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1.
Dennis P. Curran 《Tetrahedron letters》1982,23(42):4309-4310
A short, efficient approach to a key chiral intermediate for the synthesis of pseudomonic acids A and C is delineated.Pseudomonic acids A(), B(), and C() are members of a novel of “C-glycopyranoside” antimicrobial agents which have recently attracted synthetic attetion.2 Presently, we wish to report a short efficient stratedy towards the total synthesis of opticaly active pseudomonic acids. The sequence is highlighted by a novel controlled mono-Claisen rearrangement and a highly regioselective π-allylpalladium mediated displacement.Diacetyl-(L)-arabinal ()3 was converted to the bis-ketenesilylacetal and warmed to 60°C according to the Ireland ester-enolate Claisen rearrangement method.4 Over a period of ≈5h, smooth conversion to a major rearranged product was observed by 300 MHz NMR. The identity of was confirmed by direct desilylation and methylation (KF, KHCO3, H2O, HMPA, CH3I). After flash chromatography, compound was isolated in 55% overall yield from . Careful inspection of the crude methylation product revealed the presence of ≈5% doubly rearranged product .The rearrangement of to is a unique example of a selective mono-Claisen rearrangement in which the rate of a second similar Claisen rearrangement ( → ) is much slower under the reaction conditions. Although the reasons for this interesting selectivity are unclear at this time,5 in practice, the mono-Claisen rearrangement obviates the need for selective differentiation of the two hydroxyl groups, a difficult task at best, in this case.Palladium mediated allylic acetate displacement provided an ideal method for introduction of a second chemodifferentiated side chain with allylic retention and retention of stereochemistry. Alkylation of with sodiothylmalonate using 5 mole % Pd(O)dppe26 was unusually facile (<45 min, 25°C, THF). After semi-preparative HPLC, essentially a single regio- and stereoisomer was isolated in 96% yield.7 Structure was confirmed by extensive 1H-NMR decoupling, as well as an off-resonance 13C-NMR experiment. In particular, H1 (δ 4.53) was coupled vicinally to H6 and H6′ (5 Hz, 8 Hz) and H2 (1.5 Hz), and allylically to H3 (2 Hz). In contrast, H4 (δ 2.78) was coupled to H7 (10 Hz), H5e and H5a (1.8 Hz, 4 Hz), H3 (5 Hz), and H2 (<1 Hz). In addition, H1 and H4 exhibited a small long range coupling constant (J = <1 Hz). The coupling constants rule out regioisomer and are fully consistent with the indicated conformation, which minimizes 1,3-diaxial-like interactions.Finally, catalytic osmylation of gave a single cis-diol in nearly quantitative yield. Appending of suitably functionalized side chains to provide an enantiocontrolled synthesis of pseudomonic acids A() and C() is in progress.9,10 相似文献
2.
Through the insertion of a carbon dioxide molecule, the oxazolidin-2-ones () and () were prepared by treataent of the salts () and () with carbonate anion on polymeric support. The hydrolysis under basic conditions of () and () afforded the erythro-3-amino-1,2-diols () and () which were fully acetylated: the 2-amino-2-deoxyerythritol derivative () was obtained in 91% yield. 相似文献
3.
Acid-catalysed ring opening of the spirodienones () and () using p-toluene-sulphonic acid affords the styrène derivatives () and (), while treatment with acetic anhydride/H2SO4 affords the furan derivatives () and (). 相似文献
4.
Reaction of meso-4-carbomethoxy-2-methylpentanal () with crotyltri-n-butyltin at ?78°C in the presence of 1 eq BF3·OEt2, followed by the lactonization with BF3·OEt2, gave 6-(1-methylallyl)-3,4,5,6-tetrahydro-3,5-dimethyl-2-pyranone () with the correct stereochemistry (erythro, anti-Cram) in 92% yield, which was converted to the title compound () in 85% yield upon the ozonolytic cleavage of the double bond. 相似文献
5.
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
6.
A sequence of formylation followed by a carbene insertion reaction has led to the stepwise introduction of additional ethano bridges into 4,5,7,8- tetramethyl [22](1,4)cyclophane (), providing syntheses of 5,7,8-trimethyl- [23](l,2,4)cyclophane (), a mixture of 5,8-dimethyl[24(1,2,4,5)cyclophane () and 5,7-dimethyl[24(1,2,3,5)cyclophane (, and-4-methyl[25](1,2,3,4,5)-cyclophane (). This route to completes a formal eight-step synthesis of [26](1,2,3,4,5,6)cyclophane (, superphane) with an overall yield of 17%. A Birch reduction of readily gave 12,15-dihydro-5,7,8-trimethyl[23](1,2,4)-cyclophane () in 85% yield. 相似文献
7.
The Functionalized Grignard reagent reacts with allylic chloride , in the presence of Li2CuCl4, to provide lactarol-THP ether which is subsequently converted to (±)-lactaral in 72% overall yield from . 相似文献
8.
UV-irradiation of the aldehyde leads to the 7-epimeric cyclobutanols and which undergo upon treatment with NaOCH3 retroaldol-like cleavage to and . Oxidation and deacetylation of affords the 16,17-dihydro-Δ15-gibberellin-A3 (). 相似文献
9.
The diene reacted with CHCl3/aq. NaOH/PTC in CH2 Cl2 unexpectedly to give a mixture of the chlorination products and . Usual chlorination with Cl2 yielded similarly , , and dependent on the amount of Cl2. The formation of as well as the reaction of to give (besides ) shows an unusual Cl-Cl-interaction. 相似文献
10.
This paper gives an outline of the structure of a solid solution based on 7Bi2O3 · 2WO3. The experimental results using X-ray diffraction methods (precession and powder) showed that 7Bi2O3 · 2WO3 crystallizes in the space group with a = 12.5143(5)Å and c = 11.2248(6) Å. The number of formula weights per unit cell is 40, when the formula is considered to be of the oxygen-deficient fluorite-type Bi0.875W0.125O1.6875. The compound has a substructure based on a defect fluorite-type pseudocubic subcell with Å. The axial relations between the supercell and subcell are and . The solid solution was formed over a limited range of WO3 content between 21.3 mole% and 26.3 mole% at 700°C. The ordering of metal atoms is discussed and an ideal crystal structure is proposed. 相似文献
11.
Boźenna Golankiewicz Piotr Januszczyk Maria Gdaniec Zofia Kosturkiewicz 《Tetrahedron》1985,41(24):5989-5994
2-Acylamino-2-cyanoacetic acid ethyl esters react with 2,4-bis (4-methoxyphenyl)-1, 3, 2, 4-dithiadiphosphetane 2,4-disulfide in refluxing benzene with formation of 2-alkyl(aryl)-5-aminothiazole-4-carboxylic acid ethyl esters . Structure was established by spectroscopic means and an X ray crystallographic investigation of . X-Ray analysis revealed that the thiazole ring, exocyclic nitrogen and carbonyl group forming a hydrogen-bonded cycle are nearly coplanar. A resonance interaction is manifested by distinctly shortened /1.447 (3)/ C(carbonyl)-C(thiazole) distance. 相似文献
12.
4,4-Dimethyl-2-phenyl-2-thiazolin-5-thione () reacts with 2,3-diphenylcyclopropenone () at 145°C and with benzonitrilio-2-propanide () at room temperature to yield the 1,6-dithia-spiro[4.4]nonadienes and , respectively. 相似文献
13.
(η-Cyclopentadienyl)(triphenylphosphine)cobaltacyclopentadienes having an electron withdrawing substituent on the cyclopentadienyl ring, (η-C5H4R)(PPh3)(H) (1b: R = COOMe; 1c: R = COMe), were prepared in reasonable yields by treatment of a solution of (η-C5H4R)(PPh3)2Co with acetylene. A non-substituted cyclopentadienyl analog (1a: R = H) was also isolated in low yield according to a similar procedure. Novel dinuclear complexes were also formed as by-products and the structure of (η-C5H4R)Co(PPh2Me)Co(η-C5H4R) (2b: R = COOMe), having a μ2,η3-benzyl moiety, was determined by an X-ray crystallographic analysis. The X-ray analyses of 1a and 1b were also carried out. Crystals of 1a are monoclinic, space group Pa, a 8.529(3), b 16.010(6), c 8.028(4) Å, β 100.31(3)°, Z = 2; crystals of 1b are monoclinic, space group P21/a, a 8.327(2), b 36.468(7), c 8.021(1) Å, β 98.75(2)°, Z = 4; and crystals of 2b are monoclinic, space group P21/c, a 10.681(2), b 30.722(7), c 8.912(1) Å, β 93.55(1)°, Z = 4. They have been refined to R = 0.034, 0.047 and 0.050, respectively. 相似文献
14.
Reaction of the amines (CF3)2NX (X=Cl,Br) with norbornadiene either in solvent (CH2Cl2) at ?78 °C in the dark or in the vapour phase at 20 °C in daylight gives a mixture of 3-halogeno-5-(-bistrifluoromethylamino)nortricyclene (, -and , -isomers) and -5-(-bistrifluoromethylamino)- -7-halogenonorbornene in quantitative yield formed halonium ion addition to the diene. The reaction of the amine (CF3)2NBr in solvent Me2O or Et2O at ?78 °C in the dark gives the same products in low yield, together with 3-bromo-5-alkoxynortricyclene (, - and , -isomers) and the amine (CF3)2NR (R=Me, Et) in high yield. 相似文献
15.
Ulrich Schubert Andreas Schenkel Johannes Müller 《Journal of organometallic chemistry》1985,292(3):c11-c14
In the reaction of Cp2WGl2 with Li[Si(SiMe3)3] the dihydrid tungstenocene derivative [(Me3Si)3SiC5H4]WH2 (3) is formed with a 56% yield. 3 crystallizes in space group P, with a 918.0(4), b 1580.9(4), c 1621.2(7) pm, α 117.63(2), β 89.95(3), γ 94.39(3)° at ?40° C. The dihedral angle between the Cp planes is 140.9°. 相似文献
16.
Tropyliumbromide () reacts with AgSCF3 to form 7-Trifluoromethylthiocycloheptatriene (), which on oxidation with p-nitroperbenzoic acid does not form 7-Triflouromethylsulfonylcycloheptatriene () but the trifluoromethylsulfinate (). 相似文献
17.
C. Glidewell G.S. Harris H.D. Holden D.C. Liles J.S. McKechnie 《Journal of fluorine chemistry》1981,18(2):143-154
Fluorination of triphenylarsine oxide by aqueous hydrogen fluoride (1–40%) in the absence of glass readily gives triphenylarsine difluoride. When the reaction with dilute (1%) aqueous hydrogen fluoride is carried out in borosilicate glass apparatus, the glass participates in the reaction resulting in the formation of the crystalline 2:1 adduct 2Ph3AsO·HBF4. Crystals of this compound are monoclinic, 21/, = 12.926(4), = 17.819(6), = 14.994(4) Å, β = 98.97(3)°, Z = 4. The structure contains cations [(Ph3AsO)2H]+ in which O is 2.44(2)Å, and anions BF4?. 相似文献
18.
Reductive coupling of methyl-vinyl ketone with TiCl4-Mg gives pinacol (25%). According to the reducing agents, mesityl oxide yields 2,4,5,7-tetramethyl-octa-2,4,6-triene (with 4TiCl3-LialH4), triene or 2,4,5,7-tetramethyl-octa-2,6-dien-4,5-diol (with TiCl4-Mg), pinacol (with VCl3-Mg), and 2-acetyl-1,3,3,4,4-pentamethyl-cyclopentane (with CrCl3-Mg or FeCl3-Mg or ZrCl4 or ZrCl4-Mg) as major products. 相似文献
19.
The vinylbromides and are allowed to react ith AgBF4 and AgPF6 in the presence of various olefins in CH2Cl2 as the solvent. Except for the reaction of cyclopentene with all other olefins used, react with vinyl cation to form the cycloaddition products , and in high yields. 相似文献
20.
The α-anions of 2-substituted 1,3-dioxolan-4-ones derived from chiral mandelic and lactic acid (, ; ; , ) were alkylated with high stereoselectivity. The products formed were hydrolysed to α-hydroxy acids with 65–85% e.e. ((S)(+)-,,, (R)(–)-). 相似文献