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1.
An expeditious total synthesis of the physiologically active fungal metabolite 1 is described. The stereoselective formation of its β-δ-mannopyranosidic linkage is achieved in two steps upon reaction of the hexopyranos-2-ulosyl bromide 15 with the glycosyl acceptor 13, followed by reduction of the resulting β-δ-glycos-2-uloside 16. Alcohol 13 was efficiently prepared via a Suzuki reaction of the aryltriflate 11 with the 9-alkyl-9-BBN derivative 10. 相似文献
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A stereoselective synthesis of (2S,3R)-β-methoxyphenylalanine, an amino acid contained within the cyclic peptide cyclomarin A, was successfully synthesized from Lajoie’s serine aldehyde. 相似文献
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Emelyne Voss Axelle Arrault Jacques Bodiguel Brigitte Jamart-Grgoire 《Tetrahedron: Asymmetry》2009,20(15):1809-1812
The synthesis of enantiomerically pure orthogonally protected δ-azaproline has been performed in five steps including two successive Mitsunobu reactions starting from benzyloxycarbonylaminophthalimide and the (R)-α-hydroxy-γ-butyrolactone. 相似文献
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Glen B. Deacon Ewan E. Delbridge Brian W. Skelton Allan H. White 《Angewandte Chemie (International ed. in English)》1998,37(16):2251-2252
A higher degree of coordination saturation is attainable through the unusual coordination mode in the title compound 1 , in which the central pyrazolate groups function both as chelating and as bridging ligands. There is some asymmetry in the bridging, and the N atoms of each μ-η2:η2-pyrazolato ligand are 0.07–0.11 Å closer to one of the two Yb centers. 相似文献
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Reaction of potassium 3{5}-(3′,4′-dimethoxyphenyl)pyrazolide with 2-bromopyridine in diglyme at 130°C for 3 days followed by an aqueous quench, affords 1-{pyrid-2-yl}-3-{3′,4′-dimethoxyphenyl}pyrazole (L2) in 69% yield after recrystallization from hot hexanes. Complexation of [Cu(NCMe)4]BF4 by 2 molar equivalents of 1-{pyrid-2-yl}-3-{2′,5′-dimethoxyphenyl}pyrazole (L1) or L2 in MeCN at room temperature, followed by concentration and crystallisation with Et2O, gives [Cu(L)2]BF4 L = L1, L2) in good yields. Treatment of AgBF4 with L1 or L2 in MeNO2 similarly gives [Ag(L)2]BF4 L = L1, L2); reaction of AfBF4 with L2 in MeCN gives a product of stoichiometry [Ag(L2)(NCMe)]BF4. The 1H NMR spectra of the [M(L)2]BF4 complexes show peaks arising from a single coordinated environment. The single crystal X-ray structure of [Cu(L1)2]BF4 shows a tetrahedral complex cation with Cu---N = 2.011(8), 2.036(8), 2.039(8), 2.110(8) Å. The CuI centre is close to tetrahedral, the dihedral angle between the least-squares planes formed by the Cu atom and the N donor atoms of the two ligands being 88.3(3)°. Complexation of hydrated Cu(BF4)2 by L2 in MeCN at room temperature yields [Cu(L2)2](BF4)2. The cyclic voltammograms of the three AgI complexes in MeCN/0.1 M Bu4n NPF6 are suggestive of extensive ligand dissociation in this solvent. 相似文献
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Racemic 1,1′-methylene[(1RS,1′RS,3RS,3′RS,5RS,5′RS)-8-oxabicyclo[3.2.1]oct-6-en-3-ol] ((±)-6) derived from 2,2′-methylenedifuran has been resolved kinetically with Candida cyclindracea lipase-catalysed transesterification giving 1,1′-methylenedi[(1R,1′R,3R,3′R,5R,5′R)-8-oxabicyclo[3.2.1]oct-6-en-3-ol] (−)-6 (30% yield, 98% ee) and 1,1′-methylenedi[(1S,1′S,3S,3′S,5S,5′S)-8-oxabicyclo[3.2.1]oct-6-en-3-yl] diacetate (+)-8, (40% yield, 98% ee). These compounds have been converted into 1,1′-methylenedi[(4S,4′S,6S,6′S)- and (4R,4′R,6R,6′R)-cyclohept-1-en-4,6-diyl] derivatives. 相似文献
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V. V. Burlakov A. V. Letov P. Arndt W. Baumann A. Spannenberg Ch. Fischer L. I. Strunkina M. Kh. Minacheva Ya. S. Vygodskii U. Rosenthal V. B. Shur 《Journal of molecular catalysis. A, Chemical》2003,200(1-2):63-67
Zwitterionic titanoxanes {Cp[η5-C5H4B(C6F5)3]Ti}2O (I) and {(η5-iPrC5H4)[η5-1,3-iPrC5H3B(C6F5)3]Ti}2O (II), which contain two positively charged Ti(IV) centres in the molecule, are able to catalyse the ring-opening polymerization of -caprolactone (-CL) in toluene solution and in bulk. The process proceeds with a noticeable rate even at room temperature and accelerates strongly on raising the temperature to 60 °C. The best results have been obtained on carrying out the reaction in bulk. Under these conditions, the use of I as a catalyst (-CL:I = 1000:1) gives at 60 °C close to quantitative yield of poly--CL with the molecular mass of 197 000. An increase in the -CL:I ratio to 6000:1 increases the molecular mass of poly--CL to 530 000. Tetrahydrofuran (THF) is also polymerized under the action of I albeit with a lesser rate. However, the molecular mass of the resulting poly-THF can reach rather big values under optimal conditions (up to 217 000 at 20 °C and the THF:I ratio of 770:1). A rise in the reaction temperature from 20 to 60 °C results here to a decrease in the efficiency of the process. Titanoxane II is close to I in its catalytic activity in the -CL polymerization but it is much less active in the polymerization of THF. Propylene oxide (PO), in contrast to -CL and THF, gives with I only liquid oligomers in wide temperature and PO:I molar ratio ranges (−30 to +20 °C, PO:I = 500–2000:1). γ-Butyrolactone and 1-methyl-2-pyrrolidone are not polymerized under the action of I at room temperature. The reactions found are the first examples of catalysis of the cationic ring-opening polymerization by zwitterionic metallocenes of the group IVB metals. 相似文献
9.
N. W. Fadnavis S. Kumara Vadivel Mohd Sharfuddin U. T. Bhalerao 《Tetrahedron: Asymmetry》1997,8(24):2797
Baker's yeast mediated reduction of α-azido-β-keto ester lead to reduction of the carbonyl group with high enantiospecificity and diastereoselectivity at low pH (4.0, e.e. >99%, d.e. 79%). At pH 7, although the enantioselectivity is maintained, the diastereoselectivity is lost. 相似文献
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The (E)-α-selenylvinylstannanes react with acyl halides in presence of a catalytic amount of Pd(PPh3)4 to give the corresponding (Z)-α-selenyl-α,β-unsaturated ketones in good yield. 相似文献
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Cp2MoH2 reacts with methyl acrylate in the presence of acetylenes (L = C2H2, C2Me2, HCCtBu, HCCSiMe3, C2(SiMe3)2, HCCCH2OMe, HCCCH2NMe2) to form acetylene complexes Cp2Mo(L) 5. Protonation takes place with CF3CO2H at −80°C to give short-lived cations [Cp2MoH(L)+ (8) (L = C2Me2, HCCSiMe3, C2(SiMe3)2). The structure of [Cp2MoH{η2-C2(SiMe3)2}]PF6(9) was determined by an X-ray diffraction study. 相似文献
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Andrei S. Batsanov Simon P. Crabtree Judith A.K. Howard Christian W. Lehmann Melvyn Kilner 《Journal of organometallic chemistry》1998,550(1-2)
The title complex with one η2 and two η1 deuterobenzene and one monodentate BF4 ligands was isolated as a by-product in the reaction between [(dppe)RhCl]2 and EtCl in C6D6, in the presence of AgBF4 and its X-ray crystal structure determined. 相似文献
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The synthesis of α-substituted N-[((2S)-2-hydroxy-2-phenyl)-ethyl]-2-phenylglycine derivatives is reported. The key step of the sequence is the highly diastereoselective alkylation of (6R)-2,3,5,6-tetrahydro-3,6-diaryl-N-[(2′R)-(2′-methyl)phenylmethyl]-4H-1,4-oxazin-2-ones after deprotonation with t-BuOK. Opening of the resulting oxazinone with ethanolic KOH, followed by hydrogenolysis of the corresponding N-[(2R)-(2-methyl)phenylmethyl] compound to furnish the expected 2-phenylglycine derivative, is also described. 相似文献