Na_3PO_4·12H_2O选择性催化脱去芳香性叔丁基二甲基硅醚

报道了以磷酸盐为催化剂选择性脱去芳香性叔丁基二甲基硅醚的方法.以DMF为溶剂,室温下在0.5质量分数的Na3PO4.12H2O催化下,能顺利地脱去芳香性叔丁基二甲基硅醚得到相应的酚类化合物,而不影响其他的保护基和官能团.     

Diisopropylethylamine: An effective catalyst for the introduction of the t-butyldimethylsilyl group

The rapid reaction of t-butyldimethylchlorosilane with alcohols catalysed by diisopropylethylamine at room temperature gave high isolated yields of the t-butyldimethylsilyl ethers.     

A class of new silylating reagents. I. A mild method for introduction of the tert-butyldimethylsilyl group.

$\text{t}$-Butyldimethylsilyl enol ethers of pentane-2,4-dione and methyl acetoacetate react rapidly at room temperature to give high isolated yields of the t-butyldimethylsilyl ethers of a variety of alcohols.     

1,1,3,3-Tetramethylguanidine: An Effective Catalyst for the t-Butyldimethylsilylation of Alcohols

Reaction of alcohols with equimolar amounts of t-butyldimethylchlorosilane and triethylamine in the presence of 1,1,3,3-tetramethylguanidine as a catalyst affords the t-butyldimethylsilyl ethers in high yields.     

Deprotection of a silyl group with mesoporous silica

The triethylsilyl (TES) group of silyl ethers of several types is selectively and easily removed in the presence of a t-butyldimethylsilyl (TBDMS) group with a mesoporous silica MCM-41/MeOH heterogeneous system. Comparison of the efficiency was carried out among several solvents, and among such promoters as common zeolites and ion-exchange resins. Furthermore, FSM-16, another mesoporous silica, was examined for the possibility of recycling by re-calcination at 400 degrees C after the reaction.     

An in situ generated CuI/metformin complex as a novel and efficient catalyst for C–N and C–O cross-coupling reactions

An in situ generated complex of copper(I) and a biguanide, namely metformin, was found to be a highly efficient homogeneous catalyst in N/O-arylation reactions. The O-arylation of substituted phenols with various aryl iodides and bromides was also achieved using this copper catalyst to afford diaryl ethers in good to excellent yields in DMF. This heterogeneous copper catalyst also promotes the N-arylation of imidazole with a variety of aryl halides (Cl, Br, I) in acetonitrile.     

Desilylation of t-butyldimethylsilyl ethers of hydroxyquinones

Desilylation of a series of hydrolytically stable hydroxyquinone t-butyldimethylsilyl ethers was achieved in high yields by the use of potassium fluoride in the presence of catalytic amounts of aqueous 48% hydrobromic acid (HBr), or basic aluminium oxide (Al₂O₃), and tetra-n-butylammonium fluoride (Bu₄NF) as cleaving agents. Copyright © 1998 John Wiley & Sons, Ltd.     

Mild and Efficient Method for α-Thiocyanation of Ketones and β-Dicarbonyl Compounds Using Bromodimethylsulfonium Bromide–Ammonium Thiocyanate

An efficient and convenient method for α-thiocyanation of ketones and β-dicarbonyl compounds has been developed using a reagent combination of bromodimethylsulfonium bromide (BDMS) and ammonium thiocyanate in acetonitrile. The developed method is mild and gave good yield of the products at room temperature.     

Bromodimethylsulfonium bromide (BDMS): a useful reagent for conversion of aldoximes and primary amides to nitriles

An operationally simple and high yielding procedure has been developed for the preparation of nitriles from aldoximes and primary amides using bromodimethylsulfonium bromide (BDMS) as a novel and efficient reagent in the absence of any added base or catalyst. The optimal protocol is applicable to access a wide range of cyano compounds including aromatic, heterocyclic, and aliphatic species. The conversion of aldoximes to nitriles takes place at room temperature in acetonitrile, whereas acetonitrile at reflux temperature is required for rapid conversion in the case of primary amides.     

Gas chromatographic determination of two isosorbide mononitrates in plasma

A GC/EC method has been developed for the determination of 2-isosorbide mononitrate (2-ISMN) and 5-isosorbide mononitrate (5-ISMN) in blood plasma. The procedure is based on extraction of ammonium sulfate-treated plasma with ether followed by a cleanup via n-heptane/methanol partitioning. After conversion to t-butyldimethylsilyl ethers, the ISMNs are chromatographed on a 3% OV-17 column. Absolute recoveries of 76.7 and 84.8% were achieved for 2-ISMN and 5-ISMN, respectively. Using o-nitrobenzyl alcohol as an internal standard, relative standard deviations of 4.8 to 6.1% were observed over the concentration ranges of 10 to 100 ng/ml for 2-ISMN and 250 to 1500 ng/ml for 5-ISMN.     

Effects of substituents in the beta-position of 1,3-dicarbonyl compounds in bromodimethylsulfonium bromide-catalyzed multicomponent reactions: a facile access to functionalized piperidines

1,3-Dicarbonyl compounds can be converted to Mannich-type products A or highly functionalized piperidines B in the presence of a catalytic amount of bromodimethylsulfonium bromide (BDMS). The combination of aromatic aldehyde, amine, and 1,3-dicarbonyl compounds in the presence of a catalytic amount of BDMS leads to the formation of Mannich-type product A when R is a non-enolizable carbon or an alkoxy group, whereas in cases when R = CH3, the same combination yielded highly functionalized piperidines B. A synthetic study and mechanistic proposal are presented.     

Reagents and synthetic methods 55. New methods for the preparation of t-butyldimethylsilyl triflate and trimethylsilyl triflate.

An expeditious synthesis of t-butyldimethylsilyl triflate is described from triflic acid and t-butyldimethylsilane. Reaction between trichloromethyltrimethylsilane and triflic acid is also reported.     

Efficient synthesis of tris(4-imidazolyl)methanol derivatives

Biomimetic tris(4-imidazolyl)carbinol derivatives are prepared from imidazole in a short, high-yielding sequence via sulfonamide 1, which is converted to the 2-silylated carbinol 2 by one-pot, sequential 2-functionalization and then 4(5)-functionalization. Alcohol 2 can be transformed either to the parent carbinol 3 or to a desilylated sulfonamide derivative 4. The tripodal alcohol 3 is a convenient precursor to ethers by solvolysis and to metal complexes, as illustrated by the preparation of a bis-tripod complex with iron(III).     

Operationally simple and efficient workup procedure for TBAF-mediated desilylation: application to halichondrin synthesis

An operationally simple and efficient workup method for tetrabutylammonium fluoride (TBAF)-mediated t-butyldimethylsilyl (TBS) deprotection has been developed. The procedure includes addition of a sulfonic acid resin and calcium carbonate, followed by filtration and evaporation. This method eliminates the tedious aqueous-phase extraction process to remove excess TBAF and materials derived from TBAF, thereby making the protocol highly amenable to multiple TBS deprotections. Its efficiency and usefulness were demonstrated by using the transformation of 1a to 3a in the halichondrin synthesis. [reaction: see text].     

Synthesis of new heterocyclic phenols : 8-hydroxy-imidazo [1,2-a] pyridine

Preparation of the unknown title compound has been achieved by condensation of 2-amino-3-hydroxy-pyridine with chloroacetaldehyde. Activation by the free phenolic hydroxyl allows preferential nitration of the pyridine ring, in marked contrast to the behavior of the related ethers which suffer electrophilic substitution on the imidazole moiety, as usual in the series.     

pH-tunable equilibria in azocrown ethers with histidine moieties

The crown ethers with electro- and photoactive azo moieties containing substituents with mobile protons such as in the -COOH groups of histidine, show unique effect of pH switched on/off presence of the azo form. The differences observed for the electrochemical behavior of azocrown ethers with N-acetylhistidine and imidazole moieties reveal the interference of a chemical reduction pathway in strongly acidified solutions. This chemical reduction process leads to the formation of a hydrazine derivative which can be detected by its further electroreduction on the electrode surface. The involvement of chemical reduction is seen clearly in the presence of mobile protons of the -COOH group and mercury as the electrode substrate. The behaviour of the N-acetylhistidine azomacrocyle is similar to that of compounds known to exist in quinone-hydrazone tautomeric equilibria.     

A mild and efficient method for large scale synthesis of 3-aminocoumarins and its further application for the preparation of 4-bromo-3-aminocoumarins

A wide variety of 3-aminocoumarins have been synthesized in large scale from the corresponding 3-acetamidocoumarins by regioselective cleavage of carbon–nitrogen bond using 70% sulfuric acid under reflux conditions. The synthesized 3-aminocoumarins were further brominated regioselectively at the 4-position of 3-aminocoumarin using BDMS as brominating agent.     

Unexpected copper-catalyzed aerobic oxidative cleavage of C(sp3)-C(sp3) bond of glycol ethers

An unexpected Cu-catalyzed oxidative cleavage of the C(sp(3))-C(sp(3)) bond in glycol ethers by using air or molecular oxygen as the terminal stoichiometric oxidant is demonstrated. As a result, the corresponding α-acyloxy ethers and formates of 1,2-ethanediol are formed by direct coupling of carboxylic acids and aldehydes with glycol ethers under the reaction conditions. This method represents the first example of Cu-catalyzed aerobic cleavage of saturated C-C bond in ethers.     

Acceleration mechanisms in curing reactions involving model systems

The mechanisms involving some of the most common accelerators in the curing reactions of epoxy resins have been investigated by use of model systems. Phenyl glycidyl ether was used as a model compound. The characterization of the reaction products was mainly carried out by High-Performance-Liquid-Chromatography and by preparative methods. Special attention was paid to the oligomerization reactions of the oxirane ring in the presence of tertiary amines. Three different types of oligomers depending on phenyl glycidyl ethers are discussed. The mechanisms of multifunctional accelerators such as imidazoles or phenol-MANNICH-base-compounds are much more difficult. The extraordinary interaction of imidazoles depends on the formation of different oligomers. Furthermore, the cleavage of the imidazole ring was observed. It is possible that the glycidyl ether oligomerization plays an important role in understanding the network structure. Some aspects of the accelerating effect of tertiary amines in the curing of glycidyl ethers with acid anhydrides were likewise discussed. The results obtained using these model reactions may be applied to influence the curing process in commercial epoxy resin systems.     

Intramolecular Diels-Alder chemistry of 4-vinylimidazoles

An investigation of 4-vinylimidazoles as diene components in the intramolecular Diels-Alder reaction is described. In the course of these studies several parameters affecting the cycloaddition were evaluated including the nature of the imidazole protecting group, the type of dienophile and the linking group. These investigations established that amino linkers were generally more effective than either ethers or esters. In most cases, the cycloadditions were highly stereoselective, resulting in the formation of products derived from an anti transition state. The polysubstituted tetrahydrobenzimidazole core of the pyrrole-imidazole alkaloid ageliferin can be constructed through the use of pseudo dimeric 4-vinylimidazoles.