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991.
The O-silylated enolates of ketones and esters can be phenylthioalkylated by the chlorides (2) and (3) under ZnBr2-catalysis; ozonolysis and subsequent sulphoxide thermolysis then gives the corresponding unsaturated 1,5-dicarbonyl compounds. 相似文献
992.
A c-number treatment for the standing (plane) wave effects in a bistable system placed in a Fabry-Perot cavity is employed without “truncation of hierarchy” or “spatial average” procedure. The specific example of the 3-level Lambda-shape (two-photon) system is illustrated. 相似文献
993.
Ohne Zusammenfassung 相似文献
994.
A new, simple, accurate and rapid method is described for the determination of total penicillins in pharmaceutical preparations. The method is based on desulphurization with potassium plumbite whereby one mole of lead sulphide is formed per mole of penicillin. The excess of lead ions is titrated with EDTA at pH 4.5, with use of the lead ion-selective electrode. Results are reproducible within +/- 0.5% and compare favourably with those obtained by the procedures of the United States and British Pharmacopoeias. 相似文献
995.
M. F. Madkour Hassan Mahamed A. E. Sayed A. Hamed Ashraf M. Gaber Adel A. Hataba Abd El-Khalik 《中国化学》1991,9(3):262-269
The title compound was subjected to react with some electrophiles and nucleophiles, such as alkyl halides, ethyl chloroacetate or amines, hydrazines etc. The resulting compounds were used in further syntheses for the purpose of obtaining some new types of heterocycles with possible biological and pharmaceutical activities. 相似文献
996.
997.
998.
999.
Corruble A Davoust D Desjardins S Fressigné C Giessner-Prettre C Harrison-Marchand A Houte H Lasne MC Maddaluno J Oulyadi H Valnot JY 《Journal of the American Chemical Society》2002,124(51):15267-15279
The complexes between methyllithium and chiral 3-aminopyrrolidine (3-AP) lithium amides bearing a second asymmetric center on their lateral amino group were studied using multinuclear ((1)H, (6)Li, (13)C, (15)N) low-temperature NMR spectroscopies in tetrahydrofuran-d(8). The results indicate that lithium chelation forces the pyrrolidine ring of the 3-AP to adopt a norbornyl-like conformation and that robust 1:1 noncovalent complexes between methyllithium and 3-AP lithium amides form in the medium. A set of (1)H-(1)H and (1)H-(6)Li NMR cross-coupling correlations shows that the binding of methyllithium can take place along the "exo" or the "endo" face of this puckered structure, depending on the relative configuration of the lateral chiral group. This aggregation step renders the nitrogen of the 3-amino group chiral, the "exo" and "endo" topologies corresponding to the (S) and (R) configurations, respectively, of this atom. Density functional theory calculations show that the "exo" and "endo" arrangements are, for both diastereomers, almost isoenergetic even when solvent is taken into account. This result suggests that the formation of the mixed aggregates is under strict kinetic control. A relationship between the topology of these complexes and the sense of induction in the enantioselective alkylation of aromatic aldehydes by alkyllithiums is proposed. 相似文献
1000.