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51.
A general method of annellating quinones in high yield has been devised using mixed vinylketene acetals obtained directly from the enolate ions of unsaturated esters. 相似文献
52.
Jean Favre-Bonvin katia Gluchoff-Fiasson Jacques Bernillon 《Tetrahedron letters》1982,23(18):1907-1908
Stearyl-velutinal, a new natural sesquiterpenoi̋d isolated from lactarius velutinus Bert., has the structure ; this very labile compound is responsible for the dark-blue reation of the fungus to the ‘sulfo-vanilic’ mixtures. 相似文献
53.
Jacques Piette Claire-M. Calberg-Bacq Albert van de Vorst 《Photochemistry and photobiology》1977,26(4):377-382
Abstract. Thiols and disulfides protect both φX174 phage and its isolated DNA from the lethal action of proflavine plus light. The protective ability of these compounds appears to be attributed to the -SH or the -S-S- group and the property to interact with the proflavine-phage DNA complex. The phage inactivation efficiency per proflavine bound to DNA is reduced by 50 to 30% upon addition of cysteine or cystamine. Substances that affect the lifetime of singlet oxygen modify the rate of phage photoinactivation in the presence of proflavine; the inactivation rate is decreased by N- 3 and increased by D2 O. Irradiation under N2 atmosphere markedly decreases the phage photosensitization by proflavine. Irradiation with monochromatic light of 440 nm is less efficient than irradiation with light of 440 nm plus 360 nm, and the difference is more pronounced in N2 than in air. These results are discussed in relation to various possible photochemical pathways. 相似文献
54.
The Reaction of Norbornene with Lead Tetraacetate and Thallium Trinitrate. Preliminary communication
Jacques Kagan 《Helvetica chimica acta》1972,55(7):2356-2359
The reaction of norbornene with lead tetraacetate is found to be much more complex than previously reported. In acetic acid and in benzene, the syn-7-norbornenyl, 3-nortricyclyl, and syn and anti-7-acetoxy-exo-2-norbornyl acetates were characterized. In methanol, the isolated products represented most of those expected from the competition of methanol and acetate in the neutralization of the intermediate carbocations. The reaction of norbornene with thallium trinitrate in the above solvents yielded very complex mixtures besides the above mentioned products which were formed in about 50% yield. 相似文献
55.
This review gives a survey of the approaches employed to obtain, enhance and tune selectivity in nonaqueous capillary electrophoresis (NACE). Recent developments in NACE are described and the effects of background electrolyte composition and addition of selectors on separation selectivity are discussed. The use of one organic solvent, a mixture of several organic solvents or the use of additives to tune separation selectivity in NACE is presented and a list of relevant applications is included. 相似文献
56.
The electrochemically induced dissolution of ferrocene in a carbon paste electrode is investigated by using chronoamperometry at constant potential. Two types of behaviour are observed, according to the initial form of ferrocene: particles or deposit. The experimental i-t curves are respectively in agreement with the theoretical curves, derived earlier, in the case of spherical particles or planar slabs of solid. The analysis of the curve shows that the process is diffusion controlled, so that the dissolution rate of ferrocene cannot be measured. The parameters calculated from the curves (thickness of the deposit, initial distance from the electrode, area) have a reasonable order of magnitude. 相似文献
57.
Analytical solutions of the diffusion equations to obtain the diffusant concentrations in the macro- and micropores which constitute the pore system of a zeolite bed are presented. The parameter which determines the influence of each pore type on the evolution of the adsorbate/adsorbant system towards the equilibrium state is described. Examples are given to illustrate a qualitative and quantitative study based on the curves obtained from these equations. 相似文献
58.
Codée JD Litjens RE den Heeten R Overkleeft HS van Boom JH van der Marel GA 《Organic letters》2003,5(9):1519-1522
Diphenylsulfoxide in combination with triflic anhydride provides a very potent thiophilic glycosylation promotor system, capable of activating disarmed thioglycosides. The usefulness of this novel thiophilic activator is illustrated in a successful chemoselective glycosylation sequence in which the donor thioglycoside in the first condensation step may be either armed or disarmed. [reaction: see text] 相似文献
59.
Bashiardes G Chaussebourg V Laverdan G Pornet J 《Chemical communications (Cambridge, England)》2004,(1):122-123
A new synthesis of benzo[1,2]oxasiloles is described, wherein an unprecedented intramolecular allylic transposition takes place probably involving a pentavalent silicon intermediate. 相似文献
60.
The stereochemistry of the reaction of silver benzoates on chiral di-O-aroyl-1,2 iododeoxy-3-sn-glycerols has been reinvestigated. The reaction proceeds either with or without neighbouring group participation, depending on : - possible electrophilic assistance by the silver ion to the ionisation of the substrate (occuring only with dissociated silver salts), - ability of substituants R1 and R2 on the substrates to stabilize a positive charge. Rearrangements are at minimum with R1 and R2 electronreleasing groups in the substrate, silver salts un-or weakly dissociated and bearing a good nucleophile. For one case, a regio- and stereo specific reaction is observed. 相似文献