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1.
《Tetrahedron》2011,67(50):9729-9735
[3+2] Cycloadditions of (1Z,4R∗,5R∗)-1-arylmethylidene-4-benzoylamino-3-oxo-5-phenylpyrazolidin-1-ium-2-ides 1a-e to methyl methacrylate gave the 1-CO2Me regioisomers 3/3′, exclusively, in 1-67% yields. Stereocontrol was dependent on the ortho-substituents at the 1′-aryl group in dipole 1: ortho-unsubstituted dipoles 1a-c gave the major (1R∗,3R∗,5R∗,6R∗)-isomers 3a-c, whilst ortho-disubstituted dipoles gave the major (1R∗,3S∗,5R∗,6R∗)-isomers 3′d,e. The structures of cycloadducts were determined by NMR and X-ray diffraction. 相似文献
2.
The ether extract of the females of white-spotted longicorn beetle Anoplophora malasiaca showed activity as contact sex pheromone to males. The extract was fractionated, and a pheromonal activity was revealed only when three fractions; n-hexane, n-hexane/EtOAc 9:1, and EtOAc were blended. The relative structures of gomadalactone A, B, and C, three active components isolated from the EtOAc fraction, were determined by spectroscopic studies to be (1S∗,4R∗,5S∗)-5-hydroxy-4-[(E)-7-hydroxy-4-methylhept-3-enyl]-4,8-dimethyl-3-oxabicyclo[3.3.0]octan-7-en-2,6-dione, (1R∗,4R∗,5R∗)-5-hydroxy-4-[(E)-7-hydroxy-4-methylhept-3-enyl]-4,8-dimethyl-3-oxabicyclo[3.3.0]octan-7-en-2,6-dione, and (1S∗,4R∗,5S∗,8S∗)-5-hydroxy-4-[(E)-7-hydroxy-4-methylhept-3-enyl]-4,8-dimethyl-3-oxabicyclo[3.3.0]octan-2,6-dione, respectively. 相似文献
3.
Lidija Pezdirc 《Tetrahedron letters》2007,48(30):5205-5208
Treatment of (1Z,4R∗,5R∗)-1-arylmethylidene-4-benzamido-5-phenylpyrazolidin-3-one 1-azomethine imines 4a-d with potassium cyanide in the presence of acetic acid resulted in addition of HCN to the exocyclic CN double bond followed by β-eliminative N-N single bond cleavage (ring opening) to give the N-[(1R∗,2R∗)-3-amino-2-benzamido-3-oxo-1-phenylpropyl]benzimidoyl cyanides 6a-d in 28-85% yields. Reaction of dipole 4e with HCN furnished stable intermediate, (1′S∗,4R∗,5R∗)-4-benzamido-1-[cyano(mesityl)methyl]-5-phenylpyrazolidin-3-one (5e), in 76% yield. The structure of compound 6c was determined by X-ray diffraction. 相似文献
4.
Jie Chen 《Tetrahedron》2008,64(37):8899-8906
An efficient electrophilic iodocyclization of alkylidenecyclopropyl ketones with N-iodosuccinimide (NIS) or I2 in aqueous CH3CN affording 3-oxabicyclo[3.1.0]hexan-2-ols is described. NIS is a better electrophilic iodocyclization reagent than I2. Four chiral centers were formed within one step. The stereochemistry was established by the X-ray diffraction studies of compounds 2e-2h, 2n, and 2c. It is quite interesting to observe that the substituent of the cyclopropane ring plays an important role in determining the relative stereochemistry at the 4-position: with R2 being an acyl or ester group a mixture of (1S∗,2R∗,4S∗,5R∗)-2 (major) and (1R∗,2R∗,4R∗,5R∗)-2 (minor) was formed with moderate selectivity while the reaction of the substrates with R2 being sulfonyl and p-methylphenylsulfonyl or R1 being phenyl afforded (1R∗,2R∗,4S∗,5S∗)-2 or (1S∗,2R∗,4S∗,5R∗)-2f as the only product. The reaction is general for a range of different substrates to afford the products in moderate to high yields. 相似文献
5.
Anastasia A. Fesenko 《Tetrahedron letters》2007,48(48):8420-8423
A three-stage diastereoselective synthesis of (4R∗,5R∗,6S∗)-5-mercapto-4-methyl-6-phenylhexahydropyrimidin-2-one has been developed. The first stage involves the formation of 4-hydroxy-5-(4-methoxybenzylthio)-4-methyl-6-phenylhexahydropyrimidin-2-one by the reaction of N-[(phenyl)(tosyl)methyl]urea with the sodium enolate of 1-(4-methoxybenzylthio)propan-2-one. Reduction of the obtained compound by NaBH4-CF3COOH and removal of the p-methoxybenzyl protecting group results in the target compound. 相似文献
6.
Double asymmetric induction in Michael reactions has been studied. Enantioselective alkylation of a cyclic ketone (1-indanone) with α-phenyl-nor-gramine was carried out. The relative configuration of (2S∗)-2-[(R∗)-1H-indol-3-yl(phenyl)methyl]-2,3-dihydro-1H-inden-1-one was established by X-ray diffraction. The relative configuration of (R∗,R∗,S∗)- and (S∗,R∗,S∗)-2-1H-indol-3-yl(phenyl)methyl]-2,3-dihydro-1H-inden-1-ols was established by 1H NMR studies. 相似文献
7.
Praveen Kommana 《Tetrahedron letters》2008,49(43):6209-6211
Model compounds (11 and 12) for the C1-C10 tetrahydropyran fragment of amphidinol 2 were prepared from (2S)-benzyloxypropanal in 9 steps. The synthetic route relied on diastereoselective diene-aldehyde cycloaddition, stereoselective C-allylation, and reagent based enantioselective aldehyde allylation. Comparison of the NMR spectra for models 11 and 12 with that for amphidinol 2 indicated that the C1-C10 segment of the natural product possesses the 2R∗,4R∗,6R∗,7S∗,8R∗,10S∗relative configuration. 相似文献
8.
Using ozonolysis of the acid-catalyzed cyclized products of (−)-nidorellol and air-autoxidation as the key steps, (+)-ambrox was obtained in 53% overall yield. In the course of our synthesis, we discovered that (−)-nidorellol provided (+)-ambrox instead of the expected product, (−)-ambrox. Thus the absolute configuration of (−)-nidorellol was proved to be trans-(5R∗,7R∗,8R∗,9S∗,10R∗)-labda-12,14-diene-7α,8β-diol, which is opposite to that illustrated in a previous report. 相似文献
9.
Tetsuya Sengoku 《Tetrahedron》2009,65(12):2415-3097
With a view to develop a new synthetic entry for the necine bases, treatment of functionalized γ-hydroxylactams was found to undergo quite high regio- and diastereoselective carbon-carbon bond formation reactions, affording the corresponding structurally dualistic alkylated lactams in satisfactory yields. The reaction was further applied to the practical and efficient synthesis of (±)-macronecine [(1S∗,2R∗,7aR∗)-1-hydroxymethyl-2-hydroxypyrrolizidine] and (±)-2-epi-macronecine [(1S∗,2S∗,7aR∗)-1-hydroxymethyl-2-hydroxypyrrolizidine]. 相似文献
10.
Synthesis of the sex pheromone of the obscure mealybug, the first example of a new class of monoterpenoids 总被引:2,自引:0,他引:2
A diastereoselective synthesis of (1R∗,2R∗,3S∗)-1-acetoxymethyl-2,3,4,4-tetramethylcyclopentane, the sex pheromone of the obscure mealybug Pseudococcus viburni, is described. Key steps included the polyphosphoric acid-catalyzed cyclization of isobutyl methacrylate to form the core five-membered ring, and diastereoselective quenching of an enolate intermediate to give the thermodynamically less favored cis orientation of vicinal methyl groups in a cyclopentanone intermediate. 相似文献
11.
Irene Ortín 《Tetrahedron》2009,65(11):2201-6277
N-Acyliminium cyclization of 6-substituted (3R∗,6R∗,11aS∗)-3-arylmethyl-pyrazino[1,2-b]isoquinoline-1,4-diones gave with very good yields a novel tetrahydroisoquinoline pentacyclic core framework (29), while this reaction failed in all-cis-isomers to give instead conjugated enamines by deprotonation. Electronic and steric factors that govern the approach to both diastereomers from 6-substituted pyrazino[1,2-b]isoquinoline-1,4-diones have been studied. 相似文献
12.
Lidija Pezdirc 《Tetrahedron》2007,63(4):991-999
A library of 15 1,6,7,9-tetrasubstituted 6,7,9,9a-tetrahydro-5H-pyrazolo[1,2-a]pyrrolo[3,4-c]pyrazole-1,3,5(2H,3aH)-triones was prepared by combinatorial stereoselective cycloadditions of (1Z,4R∗,5R∗)-1-arylmethylidene-4-benzoylamino-5-phenylpyrazolidin-3-on-1-azomethine imines to N-substituted maleimides. Stereochemistry was controlled by the stereodirecting phenyl group at position-3 and by the ortho-substituents at the aromatic ring at position-1′ in azomethine imines. Consequently, two sets of diastereomeric cycloadducts were obtained, one set from the ortho-unsubstituted dipoles and the other set from the ortho-disubstituted dipoles. 相似文献
13.
Bruno A. Figadère J. Steven McElfresh Kent M. Daane Jocelyn G. Millar 《Tetrahedron letters》2007,48(48):8434-8437
Headspace volatiles of virgin female grape mealybugs contained a single compound that elicitited responses from antennae of males in GC-electroantennogram analyses. The structure, identified as (R∗,R∗)-trans-(3,4,5,5-tetramethylcyclopent-2-en-1-yl)methyl 2-methylpropanoate, an irregular, non-head-to-tail monoterpenoid, was confirmed by synthesis. 相似文献
14.
Knoevenagel products formed by the condensation of N-monoalkyl barbituric acids with o-tert-amino benzaldehydes undergo tert-amino effect reactions (T-reactions) yielding 1-alkyl-2,4,6-trioxoperhydropyrimidine-5-spiro-3′-(1′,2′,3′,4′-tetrahydroquinoline) derivatives as a mixture of (S∗,S∗)- and (S∗,R∗)-diastereomers. Mostly, the major diastereomer has the S∗,S∗-configuration. According to X-ray diffraction data in the solid form and NOE data in solution, diastereoselectivity of the T-reactions can be associated with the structure of the Knoevenagel products whose conformation is fixed by the strong intramolecular C-H?π interaction. 相似文献
15.
Yoon-Joo Ko 《Tetrahedron letters》2007,48(5):863-867
Intramolecular ionic Diels-Alder reaction of 2-methyl-3,9,11-tridecatriene-2-ol (1) was studied under acidic conditions. Treatment of 2-methyl-3,9,11-tridecatriene-2-ol (1) with trifluoromethanesulfonic acid yielded 7-methyl-8-isopropenyl-1,2,3,4,4aR∗,7R∗,8R∗,8aS∗-octahydronaphthalene (4) and (1Z)-1-((E)-but-2-enylidene)-2-(2-methylpropenyl)cyclohexane (5) through regioselective intramolecular ionic Diels-Alder reaction. The reaction appeared to proceed partly through a stepwise mechanism involving a carbocation intermediate. However, a concerted pathway rather than a stepwise one is suggested to be involved in the acid-catalyzed intramolecular Diels-Alder reaction of 2,11-dimethyl-1,3,9,11-dodecatetraene (13). 相似文献
16.
Laurence Dutot Michel Wakselman Cristina Peggion Fernando Formaggio 《Tetrahedron letters》2008,49(21):3475-3479
DAZ-Xaa∗-OMe amino ester derivatives with Xaa∗ = d/l-Ala, d/l-Val, l-Leu, l-Ile, l-Ser, l-β3-HAla, l-β3-HVal, l-β3-HLeu, (1S,2S)/(1R,2R)-ACHC (2-aminocyclohexanecarboxylic acid) and (1S,2S)/(1R,2R)-ACPC (2-aminocyclopentanecarboxylic acid), N-blocked as 6,7-dihydro-5H-dibenz[c,e]azepines (DAZ), have been synthesized and evaluated for the determination of the absolute configuration of α- and β-amino esters through the induced circular dichroism of the biphenyl chromophore. 相似文献
17.
Addition of diisopropylzinc, diethylzinc, and isopropylmagnesium chloride to readily available 2-(2′-pyrimidyl)ferrocenecarbaldehyde takes place with high diastereoselectivity to afford exclusively the α-ferrocenyl alcohol of (R∗,pR∗) configuration. On the other hand, the addition of ethyl- and methylmagnesium bromide leads to diastereomeric mixtures in which the major isomer has the (S∗,pR∗) configuration. A unified mechanistic model accounting for this stereochemical outcome is proposed. 相似文献
18.
An improved diastereoselective synthesis of (1R∗,2R∗,3S∗)-1-acetoxymethyl-2,3,4,4-tetramethylcyclopentane 1, the sex pheromone of the obscure mealybug, Pseudococcus viburni, is described. The key step was diastereoselective catalytic hydrogenation of the tetrasubstituted double bond in 2,3,4,4-tetramethyl-cyclopent-2-enone 4 to give the thermodynamically less favored cis-2,3,4,4-tetramethyl-cyclopentanone 3a. 相似文献
19.
Martha S. Morales-Ríos Daphne E. González-Juárez Oscar R. Suárez-Castillo 《Tetrahedron》2007,63(32):7702-7707
Diastereomeric three-, five- and six-membered spirocycloalkyloxindoles were successfully synthesized in a rapid and convenient manner from readily accessible starting materials in moderate to high yields using 1-methyl-3-acetonitriloxindole after a one-pot base-mediated double-alkylation strategy. It was found that the diastereoselection is dependent on the reaction conditions and the spirocycloalkyl ring size, with the 3R∗,8R∗ diastereomers being thermodynamically favored under the basic reaction conditions for three- and five-membered rings, and the 3R∗,8S∗ diastereomer in the case of six-membered rings, as predicted by DFT calculations. The relative stereochemistry was supported by 2D NMR spectra and X-ray crystal structural analysis. The conformational rigidity of the spirocycloalkyloxindoles in solution was established based on NMR experimental and theoretical DFT approaches. 相似文献
20.
A short and stereoselective synthesis of (3R∗,4R∗,7R∗)-3,7-epoxy-4,8-dimethyl-8-nonen-4-olide, a natural product isolated from cured tobacco leaves, has been completed in six steps and 22% overall yield. A samarium(II) iodide mediated reductive cyclisation has been used to construct the functionalised tetrahydropyranol core and subsequent sequential stereoselective addition of methyllithium and lactonisation furnished the natural product. 相似文献