A new heliangolide has been isolated from aerial parts of , and identified as (6,10)(3,3a,4,lla)-3a,5,8,11a--tetrahydro-4-acetoxy-3,6, 1O-trimethyl-2,9 (3, 4) -cyclodeca[b] furandione. The structural elucidation of the new compound, named heliangolidin, was carried out by spectral means (MS, IR, 1H and 13C NMR, and two dimensional 1H-13C chemical shift correlations) and X-ray diffraction analysis. 相似文献
During the hydrogenation of the Δ3(3a)-4-hydrindenones or on Pd or Ni, we observe a shift of the double bond to Δ3a(7a)-4-hydrindenones and . The absolute configuration established for ketones and shows that the reaction is a suprafacial process. By deuteriation experiments, we observe that the reaction is irreversible and occurs with a molecular hydrogen exchange. 相似文献
On acetone-sensitization, 5-bromo-1,3-dimethyluracil ( reacts with Nb-methoxycarbonyltryptamine ( under the assistance of an electron carrier such as 2-methoxynaphthalene to give a coupling product . A mechanism involving a double electron transfer via the triplet state of is proposed. 相似文献
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
The chemical reactions between bismuth and oxidants in a heat pipe oven are described. Strong chemiluminescence (A2Π → X2Π) was observed in the reaction with N2O and the vibrational temperature of the A2Π state was measured to be 3150 ± 300 K. 相似文献
Stereoselective reduction of 1,3-bishomocubanone acetate followed by mesylation leads to an epimeric mixture of mesylates . Base induced homoketonization of the anti-epimer affords tetracyclo[5.3.0.02,5 O4,8]decenone . 相似文献
Treatment of hydroxymethylene ketone with trimethylene dithiotosylate according to literature conditions,3b led to the novel CC ring scission product in high yield; also, the hydroxide-initiated cleavage4 of gave the β-elimination product which underwent a highly stereospecific addition of diazomethane to provide . 相似文献
Arylazides reacted with α amino-acrylonitriles to produce 1-aryl-5-amino-triazoles, and with β amino-acrylonitriles to give 1-aryl-4-cyanotriazoles. Kinetics showed the Hammett ρ to be > o and therefore, these reactions are controlled by LUMOazide-HOMOolefin interaction. Despite the captodative substitution in and (ΔΔ E≠~ 500 cal.M?1) does'nt agree with a diradical intermediate. 相似文献
A complete 1H and 13C NMR assignment of one of the latrunculins (B) was accomplished with the aid of 2D NMR COSY and CH shift-correlation experiments. The various H-H Coupling constants have been datermined and a conformation of the macrolide and the tetrahydropyran (THP) ring suggested on basis of the J-values and measured NOE's. The absolute configuration of latrunculin-A() was determined on the grounds of its earlier X-Ray analysis, and a chemical degradation to a known compound. Two novel latrunculins, -C() and -D(), were isolated from the Red Sea sponge and their structures elucidated. Starting with L-cysteine a synthon for the latrunculins has been synthesized. 相似文献
A representation of the algebraic hamiltonian for the anharmonic Morse oscillator as a quadratic form, H = T1ω(P2 + Q2), where P and Q are operators is derived. The commutator of P and Q is an operator that tends to i (times the identity operator) in the harmonic limit. Coherent states and anharmonic normal modes for a linear triatomic molecule are discussed as potential applications. 相似文献
Dialkylcarbodiimides, , react with iminium salts, , to afford the formal 1,1-diaminosubstituted 2-azaallenium salts . According to dynamic NMR measurements compounds must be regarded as alkylidene-guanidinium salts , undergoing a fast topomerization via a transition state with allene geometry (2G=265 = 45.9 ± 1 kJmol-1 for ) and a slower rotation around the peripheral C-N bonds (transition state ; 2G=290= 58.0 ± 1 kJmol-1 for ). 相似文献
An X-ray structure analysis shows that the 5, 18-dimethyl derivative () of the title compound () crystallises from xylene as a 1:1 inclusion compound in which the host molecules adopt propeller-like conformations ( and *) with almost perfect 2 symmetry. Dynamic 1H n.m.r. spectroscopy shows that the 5, 18-dibenzyl derivative () of () forms a 1:1 inclusion compound with ethanol in the solid state and undergoes ring inversion ( ? *) between enantiomeric propeller-like conformations in solution against a barrier of 21.1 kcal mol?1相似文献
The synthesis of ()-13-fluorohexadec-13-en-11-ynyl acetate , a fluorinated analog of the sex pheromone of the processionary moth Thaumetopoeapityocampa is described. The synthetic scheme involves epoxidation of the double bond, regioselective opening of the oxirane ring with Olah's reagent, tosylation of the resulting fluorohydrin and dehydrotosylation. Structural features of the intermediate diastereomeric fluorohydrins and and tosylates and are also discussed on the basis of their 1H and 19F NMR spectra. 相似文献
Purealin , a novel secondary metabolite, which modurates enzymic reactions of ATPases, has been isolated from the okinawan marine sponge and the structure has been determined by the 1H-1H homonuclear and 1H-13C heteronuclear NMR chemical shift correlations and CD spectra. 相似文献
The 1O2-induced degradation of spiro[1,8a]dihydroindolizines - a new photochromic system - may involve dioxetanes as intermediates giving fulvenylesters . 相似文献
13Cmr spectra show complete absence of scrambling of an 18O label in recovered after partial conversion to thereby precluding an -methylation mechanism for the bimolecular formation of from . 相似文献
Condensation of 1,3-bis(trimethylsiloxy)-1-methoxybutadiene () and 2-phenyl-2,2-dimethoxyethanal () under TiCl4 condition gave the γ-hydroxycyclopentenone product . The reaction was followed by INEPT29Si NMR. Implication to the mechanism of the reaction was discussed. 相似文献
Feeding experiments with (4) [5-3H;5-14C]-leucine () and with the (4) [5-3H;2-14C]-isomer () show that incorporation into the isoprenylated tryptophan derivative echinuline (), produced by , involves, to a large extent, loss of the fragment enbodying the carbon atom at position 2 of the fed amino acid. 相似文献
Bis(N-(1-benzoyl-2-propylidene)-2-pyridylmethylaminato)iron(III) hexafluorophosphate (Fe(bzpa)2PF6 is shown to be a spin-equilibrium compound between low- (S = ) and high- (S = ) spin states depending on temperature, and to have the unusual property that the relaxation time of the spin change is shorter than the Mössbauer lifetime (1 × 10?7s) of iron- 57 (l = ) in the solid state. 相似文献