共查询到18条相似文献,搜索用时 235 毫秒
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首次将穿心莲内酯与2,3,4,6-四- O -乙酰基- β -D-溴化吡喃葡萄糖通过Koenigs-Knorr反应及二丁基氧化锡脱保护方法合成穿心莲内酯糖苷衍生物,所得糖苷结构经IR,NMR及高分辨质谱分析证实。实验结果表明:用二丁基氧化锡脱乙酰保护基的方法,反应条件比较温和,可以选择脱除糖元上的乙酰基,保留苷元乙酰基,且不影响分子中的酸碱敏感基团。 相似文献
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本文采用酸为催化剂,实施了具有代表性的各种烷硫基α,α-二乙酰基二硫缩烯酮的脱乙酰基反应,得到了一条简洁、通用的α-乙酰基二硫缩烯酮的合成路线.用浓硫酸作催化剂,以极高的产率(90%—100%)制得到相应的α-乙酰基二硫缩烯酮.同时,通过控制反应时间,还可以得到硫代乙酰乙酸酯类化合物. 相似文献
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研究了二苯并噻吩(DBT)、4-甲基二苯并噻吩(4-MDBT)和4,6-二甲基二苯并噻吩(4,6-DMDBT)在非负载型NiMoW催化剂上的加氢脱硫反应产物分布及反应机理,给出了它们在非负载型催化剂上加氢脱硫反应网络.研究发现,由于甲基的空间位阻效应,二苯并噻吩类化合物加氢脱硫转化率顺序为4,6-DMDBT≈4-MDBT<DBT,而非负载型NiMoW催化剂具有很高的芳环加氢活性,有利于烷基取代的芳环加氢,减弱空间位阻效应,使烷基取代的二苯并噻吩类化合物得到有效脱除.DBT的脱硫产物会被进一步加氢,其产物分布与联苯加氢产物相似.4-MDBT有两种预加氢脱硫反应路径,甲基取代的苯环由于甲基的供电子效应会被优先加氢.非负载型催化剂存在的L酸中心会使部分4-MDBT和4,6-DMDBT通过脱甲基反应生成DBT再进行脱硫反应. 相似文献
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碳/碳复合材料新基体—聚芳基乙炔研究:I.芳基乙炔的合成与表征 总被引:1,自引:0,他引:1
用溴化-脱溴化氢一步法合制备二乙炔基苯,研究碱,催化剂,反应温度及反应时间等因素对产率的影响,结果表明,以聚乙二醇-400为相转移催化剂,二乙炔基苯的产率达68.6%,用气相色谱,红外光谱,核磁共振和质谱对产物进行了分析表征。 相似文献
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唾液酸是一类重要的具有多种生物学功能的糖酸化合物. 唾液酸糖苷化反应条件较一般糖苷化反应苛刻, 立体选择性通常较差, 端基碳的立体构型较难控制. 在唾液酸糖苷化反应中能否高效地得到α糖苷键是评价该反应优劣的重要标志之一. 唾液酸苷化方法的研究一般涉及以下几个方面: C-2上的离去基团的运用, C-1, C-3上辅助基团的参与作用, C-5上氨基保护基团的修饰, 以及一些新的糖苷化反应催化剂的发展. 近些年来, 这些研究领域, 尤其是C-5上氨基保护基团的研究, 取得了重要进展. 将着重对唾液酸糖苷化方法的新进展做一总结和评述. 相似文献
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<正>Chelate tetra(acetylacetonato) tin(Ⅳ) was prepared and used as catalyst for polytrimethylene terephthalate synthesis.It exhibited higher catalytic activity than tetrabutyl titanate,butyltinhydroxide oxide and dibutyltin oxide.Decrease in reaction time, content of terminal carboxyl group,color intensity and increase in intrinsic viscosity were observed.The unique molecular structure can be considered as factor remarkably improving the catalytic activity of tetra(acetylacetonato) tin(Ⅳ). 相似文献
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A complete study on the catalytic activity of stannous oxalate for poly(trimethylene terephthalate) (PTT) synthesis via esterification method is carried out by comparison to the well known catalysts (tetrabutyl titanate (TBT), dibutyltin oxide (Bu2SnO), and stannous octoate (SOC)). Their catalytic activity in the esterification process is monitored by measuring the amount of water generated, while intrinsic viscosity (IV) and content of terminal carboxyl groups (CTCG) are used as the index in the polycondensation process. Stannous oxalate shows higher activity than the other catalysts. Decrease in reaction time and improvements in PTT property are observed. The higher catalytic activity of stannous oxalate is attributed to its chelate molecular structure. 相似文献
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Having developed the one-pot triacetylation of indolin-3-ones, we have now devised a simple two-step reaction sequences to produce di- and mono-acetylated indoles from indolin-2-ones. The indolin-2-ones were first subjected to acetylation in the presence of acetic anhydride and a catalytic amount of N,N-dimethylaminopyridine to give 2-acetoxy-1,3-diacetylindoles. Subsequently, an enzyme-assisted deacetylation resulted in the chemoselective deprotection of the acetoxy group to produce 1,3-diacetyl-2-hydroxyindoles. However, a chemical deacetylation of 2-acetoxy-1,3-diacetylinoles under mild basic or acidic conditions resulted in the formation of 3-acetyl-2-hydroxyindoles. 相似文献
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Alcaide B Almendros P Alonso JM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(23):5793-5799
A novel application of the Grubbs carbene complex has been discovered. The first examples of the catalytic deprotection of allylic amines with reagents other than palladium catalysts have been achieved through Grubbs carbene mediated reaction. Significantly, the catalytic system directs the reaction toward the selective deprotection of allylic amines (secondary as well as tertiary) in the presence of allylic ethers. A variety of substrates, including enantiomerically pure multifunctional piperidines, are also usable. The new method is more convenient, chemoselective, and operationally simple than the palladium-catalyzed method. The current mechanistic hypothesis invokes a nitrogen-assisted ruthenium-catalyzed isomerization, followed by hydrolysis of the enamine intermediate. We believe that the reactive species involved in the reaction may be an Rubond;H species rather than the Grubbs carbene itself. Thus, the isomerization may occur according to the hydride mechanism. The synthetic utility of this ruthenium-catalyzed allyl cleavage is illustrated by the preparation of indolizidine-type alkaloids. 相似文献
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Han Wang Renyang Xu Shuobin Liang Fuxiang Ran Lihe Zhang Yongmin Zhang Demin Zhou Sulong Xiao 《中国化学快报》2020,31(2):333-336
The acetyl ester plays an important role for protection of the hydroxyl groups in carbohydrates synthesis.In the present study,we described an efficient deprotection of acetyl group of pentacyclic triterpenoid by using methanolic ammonia in THF solution.Good selectivity for cleaving gal-C2-OAc group of 3β-hydroxy-olean-12-en-28-oic acid 28-N-2,3,4,6-tetra-O-acetyl-β-D-galactopyranoside(3) was achieved in the presence of methanolic ammonia within 4 h at low temperature(-60℃) in a yield of 56%.The reaction disclosed here provides a new method for the synthesis of C2 selective modified carbohydrates,which is more useful than conventional synthesis procedure that usually requires many steps including temporary regioselective protection and deprotection.When the reaction temperature was increased from -60℃ to room temperature,the cleavage of the other three acetyl groups of galactose in an order of C4-OAc>C3-OAc>C6-OAc was observed.Based on this study,a plausible route for the deacetylation reaction has been proposed. 相似文献
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An improved method for the deprotection of benzyl ethers using a catalytic amount of Co(2)(CO)(8) in the presence of Me(2)PhSiH and CO (1 atm) is described. The deprotection reaction is compatible with double bond or sulfur-containing substrates. The method also tolerates other functional groups, such as Ac, Piv, and Bz, and shows potential selectivity in perbenzylated monosaccharides. 相似文献
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A simple and highly efficient method for deprotection of allyl ethers has been developed using dimethylsulfoxide–sodium iodide (catalytic amount). This method is inexpensive, has simple reaction conditions, has an easy workup procedure, proceduces excellent yields (60–99%), and is effective for several structurally varied allyl ethers. 相似文献