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1.
Lithiated furans have been found to cleave the S–S bond of polymerization-resistant 1,2-dithiolanes to give the ring opened products in good yields. In the case of lithiated benzofuran, the excess reagent reacted with the normal product to give a mixture. Lithiated dihydrofuran and dihydropyran gave the corresponding ring-opened products that rearranged to spiro-1,3-dithianes during acidic workup. The reaction was applied to the selective synthesis of substrates for intramolecular Diels-Alder reactions. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:281–287, 1998  相似文献   

2.
[reaction: see text] A highly diastereoselective acetate aldol reaction that uses a tert-leucine-derived thiazolidinethione auxiliary and dichlorophenylborane has been developed. The reaction proceeds in excellent yields and with high diastereoselectivities (drs range from 9.5:1 to >100:1).  相似文献   

3.
Lithiated trimethylsilylacetonitrile was allowed to react with some α,β-unsaturated carbonyl compounds to give the corresponding conjugate addition products.  相似文献   

4.
A zinc or indium-mediated Barbier-type allylation of aldehydes with 3-bromomethyl-5H-furan-2-one in aqueous solvents was developed to provide an efficient route to α-methylene-γ-butyrolactone, which is synthetically very useful. The desired products were obtained in moderate to high yields in aqueous solvents. Excellent drs were achieved, among which the best diastereomeric ratios of products were found when water was used in the indium-mediated reaction, and THF-NH(4)Cl (sat, aq) (2 : 1) mixture in the zinc-mediated reaction. Furthermore, the allylation can be induced by chiral centers, especially those in the α-position, as a substrate-controlled reaction to obtain the enantioselective homoallylation alcohols.  相似文献   

5.
[reaction: see text] alpha-Halonitriles react with alkyllithium, organomagnesium, and lithium dimethylcuprate reagents generating reactive, metalated nitriles. The rapid halogen-metal exchange with alkyllithium and Grignard reagents allows selective exchange in the presence of reactive carbonyl electrophiles, including aldehydes, providing a high-yielding alkylation protocol. Lithiated and magnesiated nitriles react with propargyl bromide by S(N)2 displacement whereas organocopper nitriles react by S(N)2' displacement, correlating with the formation of a C-metalated nitrile.  相似文献   

6.
A Michael addition reaction of cyclic ketones and piperidones to a vinyl phosphonate is described. The reaction, catalyzed by chiral diamines, produced geminal γ-oxobisphosphonates in high yields (up to 92%) and very high ees (up to >99%). Disubstituted ketones gave drs of up to 8?:?92. The synthesis and characterization of several new compounds with potential biological activity is described.  相似文献   

7.
Lithiated anions derived from (alkenyl)pentamethyl phosphoric triamides as homoenolate equivalents are used in the reaction with halogenated acetal and ketal giving regioselectively the γ-alkylation adducts. Chemoselective acidic hydrolysis of the enephosphoramide moiety in the presence of acetal or ketal groups leads to expected carbonyl products, key intermediates in the synthesis of natural compounds. The synthetic potential of the presented strategy is illustrated by stereoselective synthesis of two pheromones namely, 9-oxo-2(E)-decenoic acid 1 from queen substance and 10-hydroxy-2(E)-decenoic acid 2 from royal jelly of honeybee Apis mellifera.  相似文献   

8.
The electrochemical reactions of lithium with the intermetallic compound, InSb, were studied in lithium coin cells using laminate electrodes fabricated from either single-crystal InSb wafers or ball-milled samples. In-situ X-ray diffraction data show that the InSb zinc-blende framework is unstable to extensive reaction with lithium; In is extruded from a fixed Sb lattice during `discharge' and is partially incorporated back into the lattice during `charge'. Despite the loss of some In from the structure, the indium antimonide electrode provides capacities in excess of 300 mAh/g with excellent reversibility. Cyclic voltammetry was used to study the electrochemical processes in greater detail. Lithiated indium products are formed below ∼600 mV versus Li. The electrode can be discharged at high rates, delivering 150 mAh/g at 3.6 mA/cm2 between 1.2 and 0.2 V versus Li. These data hold exciting prospects for the development of intermetallic insertion electrodes for practical room-temperature Li-ion cells.  相似文献   

9.
Lithiated benzonitriles can be generated in high yields from reactions of bromobenzonitriles with n-BuLi in THF under standard cryogenic conditions (ca. -70 degrees C) provided the reverse addition mode is employed. The resultant aryllithiums are fairly stable at temperatures up to -60 degrees C. The formation of lithiated benzonitriles via Br/Li exchange under normal addition mode conditions is plagued by deprotonation and extensive CN-addition reactions. The generation of related aryllithiums from disilylated bromobenzonitriles is comparatively less sensitive to reaction conditions.  相似文献   

10.
The enantiopure Davis' N-sulfinylimines were found to be efficient as chiral imine equivalents in the high-temperature Reformatsky-type additions with BrZnCF(2)COOEt affording an efficient approach to the enantiomerically pure alpha,alpha-difluoro-beta-amino acids. High chemical and stereochemical yields (drs > 9:1, and as high as 99:1) render this method immediately useful for preparing the target amino acids.  相似文献   

11.
Lithiated 2′,3′-O-isopropylidine-5′-O-methoxymethyl-uridine was found to react with a variety of electrophilic reagents regiospecifically at the C-6 position. The protecting groups of the ribose moiety in the 6-functionalized products were concurrently removed under mild conditions with aqueous trifluoroacetic acid. Consequently, the present method permits simple and general syntheses of 6-substituted uridines.  相似文献   

12.
Lithiated Aminoflurosilanes. Reactions under Inter- and Intramolecular Lithium Halide-(Pseudohalide) Elimination Lithio-aminofluorosilanes react with halide-, pseudo halide silanes and chlorotrimethylstannan with intermolecular Li-halide-(pseudohalide) elimination and substitution. The reaction of lithiated aminofluorosilanes with polar element-hydrogen bonds (for example with alcohols, thioalcohols, water, hexine) proceeds via an intermolecular LiF elimination and addition.  相似文献   

13.
Lithiated poly(2,6-dimethyl-1,4-phenylene ether) has been used as an initiator for the graft polymerization of isoprene, methyl methacrylate, hexamethylcyclotrisiloxane, and phenyl isocyanate with the use of toluene and tetrahydrofuran as solvents. The products were examined by gel-permeation chromatography for evidence of homopolymerization and graft polymerization. The composition of the graft copolymers was determined by NMR, and for isoprene and hexamethylcyclotrisiloxane, termination by trialkylchlorosilanes enabled chain lengths to be determined by NMR. The use of toluene gave rise to some homopolymerization, but with tetrahydrofuran, only hexamethylcyclotrisiloxane gave homopolymer. In all cases, graft copolymers were formed. With isoprene and methyl methacrylate, soluble graft copolymers were formed in good yield. In the former case approximately 60% 3,4 and 40% 1,4 addition was found. In the latter case 1,1-diphenylethylene was used to reduce crosslinking, in its absence, methyl methacrylate gave only crosslinked gels in tetrahydrofuran. Hexamethylcyclotrisiloxane added only one molecule per lithium on the polymer, the remainder giving homopolymer. Phenyl isocyanate gave some soluble graft copolymer in toluene, but only crosslinked products were obtained when tetrahydrofuran was used as reaction solvent.  相似文献   

14.
Poly- and Spirocyclic Silylhydrazones — Synthesis and Molecular Structures Bulky aminotrifluorosilanes react with lithiated dimethylketone-hydrazone to give 1,2-diaza-3-sila-5-cyclopentenes — DSCP — ( 1, 2 ). The 4-silylated ( 3–5, 8–15 ) and siloxysilyl-substituted ( 17, 18 ) rings eliminate no halosilane or siloxane thermally. Lithiated 2 dimerises with LiF elimination to give the (2+2)cycloadduct of a 1,2-diaza-3-sila-3,5-cyclopentadiene ( 6 ). Lithiated DSCP reacts with MeSiF2N(CMe3)SiMe2CMe3 via a nucleophilic 1,3-methanide ion migration to form LiF and the spirocyclic compound 18 . A compound with spirocyclic silicon ( 21 ) is formed in the reaction of bis(1,2-diaza-3-sila-5-cyclopenten-4-yl)difluorosilane ( 19 ) and the lithium salt of dimethyl-ketone-tert-butylhydrazone. The crystal structures of 6 and 21 are reported.  相似文献   

15.
The synthesis of P-benzylic products by reaction of anions stabilised by N-phosphorylphosphazenyl, N-methoxycarbonylphosphazenyl, phosphine borane complex, and phosphine oxide groups by displacement of hydrogen of a variety of electron-deficient benzene derivatives is described. Lithium phosphazenes were the most suitable nucleophiles for the substitution of hydrogen in nitrobenzene and some ortho-, meta-, and para- substituted nitrobenzenes. Lithiated phosphine borane complexes produced efficiently the substitution of the hydrogen at the para position of a cyano group in cyanobenzenes, whereas the anion of ethyldiphenylphosphine oxide lead to complex mixtures with all electrophiles assayed. The method reported here represents a convenient alternative to the vicarious nucleophilic substitution for the synthesis of benzylic phosphorus derivatives using phosphorus-stabilised anions that do not bear a leaving group at the carbanionic centre.  相似文献   

16.
Synthesis of Functional Carboxylic Acid Silylester Di-tert-butylsilandiol reacts with organic acid chlorides to chlorosilanoles R2Si(OH)Cl 1 (R = t-Bu). The phosphoric acid silylester 2 is obtained from 1 and POCl3. Lithiated halogenosilanoles react with carboxylic acid chlorides to give silylesters ( 3 – 7 ). Lithium (trimethyl-acetoxy)silanolate 8 is obtained in the reaction of the lithiated diol with the chloride of trimethylacetic acid. The analogous reaction with benzoyl chloride lead to the formation of the bis(benzoic acid) silylester 9 . The condensation product 10 is obtained in the reaktion of the lithiated aminosilanol (t-Bu)2Si(NH2)OLi with trimethylacetic acid chlorid and condensation of the formed ester with aminosilanol.  相似文献   

17.
Lithiated (α-chloroalkyl)heterocycles, generated by deprotonation with LDA at −78 °C in THF, add to various enantiopure imines affording ‘one pot’ chiral heterosubstituted aziridines in a diastereoselective manner. Lithiated heterosubstituted aziridines, obtained by deprotonation of the corresponding aziridines with n-BuLi at −78 °C in THF, were trapped by electrophiles (D2O or CH3I) with high stereoselectivity.  相似文献   

18.
Lithiated 2-(1-chloroethyl)-4,4-dimethyl-2-oxazoline 7 adds to electron-poor alkenyl heterocycles to afford substituted cyclopropanes in excellent yields. A route to chiral nonracemic heterosubstituted cyclopropanes, starting from optically active 2-chloromethyl-2-oxazolines, is highlighted as well.  相似文献   

19.
Lithiated alkoxyallenes, nitriles, and carboxylic acids have been employed as precursors in a three-component reaction leading to highly substituted β-alkoxy-β-ketoenamides. Upon treatment with trifluoroacetic acid, these enamides could be easily cyclized to 5-acetyloxazole derivatives. The synthesis is very flexible with respect to the substitution pattern at C-2 and C-4 of the oxazole core. A mechanistic suggestion for the oxazole formation is presented on the basis of (18)O-labeled compounds and their mass spectrometric analysis. In several cases, 1,2-diketones are formed as side products or even as major components. The acetyl moiety at C-5 of the oxazole derivatives can efficiently be converted into alkenyl or alkynyl moieties, which allows a multitude of subsequent reactions. Condensation reactions of the acetyl group provided the expected oxime or hydrazone. By applying a Fischer reaction, the phenylhydrazone could be transferred into an indole, which emphasizes the potential of 5-acetyloxazoles for the preparation of highly substituted (poly)heterocyclic systems. The alkynyl group at C-2 is prone to addition reactions, providing an enamine with interesting photophysical properties. Sonogashira couplings were performed with 5-alkynyl-substituted oxazoles, furnishing the expected aryl-substituted products. This alkynyl unit was employed for the preparation of a new, star-shaped trisoxazole derivative. The ability of this multivalent compound to form self-assembled monolayers between the basal plane of highly oriented pyrolytic graphite and 1-phenyloctane was demonstrated by scanning tunneling microscopy (STM). The star-shaped compound seems to prefer the C(3)-symmetric arrangement in this two-dimensional crystal. Two 1,2-diketones were smoothly converted into functionalized quinoxaline derivatives.  相似文献   

20.
Monomeric Trilithium-tris[tert-butyldimethylsilylamido]phenylsilane, PhSi[NLi(thf)SiMe2CMe3]3 – Synthesis and Crystal Structure Lithiated tert-butyldimethylsilylamine reacts with trifluorophenylsilane in a molar ratio 2:1 or 3:1 to give the bis- and tris(silylamino)silanes 1 [(Me3CSiMe2NH)2SiFPh] and 2 [(Me3CSiMe2NH)3SiPh]. The trilithium derivative 3 [Me3CSiMe2NLi(thf)]3SiPh is obtained in the reaction of 2 with n-BuLi in hexane/thf. 3 crystallizes as a monomer forming three planar four-membered (LiNSiN)-rings. The results of the crystal structure of 3 are discussed.  相似文献   

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