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91.
Gualtiero Plazzogna Valerio Peruzzo Giuseppe Tagliavini 《Journal of organometallic chemistry》1973,60(2):229-232
The reaction between pentadeuteriophenyllithium and hexaphenyldilead combined with new measurements of isotopic exchange between Ph6Pb2 (labelled with RaD) and Ph4Pb, have shown that the dilead compound is undissociated in solution. These results cast doubt upon the previously reported equilibrium: Ph6Pb2Ph4Pb+Ph2Pb. 相似文献
92.
Graziano Guella Ines Mancini Giuseppe Chiasera Francesco Pietra 《Helvetica chimica acta》1992,75(1):310-322
93.
94.
Graziano Guella Giuseppe Chiasera Ibrahima N'Diaye Francesco Pietra 《Helvetica chimica acta》1994,77(5):1203-1221
Kinetic and equilibrium studies show that typical xenicanes such as dictyolactone ( 1 ) and 4-hydroxydictyolactone ( 3 ) undergo slow conformation medium-ring flipping between the predominant trans-( 1a or 3a ; Me(20) trans to H–C(3)) and the minor cis-conformers ( 1b or 3b ; Me(20) cis to H–C(3); see Scheme 1). The formation of the latter is inhibited in heterocyclic-ring-opened congeners such as 18-acetoxy-4-hydroxydictyo-19-al ( 7 ). Molecular-mechanics calculations suggest that typical-xenicane cis-conformers are disfavoured by mainly C(4)–C(5) torsional strain. This is confirmed by the observation of two sizably populated cis-and trans-conformers for the unnatural 4-oxoxenicanes 10–12 . Unusually facile thermal (E)→(Z) isomerization of xenicanes 1,3,10–12 , and 7 is also observed (→ 13–17 and 9 , resp.; Scheme 3), reflecting great strain relief in the transition state. Conflicting results in the literature now fit into this scheme which provides a basis for unravelling recognition phenomena with these biologically active systems. 相似文献
95.
Giuseppe Bruno Santo Lanza Francesco Nicol Giuseppe Tresoldi Giuseppe Rosace 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(5):m316-m318
The title compound, [PdPtCl(C3H5)(C6H10N2S2)(C17H14NP)]·CHCl3, was obtained by deprotonation of the initial platinum(II) complex of the dithioxamide and subsequent reaction with [Pd(η3‐C3H5)(μ‐Cl)]2. Both metal atoms exhibit a square‐planar coordination geometry, with the two planes forming a dihedral angle of 21.7 (2)°. The dithioxamide bis‐chelating bridge is flat. 相似文献
96.
Anna Maria Almerico Gaetano Dattolo Girolamo Cirrincione Giuseppe Presti Enrico Aiello 《Journal of heterocyclic chemistry》1987,24(5):1309-1311
The title compounds were prepared by nitration of compounds 2 , reduction of the dinitro derivatives 4 and diazotization of the diamino derivatives 6 followed by an intramolecular coupling reaction. Compound 4a showed good activity against Salmonella cholerasuis and Clostridium perfringens bacteria. 相似文献
97.
Mario Sechi Luciano Sannia Maria Orecchioni Fabrizio Carta Giuseppe Paglietti Nouri Neamati 《Journal of heterocyclic chemistry》2003,40(6):1097-1102
HIV‐1 integrase (IN) is a very promising and validated target for the development of therapeutic agents against AIDS. In an effort to design and synthesize biological isosteric analogs of β‐diketoacid‐containing inhibitors of IN, we prepared a series of substituted isoxazole carboxylic acids. Several of these compounds inhibited catalytic activities of purified IN at micromolar concentration range. With an aim to prepare a large number of analogues based on the isoxazole pharmacophore we focused our study on a series of 3,5‐disubstituted isoxazole isomers. For a rapid structural analysis we discovered a convenient 1H‐nmr method for distinguishing between isomeric structures based on their H‐4 assignments. This “finger print” approach to isomer identification will be useful in combinatorial chemistry settings where a mixture can be further derivatized. 相似文献
98.
[structure: see text] An approach relying on quantum mechanical calculations of proton-proton and proton-carbon J coupling values is proposed as a tool for assigning the relative configuration on chiral organic compounds. The method is suitable for carbon frameworks containing several adjacent stereogenic centers and may allow significant advances in the extensive use of spin-spin couplings in structural elucidation. 相似文献
99.
Justicia J Rosales A Buñuel E Oller-López JL Valdivia M Haïdour A Oltra JE Barrero AF Cárdenas DJ Cuerva JM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(7):1778-1788
The titanocene-catalyzed cascade cyclization of epoxypolyenes, which are easily prepared from commercially available polyprenoids, has proven to be a useful procedure for the synthesis of C(10), C(15), C(20), and C(30) terpenoids, including monocyclic, bicyclic, and tricyclic natural products. Both theoretical and experimental evidence suggests that this cyclization takes place in a nonconcerted fashion via discrete carbon-centered radicals. Nevertheless, the termination step of the process seems to be subjected to a kind of water-dependent control, which is unusual in free-radical chemistry. The catalytic cycle is based on the use of the novel combination Me(3)SiCl/2,4,6-collidine to regenerate the titanocene catalyst. In practice this procedure has several advantages: it takes place at room temperature under mild conditions compatible with different functional groups, uses inexpensive reagents, and its end step can easily be controlled to give exocyclic double bonds by simply excluding water from the medium. 相似文献
100.
The finite field approach has been implemented in the periodic ab initio CRYSTAL program and been used for calculating the dielectric constants of crystalline LiF and MgO (FCC structure) and BeO (wurtzite structure). To maintain the periodicity along the applied field direction, a "sawtooth" potential is used in conjunction with a supercell scheme. Supercells four to five times longer than the primitive cell in the direction of the applied field provide well-converged results. The influence of the computational parameters is discussed. An alternative scheme has also been implemented, for inner check, that consists of applying a static electric field to a slab of increasing thickness in the direction orthogonal to the surface; the dielectric response at the center of the slab is shown to converge rapidly to the bulk value evaluated with the sawtooth field. The method is accurate and permits the determination of nonlinear corrections to the dielectric constant. When used in conjunction with the local density approximation (LDA) scheme, it provides for the dielectric constant of the three above-mentioned compounds values close to those recently obtained with a time-dependent density functional theory approach. 相似文献