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1.
The fluoride ion-induced reactivity of a series of silyl heterocycles leads to the generation of nucleophilic species capable of interacting with electrophiles, thus disclosing new classes of formyl and acyl anion synthons. Moreover, when reacting stereodefined molecules, the stereoinformation of the reacting carbon-silicon bond is transferred to the newly formed carbon-carbon bond, suggesting possible applications in stereoselective synthesis. Thus, silyl dithiolanes, oxathiolanes, dioxolanes, thiazolidines and oxazolidines can be efficiently and stereoselectively functionalized under fluoride ion conditions in the presence of electrophiles. While direct access to silyl heterocycles is generally either prevented or troublesome, a novel protocol for their synthesis has also been developed, together with a simple general access route to several functionalized and stereodefined mercaptans, building blocks for the construction of silyl heterocycles.  相似文献   

2.
The reaction of silyl enol ethers with β-nitroacrylates, in the presence of tetrabutyl ammonium fluoride as catalyst, allows the formation of polyfunctionalized β-nitro esters, or hexahydro-4H-benzoxazine-2-oxides, depending on the nature of the starting silyl enol ethers.  相似文献   

3.
Alkylidenecyclopropanone silyl acetals are readily available from the reaction of an alkylidenemethyliodonium salt and ketene silyl acetals in the presence of triethylamine. The three different C-C bonds of the cyclopropane ring can be selectively cleaved with HCl, Lewis acid, or fluoride. The alkylideneallyl cation formed via the cleavage of C2-C3 bond with Lewis acids shows further selectivity in reacting with a nucleophile.  相似文献   

4.
Polyperfluorobut-2-yne is prepared by a fluoride ion-induced polymerization of hexafluorobut-2-yne. The mass spectrum indicates a regular fragmentation pattern but the ESCA spectrum establishes the structure as a polyene, rather than a crosslinked system, and the occurrence of a shake-up peak assists in this assignment.  相似文献   

5.
We describe the one-pot synthesis of core 2 class branched oligosaccharides initiated by chemo-selective glycosylation of silyl ether. Glycosylation of 6-O-silyl-4-benzyl-2-azido-thiogalactoside with glycosyl fluoride provided selectively 6-glycosylated thioglycoside without both O-glycosylation at the 3 position and S-glycosylation. Subsequent coupling of galactosyl fluoride and amino acids afforded the protected branched oligosaccharides in good yields.  相似文献   

6.
The fluoride ion-induced intramolecular conjugate addition of propargylsilanes to dihydropyridones is reported. Our results revealed that tetrabutylammonium triphenyldifluorosilicate (TBAT), an air-stable, non-hygroscopic fluoride ion source, catalyzes cyclocondensation to provide the corresponding 1-vinylidene indolizidines in a high yield as single isomers, while Lewis acid catalysts were ineffective. The scope of this method was further investigated in the reactions leading to compounds with larger ring size. In these cases dihydropyridones with the propargylsilane located in the side-chain underwent cyclization to give 9-vinylidene quinolizidines with significantly lower yields.  相似文献   

7.
N,N-bis(silyl)enamines react with electrohiles in the presence of catalytic amounts of nucleophile. The reaction of carbonyl compounds catalyzed by fluoride ion provides an interesting route to 2?aza?1,3?dienes. The methoxide ion catalyzed reaction of N,N—dimethyl- formade gives rise to enamidines.  相似文献   

8.
The reaction of readily generated silyl lithium reagents with various aryl fluorides to provide the corresponding aryl silanes is reported. DFT calculations reveal that the nucleophilic aromatic substitution of the fluoride anion by the silyl lithium reagent proceeds through concerted ipso substitution. In contrast to the classical nucleophilic aromatic substitution, this concerted ionic silyldefluorination also occurs on more electron‐rich aryl fluorides.  相似文献   

9.
The catalytic, enantioselective, [4 + 2] cycloaddition reaction of ortho-quinone methides with silyl ketene acetals is described. This mechanistically interesting reaction, initiated by a chiral cinchona alkaloid-derived ammonium fluoride "precatalyst" complex, affords a variety of alkyl- and aryl-substituted 3,4-dihydrocoumarin products in excellent yield and with good enantioselectivity.  相似文献   

10.
A ratiometric fluorescent turn-on probe for fluoride ion, based on modulation of the excited-state intramolecular proton transfer (ESIPT) process by chemodosimetric desilylation pathway is reported. The probe SNBT (silyl protected hydroxynaphthalene benzothiazole moiety) shows a significant increase of ratiometric absorption band at 440 nm and emission band at 477 nm by the deprotection of fluoride mediated silyl bond cleavage in CH3CN–H2O (8/2, v/v, 25 °C). The test strips based on SNBT and F are fabricated, which can act as a convenient and efficient F test kits. Furthermore, the biological application shows that it can be very useful as a selective fluoride probe in the fluorescence imaging of living cells.  相似文献   

11.
Hydrofluoric acid and tetrabutylammonium fluoride will selectively deprotect alcoholic and phenolic silyl ethers respectively.  相似文献   

12.
Treatment of silyl ethers with Jones reagent in acetone in the presence of potassium fluoride resulted in the silicon-oxygen bond cleavage and oxidation to give carbonyl compounds directly.  相似文献   

13.
A number of stereoselective reactions of 1-substituted-1,2-dimethylsilacyclopentanes are described. Reactions of the silyl chloride (II) with ZnF2 and with alcohols catalyzed by amines are stereoselective as a result of rapid isomerization of II. Alcoholysis of silicon hydride (I) catalyzed by transition metals is apparently an inversion reaction regardless of the nature of the catalyst, but can appear to be stereoselective because of isomerization of alkoxysilane product. Reduction of silyl fluoride (IV) by lithium aluminum hydride is nonstereoselective, a result which is proposed to arise through rapid isomerization of intermediates with expanded coordination.  相似文献   

14.
A fluoride ion catalyzed reaction which affords the title compounds in good yield from enol silyl ethers is described.  相似文献   

15.
In order to synthesize complicated medicinal compounds, chemists have developed increasingly satisfactory protective groups and effective methods for the formation and cleavage of protected compounds. The selective method to remove protective groups is an important tool in organic synthesis. Transformation of an alcohol to its corresponding silyl ether is a common and useful method for protecting hydroxyl groups. Within the silyl ethers,tert-butyldimethylsilyl,tert-butyldiphenylsilyl and triisopropylsilyl ethers are the most commonly used protecting groups. The cleavage of the Si-O bonds of these silyl ethers is typically performed with fluoride ion or under harsh acidic or basic conditions. Herewith, we wish to report a highly efficient and mildly acidic desilylating method for tert-butyldimethylsilyl,tert-butyldiphenylsilyl and triisopropylsilyl ethers.  相似文献   

16.
The hydrosilylation of aldehydes and ketones with dimethylphenylsilane occurs readily in dichloromethane at room temperature in the presence of catalytic amounts of caesium fluoride and 18-crown-6 to afford silyl ethers of the corresponding aryl and hetaryl carbinols in good yields.  相似文献   

17.
An exceptional intramolecular palladium-catalyzed alkenylation of silyl enol ether in the absence of a fluoride additive was developed, and this reaction led to the construction of bicyclo[3.3.1]nonane ring system in reasonable yield. In this type of reactions, trialkylamines were employed as additives instead of previously indispensable fluoride additives.  相似文献   

18.
Two types of fluoride ion-catalyzed desilylative-defluorination (intermolecular and intramolecular versions) have been reported. The intermolecular desilylative-defluorination consists of sequential reactions: generation of a nucleophile by fluoride ion-promoted desilylation, its reaction with a fluorinated electrophile, and simultaneous formation of a final product and regeneration of fluoride ion. Precursors of nucleophiles used in the catalytic reaction system involve disilane, silyl ethers, CF3-TMS, and FSO2CF2CO2TMS. The intramolecular version is quite useful for the preparation of gem-difluoroalkenes including α-substituted 2,2-difluorostyrenes, 2-trimethylsilyloxy-3,3-difluoroacrylate, tetrafluoroquinodimethane, which arise from 1,2-, 1,4- and 1,6-desilylative-defluorination, respectively. The potential advantages for both types of the desilylative-defluorinations are (1) effective preparation of base or nucleophile-sensitive products, (2) very mild and essentially neutral conditions, and (3) use of a catalytic amount of fluoride ion.  相似文献   

19.
Eight corners of a double-four ring cage-type germanoxane, containing a fluoride ion, were successfully silylated by the combination of chlorosilanes and silazanes. Three different silyl groups, trimethylsilyl, dimethylsilyl, and dimethylvinylsilyl, were attached on the corners of germanoxane cage. The solubility and reactivity of the cage modified with dimethylvinylsilyl groups were significantly increased, allowing for further reaction. Hydrosilylation reaction between dimethylvinylsilylated cage geramanoxanes and dimethylsilylated cage siloxanes afforded porous solids. Functionalization of the corners of germanoxanes with silyl groups should provide valuable building blocks in various functional materials.  相似文献   

20.
Designer chiral quaternary ammonium bifluoride 1 has been prepared, and both its catalytic and its chiral efficiency have been clearly demonstrated by achieving the first catalytic asymmetric nitroaldol reaction of silyl nitronate with aldehydes. For instance, the reaction of trimethylsilyl nitronate 2 (R(1) = Me) with benzaldehyde (R(2) = Ph) in THF in the presence of (S,S)-1 (2 mol %) proceeded smoothly at -78 degrees C, giving the corresponding nitroaldol adduct 3 (R(1) = Me, R(2) = Ph) in 92% isolated yield (anti/syn = 92:8) with 95% ee (anti isomer). The method was found to be successfully applicable to other aromatic aldehydes and silyl nitronates, and a high level of anti selectivity and enantiomeric excess was constantly observed. This finding should lead to the further development of fluoride ion-catalyzed asymmetric carbon-carbon bond-forming reactions.  相似文献   

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