查看更多>>摘要：A simple and convenient method for the esterification of various monosaccharide and disaccharide uronic acids, derived from glucose, galactose and mannose, was developed with different alcohols using the ecofriendly catalyst silica-sulphuric acid (H2SO4-SiO2). The esterification reactions proceeded at room temperature under mild conditions with excellent yields. Under the standard reaction conditions, various sensitive protecting groups, including acetyl, benzoyl, pivaloyl, isopropylidene, benzyl, naphthyl, etc., were well tolerated. Partially protected uronic acids underwent esterification without undergoing self condensation reactions. Published by Elsevier Ltd.
Calabretta, Lindsey O.Thomas, Vienna M.Raines, Ronald T.
3页
查看更多>>摘要：Octanol-water partitioning experiments in the presence of carboxylate-, phosphate-, and sulfate -containing anionic lipids revealed that Ac-Cav-NH2 (where Cav refers to delta-oxa-arginine) partitions less into octanol than does Ac-Arg-NH2, suggesting that a cell-penetrating peptide based on canavanine would be relatively ineffective. (C) 2022 Published by Elsevier Ltd.
Han, MeiShen, Mei -HuaZhu, Chi -FanXu, Hua -Dong...
4页
查看更多>>摘要：A series of gamma-lactams were synthesized by intramolecular aza-claisen rearrangement of ketenes using Meldrum's acid as ketene precursor. Derivatives of Meldrum's acid with tertiary ammonia structure were used as raw material, and the reaction was catalyzed by Lewis acid at high-temperature conditions under microwave. Ketene formation by losing acetone and CO2, cyclization and claisen rearrangement occurred in sequence to form the gamma-lactams. (C) 2022 Elsevier Ltd. All rights reserved.
Fernandez-Canelas, PaulaBarrio, PabloGonzalez, Jose M.
17页
查看更多>>摘要：Haloalkynes can enter a wide variety of metal-catalyzed transformation giving rise to the formation of products with or without showing halide-shift. This article offers an overall view of the reactivity of these substrates under gold catalysis. Particular attention is devoted to intramolecular reactions that involve a concomitant halide-shift process for the case of alkynyl iodides as starting materials.(c) 2022 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
查看更多>>摘要：A facile, solvent-free, lower-cost, and efficient high-speed ball milling reaction catalyzed by Cu (NO3)2.3H2O/P2O5 is developed for the synthesis of symmetric ethers from dehydration of benzyl alcohols by taking a benzylic carbocation as intermediate.(c) 2022 Elsevier Ltd. All rights reserved.
Suzuki, YuichiTaniguchi, KosukeHoang, Hai NamTamura, Mayumi...
5页
查看更多>>摘要：The investigation on the applicability of CO2 as a solvent has been increasingly important due to the need to develop efficient reactions replacing ordinary organic solvents derived from fossil fuel with sustainable solvents such as pressurized CO2. In our previous study of solvent engineering of a lipase-catalyzed reaction of bulky substrates, the conversions were higher for the reaction in CO2-expanded liquids, liquids expanded by dissolving pressurized CO2, than that in the liquids without CO2. This study demonstrates the detailed examination of CO2-expanded liquids as solvents for lipase-catalyzed kinetic resolution of racemic 1-tetralol, 2-tetralol, and substituted 1-tetralol analogs since chiral substituted tetralol analogs are important pharmaceutical intermediates. CO2-expanded liquids accelerated the reaction rate by up to 40 times of the reactions without CO2 while maintaining excellent enantioselectivities (E > 200). Preparative scale reactions of racemic 1-tetralol and 2-tetralol successfully gave the corresponding (R)-acetates and (S)-alcohols with high yields and excellent enantioselectivities (up to ee > 99%). (c) 2022 Elsevier Ltd. All rights reserved.
查看更多>>摘要：The facile construction of phenanthrene derivatives through the intermoletetradehydro-Diels-Alder (TDDA) reaction of benzyne in situ generated by the hexadehydro-Diels-Alder (HDDA) reaction with various substituted phenylacetylene was described. The naphthalene derivatives were obtained unexpectedly in another reaction modle when expanding substrate scope. The reaction profiles has good chemoselectivity and provided a new way for the synthesis of highly functionalized phenanthrene and naphthalene derivatives from simple materials under relatively mild conditions. (C) 2022 Elsevier Ltd. All rights reserved.
查看更多>>摘要：A highly stereoselective asymmetric Henry reaction using a double fluorous-tagged Co-salen complex was conducted. The introduction of two fluorous tags into the Co-salen complex was found to be more effective in terms of improving stereoselectivity than the introduction of a strong electron-withdrawing nitro group into the same position of the salen ligand. The observed stereoselectivity was significantly higher than that when using a Jacobsen-type Co-salen complex bearing the same asymmetric source. (c) 2022 Elsevier Ltd. All rights reserved.
查看更多>>摘要：The reduction of benzylic, tertiary, and allylic alcohols with hydrosilane was efficiently catalyzed by the rhenium complex, such as ReBr(CO)5, to give the corresponding deoxygenarated products, alkanes, in moderate to good yields. In the case of aliphatic secondary alcohol, the alkane was formed along with the formation of dehydrated products. On the other hand, in the case of primary and cyclic alcohols, silylation of alcohols proceeded to form the corresponding silyl ethers.(c) 2022 Elsevier Ltd. All rights reserved.
Jackson, Amy C.Olsen, James T.Sundstrom, SashaLambert, Kyle M....
5页
查看更多>>摘要：A ring expansion of tetramic acids (pyrrolidine-2,4-diones) to N-oxy-2,5-diketopiperazines (DKPs) is described. This method allows for the facile and late-stage construction of the hydroxamic acid moiety and can thereby serve as a general method for accessing N-oxy-2,5-DKP natural products. (C) 2022 Elsevier Ltd. All rights reserved.
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