共查询到20条相似文献,搜索用时 46 毫秒
1.
Palladium-catalyzed methoxycarbonylation of (−)-(2R,3S)-1-tert-butyldimethylsiloxy-3-methyl-2-methoxypenta-4-yne 9 derived from (2R,3S)-epoxy butanoate 5 gave the acetylenic ester 10, which was treated with MeOH in the presence of Bu3P to afford selectively (Z)-β-methoxy acrylate congener 11 in 86% yield. Treatment of (Z)-11 with 99.8% enrichment of CDCl3 followed by consecutive desilylation and oxidation afforded the left-half aldehyde (+)-2. The overall yield (10 steps from 5; 23%) of (+)-2 via the present route was improved in comparison to that (10 steps from 5; 10%) of the previously reported route. By applying the modified Julia's coupling method, selectivity (E/Z=14:1) of the (E)-form (cystothiazole A 1) against the (Z)-form was improved in comparison to the Wittig method (E/Z=4:1 to 6.9:1). 相似文献
2.
(S)-9-cis-4-Oxo-13,14-dihydroretinoic acid (S)-1, a new major endogenous vitamin A metabolite that activates retinoic acid receptor signaling both in vitro and in vivo, has been synthesized stereoselectively by Horner–Wadsworth–Emmons condensation and Stille cross-coupling as bond forming reactions. 相似文献
3.
Leila Hammoud Francisco León Ignacio Brouard Javier Gonzalez-Platas Samir Benayache Paul Mosset Fadila Benayache 《Tetrahedron letters》2018,59(27):2668-2670
Three new sesquiterpene-humulenes, (?)- asteriscunolides I (1), J (2) and (?)-(2Z,6E,9Z)-8-oxo-1α-acetoxy-2,6,9-humulatrien-12-oic acid (3) were isolated from the leaves-flowers of the Saharan medicinal plant Asteriscus graveolens along with six known compounds. The structures of the compounds were determined on the basis of spectroscopic mono and bidimensional NMR, mass spectrometry and by single-crystal X-ray diffraction. Compounds 1–3 were evaluated for cytotoxic assay, no significant activity was detected. 相似文献
4.
《Tetrahedron》2014,70(51):9661-9667
Thirteen new triterpenoids, dysotriflorins A–M (1–13), were isolated from Dysoxylum densiflorum barks, and their structures were elucidated on the basis of NMR spectroscopic data and X-ray crystallography. Dysotriflorins A, B, and K–M (1, 2, and 11–13) were concluded to be unique 13,17-secodammarane triterpenoids, and dysotriflorins C–J (3–10) to be dammarane triterpenoids. Dysotriflorins showed in vitro cytotoxic activity against several cancer cell lines. 相似文献
5.
《Tetrahedron: Asymmetry》2001,12(18):2581-2587
From stereoisomeric α,β-unsaturated nitriles (E,Z)-1, the recombinant nitrilase AtNIT1 from Arabidopsis thaliana hydrolyses the (E)-isomers exclusively to the corresponding (E)-carboxylic acids (E)-2 with high specificity. The (E)-selectivity can also be utilised for the preparation of the isomerically pure nitriles (Z)-1. From (E,Z)-2-hydroxycinnamonitrile (E,Z)-3, the otherwise difficult obtainable (Z)-3 was prepared in 66% isolated yield. With β,γ-unsaturated (E,Z)-3-heptenenitrile (E,Z)-4, however, (E)-selectivity was not observed. AtNIT1 exhibits not only diastereoselectivity but also regioselectivity. From a mixture of the four isomers A–D of 3-(2-cyanocyclohex-3-enyl)propenenitrile 6, exclusively isomer D ((E)-cis-6) was hydrolysed to 3-(2-cyanocyclohex-3-enyl)propenoic acid (E)-cis-7, as stated by X-ray crystal structure. Only after complete conversion of D and high enzyme concentrations, isomer C ((E)-trans-6) was hydrolysed to a small extent. 相似文献
6.
Four new gallotannins, maplexins F–I (1–4), two new phenolic glycosides, rubrumosides A–B (5,6), and eleven known compounds were isolated from red maple (Acer rubrum) bark. Their structures were elucidated based on spectroscopic analysis. The maplexins contained three galloylated derivatives attached to different positions of 1,5-anhydro-glucitol and were 10–20 fold more potent α-glucosidase inhibitors than the clinical drug, Acarbose (IC50=7–16 vs 161 μM), in vitro. These results support previous data suggesting that gallotannins are the main contributors to the α-glucosidase inhibitory activities of maple plant part extracts and that three substituents on the 1,5-anhydro-glucitol moiety are important for activity. 相似文献
7.
《Tetrahedron: Asymmetry》2006,17(17):2516-2530
(S)-(−)-(Benzotriazol-1-yl)- and (S)-(−)-(benzotriazol-2-yl)-alkan-2-ols 7a–9a, 7b–9b and their (R)-(+)-acetates 10a–12a and 10b–12b were prepared in high enantiomeric excess via lipase from Pseudomonas fluorescens (Amano AK) catalyzed enantioselective acetylation of racemic alcohols 4a–6a and 4b–6b with vinyl acetate in tert-butyl methyl ether or toluene at 23 °C. The enantioselectivity of this transformation was dependent on the length of the alkyl chain with E-values ranging from 30 to 57. Several benzotriazole substituted ketones 1a–3a and 1b–3b were synthesized from 1H-benzotriazole and corresponding haloketones. These compounds were stereoselectively reduced with Baker’s yeast in water or in organic solvent containing 5% v/v of water at 30 °C to give the (S)-(−)-alcohol. Better stereoselectivity was observed in the kinetic resolution of racemic alcohols 4a–6a and 4b–6b (ee = 69–92% at 44–52% conversion) compared to reduction of corresponding prochiral ketones 1a–3a and 1b–3b with Baker’s yeast (ee = 40–67% at 39–89% conversion). Enhanced enantioselectivities were observed at lower temperatures. 相似文献
8.
《Tetrahedron: Asymmetry》1999,10(22):4295-4305
Microbial hydroxylation of (Z)-2-benzylidene-1-azabicyclo[2.2.2]octan-3-one 1 by various species of fungi and actinomycetes occurred regio- and stereoselectively at the 5 position of the quinuclidinone moiety. Most of the organisms produced α-(5S)-(Z)-2-benzylidene-5-hydroxy-1-azabicyclo[2.2.2]octan-3-one 2 as the major product with enantiomeric excesses ranging from 30% to 84%. The (5β)-hydroxy epimer 3 and the (5α,7α)-dihydroxy derivative 4 were also produced by whole cell biotransformations of 1. 相似文献
9.
Trienylboronic acid 1a was prepared from iodotriene 3, which was coupled with (2Z,4Z)-3-aryl-5-iodo-2,4-pentadienol 9 by Suzuki coupling reaction to give geometrically pure 13-aryl substituted (11Z)-retinol 10. Oxidation of 10 gave 13-aryl substituted (11Z)-retinal 11. 相似文献
10.
Ahmed El-GokhaGerhard Maas 《Tetrahedron》2011,67(16):2849-2857
A diastereomeric mixture of dimethyl (2-formyl-2-methyl-1-phenylcyclopropyl)phosphonate ((Z)-6, (E)-6) was obtained by thermally induced cyclopropanation of α-methylacrolein with α-diazobenzylphosphonate 5. Application of proline or proline-derived organocatalysts accelerated the reaction, but had a minor effect on the Z/E ratio of 6. By reaction with benzylamine or methyl esters of glycine, (S)-alanine, and (S)-phenylalanine, the Z/E-mixture of 6 was converted into cyclopropylaldimines, which after reduction gave the corresponding N-substituted (2-aminomethyl-cyclopropyl)phosphonates. 相似文献
11.
《Journal of organometallic chemistry》2007,692(1-3):36-43
Reactivity of a hydrido(hydrosilylene)tungsten complex, Cp1(CO)2(H)WSi(H)[C(SiMe3)3] (1), toward oxiranes was investigated. Treatment of 1 with racemic mono-substituted oxiranes with a substituent R (R = Ph, vinyl, tBu, or nBu) at room temperature produced dihydrido(vinyloxysilyl)tungsten complexes, (E)- and/or (Z)-Cp1(CO)2(H)2W{Si(H)(OCHCHR)[C(SiMe3)3]} [(E/Z)-2: R = Ph, (E)-3: R = vinyl, (E)-4: R = tBu, (E/Z)-5: R = nBu] in high yields via regioselective ring-opening of oxiranes. When the substituent R on oxirane was relatively large, (E)-isomers (2, 3, and 4) were obtained predominantly (87–97%), while the substituent was a relatively small nBu group, an approximately 1:1 mixture of (E)- and (Z)-isomers [(E/Z)-5] was obtained. Reaction of 1 with 2,2-dimethyloxirane afforded the corresponding complex, Cp1(CO)2(H)2W{Si(H)(OCHCMe2)[C(SiMe3)3]} (6), quantitatively. A reaction mechanism is also discussed. 相似文献
12.
A general method is described, which allows the overall enantioselective α-alkylation of acyclic ketones in good overall yields (44–86%,, 4 steps) and enantioselectivities ranging routinely from > 94% ee up to virtually complete asymmetric induction (99.5% ee). The acyclic ketones are transformed to their corresponding “SAMP-hydrazones” (S)-2 by reaction with the enantiomerically pure hydrazine (S)-l-amino-2-methoxymethyl-pyrrolidine [SAMP, (S)-1], readily available from (S)-proline. Metalation to form chiral azaenolates (S)-3 of EccZcn-configuration and then alkylation to product hydrazones 4 followed by hydrazone cleavage via acidic hydrolysis of methiodides 9 in a two phase system or ozonolysis, leads to α-substituted, enantiomerically enriched, acyclic ketones 5. In special cases, where a phenyl group is directly attached to the newly generated center of chirality (5n,o,p), only low enantiomeric excesses are observed. 17 Examples, including first applications in natural product synthesis (cf 5abe and h) are summarized 相似文献
13.
Regio and stereochemistry in the addition of preformed magnesium and lithium ketone enolates (1 to 8) to α-enones (10 and 11) have been examined. When the substitution degree of the enolate is increased the formation of δ-diketone is favoured; nevertheless a good efficiency in the synthesis of the γ-ethylenic β-ketols (1-2 addition) is obtained via bromomagnesium enolates (EMgX) under kinetic conditions. Lithium enolate (ELi) and, chiefly magnesium enolates (E2MgX) give preferentially the Michael addition. Reversibility from 1-2 to 1-4 addition is commonly observed but the stereochemistry, if any, of the diastereoisomeric δ-diLetones may be quite different when using EMgBr or E2Mg as starting enolates. 相似文献
14.
Yasumasa Shikichi Kazuaki Akasaka Shigeyuki Tamogami Shruti Shankar Joanne Y. Yew Kenji Mori 《Tetrahedron》2012,68(19):3750-3760
All the eight stereoisomers of 3-acetoxy-11,19-octacosadien-1-ol (1), the male sex pheromone (CH503) of Drosophila melanogaster, were synthesized from two acetylenic starting materials and the enantiomers of 3,4-epoxy-1-butanol PMB ether. Complete separation of the eight isomers of 1 by reversed phase HPLC at ?20 °C was achieved after their esterification with (1R,2R)-2-(2,3-anthracenedicarboximido)cyclohexanecarboxylic acid (27), and the natural CH503 was found to be (3R,11Z,19Z)-1. 相似文献
15.
Sukanta Kamila Haribabu Ankati Emily Harry Edward R. Biehl 《Tetrahedron letters》2012,53(17):2195-2198
(Z)-5-(2-(1H-Indol-3-yl)-2-oxoethylidene)-3-(aryl/alkyl-2-ylmethyl)-2-thioxothiazolidin-4-ones (7a–w) have been synthesized by the Knoevenagel condensation reaction of 3-(aryl/alkyl-2-ylmethyl)-2-thioxothiazolidin-4-ones (3a–d) with suitably substituted 2-(1H-indol-3-yl)2-oxoacetaldehydes (6a–g) under microwave conditions. The thioxothiazolidin-4-ones were prepared from the corresponding aryl/alkyl amines (1a–d) and di-(carboxymethyl)-trithiocarbonyl (2). The aldehydes (6a–g) were synthesized from the corresponding acid chlorides (5a–g) using HsnBu3. 相似文献
16.
Suradet Buttachon Angsumarn Chandrapatya Leka Manoch Artur Silva Luís Gales Céline Bruyère Robert Kiss Anake Kijjoa 《Tetrahedron》2012,68(15):3253-3262
Seven new indole alkaloids including a new indoloazepinone derivative (2), two new quinazolinone derivatives (7, 8) and four new pyrazinoquinazolinone derivatives: epi-fiscalin C (10), epi-fiscalin A (12), neofiscalin A (13), epi-neofiscalin A (14) were isolated, together with 4-dihydroxy-3-methylacetophenone (1), tryptoquivaline (3), tryptoquivalines L (4), H (5), F (6) as well as fiscalins A (11) and C (9), from the culture of the fungus Neosartorya siamensis (KUFC 6349). The absolute configuration of the stereogenic carbons of the previously reported tryptoquivalines F, H, L was revised using the data obtained from an X-ray analysis of tryptoquivaline l and the NOESY correlations. The structures of the new pyrazinoquinazolinone derivatives (10, 12, 13, 14) were established based on 1D and 2D NMR spectral analysis, and the absolute configuration of their stereogenic carbons was determined by an X-ray crystallographic analysis of fiscalin C (9) and a new compound epi-fiscalin C (10), in conjunction with the correlations observed in their NOESY and long range COSY spectra. Compounds 2–8 and 12 were evaluated for their in vitro growth inhibitory activity on the human U373 and Hs683 glioblastoma, the A549 non-small cell lung cancer, the MCF-7 breast cancer and the SKMEL-28 melanoma cell lines by MTT colorimetric assay. 相似文献
17.
Pentacarbonyl(η2-cis-cyclooctene)chromium(0) (1) catalyzes efficiently reactions of diazo compounds with electron-rich furans. The reaction of 2-methoxyfuran (2) with alkyl α-diazoarylacetate (3a-g) furnishes the (2E,4Z)-2-aryl-hexadienedioic acid diesters (4a-g) in excellent yields. These reactions are highly regioselective. The cyclopropanation intermediates formed from 1 and diazo compounds 3a-g always arise from a carbene addition to the less substituted CC bond of 2. The resulting cyclopropanation product undergoes a ring opening reaction to form the corresponding (2E,4Z)-2-aryl-hexadienedioic acid diesters (4a-g). The pentacarbonylchromium(0)-catalyzed reactions of 2-alkylfuran (5a-b) with ethyl α-diazophenylacetate (3a) and 9-diazo-9H-fluorene (3h) produce the 1(E),3(E)-butadienes (6a-d) in very good yields. 相似文献
18.
Ping He 《Tetrahedron》2006,62(4):549-555
The reactions of fluoroalkanesulfonyl azides 1 with some electron-rich compounds have been studied in detail. Cycloalkenyl vinyl ethers reacted with 1 readily at 0 °C to give the corresponding ring-contraction N-fluoroalkanesulfonyl amidine analogues 3. In contrast, aryl ynamine generated in situ reacted with 1 affording fluorinated α-diazoamidines 9, which were decomposed slowly at room temperature to form [1-diethylamino-2-(4-nitro-phenyl)-2-oxo-eth-(Z)-ylidene]-fluoroalkanesulfinyl imine 10 with elimination of nitrogen gas. Possible mechanisms for these reactions were proposed. 相似文献
19.
《Tetrahedron: Asymmetry》2000,11(23):4725-4736
Asymmetric Wittig rearrangement of crotyl furfuryl ethers was investigated in diastereo- and enantioselective manners. Both (2S,3Z)- and (2S,3E)-3-penten-2-yl furfuryl ethers 3 and 9 rearranged with complete chirality transfer to give the syn- and anti-isomers 4 and 10, respectively. Enantioselective Wittig rearrangement of both (Z)-and (E)-crotyl furfuryl ethers 15 and 17 using butyllithium and (−)-sparteine was examined to afford (1S,2R)-1-(2-furyl)-2-methyl-3-buten-ol 16 in up to 43% ee. 相似文献
20.
Chiramet Auranwiwat Alan T. Maccarone Anthony W. Carroll Roonglawan Rattanajak Sumalee Kamchonwongpaisan Stephen J. Blanksby Stephen G. Pyne Thunwadee Limtharakul 《Tetrahedron》2019,75(15):2336-2342
The phytochemical investigation of the leaf extract of Uvaria cherrevensis (Annonaceae) yielded three new cyclohexene (9Z)-octadec-9-enyl ethers, cherrevenols M-O (1–3), and a known fatty ester derivative (4). The structures of the isolated compounds were elucidated by spectroscopic and computer-aided molecular modelling methods. Ozone Induced Dissociation (OzID) mass spectrometry was employed to determine the C-9 position of the side chain olefinic double bonds, while 13C NMR spectroscopy indicated their (Z)-configurations. All isolated compounds were evaluated for their antimalarial and cytotoxic activities; all were inactive. 相似文献