromatic and aliphatic ketones. Extension to acetal substrates is also described, demonstrating the overall synthetic utility of this methodology for complex ether synthesis.
- Rossolini, Thomas,Ferko, Branislav,Dixon, Darren J.
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supporting information
p. 6668 - 6673
(2019/09/03)
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- Zinc chloride as an efficient catalyst for chemoselective dimethyl acetalization
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Commercially available anhydrous zinc chloride has been found to be a highly efficient catalyst for dimethyl acetalization in high yields by treatment of aldehydes and ketones with trimethyl orthoformate in methanol-cyclohexane at reflux temperature. Copyright Taylor & Francis Group, LLC.
- Roy, Anupam,Rahman, Matiur,Das, Sudarshan,Kundu, Dhiman,Kundu, Shrishnu Kumar,Majee, Adinath,Hajra, Alakananda
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experimental part
p. 590 - 595
(2009/07/04)
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- Catalytic asymmetric phase-transfer reactions using tartrate-derived asymmetric two-center organocatalysts
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A new highly versatile asymmetric two-center catalyst, tartrate-derived diammonium salt (TaDiAS), was designed and a catalyst library containing more than 70 new two-center catalysts was constructed. A variety of (S,S)- and (R,R)-TaDiAS were easily synthesized from diethyl L- and D-tartrate, respectively, using common and inexpensive reagents under operationally simple reaction conditions. TaDiAS was used in phase-transfer alkylations and Michael additions to afford various optically active α-amino acid equivalents in up to 93% yield. Moreover, dramatic counter anion effects were observed in phase-transfer catalysis (PTC) for the first time, making it possible to further improve reactivity and selectivity. These findings validate the usefulness of three-dimensional fine-tuning of the catalyst (acetal, Ar, and counter anion) for optimization. Recovery and reuse of the catalyst was also possible using simple procedures. The present asymmetric PTC was successfully applied to enantioselective syntheses of serine protease inhibitor aeruginosin 298-A and its analogues.
- Ohshima, Takashi,Shibuguchi, Tomoyuki,Fukuta, Yuhei,Shibasaki, Masakatsu
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p. 7743 - 7754
(2007/10/03)
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