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1.
A short synthesis of a functionalized gibbane is described. The key-step involves the intramolecular Diels-Alder reaction of furan-diene , leading to a 3:1 ration of two diastereoisomers, tentatively identified as and . The precursor is obtained form-m-methoxybenzoic acid in 7 steps. 相似文献
2.
3-Bromo-2-(tert-butylsulfonyl)-1-propene is easily available in two steps from allyl-tert-butylthioether (70% overall yield). It reacts with a great variety of carbanions to give functionnalized α, β-unsaturated sulfones of type in high yields. A second nucleophile (lithium cuprates) can then be added to compounds to furnish functionnalized sulfones of type (Y=SO2-tert-butyl). 相似文献
3.
Ernst-Ulrich Würthwein Jayaraman Chandrasekhar Eluvathingal D Jenmis Paul von Ragué Schleyer 《Tetrahedron letters》1981,22(9):843-846
Semi-empirical (MINDO/3 and UNDO) MO calculations on highly strained planar tetracoordinate carbon candidates indicate the central carbons in - [4.4.4.4] fenestrane () to have pyramidal () and in trans-[4.4.4.]fenestrane () to have distorted tetrahedral () geometries. In [2.2.2.2]paddlane (), the two central carbons are pentacoordinate. Each is nearly coplanar with four carbon neighbours; additionally, the two bridgehead carbons are connected by a single bond (). 相似文献
4.
Two cleavage products, -dimethylmuconate () and -dimethyl-muconate (), are inefficiently produced in the 9,10-dicyanoanthracene (DCA) sensitized photooxidation of -dimethoxybenzene (-DMB) in polar solvents. An electron transfer mechanism is proposed in which superoxide ion (O?20 combines with ortho-dimethoxybenzene to form a dioxetane (3), which cleaves to form (). The initial products is , which is rapidly converted to and other products under the conditions; cis-trans isomer is formed. 相似文献
5.
New synthesis of Eucarvone , (±)-Nuciferal and (±)-Manicone are described from trimethylsilyl enol ethers , and via their chloromethylenation products by means of a two carbons homologation reaction. 相似文献
6.
Depending on the reaction conditions the intramolecular Diels-Alder reaction of furan-diene yields predominantly either one of two adducts and , which possess the necessary functionality for eventual transformation into corticosteroids. The dienophile was introduced via alkylation of the enolate, formally obtained upon lithium-liq. ammonia reduction of 3-furyl-2-methyl-2-cyclopentenone (). 相似文献
7.
Jayaraman Chandrasekhar Eluvathingal D. Jemmis Paul von Ragué Schleyer 《Tetrahedron letters》1979,20(39):3707-3710
The 3,5-dehydrophenyl cation (I), which may represent the structure of C6H3 ions observed mass spectroscopically, illustrates : two different aromatic systems in orthogonal planes. 相似文献
8.
13C-NMR analysis of the Reformatsky intermediates from t-btyl-α-bromo acetate, t-btyl-α-bromo isobutyrate and t-btyl-α-bromo prpionate have evidenced C-metallated species. Their ability to act as ncleophilic reagents under mild conditions and their selectivity towards hlogen-and oxygen containing electrophiles is reported. 相似文献
9.
Three new electron donors, acenaphtho[5,6-]-1,2-dithiole (), acenaphtho[5,6-]-1,2-diselenole (), and acenaphtho[5,6-]-1,2-ditellurole (), can be prepared in 28%, 22%, and 14% yields respectively by reaction of the elemental chalcogens (S, Se, Te) with 5,6-dilithioacenaphthylene (). Compound is generated by treatment of 5,6-dibromoacenaphthylen (), for which a convenient preparation is described, with -butyllithium (2 equiv.) in THF at ?78°C. 相似文献
10.
Paul Ronald Jones Thomas F.O Lim Mark L McBee Richard A Pierce 《Journal of organometallic chemistry》1978,159(1):99-110
The reaction of two equivalents of vinyldimethylethoxysilane or vinyldimethylmethoxysilane with hydrocarbon soluble alkyllithium reagents; -BuLi, -BuLi, or -BuLi; in hexane at low temperature gives high yields of 1,1-dimethyl-2-alkyl-4-(dimethylalkoxysilyl)silacyclobutanes. With methyl- or phenyllithium substituted vinylsilanes are obtained. The stereochemistry of the silacyclobutanes is assigned on the basis of Si-29 and H-1 NMR. For vinyldimethylethoxysilane the ratio of cis to trans silacyclobutane is about , and is independent of the alkyllithium reagent used. In the reaction of vinyldimethylmethoxysilane with -BuLi a ratio of the cis and trans silacyclobutane is obtained. A pathway is proposed which is consistent with the stereochemical results and with the products isolated in the reaction run in THF. 相似文献
11.
Malvina Farcasiu Edward W. Hagaman Ernest Wenkert Paul von Ragué Schleyer 《Tetrahedron letters》1981,22(16):1501-1504
Unexpected differences in the aluminium bromide-catalyzed rearrangement behaviour of 1,2--trimethylenenorbornane () and its 1,2--isomer () are interpreted. Isotopic labelling studies indicate that reversible abstraction of the tertiary 2- hydride in does not occur. Instead, rearrangement to is favored. The label scrambling in the final product, adamantane (), is attributed to degenerate isomerization in the proto-adamantyl precursor, . 相似文献
12.
Eleven homoerythrina-type alkaloids (-, , ) have been isolated from A. cupressoides (Taxodiaceae), of which six (-, ,) had not previously been reported. 相似文献
13.
Paul von Ragué Schleyer Peter Grubmüller Wilhelm F. Maier Otto Vostrowsky Lars Skattebøl Kjetil H. Holm 《Tetrahedron letters》1980,21(10):921-924
Tricyclo(4.2.2.o1,5)decane () in the presence of AlBr3 rearranges partly “forwards” to adamantane () and partly “backwards” to tetrahydrodicyclopentadiene (, largely the oxo isomer). Intermediate , characterizing the →exo-→→→ forward pathway, is found only in small amounts. The detection of a new intermediate, , also shows that a second major rearrangement route from to is being utilized (see dashed lines in Figure 1). 相似文献
14.
6, 7-Dimethoxy-2-l,3-benzothiazine derivatives (, ) react with substituted acetyl chlorides to give angularly condensed β -lactams (-, , ). The compound was epimerised to the derivative . From the interaction of 2-phenyl-6,7-dimethoxy-4-1,3-benzothiazine () and α -chloro-phenylacetyl chloride two stereoisomeric β -lactam derivatives (, ) were isolated, whereas in the other cases studied the reactions leading to β -lactams proved to be stereospecific. Analogous reactions of -methyl-6,7-dimethoxy-2-l,3-benzothiazine () furnished the enamides ,, . Structures of the new compounds and configurations of the diastereomers were elucidated by IR and NMR spectroscopy. 相似文献
15.
John F. Blount Glenna D. Gray Karnail S. Atwal Thomas Y.R. Tsai Karel Wiesner 《Tetrahedron letters》1980,21(46):4413-4416
The α,β-unsaturated ketone yields with allene the photocycloadduct predicted by our empirical photoaddition rule and the byproduct 7. The formation of this material may be rationalized by the sequence → → → → . The isomeric ketone is unreactive under the same conditions, since α addition is prohibited by the rule and β addition is severely blocked. 相似文献
16.
Andreas Beck Lothar Knothe Dieter Hunkler Horst Prinzbach 《Tetrahedron letters》1982,23(24):2431-2434
Upon thermal activation the vinylogous fidecene is isomerised into the pentacyclic indenoid hydrocarbon (benzene, t (150°C) ca. 5 min), the formation of which is explained by an initial conrotatory (“symmetry-forbidden”) 18-electron electrocyclisation followed by two fast hydrogen migrations ([1.9], [1.5]) and 14π-electrocyclisation. 相似文献
17.
Herbert Muffler Guenter Siegemund Werner Schwertfeger 《Journal of fluorine chemistry》1982,21(2):107-132
4.5-Perfluoro-1.3-dioxolanes are available by reaction of 2(α-chloroalkoxy)perfluoro-carbonyl halides or -ketone with fluoride ions. A mechanism for the intramolecular ring- closure-reaction is proposed. Hydrogen atoms at C-2 in can be exchanged photochemically by chlorine. Starting from the 2-monochloro-derivatives the 2-monofluoro-4.5-perfluoro- 1.3-dioxolanes are formed by reaction with triethylamine- hydrofluoride. 相似文献
18.
The palladium-catalyzed addition of a vinyl or aryl halide to the enolate of β-allenyl malonate leads to the formation of either of the two cyclized products and depending mainly on the bulk of the starting unsaturated halide. 相似文献
19.
Functionalized cyclopentene is cyclized via thermal ene reaction to . All steps in the synthesis of are highly stereoselective. 相似文献
20.
In this study we demonstrate that the tetraisopropyldisiloxane-1,3-diyl protecting group could be introduced, in a two step procedure, at the 3'- and 4'-hydroxyl functions of α-glucosyldiglyceride to give derivative . Compound could be selectively condensed with a suitably protected phosphatidyl part at its primary hydroxyl function to afford the protected glycophospholipid . The phosphatidyl part was obtained by phosphorylation of optically pure 1,2-di-O-oleoyl-sn-glycerol () with phosphoditriazolide . Finally, the 2,4-dichlorophenyl and TIPS protecting groups were removed from by syn-4-nitro-benzaldoximate and fluoride ions, respectively, to afford glycophospholipid . 相似文献