Nucleophilic attack solubility

The (V-hydroxysuccinimide that is liberated is easily removed because of its solubility in dilute base. The relative stability of the anion of A-hydroxysuccinimide is also responsible for the acyl derivative being reactive toward nucleophilic attack by an... 

TL5981>. The proposed mechanism involves the oxidation of the amine to an imine, tautomerization to an enamine, and a sequence of nucleophilic attacks on the pyridazine rings followed by oxidation steps. The oxidant of choice is (bispyridine)silver permanganate <1982TL1847>, which is easily prepared, mild in action, and is soluble in organic media. If R1 = H in the product 77, electrophilic substitution (e.g., bromination, nitration, Mannich, and Vilsmeier-Haack-Arnold reactions) occurs at this position. 

It is the thiol grouping that acts as a nucleophile, attacking the epoxide function of the toxin (see Box 6.6). In this way, the toxin becomes irreversibly bound to glutathione, and the additional polar functionalities in the adduct mean that the product becomes water soluble. The glutathione-toxin adduct can thus be excreted from the body. 

Scheme 6.8 Epoxide recognition for epoxide hydrolase that detoxify living cells by catalyzing alcoholysis to water soluble diols. The working model involves the phenolic H-atoms of two tyrosines activating the epoxide for nucleophilic attack. This principle is realized analogously by double hydrogenbonding thiourea catalyst 9 in the natural medium water.

Enzyme catalysed hydrolysis of racemic epoxides is interesting from a practical point of view. This reaction is catalysed by epoxide hydrolases (EHs, EC 3.3.2.3) (Archelas and Furstoss, 1998). Mammalian EHs are the most widely studied and they are divided into five groups among which the soluble (cytosolic) epoxide hydrolases (sEH) and microsomal epoxide hydrolases (mEH) are best charactelised. The mechanism of sEH from rat starts with a nucleophilic attack by Asp333 on a carbon of the epoxide (usually the least hindered one) to form a glycol monoester intermediate which is stabilised by an oxyanion hole. A water molecule activated by His523 releases the 1,2-diol product. An... 

Reactions of substituted a-ketoalkynes (RC=CCOR ) with 6-amino-l,3-dimethyluracil and a water-soluble nickel catalytic system [Ni(CN)2-CO-KCN-NaOH] afforded 2,4-dioxopyrido[2,3- pyrimidine derivatives 532 under very mild conditions (room temperature and atmospheric pressure). The mechanism involved a nucleophilic attack by Ni(0), formed in situ, onto the triple bond of the substrate. The reaction terminates within 30 min, giving 98% of 532, while in the absence of this catalytic system the reaction took a longer time (lOh) to reach a maximum yield of 30% <2001J(P1)2341>. A regioselective interaction of 6-aminouracil derivatives with GF3COCH2COR in boiling AcOH afforded the cyclized 5-trifluoromethylpyrido[2,3-, pyrimidines 533 <200381531 >. 

Note A precise adjustment of the amount of KOH is required in the present procedure. While OH undergoes highly preferential nucleophilic attack onto the electrophilic carbonyls of K[Ru(CO)3Cl3] even in the presence of Ru3(CO)i2 (this is also favored by the insolubility of the latter in 2-ethoxyethanol below a critical temperature of 80°C), any excess of OH that would be still present after total consumption of Ru(ll) is potentially able to react with Ru3(CO)i2 to produce the soluble anionic complex [Ru3(p-H)(CO)n] (char-... 

If this is done carefully, extensive cross-linking does not take place and the polymer (n = 15,000) remains soluble in organic solvents. The reactive chlorine atoms are still susceptible to nucleophilic attack and displacement ... 

Concerted mechanisms have been proposed on the basis of work carried out with soluble Movl, Wvl and TiIV peroxo compounds. The experimental evidence is consistent with the hypothesis that these compounds act as oxidants in stoichiometric epoxidations and that the reactions involve electrophilic attack of the peroxo compound on the organic molecule or, what is equivalent, a nucleophilic attack of the organic molecule on the peroxidic oxygen, in a butterfly transition state. The reaction product is formed and, after desorption, the peroxo compound is regenerated by reaction of TiIV with H202 this accounts for the catalytic nature of the reaction (Amato et al, 1986). The same type of mechanism... 

Palladium(II) salts, in the form of organic solvent soluble complexes such as PdCl2(RCN)2, Pd(OAc>2 or Li2PdCU, are by far the most extensively utilized transition metal complexes to activate simple (unactivated) alkenes towards nucleophilic attack (Scheme 1). Alkenes rapidly and reversibly complex to pal-ladium(II) species in solution, readily generating alkenepalladium(II) species (1) in situ. Terminal monoalkenes are most strongly complexed, followed by internal cis and trans (respectively) alkenes. Geminally disubstituted, trisubstituted and tetrasubstituted alkenes are only weakly bound, if at all, and intermolecular nucleophilic additions to these alkenes are rare. 

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