Anionic -elimination

Only in 1961 did Woodward and Olofson succeed in elucidating the true mechanism of this interesting reaction by making an extensive use of spectroscopic methods. The difficulty was that the reaction proceeds in many stages. The isomeric compounds formed thereby are extremely labile, readily interconvertible, and can be identified only spectroscopically. The authors found that the attack by the anion eliminates the proton at C-3 (147) subsequent cleavage of the N—0 bond yields a -oxoketene imine (148) whose formation was established for the first time. The oxoketene imine spontaneously adds acetic acid and is converted via two intermediates (149, 150) to an enol acetate (151) whose structure was determined by UV spectra. Finally the enol acetate readily yields the W-acyl derivative (152). 

The sulphonyl group involved in cathodic and anionic eliminations. 1036... 

Triflate anions, elimination of 639 Triflinates, rearrangement of 669 Triflones 669... 

The mechanism of the process seems to be as follows. At first, the carbon atom of the terminal multiple bond is attacked by the N-nucleophile to form an internal salt stabilized by fluoride anion elimination from the a-CF2 fragment. This leads to compound 123, whose hydrolysis... 

Apparently, ethylenediamine initially attacks the carbon atom of the double bond to give an anion. Elimination of the fluoride ion from the CF3 group and elimination of HF affords A(2-(trifhioromethyl)-perfluoropent-1 -en-3-ylidene)ethylene-1,2-diamine. Subsequent transformations of this compound can follow different pathways. For instance, one pathway includes intramolecular nucleophilic cyclization, resulting in compound A. This product can react with perfluoro-2-methylpent-2-ene... 

One fluorine atom is leaving as a fluoride ion, and the exocylic double bond to the difluoromethylene group is attacked by a hydroxide anion. Elimination of hydrogen fluoride gives an acyl fluoride that is readily hydrolyzed to the final product, 2-amino-4-trifluoromethylbenzoic acid (K) [59],... 

The antibiotics rifamycin SV and rifampicin reduce Sulfobromophthalein (BSP) elimination in humans. Using injected oocytes, Vavricka et al. (2002) demonstrated that rifampcin is transported by OATP-C and OATP8 and that both rifampicin and rifamycin SV inhibit OATP-C, 8, -B and -A mediated BSP uptake. These results show that rifamycin SV and rifampicin interact with OATP-mediated substrate transport to different extents. Inhibition of human liver OATPs can explain the previously observed effects of rifamycin S V and rifampicin on hepatic organic anion elimination. 

It is not requisite that the anion eliminated in the step 19 to 20 be a hydroxyl ion, because acid hydrolysis of 5-amino-5-deoxy-l,2-0-isopropylidene - 3 - O - (methylsulfonyl )-a- D -xylofuranose likewise yields 3-pyridinol (21). On subjection to acid hydrolytic conditions which remove the 2V-acetyl group, such N-acetyl derivatives as 5-acetamido-5-deoxy-a-D-xylopyranose (see p. 167) are immediately transformed, through 17, into 3-pyridinol (21). Furthermore, acid hydrolysis of methyl 5-acetamido-5-deoxy-2,3,4-tri-0-methyl-a-D-... 

The intermediate p-hydroxyphosphine oxide is isolated only if lithium is used to deprotonate the phosphine oxide. Sodium or potassium anions eliminate in situ to form the alkene direedy. Eliminations of... 

Anionic eliminations of the following type will also be considered as belonging to the ElcB class of eliminations. Since protons on heteroatoms are usually rather acidic because of the electronegativity of the heteroatom, the first step, deprotonation, can occur with a rather weak base. The second step is beta elimination from an anion, Ep, the reverse of nucleophile addition to a polarized multiple bond. 

A peculiai- case of phosphoryl radical addition to difluoroalkenes involves the reaction of trialkyl phosphites with l-bromo-2-iodo-l,l,2,2-tetfafluoroethane under ultraviolet irradiation (254 nm). Surprisingly, the corresponding 2-iodo-l,l,2,2-tetrafluoroethylphosphonates are formed in 42 8% yields with no detectable amount of the bromo derivative (Scheme 3.39). The proposed mechanism involves a halide-induced dealkylation of the trialkyl phosphite radical cation followed by addition of the product phosphoryl radical to tetrafluoroethene (generated by halide anion elimination) and iodide radical abstraction from the starting haloalkane. s... 

Fig. 2.—The Anion-elimination Scheme for the Formation of D-Glucosaccharinates (where R = the remaining portion of the polysaccharide molecule).

In the three mechanisms given (see Figs. 2, 3, and 4), only those ions necessary for the alkoxy-anion elimination have been presented. However, it must be remembered that a ketose can afford two ions, one of which is... 

In the case of tosylates of secondary amines, the effect of bases appears to be more harmful for the stability of the amine moiety in the course of the electrolysis. Here, the deprotonation process involves a proton located in the a-position to the nitrogen atom and may lead37 therefore to an anionic elimination. The formation of an imine and its further degradation during the work-up are the principal causes of the low yields when the deprotection process is conducted without a sufficient amount of a proton source. By... 

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